Department of Municipal Affairs and Transport PO Box 20 Abu Dhabi, United Arab Emirates

© Copyright 2016, by the Department of Municipal Affairs and Transport. All Rights Reserved. This manual, or parts thereof, may not be reproduced in any form without written permission of the publisher PAVEMENT DESIGN MANUAL

TABLE OF CONTENTS

List of Figures ...... vii List of Tables ...... ix Glossary ...... xi abbreviations and acronyms ...... xvi 1 Introduction ...... 1 1.1 Overview ...... 1 1.2 Purpose and scope ...... 1 1.3 Application of this manual ...... 2 1.4 Content and format ...... 2 1.5 Pavement structure design ...... 3 1.5.1 Pavement structure ...... 3 1.5.2 Pavement design methods ...... 5 1.6 General Requirements for Pavement Design ...... 7 2 Pavement Design Components ...... 8 2.1 Overview ...... 8 2.2 Environment ...... 8 2.2.1 Environmental factors for empirical design ...... 8 2.2.2 Environmental factors for mechanistic-empirical design ...... 10 2.3 Traffic analysis procedures ...... 13 2.3.1 Design life ...... 13 2.3.2 Vehicle classification ...... 14 2.3.3 Axle group configuration ...... 15 2.3.4 Tire pressure ...... 16 2.3.5 Vehicle count ...... 17 2.3.6 Traffic projections ...... 17 2.3.7 Design lanes ...... 18 2.3.8 Directional factor ...... 18 2.3.9 Percentage of trucks ...... 18 2.3.10 Equivalent axle load factor ...... 18 2.3.11 Truck factor ...... 19 2.3.12 ESAL calculation ...... 20 2.3.13 Mechanistic-Empirical traffic analysis ...... 20 3 Pavement Materials ...... 22 3.1 Subgrade materials ...... 22 3.1.1 Empirical design for subgrade materials ...... 23 3.1.2 Mechanistic-Empirical design for subgrade materials ...... 24

Page i

TOC FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

3.2 Granular base and subbase materials ...... 25 3.2.1 Empirical design for granular base and subbase materials ...... 25 3.2.2 Mechanistic-Empirical design for granular base and subbase materials ...... 27 3.3 Modified granular materials ...... 29 3.4 Stabilized materials ...... 29 3.4.1 Empirical design for stabilized materials ...... 29 3.4.2 Mechanistic-Empirical design for stabilized materials...... 31 3.5 Asphalt concrete materials ...... 32 3.5.1 Empirical design for asphalt concrete materials ...... 33 3.5.2 Mechanistic-Empirical design for asphalt concrete materials ...... 33 3.6 Portland cement concrete ...... 38 3.7 Geo-textiles and geo-grids ...... 39 3.8 Recycled materials ...... 40 3.9 Warm mix asphalt ...... 40 3.9.1 Benefits of warm mix asphalt ...... 41 3.9.2 Methodology for warm mix asphalt...... 41 3.9.3 Testing for warm mix asphalt ...... 42 3.10 General Procedure for Dealing with Application of New Material/ Technology in Pavement Design for Abu Dhabi Emirate Roads ...... 42 4 New Pavement Design ...... 43 4.1 Purpose and scope ...... 43 4.2 Flexible pavement thickness design ...... 43 4.2.1 Empirical pavement design ...... 43 4.2.2 Mechanistic-Empirical pavement design ...... 49 4.3 Rigid pavement thickness design ...... 55 4.3.1 Empirical pavement design ...... 55 4.3.2 Supplemental procedures for rigid pavement design and rigid joint design ...... 57 4.3.3 Joint details ...... 62 4.3.4 Mechanistic-Empirical pavement design ...... 64 4.4 Interlocking pavers design ...... 70 4.4.1 Introduction ...... 70 4.4.2 Principle of paver blocks ...... 70 4.4.3 Construction procedure ...... 70 4.4.4 Structural design procedure ...... 70 4.5 Empirical pavement design example ...... 71 4.5.1 Environment ...... 71 4.5.2 Traffic ...... 72 4.5.3 Materials ...... 75

Page ii

TOC FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

4.5.4 Structure design...... 76 4.5.5 Cost analysis ...... 77 4.6 Mechanistic-Empirical pavement design example ...... 77 4.6.1 Climate ...... 78 4.6.2 Materials ...... 78 4.6.3 Structure design...... 78 5 Rehabilitation Design ...... 81 5.1 Purpose and scope ...... 81 5.2 Overlay feasibility ...... 81 5.3 Important considerations in overlay design ...... 82 5.3.1 Pre-overlay repair ...... 82 5.3.2 Reflection crack control ...... 82 5.3.3 Traffic loadings ...... 83 5.3.4 Drainage ...... 83 5.3.5 Rutting in Asphalt Concrete pavements ...... 83 5.3.6 Milling Asphalt Concrete surfaces ...... 83 5.3.7 Recycling existing pavement...... 83 5.3.8 Need for structural or functional overlay ...... 83 5.3.9 Overlay materials ...... 83 5.3.10 Shoulders ...... 83 5.3.11 Durability of PCC ...... 83 5.3.12 Overlay joints for PCC ...... 84 5.3.13 Overlay reinforcement for PCC ...... 84 5.3.14 Overlay bonding and separation layers for PCC ...... 84 5.3.15 Overlay design reliability and overall standard deviation ...... 84 5.3.16 Pavement widening ...... 84 5.3.17 Potential errors and possible adjustments to thickness ...... 84 5.4 Pavement evaluation for overlay design...... 85 5.4.1 Design of overlay along project ...... 85 5.4.2 Functional evaluation of existing pavement ...... 85 5.4.3 Structural evaluation of existing pavement ...... 86 5.4.4 Determination of subgrade resilient modulus for a design ...... 89 5.5 Flexible pavement overlays...... 90 5.5.1 Feasibility...... 90 5.5.2 Pre-overlay repair ...... 91 5.5.3 Reflection crack control ...... 91 5.5.4 Surface milling ...... 91 5.5.5 Empirical thickness design ...... 92 Page iii

TOC FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

5.5.6 Mechanistic-Empirical design ...... 93 5.6 Rigid pavement overlays ...... 94 5.6.1 Empirical Design ...... 94 5.6.2 Mechanistic-Empirical design ...... 97 6 Low-volume Roads ...... 99 6.1 Introduction ...... 99 6.2 Design considerations for LVRs ...... 99 6.2.1 Land use ...... 99 6.2.2 Axle loads ...... 99 6.2.3 Traffic volumes ...... 99 6.2.4 Environmental impacts ...... 100 6.2.5 Reliability ...... 100 6.2.6 Drainage systems ...... 100 6.3 Material specifications for pavement structural layers ...... 100 6.3.1 Subgrade evaluation ...... 100 6.3.2 Unbound granular material ...... 100 6.3.3 Asphalt concrete ...... 101 6.4 Maintenance strategy for LVRs ...... 101 6.5 Sustainability for LVRs ...... 102 6.6 Pavement design method ...... 102 6.6.1 Flexible pavement ...... 102 6.6.2 Roads with aggregate surfaces ...... 104 7 Drainage Design...... 105 7.1 General considerations ...... 105 7.2 Drainage design objectives and philosophy ...... 105 7.2.1 Importance of having good pavement drainage ...... 105 7.2.2 Maintaining the design high water level ...... 106 7.3 Subsurface drainage ...... 107 7.3.1 Subsurface drainage design for new pavements ...... 111 7.3.2 Subsurface drainage design for rehabilitation projects ...... 113 8 Pavement Maintenance ...... 116 8.1 Introduction ...... 116 8.1.1 Why pavement preservation is important ...... 116 8.1.2 Purpose of pavement preservation ...... 116 8.1.3 Definition...... 116 8.1.4 Preventive maintenance ...... 116 8.1.5 Corrective maintenance ...... 117 8.1.6 Emergency maintenance ...... 117 Page iv

TOC FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

8.2 Pavement management system integration ...... 118 8.3 Flexible pavement distress identification ...... 119 8.3.1 Type of distresses ...... 119 8.3.2 Fatigue (alligator) cracking ...... 120 8.3.3 Bleeding ...... 121 8.3.4 Block cracking ...... 122 8.3.5 Corrugation and shoving ...... 123 8.3.6 Reflection cracking ...... 124 8.3.7 Longitudinal cracking ...... 124 8.3.8 Patching ...... 125 8.3.9 Polished aggregate ...... 126 8.3.10 Potholes ...... 126 8.3.11 Ravelling ...... 127 8.3.12 Rutting ...... 128 8.3.13 Slippage cracking ...... 129 8.3.14 Stripping ...... 129 8.3.15 Transverse (thermal) cracking ...... 130 8.3.16 Edge cracking ...... 131 8.4 Pavement preservation treatments ...... 131 8.4.1 Introduction ...... 131 8.4.2 Treatment selection ...... 132 8.4.3 Cause of pavement distress ...... 132 8.4.4 Flexible pavement maintenance decision matrix ...... 133 8.4.5 Overview of treatment costs...... 134 8.5 Preservation treatments ...... 135 8.5.1 Crack sealing and filling ...... 135 8.5.2 Seal coat...... 136 8.6 Rigid pavement maintenance ...... 144 8.6.1 Joint and crack sealing ...... 144 8.6.2 Slab stabilisation ...... 145 8.6.3 Diamond grinding ...... 145 8.6.4 Patches ...... 145 9 Life-cycle Cost Analysis ...... 148 9.1 Introduction ...... 148 9.2 LCC process ...... 148 9.3 Establishing alternatives ...... 148 9.3.1 Determine an analysis period ...... 149 9.3.2 Determine a discount rate ...... 150 Page v

TOC FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

9.3.3 Determine maintenance and rehabilitation frequencies ...... 150 9.3.4 Estimating costs ...... 151 9.3.5 Analyze LCC results ...... 155 9.4 LCC example ...... 156 9.4.1 Project description ...... 156 10 Pavement Management Systems ...... 164 10.1 Overview ...... 164 10.2 Tasks that involve using a PMS ...... 164 10.3 PMS Methodologies ...... 165 10.4 Network-level pavement management ...... 165 10.4.1 Advantages of network-level pavement management ...... 166 10.5 Project-level pavement management ...... 167 10.5.1 Advantages of project-level pavement management ...... 167 11 Existing Pavement Evaluation ...... 169 11.1 Overview ...... 169 11.2 Data collection ...... 169 11.2.1 Distress survey ...... 170 11.2.2 Structural capacity ...... 172 11.3 Data analysis ...... 181 11.3.1 Delineation methodology ...... 182 11.3.2 Analysis report ...... 183 Cited References ...... 187 Other References ...... 189 Index ...... 190 Appendix A: Developing Effective Modulus of Subgrade Reaction (K-value) ...... 193 Appendix B: AASHTO 1993 Design Chart ...... 208 Appendix C: AASHTO Supplemental Design Tables ...... 210 ANNEX 1 ...... 228 ANNEX 2 ...... 234 ANNEX 3 ...... 237

Page vi

TOC FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

LIST OF FIGURES

Figure 1-1: Conventional asphalt pavement ...... 4 Figure 1-2: Full depth asphalt pavements ...... 4 Figure 1-3: Rigid pavements ...... 5 Figure 1-4: Composite pavements ...... 5 Figure 2-1: Relative damage calculation ...... 9 Figure 2-2: Abu Dhabi cumulative annual rainfall ...... 10 Figure 2-3: Abu Dhabi mean annual air temperature ...... 12 Figure 2-4: FHWA vehicle classification ...... 15 Figure 2-5: Axle Group Configuration ...... 16 Figure 2-6: Tire Pressure Distribution ...... 17 Figure 2-7: 80 kN Standard Axle ...... 19 Figure 3-1: Layer coefficient for granular base layer ...... 26 Figure 3-2: Layer coefficient for granular subbase layer ...... 27 Figure 3-3: Cement treated base layer coefficient ...... 30 Figure 3-4: Asphalt treated base layer coefficient...... 31 Figure 3-5: Dense graded asphalt concrete layer coefficient ...... 33 Figure 3-6: Nomograph to determine conventional asphalt binder modulus ...... 36 Figure 3-7: Nomograph to determine asphalt concrete modulus ...... 37 Figure 4-1: AASHTO's flexible pavement design chart ...... 46 Figure 4-2: Layered design analyses ...... 48 Figure 4-3: Mechanistic-Empirical design flowchart ...... 50 Figure 4-4: Critical locations for mechanistic design ...... 50 Figure 4-5: 1993 AASHTO design equation for rigid pavement ...... 56 Figure 4-6: Design equations for rigid pavement (part 1) ...... 59 Figure 4-7: Design equations for rigid pavement (part 2) ...... 60 Figure 4-8: Design equations for rigid pavement (part 3) ...... 61 Figure 4-9: Design equations for rigid pavement (part 4) ...... 62 Figure 4-10: Linear Elastic Analysis Results for the M-E Example ...... 80 Figure 6-1: Flexible LVR cross section ...... 103 Figure 6-2: Cross section of an aggregate surface for a LVR ...... 104 Figure 7-1: Typical subsurface drain for draining pavement layers – kerbed road section ...... 109 Figure 7-2: Typical examples of pavement edge drains ...... 110 Figure 7-3: General view of pattern drainage ...... 110 Figure 7-4: Typical vertical/trench drains for lowering groundwater ...... 111 Figure 7-5: Typical subsurface drain for sub-base water removal in widened roadway section ... 113 Figure 7-6: Typical example of agricultural fill blocking the pavement surface and subbase drainage ...... 114 Figure 7-7: Method for providing pavement drainage where edge of rural roadway has been backfilled and landscaped – typical section ...... 114 Figure 8-1: Categories of pavement maintenance ...... 117 Figure 8-2: Performance of preventive maintenance treatments ...... 118 Figure 8-3: Pavement preservation and rehabilitation tool box ...... 132 Figure 8-4: Crack sealing operation ...... 136 Figure 8-5: Scrub seal application ...... 138 Figure 8-6: Slurry seal surface ...... 139 Figure 8-7: Chip seal application ...... 140 Figure 8-8: Microsurfacing placement ...... 141 Figure 8-9: CIPR train on a southern California project ...... 142

Page vii

TOC FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

Figure 8-10: HIPAR process ...... 143 Figure 8-11: Joint sealing ...... 144 Figure 8-12: Diamond grinding machine ...... 145 Figure 8-13: Full-depth patch preparation ...... 146 Figure 9-1: LCC analysis period ...... 149 Figure 9-2: Costs to be considered when conducting LCC ...... 152 Figure 9-3: Example highway ...... 156 Figure 9-4: Reasonable unit prices ...... 159 Figure 9-5: LCC summary ...... 163 Figure 11-1: Digital survey vehicle ...... 172 Figure 11-2: Automatic crack mapping ...... 172 Figure 11-3: Trench cutout showing severe rutting ...... 173 Figure 11-4: Asphalt cores showing surface and base courses ...... 174 Figure 11-5: Dynamic cone Penetrometer ...... 176 Figure 11-6: Falling weight Deflectometer ...... 176 Figure 11-7: Ground penetration radar ...... 178 Figure 11-8: Dipstick Profiler ...... 179 Figure 11-9: Profilograph ...... 179 Figure 11-10: Automatic road analyser vehicle ...... 180 Figure 11-11: Locked wheel tester ...... 181 Figure 11-12: Graphical manual pavement condition survey data collection ...... 183 Figure 11-13: Tabular manual pavement condition survey data collection ...... 184 Figure 11-14: Example delineation of a roadway ...... 184

Page viii

TOC FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

LIST OF TABLES

Table 2-1: Abu Dhabi cumulative annual rainfall ...... 11 Table 2-2: Weighted mean temperatures ...... 13 Table 2-3: Standard axle load by axle group ...... 19 Table 2-4: Load damage exponent ...... 19 Table 3-1: Structural and functional requirements for pavement layers ...... 22 Table 3-2: Granular base layer modulus – Austroads 2008 ...... 28 Table 3-3: Stabilized bases flexural modulus default values ...... 32

Table 3-4: Relationship to determine T800 pen and PI values ...... 35 Table 4-1: Typical Reliability levels ...... 44 Table 4-2: Typical Initial and terminal serviceability levels ...... 45 Table 4-3: AASHTO material coefficient ...... 47 Table 4-4: Minimum asphalt concrete (AC) layer thicknesses for granular base pavements ...... 49 Table 4-5: RF to determine cemented materials' fatigue criteria ...... 53 Table 4-6: RF for asphalt materials fatigue criteria ...... 54 Table 4-7: Required Pavement Dowel Bar ...... 63 Table 4-8: Minimum subbase thickness for rigid pavements ...... 65 Table 4-9: Load safety factor for rigid pavements...... 66 Table 4-10: Coefficients for prediction of equivalent stresses ...... 68 Table 4-11: Coefficients for prediction of erosion factors for un-dowelled slabs ...... 68 Table 4-12: Minimum concrete slab thickness ...... 69 Table 4-13: Gradation for bedding sand ...... 71 Table 4-14: Vehicle classification distribution ...... 72 Table 4-15: Single axle load distribution ...... 73 Table 4-16: Tandem axle load distribution ...... 74 Table 4-17: Tridem axle load distribution ...... 75 Table 4-18: Asphalt material properties for M-E design ...... 79 Table 4-19: Calculated strain and N for M-E design ...... 79 Table 5-1: Causes and solutions for rutting ...... 86 Table 5-2: Repairs needed before overlay ...... 91 Table 6-1: Layer coefficients for pavement materials ...... 103 Table 8-1: Example of State of Iowa customised preservation treatments ...... 119 Table 8-2: Index of pavement distresses ...... 120 Table 8-3: Flexible pavement decision matrix ...... 133 Table 8-4: Pavement treatments ...... 134 Table 8-5: Pavement treatment cost and expected life ...... 135 Table 8-6: Preservation and rehabilitation treatments ...... 135 Table 8-7: Chip seal aggregate gradation limits ...... 139 Table 9-1: Potential design alternatives for LCC ...... 149 Table 9-2: LCC analysis period ...... 150 Table 9-3: Pavement treatments expected life ...... 150 Table 9-4: LCC summary with agency and user costs ...... 153 Table 9-5: User cost ($/Vehicle-Hr) based on NCHRP-133 study ...... 153 Table 9-6: Recommended values of time and value ...... 153 Table 9-7: Conversion of future costs to present value ...... 155 Table 9-8: Project summary ...... 156 Table 9-9: Potential design alternatives for LCC ...... 157 Table 9-10: LCC analysis period ...... 157 Table 9-11: Pavement treatments expected life ...... 158

Page ix

TOC FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

Table 9-12: Rehabilitation and preservation alternatives over a 20-year analysis period ...... 158 Table 9-13: LCC result (alternative 1) ...... 160 Table 9-14: LCC result (alternative 2) ...... 161 Table 9-15 : LCC result (alternative 3) ...... 162 Table 9-16: LCC summary table ...... 163 Table 11-1: Pavement distress types ...... 183 Table 11-2: Pavement condition rating for different severity levels and threshold levels...... 185 Table 11-3: Assigned severity levels for pavement condition rating criteria levels ...... 185 Table 11-4: IRI maximum limits and severity ...... 186 Table 11-5: Skid resistance criteria ...... 186

Page x

TOC FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

GLOSSARY

Analysis Period: the period of time for which the economic analysis is to be made.

Annual Average Daily Traffic (AADT): The total annual volume of traffic passing a point or segment of a road in both directions divided by the number of days in a year.

Asphalt base course: an asphalt layer under the wearing surface layer and above the aggregate base/Subbase courses. It is a uniform, non-erodible, and stable construction platform. It is designed to resist fatigue cracking.

Asphalt binder (intermediate) course: the second asphalt layer following the surface layer. Its properties are coarser than the surface layer. It is designed to resist permanent deformation.

Asphalt binder: It is a viscous material that binds the aggregate particles together to form the asphalt concrete mixture. It is referred to as Asphalt, Bitumen, or asphalt cement

Asphalt concrete: is a mixture of aggregate (about 96% by weight) and asphalt binder (about 4 % by weight). It is also referred to as Hot Mix Asphalt (HMA) since hot ingredients and heat is used for mixing.

Asphalt structural course: A separation layer that prevents fine soils from entering the ATB or CTB.

Asphalt wearing course (Surface): one or more layers of a pavement structure designed to accommodate the traffic load. The top layer resists skidding, traffic abrasion, and the disintegrating effects of climate. Sometimes referred to as surface course.

Average Daily Traffic: The total volume during a given time period, in whole days, greater than one day and less than one year, divided by the number of days in the time period.

Backcalculation: mathematical analysis to estimate the modulus of a pavement layer using deflection measurement.

Base course: the layer or layers of specified or selected material of designed thickness placed on a Subbase or a subgrade to support a surface course.

Change in serviceability (ΔPSI): A value that indicates the degradation in a road’s condition over time, which is the difference between the road’s initial serviceability rating and its terminal serviceability.

Chip seal: asphalt surface treatment to improve Rideability and seal surface. It consists of applying asphaltic emulsions or liquid paving grade asphalts and covers with aggregate and rolling.

Climatic (Environmental) conditions: parameters that impact the pavement performance and are related to the environment, such as temperature and rainfall.

Composite pavements: a pavement structure composed of an asphalt concrete surface and Portland cement concrete (PCC) slab.

Concrete modulus of rupture (S'c): A 28-day flexural strength based on third point loading that indicates the extreme fibre stress under the breaking load in a beam-breaking test. In accordance with section 2.3.4 of the 1993 AASHTO Guide for Design of Pavement Structures (4), pavement designs for department projects use a standard S’c value of 635 psi.

Page xi

TOC FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

Concrete pavement slab: Normally consisting of plain cement concrete pavement, slabs serve as the main structural element in the rigid pavement system. Such slabs must be at least 8 inches thick.

Construction Joint: a joint made necessary by a prolonged interruption in the placing of concrete.

Contraction Joint: a joint normally placed at recurrent intervals in a rigid slab to control transverse cracking.

Crack seal: is the placement of materials into working cracks to fill and seal the crack.

Dowel: a load transfer device in a rigid slab, usually consisting of a plain round steel bar.

Drainage coefficients: Factors used to modify layer coefficients in flexible pavements or stresses in rigid pavements as a function of how well the pavement structure can handle the adverse effect of water infiltration.

Drainage factor (CD): A pavement subsurface’s ability to drain over a period from 1 hour to 72 hours. In accordance with section 2.4.1 of the 1993 AASHTO Guide for Design of Pavement

Structures (4), pavement designs for department projects use a standard CD value of 1.0.

Empirical Pavement Design: methodology to design pavement based on test sections or empirical models.

Equivalent Single Axle load (ESAL): the accumulation of the damage caused by mixed truck traffic during the design period compared to the damage caused by equivalent single axle load.

Expansion joint: a joint located to provide for expansion of a rigid slab, without damage of itself, adjacent slabs, or structures.

Fatigue cracking: a series of interconnected cracks that is caused by fatigue failure of the asphalt surface (or the stabilized base) under repeated traffic loading.

Finite element analysis: the use of Finite element analysis to model and analyze a pavement structure under traffic loads.

Flexible pavements: a pavement structure which distributes loads to the subgrade by means of aggregate interlock, particle friction, and cohesion for stability. Asphalt concrete is mainly used at the surface layer.

Fog seal: A fog seal is a light application of a slow-setting asphalt emulsion diluted with water to seal the pavement surface.

Initial serviceability (PI): A value, generally between 4.2 and 4.5, that indicates the condition of a newly constructed roadway.

Joint transfer factor (J): A concrete joint’s ability to transfer load. In accordance with section 2.4.2 of the 1993 AASHTO Guide for Design of Pavement Structures (4), pavement designs for department projects use a standard J value of 3.2.

Layer coefficients: the empirical relationship between structural number (SN) and layer thickness which expresses the relative ability of a material to function as a structural component of the pavement.

Life Cycle Cost (LCC): the estimated cost of the pavement during its life span. The cost includes construction, maintenance, and other user related costs. Page xii

TOC FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

Linear elastic analysis: the use of fundaments material properties to estimate how will deform and stress due to load application. The analysis is based on assumed linear and elastic behaviour of the material.

Load transfer device: a mechanical means designed to carry loads across a joint in a rigid slab.

Longitudinal joint: a joint normally placed between traffic lanes in rigid pavements to control longitudinal cracking.

Low Volume Road (LVR): a roadway generally subjected to low levels of traffic.

Material Characterization: the use of testing or prediction models to obtain material properties that is needed in the design methodology.

Mechanistic-Empirical (M-E) Pavement Design: pavement design that is based on the use of fundamental properties (such as stiffness) in mechanistic model to obtain material response (deformation and stresses) due to applied loads. The material response is then used in empirical models to predict pavement performance.

Modulus of elasticity (EC): Known as Young’s modulus or stress-to-strain ratio, a measurement of the stiffness of a concrete slab. The standard EC value for concrete slabs is 4,000,000 psi.

Modulus of subgrade reaction (k-value): Westerfaard’s modulus of subgrade reaction for use in rigid pavement design (the load in pounds per square inch on a loaded area of the roadbed soil or subbase divided by the deflection in inches or the roadbed soil or subbase. The default value is 200 lbs/inch2/in for special select soil material (sand).

Natural ground or fill: Natural material or embankment material that resides under the constructed pavement structure.

Nomograph: is a graphical presentation of the solution of an empirical model.

Panel length: the distance between adjacent transverse joints.

Pavement condition survey: a survey that is conducted on existing pavements to access the pavement condition. The survey includes visual and physical measurement of the pavement distress.

Pavement distress: is the failure of the pavement to provide its purpose of a smooth and stable ride-able surface. The distresses have different types such as roughness, fatigue cracking, permanent deformation, pot holes and others.

Pavement maintenance: the preservation of the entire roadway, including surface, shoulders, roadsides, structures, and such traffic control devices as are necessary for it safe and efficient utilization

Pavement Management Systems (PMS): a tool for designers and decision makers to collect a comprehensive database of current and historical information on pavement conditions, pavement structures, and traffic. Then analyze the data to determine existing and future pavement conditions, predict financial needs, and identify and prioritize pavement preservation and maintenance plans.

Pavement rehabilitation: Methodologies to renovate the existing pavement by removing damaged layers and replace/add new layers to restore the structural capacity of the pavement.

Pavement structural capacity: the carrying load capacity of a pavement structure. This can be measured by deflection testing, amount of distress, material properties and layer thickness. Page xiii

TOC FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

Pavement structural design: a process to estimate the layers thickness for a pavement structure.

Pavement Structure: Pavement structure is a combination of Subbase, base course (treated or untreated), and surface course placed on a subgrade to support the traffic load and distribute it to the roadbed soil or embankment material.

Performance period: the period of time that an initially constructed or rehabilitated pavement structure will perform before reaching its terminal serviceability.

Permanent deformation (rutting): Surface depression in the wheel path that might be accompanied by pavement uplift (shearing) along the sides of the rut.

Present serviceability index (PSI): A roadway’s ability to serve the traffic that uses the related facility. A roadway’s PSI can rate from 0 to 5, with 5 being the best and 0 being the worst. As a road’s smoothness deteriorates, its PSI decreases.

Pumping: The ejection of foundation material through joints or cracks or along edges of rigid slabs, resulting from vertical movements of the slab under traffic.

Reinforcement: steel embedded in a rigid slab to resist tensile stresses and detrimental opening of cracks.

Reliability (%R): Statistical probability that a facility will achieve its desired design life. This factor that enables design engineers to tailor designs to more closely match the needs of the project. A high reliability value, however, may substantially increase concrete depth. Reliability models are based on serviceability rather than specific failure mechanisms, such as cracking and pumping. In accordance with section 2.1.3 of the 1993 AASHTO Guide for Design of Pavement Structures (4), recommended values range from 75% to 95%. Reliability, however, is not an input value for the

AASHTO design equation. Rather, engineers input the standard normal deviate (ZR) into the equation.

Required depth (DR): A pavement structure’s required strength, represented by the slab depth as determined from traffic load information and roadbed soil strength.

Resilient modulus (Mr): a measure of the modulus of elasticity of subgrade soil or other pavement material.

Rigid pavement: a pavement structure which distributes loads to the subgrade, having as one course a Portland cement concrete slab of relatively high bending resistance.

Selected material: a suitable native material obtained from a specified source such as a particular roadway cut or borrow area, of a suitable material having specified characteristics to be used for a specific purpose.

Serviceability: the ability of time of observation of a pavement to serve traffic which uses the facility.

Slurry seal: is a mixture of slow-setting emulsified asphalt, well-graded fine aggregate, mineral filler, and water. It will fill fine cracks in the pavement surface.

Standard deviation (SO): A value used in design calculations to represent the variability in construction and loading prediction for rigid pavements. The pavement designs use a fixed value of 0.35.

Page xiv

TOC FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

Standard normal deviate (ZR): A value derived by converting a corresponding Reliability (%R) value into logarithmic form.

Structural Number (SN): an index number derived from an analysis of traffic, roadbed soil conditions, and environment which may be converted to thickness of flexible pavement layers thought the use of suitable layer coefficients related to the type of material being used in each layer of the pavement structure.

Subbase: A vertically drainable and stable layer or layers, at least 6 inches thick, of specified or selected material of designed thickness placed on a subgrade to support a base course or the concrete slab.

Subgrade: the top surface of a roadbed upon which the pavement structure and shoulders are constructed.

Tandem axle load: the total load transmitted to the road by two consecutive axles extending across the full width of the vehicle.

Terminal serviceability (PT): A value, generally between 2.0 and 2.5, that indicates that a road requires some type of rehabilitation or reconstruction.

Tie bar: a deformed steel bar or connector embedded across a joint in a rigid slab to prevent separation of abutting slabs.

Traffic equivalence factor: a numerical factor that expresses the relationship of a given axle load to another axle load in terms of their effect on the serviceability of a pavement structure.

Traffic studies: Studies that are conducted to obtain vehicle count and distribution, vehicle classification and axle loads.

Treated permeable base: A non-structural layer underneath the pavement slab that provides lateral drainage for water that infiltrates through pavement joints. Many types of material, including asphalt treated permeable base (ATB) and cement treated permeable base (CTB), are available for this base layer.

Tridem Axle load: the total load transmitted to the road by three consecutive axles extending across the full width of the vehicle.

Page xv

TOC FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

ABBREVIATIONS AND ACRONYMS

AADT: Annual Average Daily Traffic

AASHTO: American Association of State Highway and Transportation Officials

AC: Asphalt concrete

ADT: Annual daily traffic

AED: Arabic Emirates Dirham

ASL: Aggregate Severity Level

ASTM: American Society for Testing and Materials

ATB: Asphalt treated base

Austroads: Association of Australian and New Zealand road transport and traffic authorities

CBR: California Bearing Ratio

CIPR: cold-in-place recycling

CRCP: Continuous reinforced concrete pavement

CTB: Cement treated base

DCP: Dynamic Cone Penetrometer

DF: Directional factor

DL: Design Life

ADM: Abu Dhabi City Municipality

DMAT: Department of Municipal Affairs and Transport , Abu Dhabi

EALF: Equivalent Axle load factor

EC: Modulus of elasticity

ESAL: Equivalent Single Axle load

FWD: Falling Weight Deflectometer

GF: Growth factor

GPR: Ground Penetrating Radar

HIPAR: Hot-in-place asphalt recycling

HMA: hot mix asphalt

IRI: International roughness index

J: Joint transfer factor

JPCP: Jointed plain concrete pavement Page xvi

TOC FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

JRCP: Jointed reinforced concrete pavement k-value: Modulus of subgrade reaction kPa: Kilo Pascal

LCC: Life Cycle Cost

LDF: lane distribution factor

LSF: load safety factor

LTPP: Long-term pavement performance

LVR: Low Volume Roads

MAAT: Mean annual air temperature

M-E: Mechanistic – Empirical

MPa: Mega Pascal

N: Allowable number of standard axle repetitions

NDT: non-destructive deflection testing

PCC: Portland cement concrete pavement

PI: Penetration Index

PMS: Pavement Management Systems

PSI: Present serviceability index

QADT: Quad axle with dual tires

R%: Reliability

RTFO: Rolling Thin Film Oven tests

SADT: Single axle with dual tires

SAST: Single axle with single tire

S'c: Concrete modulus of rupture

SN: Structural Number

SO: Standard deviation

T: percentage of trucks

T800 pen: temperature, in degrees Celsius, when binder penetration (100 g, 5 s) is 800.

TADT: Tandem axle with dual tires

TAST: Tandem axle with single tire

TF: Truck factor

Page xvii

TOC FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

TRDT: Tridem axle with dual tires

UCS: unconfined compressive strength

UPC: Urban Planning Council

WIM: Weigh-in-motion

WMA: warm mix asphalt

WMAAT: weighted mean annual air temperature

WMAPT: Weighted mean annual pavement temperature

ZR: Standard normal deviate

Zx: Cumulative difference variable

Page xviii

TOC FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

1 INTRODUCTION 1.1 Overview In 2010, the Department of Transport (DoT) in Abu Dhabi commenced with the “Unifying and Standardizing of Road Engineering Practices” Project. The objective of the project was to enhance the management, planning, design, construction, maintenance and operation of all roads and related infrastructures in the Emirate and ensure a safe and uniform operational and structural capacity throughout the road network.

To achieve this objective a set of standards, specifications, guidelines and manuals were developed in consultation with all relevant authorities in the Abu Dhabi Emirate including the Department of Municipal Affairs and Transport (DMAT) and Urban Planning Council (UPC). In future, all authorities or agencies involved in roads and road infrastructures in the Emirate shall exercise their functions and responsibilities in accordance with these documents. The purpose, scope and applicability of each document are clearly indicated in each document.

It is recognized that there are already published documents with similar objectives and contents prepared by other authorities. Such related publications are mentioned in each new document and are being superseded by the publication of the new document, except in cases where previously published documents are recognized and referenced in the new document. 1.2 Purpose and scope Pavement design, an integral and critical part of the transportation system, focuses on thickness design of pavement layers. In general, pavement design requires knowledge about the materials in any existing pavement layers, the foundation upon which the pavement will reside, traffic levels, and climatic conditions. Selecting a final design, however, depends on the availability of materials, funding, and local experience.

This manual provides comprehensive information needed to develop complete structural pavement designs. Topics include required data, material characterization, new pavement design, rehabilitation techniques, pavement maintenance, pavement management, low volume roads (LVR), and life cycle cost (LCC) analysis. This manual also covers the empirical and mechanistic- empirical (M-E) design methods. Using the information in this manual, a designer can apply several design methods and select a final design based on LCC analysis.

Several pavement design methods are currently used by different agencies and countries. These methods vary somewhat for differing local conditions and resources. The procedures range from empirical to M-E approaches. New M-E pavement design analysis procedures developed over the last 20 years focus on the design and construction of high quality, long-lasting and well-performing highways that accommodate the increase in traffic volumes and loads in ways that exceed the empirical methods. These new approaches are challenging in that they require advanced analysis methods and material characterization. In response to these technical advances and increasingly easy computation, DMAT has replaced the older empirical methodologies for pavement engineering with newer and more fundamental mechanistic design approaches.

Combining information about conditions and resources from different international manuals, while including ways to use sustainable and economical materials, this manual is highly applicable to Abu Dhabi. It covers different options for obtaining traffic count and loads, environmental factors, and advanced material characterizations that apply to Abu Dhabi.

Page 1

01-INTRODUCTION FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

This manual provides only brief descriptions for some pavement design topics. It frequently includes references to other DMAT manuals that cover such topics in more detail. 1.3 Application of this manual Information in this manual focuses on structural pavement design, with methods for determining layer thickness and pavement structural capacity. This manual is intended for use by pavement engineers conducting structural design for either existing or new pavement structures.

Structural calculations for pavement design require knowledge of existing traffic flow, predictions of anticipated future traffic, and environmental factors at the road’s location. Pavement designers must also obtain information about the properties of the materials (such as asphalt, Portland cement, or granular road base) that will be used in each pavement layer. Designs must account for these material properties in conjunction with the material specifications and asphalt mixture designs, as detailed in the DMAT Standard Specifications Volume 1 for Road Works (1).

Completing the pavement design process involves using either the 1993 American Association of State Highway and Transportation Officials (AASHTO) (4) nomograph or Association of Australian and New Zealand Road Transport and Traffic Authorities (6) (Austroads) software to determine the required layer thickness. After generating several designs using different methods, a pavement engineer shall conduct an LCC analysis to compare the designs for cost effectiveness. For details about LCC analysis, refer to Chapter 9, Life-cycle Cost Analysis, in this manual, as well as the DMAT’s Project Cost Estimating Manual (2) and Bill of Quantities Manual for Road Projects (3).

Pavement design requires not only designing new pavements, but also evaluating existing pavement. Ensuring that existing pavement facilities have sufficient functional capacity and ride quality involves maintenance, possibly including the construction of additional layers. Optional methods for maintaining existing pavements such as chip sealing, fog sealing, slurry sealing, and crack sealing are described in Chapter 8. Such maintenance or rehabilitation requires conducting pavement condition surveys to get information about the condition of the existing pavement. Refer to Chapter 10, Pavement Management Systems, in this manual for information about the pavement management system and Chapter 11 for the existing pavement evaluation and pavement condition surveys.

Evaluating existing pavements requires significant engineering judgement and effective application of the backcalculation procedure. Based on the pavement design guidelines in this manual, design engineers apply their own methodologies and experienced judgment to arrive at final rehabilitation methods.

This manual provides guidelines for the design of new and rehabilitation of asphalt and concrete pavements. The concrete pavement design guidelines are given in less detail. Applicable international standards for concrete pavement design are followed in the manual. 1.4 Content and format This manual includes sections detailing inputs such as traffic, climate, and material properties, as well as sections on maintenance, rehabilitation, and LCC analysis. It also provides appropriate charts and nomographs. Calculations frequently include examples for clarification. The section on LVR is particularly relevant for rural areas.

Because different design methodologies deal with inputs in different ways, this manual advises designers on how to estimate these inputs and how to obtain valid condition inputs for Abu Dhabi. It also includes ways to ensure that pavement designs support sustainability.

Page 2

01-INTRODUCTION FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

This manual includes the following chapters:

 Chapter 1 – Introduction: Outlines the purpose, scope, intended users, and application of this manual.  Chapter 2 – Pavement design components: Describes elements, such as environmental and traffic factors, that must be considered in pavement design, and provides instructions on how to determine such factors.  Chapter 3 – Pavement material : Identifies properties of pavement materials and provides instructions on how to determine such properties through tests of the use of models.  Chapter 4 – New Pavement Design: Details the rehabilitation of flexible and rigid pavement structures.  Chapter 5 – Rehabilitation Design : Details the design of new flexible and rigid pavement structures.  Chapter 6 – Low-volume roads: Covers the design of LVR.  Chapter 7 – Drainage design: Focuses on the design of granular drainage layer in a pavement structure.  Chapter 8 – Pavement maintenance: Offers different maintenance options.  Chapter 9 – Life-cycle cost analysis: Details LCC analysis for pavement structures.  Chapter 10 – Pavement management systems: Provides an overview of the Abu Dhabi PMS and summarises related concepts.  Chapter 11 - Existing Pavement Evaluation: Provides overview of different methods to conduct pavement condition surveys and how to analysis the collected distress data.

The appendices of this manual provide supplementary charts and tables for the design on the rigid pavements. 1.5 Pavement structure design This section introduces different types of pavement structures and describes different design methods. This manual’s remaining chapters provide greater detail on these topics. 1.5.1 Pavement structure Selecting the best pavement structure design method depends primarily on the type of the pavement structure. Three main types of pavement structures include flexible pavements, rigid pavements, and composite pavements. Each type of structure differs in the way it reacts to applied traffic loads, reflecting the characteristics of the structure’s surface layer. 1.5.1.1 Flexible pavements Flexible pavements use bituminous (asphalt) material on their surfaces. A granular or treated base (or subbase) resides under the asphalt layer, on top of the subgrade. Materials of the best quality reside on the top, where stress intensity is highest. In some cases, full-depth asphalt resides on top of the subgrade without the use of a granular base layer. Figure 1-1 shows conventional asphalt pavement. Figure 1-2 shows full depth asphalt pavements.

About 90% of the roads in the world are flexible, asphalt. In United Arab Emirates (UAE), 99% of road surfaces are asphalt pavements. Flexible pavements are standard practice in UAE because the required binder materials are relatively inexpensive and readily availability, and because contractors who are familiar with this process are also readily available. Flexible pavements typically require more extensive maintenance.

Page 3

01-INTRODUCTION FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

Analysis of flexible pavement involves applying a multilayer elastic theory that assesses deflections and strains. Major distresses occur in flexible pavements because they have either structural or functional deficiencies. Permanent deformation and fatigue cracking (both area and longitudinal) are caused by structural deficiencies, while low temperature, non-wheel path and block cracking result from functional deficiencies. In UAE, prevalent major distresses include permanent deformation, fatigue cracking, and asphalt pavement oxidation. Thermal cracking is not a concern in UAE, because it occurs when temperatures drop below zero degrees.

Figure 1-1: Conventional asphalt pavement

Figure 1-2: Full depth asphalt pavements

1.5.1.2 Rigid pavements Rigid pavements typically consist of Portland cement concrete pavement (PCC) over a stabilized or un-stabilized base course, subbase course, or subgrade. Rigid pavements are mainly applicable for freeways and expressways where opportunities to close the facility for maintenance are limited or where traffic loads are too heavy for flexible pavements. Rigid pavement typically has a higher initial cost, but requires less extensive maintenance over its intended lifetime. To determine whether to use flexible or rigid pavement, designers should conduct LCC analysis to determine the full cost over the pavement’s intended life rather than just the initial cost. Figure 1-3 shows a typical rigid pavement structure.

In rigid pavement analysis, which is based on plate theory, the flexural stress in concrete as the major design factor. Concrete slabs in the rigid pavement can be plain jointed concrete pavement (JPCP), jointed reinforced concrete pavement (JRCP), and continuous reinforced concrete pavement (CRCP).

Page 4

01-INTRODUCTION FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

Major distresses that occur in rigid pavements include faulting, longitudinal and transverse cracking, corner breaks, spalling, and polished aggregate.

Figure 1-3: Rigid pavements 1.5.1.3 Composite pavements In a composite pavement configuration, a flexible layer resides on top of a rigid surface layer to increase the performance of the rigid pavement. Acting as a thermal and moisture blanket, the flexible layer reduces the vertical temperature and moisture gradient within the rigid surface layer. In addition, this layer acts as a wearing course, reducing wearing caused by wheel loads on the rigid surface layer. Figure 1-4 shows a typical composite pavement.

Analysis of composite pavements is based on a combination of layered and plate theory. Initially, engineers develop a rigid pavement design to ascertain the cracking in the concrete layer, then apply layered theory to design the top asphalt layer. For composite pavements, critical distress predominantly involves reflective cracking, in which cracks in the upper concrete layer result from cracks in the underlying asphalt layer.

Figure 1-4: Composite pavements 1.5.2 Pavement design methods Historically, pavement design has been based on empirical models formulated from pavement test tracks or lab testing. Such empirical methods, which use Nomograph, equations, or software to determine the thickness of the layers, were developed using limited data. Agencies that apply

Page 5

01-INTRODUCTION FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL these methods often face issues when the traffic conditions exceed those upon which the methods were based.

Advances in technology have enabled designers to use computers to easily perform related complicated computations. New technology has also enabled designers to better assess and predict traffic loads and traffic counts, characterize materials, and model environmental factors. To adjust to increasing traffic loads, however, agencies have started to use mechanistic-empirical (M- E) methods that, based on fundamental properties and advanced material characterization, enable engineers to more effectively design economical pavement structures. 1.5.2.1 Empirical method For a good example of empirical methods, refer to the 1993 AASHTO Guide for Design of Pavement Structures (4). Most countries around the world use the 1993 AASHTO guide with some modification to reflect local experience and conditions. Refer to the Abu Dhabi Municipality Roadway Design Manual (5), which is based on the 1993 AASHTO guide, for more information.

To develop the Guide for Design of Pavement Structures (4), AASHTO compiled results from road tests conducted from 1958 to 1960 in Ottawa, Illinois, U.S.A. Data from these tests reflect one climatic condition, one foundation type, and one million equivalent single axle loads (ESALs). From 1960 to 1993, AASHTO added several enhancements, such increased reliance on traffic data and a limiting layer approach.

Covering both flexible and rigid pavement design, The 1993 AASHTO Guide for Design of Pavement Structures (4) describes material characterization, equivalent traffic estimation, life cycle costs, and existing pavement evaluation. It applies an ESAL as the basic unit for traffic estimation. Its material characterizations use an empirical factor to reflect layer stiffness.

Pavement designers around the world have used this guide successfully for many years. Reasons for designers’ success with this guide include the following:

1. Pavement designers can easily use the Nomograph or software. 2. Inputs defined by the guide are simple, many of which can be assumed easily. 3. Designers are very familiar with the methodology. 1.5.2.2 Mechanistic-Empirical method Advances in technology have encouraged the pavement community to start shifting from the empirical method to the M-E method, which is based on fundamental material properties and actual traffic loads.

Applying the fundamental stresses and strains of the materials in different layers at different depths of the pavement structure, the mechanistic method enables designers to evaluate the validity of proposed layer thicknesses. Designers calculate stresses and strains using either linear elastic analysis or a more complicated model that focuses on finite elements under actual traffic loads. Analysis using the mechanistic method also depends on detailed material characterizations, which vary based on temperature (for hot mix asphalt layers), ground water table depth, and moisture content (for granular layers). All M-E methods involve using a software package to analyse and design the pavement structure.

Austroads, the association of Australian and New Zealand road transport and traffic authorities, has developed an M-E pavement design guide, Guide to Pavement Technology, Part 2: Pavement Structural Design (6). This manual contains ten different sections that cover all aspects of pavement design, including structural design, surfacing, materials, pavement evaluation and Page 6

01-INTRODUCTION FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL treatment, maintenance, construction work practices, and drainage. Austroads also has a software package for pavement analysis.

According to the Austroads guide (6), engineers apply structural analysis of the trial pavement configuration to quantify critical strains and stresses that are caused by traffic loads. They can vary the method to consider pavement layers as either fully elastic (visco-elastic), uniform in lateral extent, or variable, with either full friction or no friction between the layers. By using these variations, engineers attempt to establish theoretical estimates that agree with observed reactions to traffic loading.

In addition, engineers can analyse pavement designs based on varying traffic loads, from a single vertical load with uniform tire contact stress to multiple loads with multi-directional components and non-uniform stress distribution. They can also vary traffic speeds to further assess potential traffic loads. Engineers must be careful, however, to ensure that the sophistication of the analysis method is compatible with the quality of the input data. Otherwise, they need to make too many assumptions to fill the gaps, resulting in misleading, if not worthless, analysis.

Austroads (6) states that engineers can reliably obtain required input for analysis based on the M-E method. Results from such analysis provide predictions of pavement performance that reasonably match pavement performance in Australasian.

Upon completing the structural analysis, engineers can use the results to estimate the allowable loading of the pavement configuration. Austroads (6) states that, in the M-E method, most performance criteria assigned to pavement materials and to the subgrade relate the level of strain induced by a standard single axle load and the number of such loads that exceed the pavement’s tolerance level, based on material characteristics. 1.6 General Requirements for Pavement Design The general requirements for road pavement design procedures, reports, quality assurance, and check lists for Abu Dhabi projects shall be as shown in Annex 1.

Page 7

01-INTRODUCTION FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

2 PAVEMENT DESIGN COMPONENTS 2.1 Overview Environment, the subgrade, and traffic significantly impact pavement design. Because these components vary over time and by location, however, they cannot be fully controlled. Careful study and characterization of these factors are critical for pavement design.

This chapter addresses both environment and traffic. Refer to Chapter 3, Pavement Material Characterization, for information about the subgrade. This manual includes details about the required input and data collection needed for designs using the empirical method and the M-E method.

Two major environmental factors that influence pavement are water and temperature. Temperature affects the properties of the asphalt layer. Water affects the performance and stiffness of the unbound base, subbase, and subgrade layers. Water can infiltrate from the surface as a result of rainfall or from high-ground water tables.

Traffic is another major uncontrolled factor that impacts pavement design. Mathematically, traffic is represented in terms of applied loads on pavement structures. Vehicle classification, loads, and traffic studies are crucial for designing adequate pavement cross sections. This chapter explains both the traffic details that are required for M-E design and the equivalent axle load calculations that empirical design requires. 2.2 Environment Environment includes many variables, including temperature, rainfall, sunshine, humidity, and wind. These factors impact a road’s performance and condition over time. Changing temperatures can change the properties of materials in hot mix asphalt (HMA); higher temperatures result in a softer asphalt mixture for the same binder type. Wet soils have a lower strength (less stiffness) than dry soils. A good design accounts for known and anticipated environmental influences. 2.2.1 Environmental factors for empirical design According to the 1993 AASHTO Guide for Design of Pavement Structures (4), designers following the empirical method consider environmental factors only regarding how changes in moisture impact the subgrade layer modulus. This method uses the resilient modulus (Mr), or stiffness, to characterize the subgrade material layer. Designers can determine the Mr either through laboratory testing (AASHTO T-274) or backcalculation of the modulus values using deflection data. They can also correlate soil properties, such as moisture content and plasticity index, to determine the modulus. Refer to Chapter 3, Pavement Material Characterization, for details.

Designers can perform Mr testing to consider seasonal variations in the subgrade modulus. By developing a relationship between moisture changes and the Mr, then comparing this relationship with the in-situ moisture content, they can determine the corresponding modulus. Designers can apply Equation 2-1 to determine a relative damage factor (Uf) that accounts for seasonal variations.

8 -2.32 Uf = 1.18 * 10 * Mr

Equation 2-1: Relative damage Page 8

02-PAVEMENT DESIGN COMPONENTS FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

Where: Uf= Relative damage

Mr = Subgrade resilient modulus (psi).

Designers can also graphically determine a relative damage factor (Uf) that accounts for seasonal variations, as shown in Figure 2-1. Using this method, a designer determines the subgrade resilient modulus for each seasonal period and calculates the relative damage for the same period.

Figure 2-1: Relative damage calculation

A seasonal period can be a single month or up to several months, depending on how much these factors change for different periods. When all the seasonal figures are available, a designer calculates the average relative damage and applies this average to back-calculate the corresponding modulus of the subgrade.

Page 9

02-PAVEMENT DESIGN COMPONENTS FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

2.2.2 Environmental factors for mechanistic-empirical design The M-E design methodology incorporates the environmental effect on pavement through two significant factors, moisture and temperature. The following sections provide guidance on how to consider effect of moisture and temperature on pavement design, based on information in the Austroads Guide to Pavement Technology, Part 2: Pavement Structural Design (6). 2.2.2.1 Moisture content Moisture content has a significant effect on the stiffness (strength) of unbound layers and the subgrade. According to Austroads, moisture in the pavement structure can result from seepage, fluctuations of ground water tables, and infiltration of water through the surface. Accordingly, designers must study several factors, including rainfall, the permeability of surface layers, the depths of ground water tables, vegetation, and pavement drainage.

According to UAE National Centre of Meteorology and Seismology (7), the average value for rainfall in Abu Dhabi Emirate and the Western Region is 56.3 mm, based on cumulative annual rainfall for 28 different weather stations in the area. Figure 2-2 shows a contour of the cumulative annual rainfall, in mm.

Figure 2-2: Abu Dhabi cumulative annual rainfall

Table 2-1 provides details about annual rainfall in Abu Dhabi, as reflected by the rainfall values for the 28 weather locations.

Page 10

02-PAVEMENT DESIGN COMPONENTS FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

Table 2-1: Abu Dhabi cumulative annual rainfall

Cumulative Cumulative Station Annual Rainfall Station Annual Rainfall (mm) (mm) Madinat Zayed 40.8 Abu Dhabi 60.7 AL Gheweifat 47.5 Al Wathbah 78.1 Al jazeera BG 27.3 Al Khazna 82.9 Mukhariz 31.6 Al Rowdah 51.9 Owtaid 61.7 Al Arad 69.3 Mezaira 26.6 Unknown 80.5 Hamim 33.9 Jabal Hafeet 95.3 Um Azimul 42.5 Um Ghafa 44.1 Bu Hamrah 32.3 Khatam Al Shadah 121.6 Al Qlaa 29.0 Al Ain 43.9 Sir Bani Yas 47.5 Al Qattara 20.3 Rezeen 69.9 Al Foah 128.0 Al Quaa 44.1 Raknah 75.9 Abu Abyad 45.2 Sweihan 44.6

2.2.2.2 Temperature Changes in temperature mainly affect the asphalt layer. Asphalt becomes stiff and brittle at low temperatures. Higher temperatures accelerate the aging of the asphalt materials, causing the asphalt mixture to become stiffer with time. Refer to Chapter 3, Pavement Material Characterization, for an asphalt layer modulus calculation, which accounts for temperature effects.

Considering temperature effects is also important when selecting the binder for a road design. Typically, designers follow the binder performance grade in the Superpave mix design system to select the binder. Given Abu Dhabi Emirate’s relatively insignificant temperature changes, however, designers can select the same binder grade for all road designs for the region.

According to Austroads Guide to Pavement Technology, Part 2: Pavement Structural Design (6), designers consider the effects of temperature on the asphalt layer modulus by estimating the weighted mean annual pavement temperature (WMAPT). To estimate the WMAPT, perform the following steps:

1. Obtain the monthly average daily maximum air temperature and the annual monthly daily minimum air temperature. 2. Calculate the monthly average air temperatures by averaging the maximum and minimum air temperatures. 3. Using Equation 2-2 and the monthly average air temperature, calculate the temperature weighting factors (WF) for each month. 4. For each site, average the 12 WFs obtained in step 3. 5. Using the average WF from step 4, apply Equation 2-3 to estimate the weighted mean annual air temperature (WMAAT) for each site. 6. Using the WMAAT, apply Equation 2-4 to estimate the WMAPT for each site.

The following equations are based on the Shell International Petroleum Company’s Pavement Design Manual: Asphalt pavement and overlays for road traffic, 1978 (8).

Page 11

02-PAVEMENT DESIGN COMPONENTS FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

Equation 2-2: Temperature weight factor

Equation 2-3: Weighted mean annual air temperature

Equation 2-4: Weighted mean annual pavement temperature

According to UAE National Center of Meteorology and Seismology (7), temperature changes in Abu Dhabi Emirate are generally not significant, based on maximum and minimum air temperatures recorded at 30 different weather stations in the area. Figure 2-3 shows the mean annual air temperature in the Abu Dhabi Emirate.

Figure 2-3: Abu Dhabi mean annual air temperature

Table 2-2 provides details about annual air temperatures in Abu Dhabi, based on the data gathered at 30 area weather stations. The WMAPT values in this table are based on the steps provided above. The WAMPT values are based on the calculation in Equation 2-4 WMAPT values in the region range from 45.0° C to 38.7° C, with an average value of 43.5° C. The average value is representative for the entire Abu Dhabi Emirate.

Page 12

02-PAVEMENT DESIGN COMPONENTS FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

Table 2-2: Weighted mean temperatures

Station WMAAT (oC) WMAPT (oC) Madinat Zayed 30.5 44.0 AL Gheweifat 30.2 43.7 Al jazeera BG 30.6 44.1 Mukhariz 30.8 44.4 Owtaid 30.8 44.3 Mezaira 31.1 44.8 Hamim 30.0 43.3 Um Azimul 31.3 45.1 Bu Hamrah 30.1 43.4 Al Qlaa 29.6 42.9 Sir Bani Yas 30.9 44.6 Rezeen 29.5 42.7 Al Quaa 30.1 43.5 Abu Abyad 30.4 43.8 Al Aryam 30.3 43.7 Abu Dhabi 30.6 44.2 Al Wathbah 30.0 43.4 Al Khazna 29.8 43.1 Damsa 29.5 42.7 Al Rowdah 30.3 43.8 Al Arad 29.5 42.7 Unknown 30.5 44.0 Jabal Hafeet 26.5 38.7 Um Ghafa 31.1 44.7 Khatam Al Shadah 30.3 43.7 Al Ain 31.1 44.8 Al Qattara 31.0 44.7 Al Foah 29.9 43.2 Raknah 28.2 40.9 Sweihan 30.2 43.6 AVERAGE 30.2 43.5

2.3 Traffic analysis procedures Traffic analysis factors detailed in this section apply to both flexible and rigid pavements on heavily trafficked roadways. For design guidelines for lightly trafficked roads, refer to Chapter 6, Low- volume Roads. Traffic analysis for pavement design involves the application of data collected from traffic surveys to estimate equivalent single axle loads (ESALs), which are the standard measure for traffic load forecasts for empirical and M-E pavement design methods. 2.3.1 Design life One of the important factors that determine pavement structure thickness requirements is the design life (DL) of the pavement. A road’s DL corresponds to a total number of truck loads (the wear equivalent to that caused by the passing of one truck), which directly impact the thickness of a pavement structure. A road’s DL is the duration over which the pavement is expected to function

Page 13

02-PAVEMENT DESIGN COMPONENTS FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL properly without major rehabilitation or reconstruction that is why it might be referred to as analysis period.

Engineers select a road’s DL based on the pavement’s intended function. Typically, flexible pavements have a DL of 20 years, while rigid pavements have a DL of 30 years. For temporary pavements, such as detours, however, DLs range from six months to a maximum of two years. Designers can propose DLs that exceed 20 years for pavement structures for important roads or for roads that will require less frequent maintenance. DMAT must approve such proposed DL increases before further pavement design activities can proceed. 2.3.2 Vehicle classification Pavement must be designed to carry the loads applied on it by the vehicles using the roadway. Although vehicles vary in their configuration, loads, and number of passes, designers must classify vehicles in a uniform way by grouping them according to their configurations and expected permissible loads. Based on these groups, a designer can determine the number of axle passes that will accumulate over time.

Figure 2-4 shows vehicle classifications for pavement designs, as defined in the USA Federal Highway Administration’s (FHWA) Guide to LTPP Traffic Data Collection and Processing (9). These classifications are as follows:

1. Motorcycle 2. Passenger cars 3. Other two-axle, four-tire single units 4. Buses 5. Two-axle, six-tire single units 6. Three-axle single units 7. Four or more axle single units 8. Four or less axle single trailers 9. Five-axle single trailers 10. Six or more axle single trailers 11. Five or less axle multi-trailer 12. Six-axle multi-trailer 13. Seven or more axle multi-trailer

Vehicles in classes 4 to 13 (buses to multi-trailer vehicles with seven or more axles) are the most critical vehicles for pavement design. Motorcycles and passenger cars cause insignificant pavement damage.

Page 14

02-PAVEMENT DESIGN COMPONENTS FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

Figure 2-4: FHWA vehicle classification 2.3.3 Axle group configuration According to Austroads Guide to Pavement Technology, Part 2: Pavement Structural Design (6), vehicles damage pavement based on how many axles they have, how their axles are grouped together, and the total mass of their axle group loads. The different axle groups are shown schematically in Figure 2-5 and are described as follows:

1. Single axle with single tire 2. Single axle with dual tires 3. Tandem axle with single tire 4. Tandem axle with dual tires 5. Tridem axle with dual tires 6. Quad axle with dual tires

Based on the axle grouping, engineers can use the axle group load to calculate the damage factor, how much damage a vehicle will cause, which will be explained later in this section.

Page 15

02-PAVEMENT DESIGN COMPONENTS FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

1) Single Axle Single Tire 2) Single Axle dual Tires 3) Tandem Axle Single Tire

4) Tandem Axle dual Tires 5) Tridem Axle dual Tires 6) Quad Axle dual Tires

Figure 2-5: Axle Group Configuration 2.3.4 Tire pressure For pavement design, tire inflation pressure represents the contact stress that is applied by a tire to the pavement surface. Contact stress is based on a tire’s load and its contact area (the tire’s imprint on the pavement). The actual tire contact stress varies by the load value and its imprint on the pavement surface depends on the tire pattern as seen in Figure 2-6. However, to simplify the analysis the contact stress is assumed to be uniform with a circular contact area. Equation 2-5 demonstrates the relationship of the three factors, contact stress, load and contact area based on a circular area.

q = P/A

Equation 2-5: Tire contact stress and load relationship

Where,

 q = Contact stress, kPa (kilopascals)  P = Applied load, kN (kilonewtons)  A = Area of contact, m2 = π a2  a = Contact radius, m

The actual shape of the tire imprint depends on the tire load. A tire’s imprint might be rectangular, trapezoidal, circular, or some irregular shape. Calculating the relationship between contact stress and load, as shown in Equation 2-5, assumes a circular tire imprint to facilitate the calculation process in a mechanistic model for the interaction between tire and pavement.

Typical tire pressures recorded by tire manufactures for heavy trucks range from 500 kPa to 1000 kPa, with an average value of 700 kPa.

Page 16

02-PAVEMENT DESIGN COMPONENTS FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

P q

a) Actual Tire pressure b) Assumed Tire pressure

Figure 2-6: Tire Pressure Distribution 2.3.5 Vehicle count Vehicle counts represent the total number of vehicles expected to use a road in both directions for a given time period, based on the vehicle classification. Time periods can vary from just a few days to entire seasons or a full 365 days.

Refer to Abu Dhabi DMAT Road Structures Design Manual (10) for directions on how to conduct traffic surveys to obtain vehicle counts. In such surveys, engineers count traffic over several days, then calculate an Average Daily Traffic (ADT) factor that serves as a base current two-way traffic volume. For new roadways for which engineers can’t obtain actual vehicle counts, engineers can apply traffic forecasting and trip generation models. 2.3.6 Traffic projections Pavement designers must estimate projected traffic loads over a road’s DL, which is typically 20 years. To project traffic volumes, engineers shall use the transportation modelling software of the City of Abu Dhabi.

If a model projection is not available, a designer shall assume a rational growth factor (GF), based on the current ADT, to estimate future traffic. To predict future traffic, use either the general GF, as shown in Equation 2-6, or one of the GF formulas. According to the Abu Dhabi Municipality’s Roadway Design Manual, engineers can use either the linear GF formula, as shown in Equation 2-7, or the compound GF formula, as shown in Equation 2-8, to estimate traffic.

ADT (Future) = ADT (current) * GF

Equation 2-6: General traffic projection relationship

GF = 1 + (GR/100)*DL

Equation 2-7: Linear growth factor

GF = (1 + (GR/100))DL

Page 17

02-PAVEMENT DESIGN COMPONENTS FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

Equation 2-8: Compound growth factor

Where

 ADT(Future) = Projected ADT at the end of DL, vehicle  ADT(current) = Current ADT, vehicle  GF = Growth factor, in decimal  GR = Growth rate in percentage  DL = Design life, years

GF ranges from 0 (which indicates no growth) to 10%. Engineers should base assumed GFs on a highway’s functional classification, as well as vehicle ownership, population, employment rates, and land uses within the area. 2.3.7 Design lanes In common practice, pavement construction uses the same structure for all lanes. A pavement designer bases this structure on the lane with the heaviest traffic, typically the slow outermost lane, which is called the design lane. Traffic analyses apply a lane distribution factor (LDF) to represent the design lane.

Practice in Abu Dhabi Emirates requires trucks to use the outer lane, for which the lane distribution factor (LDF) should be 1. 2.3.8 Directional factor If a roadway is a dual carriageway, engineers shall conduct the traffic count separately for each direction, applying a directional factor (DF) of 1.0. When counting traffic for an undivided roadway to determine a total volume for both directions, use a directional factor of 0.5. If traffic is higher in one direction, however, obtain an estimate from a traffic survey for better accuracy. 2.3.9 Percentage of trucks Pavement design requires determining the percentage of trucks (T), vehicles of classes 4 to 13 (buses to multi-trailer vehicles with seven or more axles), in the total traffic volume. If a traffic survey is available, engineers can obtain this percentage directly from the traffic data. 2.3.10 Equivalent axle load factor Pavement designs apply an equivalent single axle load factor (ESAL) to represent the accumulation of damage caused by traffic. This standard unit represents a truck with a single axle, dual tires, and total axle load of 80 kN as shown in Figure 2-7. To represent other axle groups (trucks with different loads and configurations), designers must apply an equivalent axle load factor (EALF) to transform such loads to the ESAL standard. An EALF represents the damage to a pavement caused by the actual mixed axle load and axle configuration traffic relative to the damage of the standard axle. Although the damage associated with the equivalent axle can be defined in numerous ways, the 1993 AASHTO Guide for Design of Pavement Structures (4) and Asphalt Institute’s Asphalt Pavements for highways & Streets Manual Series 1 (MS-1) (9) define it in terms of serviceability. These manuals provide tables to convert actual axle loads to ESALs. As an alternate method, designers can apply Equation 2-9, also called the ‘power law’, to calculate EALFs.

Page 18

02-PAVEMENT DESIGN COMPONENTS FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

Figure 2-7: 80 kN Standard Axle

EALF = (L/SL)m

Equation 2-9: EALF power law

Where:

 EALF = Equivalent axle load factor  L = Actual axle load  SL = Standard axle load (refer to Table 2-3)  m = Load damage exponent (refer to Table 2-4)

Table 2-3: Standard axle load by axle group

Axle Group type Load (kN) Single axle, single tire 53 Single axle, dual tire 80 Tandem axle, single tire 90 Tandem axle, dual tire 135 Tridem axle, dual tire 181 Quad axle, dual tire 221

Table 2-4: Load damage exponent

Load Damage Design Method Exponent (m) Empirical 4 Mechanistic – Control Fatigue 5 Mechanistic – Control Rutting 7

Engineers can obtain actual axle loads from a weigh-in-motion (WIM) system data or from a traffic survey that collects axle loads in addition to vehicle counts. 2.3.11 Truck factor Pavement designs apply a truck factor (TF), which represents the percentage of different truck classes in the total traffic volume and the average number of axles per truck in the traffic volume. Because different truck classes have a different axle configurations and different loads, a truck factor is the summation of the percentage of each truck class multiplied by the load factor for each class or group of trucks and the average number of axles. Designers shall obtain the percentage of each class from a traffic survey. If only one class is available, designers can apply Equation 2-10 to determine the truck factor.

Page 19

02-PAVEMENT DESIGN COMPONENTS FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

TF = (∑ p*EALF)

Equation 2-10: Truck factor

Where:

 TF = Truck factor  p = Percent of each truck class  EALF = Equivalent axle load factor

A sample EALF calculation sheet for a typical public bus based on the AASHTO (appendix D, table D.4) is attached in the Annex 2. 2.3.12 ESAL calculation Engineers can apply Equation 2-11 to convert the accumulation of the mixed traffic load passes to ESALs (a standard axle load for an 80-kN single axle vehicle).

ESAL = ADT(current)*T*TF*GF*LDF*DF*DL*365

Equation 2-11: ESAL calculation

Where:

 ESAL = Equivalent single axle load  ADT = Average daily traffic volume for current condition  T = Percentage of trucks  TF = Truck factor  GF = Growth factor  LDF = Lane distribution factor  DF = Directional factor  DL = Design life, in years 2.3.13 Mechanistic-Empirical traffic analysis The M-E method uses the concept of load spectra to characterize traffic. Each axle type (such as single or tandem) is divided into a series of load ranges. Vehicle class distributions, daily traffic volume, and axle load distributions define the number of repetitions of each axle load group at each load level. Specific traffic inputs include the following:

1. Traffic volume – base year information

a. Two-way annual average daily truck traffic (AADTT) b. Number of lanes in the design direction c. Percent trucks in design direction d. Percent trucks in design lane e. Vehicle (truck) operational speed

2. Traffic volume adjustment factors

a. Vehicle class distribution factors b. Monthly truck distribution factors c. Hourly truck distribution factors Page 20

02-PAVEMENT DESIGN COMPONENTS FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

d. Traffic growth factors

3. Axle load distribution factors 4. General traffic inputs

a. Number axles/trucks b. Axle configuration c. Wheel base d. Lateral traffic wander

Engineers can obtain this data from automatic vehicle classification (AVC) and weigh-in-motion (WIM) stations. Engineers shall sort this data by axle type and vehicle class to be used in the M-E design methodology. If site-specific data are not available, use the M-E design procedure’s default values.

Using load spectra enhances pavement design, enabling the direct analysis of mixed traffic and avoiding the need for load equivalency factors. Additional advantages of applying the load spectra approach include the possibility of special vehicle analyses, analysis of the impact on performance of overloaded trucks, and analysis of weight limit changes during critical climate conditions.

Page 21

02-PAVEMENT DESIGN COMPONENTS FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

3 PAVEMENT MATERIALS

In addition to external factors, such as traffic and environment, materials are critical elements that impact pavement designs. Designers, however, can make the best use of pavement materials by knowing their properties through testing. To obtain properties for different pavement materials, designers may conduct laboratory tests or use empirical material characterization models. This chapter covers the material characterizations for all types of materials used in pavement structures. It details material characterizations related to pavement structural design and compliments material specifications in the DMAT Standard Specifications Volume 1 for Road Works manual (1).

A pavement is composed of different layers. Refer to Austroads’ Guide to Pavement Technology, Part 2: Pavement Structural Design (6) and Table 3-1 for information on how the functional and structural purposes of layers differ. These differences require that each layer have specific materials and properties.

Table 3-1: Structural and functional requirements for pavement layers

Pavement layer Structural considerations Functional considerations  Deformation resistance  Roughness  Durability (including  Skid resistance/surface ageing) texture Wearing surface (flexible or  Strength  Surface drainage rigid pavement)  Propensity for cracking characteristics  Noise characteristics  Reflectivity/aesthetics  Deformation resistance  Durability (including Base ageing)  Strength  Propensity for cracking  Deformation resistance  Durability (including Subbase ageing)  Strength  Propensity for cracking  Deformation resistance Subgrade  Volume stability

The following sections describe the material properties that are needed for pavement design when applying either the empirical method or M-E method. Because these two design methods have different approaches and models, methods to account for material properties in the pavement design process also differ. 3.1 Subgrade materials One of the most important factors in pavement design is the subgrade layer, which is the foundation of a pavement’s structure. Subgrade can be fill materials or cut materials, depending on a pavement’s elevation. Subgrade material is characterized by its stiffness, which depends on soil Page 22

03-PAVEMENT MATERIALS FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL type, density, and moisture content. A pavement primarily uses in situ material for its subgrade layer.

Pavement construction requires performing the following tests on subgrade samples:

 Atterberg limits: liquid and plastic limits  In situ moisture content  Soil gradation

 Resilient Modulus (Mr) or California Bearing Ratio (CBR)

A structural pavement design’s most critical parameter is stiffness, which is represented by resilient modulus or CBR (a factor that is related to the resilient modulus). In assessing stiffness, a designer needs to consider a subgrade’s variability, which is reflected through changes in soil types and drainage conditions along a road’s alignment. For consistency, a design must sustain a minimum CBR of 10% throughout a road’s entire length. If a sample’s CBR is lower than the CBR required by the design, designers shall consider improvements to the subgrade to increase stiffness. A pavement must sustain its required subgrade stiffness at least 45 cm below the existing subgrade level. If a weak layer exists in the subgrade, designers shall consider improving the weak material for the top 90 cm.

Subgrade varies based on different topography and soil types. Weak subgrade exits in some areas. Designers shall properly investigate the effects of weak soils. Weak soils shall be treated by soil stabilization methods to sufficiently support pavement structures. 3.1.1 Empirical design for subgrade materials Based on the design method described in the 1993 American Association of State Highway and Transportation Officials (AASHTO) Guide for Design of Pavement Structures (4), the subgrade soil characterization depends on the soil resilient modulus (Mr). Designers should perform laboratory Mr testing (AASHTO T-274) on subgrade soils with moisture content similar to the in situ moisture content. However, due to the difficulty of performing the Mr tests, designers should use a CBR test. CBR testing is described in the American Society for Testing and Materials (ASTM) Standard Test Method for CBR (California Bearing Ratio) of Laboratory-Compacted Soils (D1883-07e2) (12) for laboratory-prepared samples, the ASTM Standard Test Method for CBR (California Bearing Ratio) of Soils in Place (D4429) (13) for soils in field, and AASHTO’s Standard Method of Test for The California Bearing Ratio (AASHTO T-193) (14) for all soils. Equation 3-1 and Equation 3-2 show the correlation between the subgrade Mr and CBR. Option 2 shown in Equation 3-2 should be used for CBR values greater than 20% since it will produce more rational modulus values.

Mr = 1500 * CBR

Mr = 10 * CBR

Equation 3-1: Correlation between subgrade Mr and CBR (option 1) Where: CBR = California Bearing Ratio (%)

Mr = Resilient Modulus in pounds per square inch (psi) for first equation

Mr = Resilient Modulus in mega Pascal (MPa) for second equation

Page 23

03-PAVEMENT MATERIALS FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL or

0.64 Mr = 2555 * CBR

Equation 3-2: Correlation between subgrade Mr and CBR (option 2)

Where: CBR = California Bearing Ratio (%)

Mr = Resilient Modulus in pounds per square inch (psi)

There is no seasonal adjustment for subgrade Mr for Abu Dhabi, because the region’s moisture content is consistent all year long.

Rigid pavement designs use the modulus of subgrade reaction (k) instead of the resilient modulus. A modulus of subgrade reaction is related to the resilient modulus, as shown in Equation 3-3, when there is no subbase layer between the subgrade and the PCC slab.

Equation 3-3: Modulus of subgrade reaction

Where: k = modulus of subgrade reaction (pci)

Mr = subgrade resilient modulus (psi)

a = radius of the tire (inch)

ᵧ = Poisson ratio

Refer to Chapter 4, New Pavement Design, for additional details on the modulus of subgrade reaction calculation. 3.1.2 Mechanistic-Empirical design for subgrade materials Similar to the empirical design method, M-E design requires the subgrade stiffness or modulus. This method also requires Poisson’s ratio. Due to the difficulty of obtaining the subgrade stiffness by testing, the M-E method uses a simpler test, such as California Bearing Ratio (CBR), to determine the subgrade support value. There are two modes of testing – either field testing or laboratory testing.

In situ field tests for CBR are difficult. Accordingly, DMAT recommends either Dynamic Cone Penetrometer (DCP) (ASTM D 5778) tests or deflection tests using Falling Weight Deflectometer (FWD), which are easier to perform. The test results are correlated to the subgrade stiffness or CBR value.

Equation 3-4 shows the correlation between the DCP and the CBR, as given in Austroads’ Guide to Pavement Technology, Part 2: Pavement Structural Design (6).

Log CBR = 2.494 – 1.131 log (DCP)

Equation 3-4: Correlation between DCP and CBR Page 24

03-PAVEMENT MATERIALS FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

Where DCP = penetration mm/blow.

The deflection test is better suited for pavement rehabilitation design than for new design. Several commercial programs, including Dynatest’s ELMOD, use the deflection data obtained from FWD testing to backcalculate the resilient modulus of a subgrade.

A designer then correlates the subgrade modulus to the CBR using Equation 3-2. This equation is applicable with a maximum value of 150 MPa. Poisson’s ratio is assumed to have a default value of 0.35 for non-cohesive materials and 0.45 for cohesive materials. 3.2 Granular base and subbase materials A granular base and subbase serve as a platform for the construction of asphalt or concrete layers. Base and subbase layers consist of coarse and fine aggregates that are compacted to provide stability. The most important characteristics of a granular base layer are stiffness and Poisson’s ratio. 3.2.1 Empirical design for granular base and subbase materials Based on the empirical design method, unbound granular material is characterized by the CBR, which is related to the layer resilient modulus and the layer coefficient. Equation 2-1 shows how the CBR relates to the resilient modulus.

Designers can use Equation 3-5, from AASHTO’s Guide for Design of Pavement Structures (4), to determine the granular base layer coefficient. Figure 3-1 provides additional detail. The AASHO Road Test basis of these correlations is that a granular base has a layer coefficient of 0.14, which corresponds to a modulus of 30,000 psi and a CBR of 100 (4). A designer can use either Equation 3-5 or Figure 3-1 to obtain the layer coefficient, applying the CBR from laboratory testing, which complies with AASHTO’s Standard Method of Test for the California Bearing Ratio (AASHTO T- 193) (14).

a2 = 0.249(log10EBS) – 0.977

Equation 3-5: Granular base layer coefficient

Where:

a2 = Granular base layer coefficient

EBS = Granular base layer modulus (psi)

Page 25

03-PAVEMENT MATERIALS FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

Figure 3-1: Layer coefficient for granular base layer

Designers can use Equation 3-6, from AASHTO’s Guide for Design of Pavement Structures (4), to determine the granular subbase layer coefficient. Figure 3-2 provides additional detail. The AASHO Road Test basis of these correlations is that a granular subbase has a base layer coefficient of 0.11, which corresponds to a modulus of 15,000 psi and a CBR of 30 (4). A designer can use either Equation 3-6 or Figure 3-2 to obtain the layer coefficient, applying the CBR from laboratory testing, which complies with AASHTO’s Standard Method of Test for the California Bearing Ratio (AASHTO T-193) (14).

a3 = 0.227(log10ESB) – 0.839

Equation 3-6: Granular subbase layer coefficient

Page 26

03-PAVEMENT MATERIALS FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

Where:

a3 = Granular subbase layer coefficient

ESB = Granular subbase layer modulus (psi)

Figure 3-2: Layer coefficient for granular subbase layer

3.2.2 Mechanistic-Empirical design for granular base and subbase materials Based on the M-E design method, unbound granular material is characterised by the resilient modulus and Poisson’s ratio. Because unbound granular materials are stress dependant,

Page 27

03-PAVEMENT MATERIALS FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL designers must conduct an in-depth element analysis to fully model their behaviour. With a few assumptions, however, designers can use a linear elastic analysis as a simplification.

Key elastic parameters are the modulus and Poisson’s ratio. Because variations in Poisson’s ratio have limited effect on structural pavement designs, designers can assume a Poisson’s ratio of 0.35.

Variations in the resilient modulus, however, are very critical, because they are affected by aggregate composition, moisture content, density, and stress levels. Designers can obtain the modulus through repeated load triaxial testing of subbase materials at their in situ density, moisture content, and stress levels. Tests to determine the modulus for unbound granular material are sophisticated, hard to perform, and not available locally in Abu Dhabi. Designers in Abu Dhabi should use a simpler method for local material.

As another method to determine the modulus for the granular layer, designers can use default values until testing yields more precise values. In 2008, Austroads provided two tables, shown below in Table 3-2, that designers can use to estimate the modulus for a granular base layer (6). The top half of Table 3-2 is applicable for granular material that has a CBR greater than 30% (6).

Table 3-2 requires designers to know the modulus of the overlying bound layers, which can be obtained for each material type (asphalt or cement). For pavement that is composed of different bound layers overlying a granular base layer, designers shall use Equation 3-7 to obtain an equivalent modulus for the total overlying layers.

Equation 3-7: Equivalent modulus

Where:

Ee = Equivalent modulus of total thickness of bound material (MPa)

Ei = Modulus of layer i (MPa)

ti = Thickness of layer i (mm)

T = Total thickness of overlying bound materials (mm)

Based on the values of Ee and T, designers can use Table 3-2 to obtain the modulus for a granular layer.

Table 3-2: Granular base layer modulus – Austroads 2008

Suggested vertical modulus (MPa) of top sublayer of normal standard base material

Modulus of overlaying(1) bound material (Mpa) Thickness of overlying bound material 1000 2000 3000 4000 5000 40 mm 350 350 350 350 350 75 mm 350 350 340 320 310 100 mm 350 310 290 270 250 125 mm 320 270 240 220 200 150 mm 280 230 190 160 150 Page 28

03-PAVEMENT MATERIALS FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

175 mm 250 190 150 150 150 200 mm 220 150 150 150 150 225 mm 180 150 150 150 150 >=250 mm 150 150 150 150 150 (1) Overlaying bound material is either asphalt or cemented material or a combination of these materials.

Suggested vertical modulus (MPa) of top sublayer of high standard base material

Modulus of overlaying(1) bound material (Mpa) Thickness of overlying bound material 1000 2000 3000 4000 5000 40 mm 500 500 500 500 500 75 mm 500 500 480 460 440 100 mm 500 450 410 390 360 125 mm 450 390 350 310 280 150 mm 400 330 280 240 210 175 mm 360 270 210 210 210 200 mm 310 210 210 210 210 225 mm 260 210 210 210 210 >=250 mm 210 210 210 210 210 (1) Overlaying bound material is either asphalt or cemented material or a combination of these materials. 3.3 Modified granular materials Modified granular material is a granular material that is stabilized with small amounts of cement, lime, or asphalt to increase stiffness without creating a bound layer. Low-volume roads use modified granular materials to increase the stiffness of the aggregate surface. Austroads specifies that modified granular materials have a 28-day unconfined compressive strength from 0.7 MPa to 1.5 MPa (6).

Because the characterizations for modified granular materials are similar to those of unbound granular materials, designers can apply empirical and M-E design methods in the same ways for both types of materials. Accordingly, designers can assume a Poisson’s ratio of 0.35 and default values as shown in Table 3-2. 3.4 Stabilized materials Stabilized materials are granular materials that are mixed with a cementitious agent such as Portland cement, lime, or asphalt. Sufficient amounts of the cementitious agent in the mix produce a bound layer. For more details about stabilized materials, refer to the DMAT Standard Specifications Volume 1 for Road Works manual (1).

Stabilized materials are affected by mixture proportions, moisture content, the extent of cracking and ageing, and curing. 3.4.1 Empirical design for stabilized materials According to AASHTO, the empirical design method requires use of an elastic modulus to estimate the layer coefficient for different material types (4). Stabilized materials are either cement-treated bases (CTBs) or asphalt-treated bases (ATBs).

Page 29

03-PAVEMENT MATERIALS FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

A CTB is a granular base treated with Portland cement. According to ASTM’s Standard Test Method for Compressive Strength of Molded Soil-Cement Cylinders (ASTM D-1633) (15), a CTB’s elastic modulus is related to a material’s seven-day unconfined compressive strength. Designers use either the modulus or the unconfined compressive strength to obtain a CTB’s layer coefficient, as shown in Figure 3-3.

Similarly, designers use an ATB’s elastic modulus or Marshall Stability to obtain its layer coefficient. Designers can use either AASHTO’s Standard Method of Test for Resistance to Plastic Flow of Bituminous Mixtures Using Marshall Apparatus (AASHTO T-245) (16) or ASTM’s Test Method for Resistance of Plastic Flow of Bituminous Mixtures Using Marshall Apparatus (ASTM D 1559) (17) to determine an ATB’s Marshall Stability. Figure 3-4 shows the correlation between an ATB’s modulus, Marshall Stability, and layer coefficient.

Figure 3-3: Cement treated base layer coefficient

Page 30

03-PAVEMENT MATERIALS FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

Figure 3-4: Asphalt treated base layer coefficient 3.4.2 Mechanistic-Empirical design for stabilized materials According to Austroads, the M-E design method defines the modulus of a stabilized base as an estimate of its in situ flexural modulus after 28 days (6). Designers can obtain a stabilized material’s in situ modulus through laboratory flexural beam testing, estimation of flexural beam values from other tests, or an assumed default value. Because a standardized test to determine a material’s flexural modulus is not available, designers mainly use default values. Designers can use a third-point flexure beam test for modulus characterization, with an understanding that the rate of loading, curing times, and test conditions are not standardized.

As another method to estimate a material’s flexural modulus, designers can conduct a 28-day, unconfined compressive strength (UCS) test, using Equation 3-8 to correlate to the UCS to the flexural modulus.

Eflex = k UCS

Equation 3-8: Layer coefficient for stabilized materials

Where:

Eflex = flexural modulus of field beams at 28 days (MPa)

Page 31

03-PAVEMENT MATERIALS FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

UCS = Unconfined Compressive strength at 28 days (MPa)

k = values of 1000 to 1250 used for general purpose

Table 3-3, from Austroads’ Guide to Pavement Technology, Part 2: Pavement Structural Design (6), provides the default flexural modulus values for stabilized bases.

Table 3-3: Stabilized bases flexural modulus default values

Subbase Subbase quality quality Lean Mix Base 4-5% Property crushed crushed Concrete cement rock 2-4% rock 4-5% cement cement Range of Modulus (MPa) 5000-15000 3000-8000 2000-5000 1500-3000 Typical Modulus (MPa) 7000 5000 3500 2000 Degree of anisotropy 1 1 1 1 Range of Poisson’s ratio 0.1-0.3 0.1-0.3 0.1-0.3 0.1-0.3 Typical value of Poisson’s ratio 0.2 0.2 0.2 0.2

3.5 Asphalt concrete materials Asphalt concrete (AC) is a mixture of asphalt binder and aggregates. Because an AC mixture is mixed while it is hot, it is called hot mix asphalt (HMA). HMA is the main surface layer for flexible pavements. Pavements can use AC as a wearing course (the surface layer), a binder course (the intermediate layer), or a base course (the bottom layer, which resides on top of an aggregate layer). An AC layer’s quality and stiffness change at different depths. Major distresses in AC are fatigue cracking and permanent deformation (rutting).

Each course in a pavement structure serves a different function, which determines a course’s required properties. For example, a surface layer should be stiff to resist permanent deformation. A base course, however, should be soft to resist fatigue cracking. AC stiffness results from interlocking friction between aggregate particles, binder viscosity, and adhesion between the binder and aggregate. The follow factors affect an AC mixture:

 Aggregate properties, such as texture, absorption, and angularity  Binder grade  Mix composition  Volumetric properties of the AC mixture, such as air voids and binder content  Temperature  Rate of loading, based on the viscous nature of the binder  Age (AC pavements tend to get stiffer with time due to oxidation of their binder)

An asphalt binder in the AC mixture can be a conventional binder or polymer modified binder, depending on the required stiffness of the AC layer. An asphalt wearing course that is heavily loaded uses a polymer modified asphalt, which is resistant to permanent deformation. Refer to DMAT Standard Specifications Volume 1 for Road Works manual (1) for asphalt and aggregate specifications and details about HMA mixture design.

Material characterization for HMA has advanced significantly through testing protocols, such as the Dynamic Modulus testing (AASHTO TP62-03), that measure mechanical properties. This manual,

Page 32

03-PAVEMENT MATERIALS FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL however, focuses only on material characterizations as described by AASHTO’s empirical design method (4) and Austroads’ M-E design method (6). 3.5.1 Empirical design for asphalt concrete materials AASHTO’s empirical design method characterises the properties of an AC layer by its layer coefficient, which is related to the modulus of the material. Figure 3-5, from AASHTO’s Guide for Design of Pavement Structures (4), shows the relationship between an AC layer’s resilient modulus at 21° C and its layer coefficient.

The structural coefficient of AC varies between 0.2 and 0.44. AC with a layer coefficient of 0.44 corresponds to an AC resilient modulus of 3.1 GPa (450,000 psi) (4).

Figure 3-5: Dense graded asphalt concrete layer coefficient 3.5.2 Mechanistic-Empirical design for asphalt concrete materials Austroads’ M-E design process requires use of an AC layer’s modulus and Poisson’s ratio to determine a pavement’s structural design. Because Poisson’s ratio is difficult to measure through laboratory testing and its variability has limited impact on a pavement’s structural design, Austroads recommends using a Poisson’s ratio value of 0.4 (6).

Page 33

03-PAVEMENT MATERIALS FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

Austroads defines the following methods to obtain the modulus of an AC mixture:

 Measure the resilient modulus using a standard indirect tensile test (ITT), adjusted for in- service temperatures (WMAPT) and for the rate of loading in the road-bed.  Estimate the resilient modulus based on the bitumen properties and mix volumetric, using Shell nomographs (refer to Figure 3-6 and Figure 3-7), the in-service temperature (WMAPT), and the rate of loading in the road-bed.

This manual assumes that designers shall estimate an AC pavement’s modulus until a testing protocol is available and DMAT has gained a full understanding of local materials. In 1978, Shell International Petroleum Company developed a method to obtain the modulus of a conventional AC mixture, as outlined in their Pavement Design Manual: Asphalt pavement and overlays for road traffic (8).

Shell’s method has two stages:

1. Determine the modulus of the asphalt binder from traffic speed and operating temperature. 2. Determine the modulus of the asphalt concrete from the asphalt binder modulus and volumetric properties of the mixture.

Figure 3-6 and Figure 3-7 show the two nomographs developed by Shell. The first nomograph (Figure 3-6) requires the following inputs:

 Time of loading: This is the duration of a step load for which the bitumen modulus equals the stiffness under traffic loading. Designers may take this value as 1/V, where V (km/h) is the design heavy vehicle speed.  Operating temperature: This is the effective temperature, in degrees Celsius (°C), of the asphalt (WMAPT).

 T800 pen: This is the temperature, in degrees Celsius (°C), at which the penetration (100 g, 5 s) of the bitumen is 800 (0.1 mm).  Penetration Index (PI): This is an index of the bitumen’s susceptibility to penetration at different temperatures.

According to Austroads, a designer can refer to the relationships shown in Table 3-4 to determine

T800 pen and PI values based on bitumen penetration or viscosity data (6). Binder properties on Table 3-4 are for short term aged binders and are based on Rolling Thin Film Oven (RFTO) tests (AASHTO T-240 and ASTM D 2872).

Shell’s nomograph for determining an asphalt modulus (as shown in Figure 3-7) requires the following input:

 Equivalent built-in temperature (EBIT) modulus of the bitumen at the assumed temperature and loading rate, as derived from the nomograph.  Volume of the binder (Vb), as the percentage of bitumen in the asphalt, by volume. For a typical mix that contains 5% bitumen by mass, designers can assume a Vb of 11%.  Volume of mineral aggregate (Vg), as the percentage of aggregate in the mix, by volume. A typical mix that contains 5% bitumen by mass, when compacted so that it contains 6% air voids, has a Vg of approximately 83%.

When a pavement uses polymer modified binders rather than conventional binders, the modulus of the asphalt will differ significantly. To develop an adjustment factor to obtain the modulus of asphalt with polymer modified binders, designers must conduct laboratory testing to compare the polymer

Page 34

03-PAVEMENT MATERIALS FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL modified binders with the conventional binders. Such adjustments will vary based on the types of modifiers and the amount of each such modifier used (as a percentage of the total mix).

Table 3-4: Relationship to determine T800 pen and PI values

Page 35

03-PAVEMENT MATERIALS FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

Figure 3-6: Nomograph to determine conventional asphalt binder modulus

Page 36

03-PAVEMENT MATERIALS FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

Figure 3-7: Nomo graph to determine asphalt concrete modulus

Page 37

03-PAVEMENT MATERIALS FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

3.6 Portland cement concrete Portland Cement Concrete (PCC) is a mixture of cement, aggregates, and water. Rigid pavements use PCC for their surface layers. For PCC material specifications and mix design details, refer to DMAT Standard Specifications Volume 1 for Road Works manual (1). For rigid pavement designs with PCC, apply a 28-day flexural strength, which is typically between 4 and 5 MPa. According to Austroads, concrete with steel-fibre reinforcement has a 28-day flexural strength from 5 to 5.5 MPa (6).

To ensure durability, concrete has a minimum 28-day compressive strength of 32 MPa. Equation 3-9 shows the typical conversion of compressive strength to flexural strength.

Equation 3-9: Conversion of compressive strength to flexural strength

Where:

fcf = 28-day flexural strength (MPa)

fc = 28-day compressive strength (MPa)

Equation 3-10 shows the relationship between indirect tensile strength and flexural strength.

fci = 1.37 fc

Equation 3-10: Relationship between indirect tensile strength and flexural strength

Where:

fci = 28-day indirect tensile strength (MPa)

fc = 28-day compressive strength (MPa)

Although concrete properties vary with different constituent types and aggregate sizes, designers can use Equation 3-10 to effectively estimate the required properties.

Using AASHTO’s empirical design method (4), Equation 3-11 predicts the modulus of elasticity for PCC.

Equation 3-11: Modulus of elasticity of PCC

Where:

Ec = modulus of elasticity (psi)

f’c = concrete compressive strength (psi)

Page 38

03-PAVEMENT MATERIALS FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

3.7 Geo-textiles and geo-grids Geo-textiles, which are also called geo-grids, are synthetic fabric materials that some pavement’s use for separation, reinforcement, filtration, or drainage. They can also be combined with asphalt binders to form a waterproofing membrane. For details, refer to DMAT Standard Specifications Volume 1 for Road Works manual (1).

Because geo-textiles use different synthetics and different products, their properties and characteristics vary. Modern pavement designers have limited understanding of how the inclusion of geo-grids impacts pavement design. In general, DMAT recommends avoiding the inclusion of geo-grids as structural elements in pavement designs until the industry better understands their fundamental properties and has developed proven standards for their inclusion.

Some designers, however, may want to use geo-grids on a small scale and monitor the pavement performance over time to better understand their impact on pavement designs. According to AASHTO’s Recommended Practice for Geosynthetic Reinforcement of the Aggregate Base Course of Flexible Pavement Structures (AASHTO R 50-09) (18), designers should conduct field tests by including geo-grids to reinforce sections of aggregate base layers in pavement structures. Suppliers of geo-grids should follow this process to provide sufficient evidence of such materials’ potential adequacy in pavement structures.

According to Austroads, geo-grids reinforce asphalt to control reflection cracking (6). Geo-grid reinforcement action to control reflection cracking differs from that of a strain alleviating membrane interlayer (SAMI). SAMI treatments, including geo-textile reinforced seals, use bitumen as a waterproofing and strain alleviating membrane layer. Geo-grids control strain in the asphalt through the tensile strength of the reinforcing grid.

Austroads defines a SAMI as a sprayed seal which is applied to the surface prior to overlay with asphalt A SAMI contains bitumen that is either modified with polymer or crumb rubber or reinforced with a geo-textile. SAMI treatments over cracked pavements or pavements with high deflections can waterproof the pavement and delay or reduce reflective cracking. Waterproofing, crack propagation resistance, and strain alleviating capabilities are achieved through a combination of high binder application rates and polymer modified binders or reinforcement of a seal using geo- textile fabric.

Some research suggests that geo-grids may also reduce rutting in asphalt layers or improve structural performance to allow a reduced thickness of asphalt. Design criteria for such applications are not well defined and selection is largely based on reports of observed performance.

To avoid void spaces between a geo-grid and an underlying surface, designers generally place a geo-grid on an asphalt corrective layer or use a sprayed seal to hold it in place. Some fibreglass geo-grids have an adhesive backing to hold them in place while crews place asphalt. Sliding and buckling of polyester and polypropylene geo-grids during the placing of asphalt can be difficult to control unless a sprayed seal holds a geo-grid in place.

A geo-grid normally resides directly under a wearing course. DMAT recommends a minimum covering thickness of 50 to 70 mm to ensure that a geo-grid is firmly held within an asphalt structure.

Moreover, pavement designers utilizing mechanically stabilized flexible pavement using Geo-grids shall comply with Acceptance criteria given in ANNEX 3.

Page 39

03-PAVEMENT MATERIALS FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

3.8 Recycled materials Sustainability shall be part of long-term maintenance plans for all DMAT road and pavement projects. Sustainable designs have environmental, economic, and social dimensions, and encompass responsible resource management and use. To foster sustainability, DMAT mandates the reuse of pavement materials wherever such reuse is feasible.

Benefits of reusing or recycling pavement materials include the following:

 Energy savings (when compared to the cost of using new resources)  Reduced noise (through the use of quiet pavement materials)  Reduced need to dispose materials in landfill sites  Protection of natural resources  Protection of the environment to prevent further degradation  Potential cost savings  Establishment of ecologically sustainable development

The value of recycled products, in terms of energy savings and environmental benefits, is growing. There are now a number of industry by-products, including the following that are regularly used in the manufacture of pavement materials:

 Slag products  Coal combustion products  Recycled building materials  Recycled rubber products  Recycled asphalt products

Although the use of recycled material is relatively new in pavement development, several different types of asphalt recycling, including recycled asphalt product (RAP), hot in-place recycling, and cold in-place recycling, are available. Each type of recycling handles different material compositions and mixtures.

RAP recycling can impact 10-20% of new asphalt mixtures. Testing and properties required for pavement designs to support RAP are similar to tests for conventional asphalt concrete mixtures. Nomographs used to predict the modulus of conventional asphalt modulus, however, do not apply for RAP mixtures, because recycled materials vary too much. Designers shall subject RAP mixtures to laboratory testing to determine material properties.

Recycled concrete is concrete that has been broken into smaller pieces, making it available for use in granular layers. Designers shall perform laboratory testing to estimate the modulus of recycled concrete before including it in pavement structural designs. Such materials have different properties based on the size and gradation of the crushed concrete. 3.9 Warm mix asphalt For decades, producers of hot mix asphalt (HMA) explored enhancements in performance, construction efficiency, resource conservation, and environmental stewardship. Their efforts lead to the development of warm mix asphalt (WMA). WMA is asphalt that is mixed at temperatures that are generally from 50o F to 100o F lower than the mixing temperatures for conventional asphalt. Conventionally, WMA operates at 230o F, rather than 315o F, which is the mixing temperature for HMA. WMA is a more sustainable alternative to HMA. Despite the lower mixing temperatures, the quality and effectiveness of WMA match those of HMA.

Page 40

03-PAVEMENT MATERIALS FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

3.9.1 Benefits of warm mix asphalt Lower temperatures and additional additives in the mix make WMA better for the environment. Specific advantages of using WMA include the following:

 Significantly reduces emissions of toxic and non-toxic gases that contribute to global warming and ozone depletion  Saves energy and energy costs by reducing related fuel burning by up to 25%  Improves the workability of the asphalt  Extends the paving season  Allows for paving during cooler temperatures  Enables hauling over longer distances  Improves compaction of the pavement  Improves road smoothness, reduces International Roughness Index (IRI) values, and enhances ride quality  Reduces fumes and poly-cyclic aromatic hydrocarbons (PAHs) that are produced during construction by up to 50% when compared to HMA pavements  Reduces binder aging  Reduces plant wear  Increases plant production  Enables longer storage durations  Supports easier compaction  Enables paving during colder weather

For more information, refer to Payne and Dolan Incorporated’s presentation to an AASHTO subcommittee, Warm Mix Asphalt – a Contractor’s Perspective (19).

In addition to the benefits brought about by the materials that constitute a WMA mixture, lower temperatures ensure that WMA-paved roads are more quickly available for use by traffic, which is a significant benefit when time schedules are tight or critical. 3.9.2 Methodology for warm mix asphalt As innovations in the industry introduce new technologies for pavement and asphalt design, some of these new technologies have impacted WMA mixes in the following ways:

 Creating a foaming effect in the asphalt binder through the addition of synthetic zeolite, known as Aspha-Min®, at the plant while mixing.  Creating a soft binder and hard foamed binder during the plant production at various stages through the addition of a two-component binder system called WAM-Foam®.  Using organic additives such as Sasobit®, a Fischer-Tropsch paraffin wax, and Asphaltan B®, a low molecular weight esterified wax.  Using Evotherm™, an asphalt emulsion product that uses a chemical additive technology and a “dispersed asphalt technology” delivery system, during plant production.  Creating a foaming effect in the binder through the addition of Advera® WMA, a synthetic zeolite, at the plant during mixing.

Plants that produce HMA may also produce WMA. The only necessary adjustments are the lower temperatures and additional additives. Some installations, modifications, and alterations may be introduced to a plant to account for these changes, facilitate production, and support procedures.

Page 41

03-PAVEMENT MATERIALS FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

3.9.3 Testing for warm mix asphalt Because of WMA’s relative newness in the industry, testing the performance of a WMA mix requires testing measures, such as tests for moisture sensitivity, rutting resistance, mixture stiffness, and fatigue cracking. 3.10 General Procedure for Dealing with Application of New Material/ Technology in Pavement Design for Abu Dhabi Emirate Roads As the application of latest best practices and sustainable materials and technologies, in design, construction and maintenance of roads and infrastructure projects, is a major objective for Abu Dhabi Government, the following general steps are followed in dealing with newly proposed material / technology for application in Abu Dhabi Road Pavements;

1. The supplier/contractor proposing the new material/technology conduct a preliminary meeting with Abu Dhabi Government relevant technical team, explaining the nature, history, previous applications, previous approvals, testing results, design calculations, cost estimates, environmental impacts, quantified benefits and recommendation for application in Abu Dhabi Road Pavement, 2. In the first meeting, the supplier/contractor deliver a full set of document (Hard & Soft) copies, including all relevant information mentioned above (in Item #1), 3. Abu Dhabi Government relevant technical team, Conducting the preliminary technical – financial – environmental review and disc study, by reviewing all documents delivered by the supplier; material (or technology) characteristics, previous applications, design calculations, considering the following:-  Ensure Availability in Abu Dhabi (or UAE market),  Comparing with Abu Dhabi relevant specifications,  Suitability for Abu Dhabi environment,  Considering Constructability and Required Maintenance Activities, 4. Quantification of the new material (technology) benefits from Technical, Financial and Environmental Points of view, considering:-  Extending Pavement Service Life,  Less Life – Cycle Cost, when compared with conventional practice,  Minimized Carbon Emissions and Saving Natural Environment,  Reducing the use of Row Materials,  Saving Water Resources and Energy Consumption, and  Reduced Construction Time. 5. After passing the above steps successfully, conducting a pilot project (or sample, ….) as a practical test on Abu Dhabi Environment and conditions, 6. After an agreed suitable monitoring period, The Whole Study is recorded in a brief report, including all steps of studying this subject and the quantified benefits, to the relevant Abu Dhabi Government Management, ending with the recommendation to apply this material (or technology) in Abu Dhabi Emirate Road Pavements, 7. Finally, after passing all the above procedure, the relevant Abu Dhabi Government Authority approaches to Abu Dhabi Quality and Conformity Council (AD-QCC) with the study report, attached with a proposed draft specification, to be studied within AD-QCC relevant committee, and then to be included in Abu Dhabi relevant Specification.

Page 42

03-PAVEMENT MATERIALS FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

4 NEW PAVEMENT DESIGN

4.1 Purpose and scope This chapter provides information to help engineers and consultants develop the necessary input data and apply proper engineering principles when designing new pavement projects. Pavement engineers must ensure that designs are in accordance with the Abu Dhabi DMAT’s policies, procedures, standards, and guidelines, as well as good engineering practices.

Pavement design is primarily a matter of soundly applying acceptable engineering criteria and standards. Standards in this manual provide a general basis for uniform design practices for typical pavement design situations.

Design procedures incorporated into this document are based on the 1993 AASHTO Guide for Design of Pavement Structures (4) and the Guide to Pavement Technology, Part 2: Pavement Structural Design (6) from Austroads. This manual applies AASHTO’s empirical design methodology and Austroads’ M-E design methodology.

This chapter discusses the design of new flexible and rigid pavements, with descriptions on how to apply the empirical method and M-E method for each type. This chapter also outlines methodology that designers can use to design new pavements functionally and, more importantly, structurally. 4.2 Flexible pavement thickness design Flexible pavements are pavement structures that have an asphalt concrete (AC) surface layer. Flexible pavement designs require the use of different materials and determine the layers thicknesses that can stand the applied traffic loads. This involves a complex combination of numerous variables such as external factors, material characterization and structural interaction factors between different layers. Several methods are available to combine these factors into a design process, some are empirical and others are M-E.

The flexible pavement design is based on layered system analysis. The layered system analysis approach is to use the better quality material with a higher modulus on the top. The asphalt layer has higher modulus than the granular base. While, the granular base has better material than the granular subbase, which supersedes the subgrade in quality. According to layered system, the asphalt should be on the top of the granular base and the subbase beneath the base. This approach is followed in almost all designs except in cases where a lower quality material is needed on top of another layer for a specific purpose. For example, a granular base layer might be used between two asphalt layers to prevent cracking the lower asphalt layer to reflect to the surface, the granular base in this case is known as crack arresting layer. 4.2.1 Empirical pavement design This section outlines an empirical pavement design methodology that is based on the 1993 AASHTO Guide for Design of Pavement Structures (4). Inputs required for the AASHTO method are explained in Chapter 2, Pavement Design Components, and Chapter 3, Pavement Materials. This section details the steps for a complete empirical design.

When following an empirical design process, a designer will typically produce a number of designs for comparison and consideration. Abu Dhabi DMAT recommends that designers apply LCC, as described in Chapter 9, Life-cycle Cost Analysis, to compare different alternative and come up with an economical and structurally safe design. Page 43

04- NEW PAVEMENT DESIGN FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

Applying AASHTO’s empirical design method, designers estimate the required structural capacity, based on an array of inputs, including traffic loads and subgrade strength. Designers check the estimate for required structural capacity against a presumptive pavement structure, which they can adjust or modify based on the required structural capacity and LCC. When applying AASHTO’s empirical method, pavement designers shall conduct the following actions:

1. Determine values for the parameters required to calculate a structural number (SN) for the pavement design.

A pavement’s SN defines its structural capacity. To determine a pavement’s SN, designers need the following parameters:

• An estimated count of future traffic, expressed in equivalent single axle loads (ESALs), as explained in Chapter 2, Pavement Design Components. • A reliability percentage, which represents a degree of accuracy for the estimation of future traffic and reflects the likelihood that the pavement will withstand the applied traffic for its intended design life. Reliability value shall be greater for roadway’s with greater levels of traffic. Table 4-1 indicates the level of reliability required for each roadway class (based on traffic loads). It has to be noted that the reliability levels listed below should be used if all design inputs are based on average value. While, if maximum value is used the reliability level can be reduced.

Table 4-1: Typical Reliability levels

Roadway classification Reliability level (%) Truck route 99.9 Rural or urban road 99.9 Expressway 99.9 Main road 99 Sector road 95 Low-volume road 50

• An overall standard deviation (So), which accounts for variability in determining all parameters in the design process. Flexible pavement designs typically use an overall standard deviation of 0.45.

• An effective resilient modulus (Mr) for the subgrade material, which reflects the strength of the subgrade foundation upon which the pavement will reside. As

mentioned in Chapter 3, Pavement Materials, because Mr testing is difficult to conduct. Designers should perform a California Bearing Ratio (CBR) test and use

the results to estimate a pavement subgrade’s Mr, as given in Equation 3-1.

A design serviceability ) rating for the pavement. This parameter reflects the difference between a pavement’s initial serviceability rating immediately after construction and the lowest serviceability at which the pavement will require maintenance.

Table 4.2 shows typical initial, terminal, and loss in serviceability ratings for each roadway class (based on traffic load).

Page 44

04- NEW PAVEMENT DESIGN FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

Table 4-2: Typical Initial and terminal serviceability levels

Roadway Initial Terminal Design classification serviceability serviceability serviceability loss

(po) (pt) (PSI) Truck route 4.2 3.0 1.2 Rural or urban road 4.2 3.0 1.2 Expressway 4.2 3.0 1.2 Main road 4.1 2.6 1.5 Sector road 4.0 2.4 1.6 Low-volume road 4.0 2.0 2.0

2. Determine the pavement’s Structural Number (SN).

Designers can use Equation 2-5, from the 1993 AASHTO Guide for Design of Pavement Structures (4), to calculate a pavement’s SN. Figure 4-1, however, shows a chart from AASHTO that designers can use to solve the equation graphically. DMAT recommends using the equation, which provides a more accurate value.

Equation 4-1: AASHTO structural number calculation (1)

Where:

W18 = Equivalent single axle load (ESAL)

Mr = Soil’s resilient modulus

So = Overall standard deviation

ZR = Standard normal deviate

PSI = Design serviceability loss

Page 45

04- NEW PAVEMENT DESIGN FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

Figure 4-1: AASHTO's flexible pavement design chart

Page 46

04- NEW PAVEMENT DESIGN FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

3. Analyse thickness design and layer design.

In designing pavement thickness, begin with a pavement layer thickness that, when combined, meets a pavement’s required structural capacity (SN). Equation 4-2 relates a pavement’s design SN to layer thicknesses.

SN = (a1t1+a2t2m2+a3t3m3+⋯+antnmn) / 2.54

Equation 4-2: Relationship between design SN and layer thickness

where:

ai = material coefficient for each material in the pavement section

ti = thickness of each material in the pavement section (cm)

mi = drainage coefficient of each base or subbase layer

SN = Structural number desired for the pavement section

As described in Chapter 3, Pavement Materials, designers correlate the material coefficient to either the layer modulus or CBR. Table 4-3 shows typical material coefficient values. DMAT recommends that designers use the equations given in chapter 3. Note that Table 4-3 uses centimetres as the unit for coefficients, while the equations in chapter 3 use inches.

Table 4-3: AASHTO material coefficient

Pavement material Coefficient Asphalt concrete 0.44 Aggregate base 0.14 Sand-asphalt base 0.20 Soil subbase 0.11

For Abu Dhabi, apply a drainage coefficient of 1.0 for typical designs. For designs which utilize a drainage layer, use a coefficient of 1.2.

Flexible pavement is a layered structure that requires different SN values for different layers. Determine a different SN for subgrade, subbase, and base layers. For each SN, use

the modulus of a carrying layer to solve of the equation. For example, to determine SN2 over the subbase, use the subbase modulus as the Mr in Equation 2-5. Figure 4-2, from AASHTO’s Guide for Design of Pavement Structures (4), shows their procedure for layered design analysis. Layered design analysis shall confirm that each layer in the pavement structure has sufficient strength to carry the applied load safely, without any weak layers in the middle of the pavement structure.

Page 47

04- NEW PAVEMENT DESIGN FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

Figure 4-2: Layered design analyses

Although many pavement designs will meet calculated requirements, not all designs meet the needs of local conditions, such as underground utilities close to the surface, poor drainage, or flooding, equally. One design might function more efficiently than another. Pavement designers shall use construction consideration and judgement, based on past experience, to select a final pavement design.

4. Determine minimum thickness.

Consider practical aspects for the construction process, which require a minimum thickness for each layer type. These minimum thicknesses are governed by the aggregate size and constructability considerations. Minimum thickness for an aggregate base layer is 20 cm.

Table 4-4 shows the minimum thickness (in cm) for asphalt concrete (AC) layers for different road classes (based on traffic loads) for roads using aggregate base layers. An AC layer is divided into 3 courses, a wearing course, a binder course, and a base course. Minimum thicknesses in table 4-4 are for an entire AC layer; do not confuse these values with the required minimum thickness for different courses. Each course requires a minimum thickness based on the maximum aggregate size used in its AC mixture. A course has a maximum thickness, which is the thickness it requires to achieve its specified level of compaction. Refer to the DMAT Standard Specification Volume 1 for Road Works manual (1), for more information on maximum aggregate sizes and lift thicknesses.

Page 48

04- NEW PAVEMENT DESIGN FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

Table 4-4: Minimum asphalt concrete (AC) layer thicknesses for granular base pavements

Roadway classification Minimum AC thickness (cm) Truck route 30 Freeway 28 Arterial Road 28 Collector Road 21 Local Road 11 Low-volume road 6 • consultants should use this table as a final check after conducting design calculations 4.2.2 Mechanistic-Empirical pavement design Austroads describes a M-E pavement design method in their Guide to Pavement Technology, Part 2: Pavement Structural Design (6). Figure 4-3 shows a flow diagram for Austroads’ M-E design process.

To start Austroads process, a designer selects a section of pavement for initial trials, then applies M-E pavement analysis to the trial section to predict critical strains. Applying the computed critical strains, a designer then predicts the number of load repetitions that will cause failure for each type of distress. Finally, a designer compares the predicted load repetitions to actual estimated traffic repetitions. If the predicted loads exceed the actual loads, a designer can accept the design used for the trial section; if actual loads exceed predicted loads, however, a designer shall revised the design. In summary, this procedure consists of the following steps:

1. Evaluate the input parameters (materials, traffic, and environment). 2. Selecting a trial pavement. 3. Analyse the trial pavement to determine allowable traffic. 4. Compare allowable traffic to design traffic. 5. Accepting or rejecting the trial pavement design.

Appropriate inputs for M-E pavement design include the following:

 Desired project reliability (refer to Table 4-1)  Environment (refer to Chapter 2, Pavement Design Components)  Subgrade and materials (refer to Chapter 3, Pavement Materials)  Performance criteria (fatigue cracking or permanent deformation)  Design traffic loading (refer to Chapter 2, Pavement Design Components)

Using Austroads’ M-E pavement analysis, a designer applies fundamental material properties, using the relationship between applied load and a material’s modulus to calculate strains at critical locations. Critical locations for analysis of a multiple layer pavement are those that yield the highest strains due to applied loads. Figure 4-4, from Austroads’ Guide to Pavement Technology (6), shows the critical locations in a multi-layer pavement structure. Designers then use the critical strains to predict the following pavement distresses and future performance:

 Tensile strain at the bottom of an AC layer, from which a designer can compute fatigue cracking for the AC layer  Tensile strain at the bottom of a stabilised layer, from which a designer can compute fatigue cracking for the stabilised layer  Compressive strains at the top of a subgrade to determine permanent deformation

Page 49

04- NEW PAVEMENT DESIGN FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

Traffic Foundation Climate Material Properties Inputs

Project Reliability Trial Section Analysis

Performance Criteria Pavement Analysis

No Accept

Yes

Comparison of Designs Selection

Viable Design

Select Design

Figure 4-3: Mechanistic-Empirical design flowchart

Figure 4-4: Critical locations for mechanistic design

To determine a flexible pavement’s response to traffic loads, a designer shall fully model this complicated process. According to Austroads, a designer can do the following to simplify this modelling effort:

 Consider pavement materials to be homogeneous, elastic, and isotropic (except for unbound granular materials and subgrade, which are anisotropic). Page 50

04- NEW PAVEMENT DESIGN FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

 Use the linear elastic model to calculate response to load.  Assess the following critical responses for pavement and subgrade materials:

• Horizontal tensile strains at the bottom of asphalt layers • Horizontal tensile strains at the bottom of cemented layers • Vertical compressive strains at the top of layers with subgrade and selected subgrade materials

Note: Austroads’ M-E method does not consider unbound granular materials.

 Assume that a standard axle load reflects a dual-wheeled single axle that applies a load of 80 kN. For flexible pavements, critical responses occur either along the vertical axis directly below the inner-most wheel of the dual wheel group or along the vertical axis located symmetrically between a pair of dual wheels.  Assume that a standard axle load is represented by four uniformly-loaded circular areas of equal area that are separated by centre-to-centre distances of 330 mm, 1470 mm, and 330 mm, respectively, as illustrated in Figure 4-4.  Assume that contact stress is uniform over the loaded area and, for the purpose of design, has a consistent value of 750 kPa. Contact stress relates to tire pressure; for highway traffic, assumed contact stress levels from 500 to 1000 kPa.  Vary the values in the previous bullet items for pavements that support unusual axle types and loadings. For example, for pavements in which sharp turning movements, acceleration, or braking will occur, adopt a model that more closely corresponds to the actual axle configuration and loading. For most pavement design, however, such adjustments are unnecessary.  For some projects, M-E modelling may indicate that a pavement with a thin asphalt surface, with a thickness less than 40 mm, will suffice. DMAT, however, cautions against selecting pavement with a thin asphalt surface as a design option, because M-E design does not effectively address dominant damage types.

Subsequent sections detail the steps of M-E design. 4.2.2.1 Selection of trial section By applying a pavement design within a selected trial section, designers can determine what type of materials to use and required layer thicknesses. 4.2.2.2 Determination of a subgrade’s elastic parameters A subgrade’s elastic parameters are vertical modulus (Ev), horizontal modulus (EH), Poisson’s ratio (ᵧ) and stress parameter (f). Designers can use Equation 4-3, Equation 4-4, Equation 4-5, and Equation 4-6 to calculate these parameters.

Page 51

04- NEW PAVEMENT DESIGN FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

(Ev) = 10 * CBR (MPa)

Equation 4-3: Vertical modulus

(EH) = 0.5 * Ev

Equation 4-4: Horizontal modulus

(ᵧ) = 0.35

Equation 4-5: Poisson's ratio

(f) = Ev / (1+ ᵧ)

Equation 4-6: Stress parameter

Subgrade parameters vary based on both the stiffness of the upper layer and the properties of underlying layers. Select an appropriate thickness (not greater than 6m) for the entire subgrade, then divide this thickness into 5 equal thicknesses for five equivalent sublayers. Use the CBR test and equation 3-1 in Chapter 3, Pavement Materials, to determine the modulus of each sublayer. 4.2.2.3 Determination of a granular base layer’s elastic parameters Because a granular base layer’s elastic parameters vary under different stress levels, determining these parameters requires a finite element analysis. To simplify this determination, however, designers can use a linear elastic analysis that subdivides a granular base layer into five equivalent sublayers (as described in 4.2.2.2). When a stabilized layer resides under a granular base, however, division of the base into sublayers is not necessary.

To determine a granular base layer’s elastic parameters, refer to the explanations in chapter 3, Pavement Materials, section 3.2.2, and the following equations.

 Use the default values in Table 3-2 to determine a granular base layer’s vertical modulus (Ev).  Use Equation 4-4 to determine a granular base layer’s horizontal modulus (EH).  Use Equation 4-5 to determine a granular base layer’s Poisson’s ratio (ᵧ).  Use Equation 4-6 to determine a granular base layer’s stress parameter (f). 4.2.2.4 Determination of a stabilized layer’s elastic parameters To eliminate cracking in a cement stabilized base layer, use an asphalt layer that us at least 175 mm thick. Refer to section 3.4.2 in Chapter 3, Pavement Materials, for the elastic parameters of a cement stabilized layer. 4.2.2.5 Determination of elastic parameters for asphalt Refer to section 3.5.2 in Chapter 3, Pavement Materials, for details on how to determine an elastic modulus for asphalt concrete.

Page 52

04- NEW PAVEMENT DESIGN FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

4.2.2.6 Determination of strains at critical locations After determining all the material parameters, a designer can use a linear elastic program to calculate strains at critical locations under an applied load, as shown in Figure 4-4. Proven linear elastic programs include CIRCLY. 4.2.2.7 Determine a subgrade’s strain criterion M-E design of flexible pavement involves limiting vertical compressive strains at the top of a subgrade. Although such vertical strains are mostly elastic, traffic repetitions across a portion of a subgrade can cause permanent deformation, which is visible as rutting on the pavement’s surface.

Designers can use Equation 4-7, which applies calculated strains, to obtain the allowable number of load repetitions for a subgrade.

Equation 4-7: Allowable number of load repetitions

Where:

 = Vertical strain (micro-strains) at the top of a subgrade

N = Allowable number of standard axle repetitions 4.2.2.8 Determine fatigue criterion for cemented materials If a pavement structure includes cemented material, a designer shall apply Equation 4-8 to check the fatigue cracking potential of the cemented layer.

Equation 4-8: Fatigue cracking potential of cemented layer

Where:

= Tensile strain (micro-strains)

N = Allowable number of load repetitions

E = Cemented material modulus (MPa)

RF = Reliability factor for cemented materials fatigue; refer to Table 4-5 for appropriate values

Table 4-5: RF to determine cemented materials' fatigue criteria

Reliability level 80% 85% 90% 95% 97.5% RF 4.7 3.3 2.0 1.0 0.5

Page 53

04- NEW PAVEMENT DESIGN FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

4.2.2.9 Determine fatigue criterion for asphalt Fatigue cracking in a pavement structure’s asphalt layer is a very critical distress. Several factors, including the following, affect the fatigue life of asphalt:

 Stiffness of underlying pavement layers  Modulus of the asphalt  Binder type  Applied load  Temperature

Shell laboratory conducted testing to relate fatigue cracking to axle load repetitions and included this information in their 1978 Pavement Design Manual: Asphalt pavement and overlays for road traffic (8). Austroads adjusted Shell’s findings and included these results in their 2008 Guide to Pavement Technology (6). Austroads added a reliability factor (RF) to the laboratory model to shift the laboratory results into field fatigue life.

Designers can use Equation 4-9 to calculate asphalt fatigue cracking.

Equation 4-9: Asphalt fatigue cracking

Where:

= Tensile strain (micro-strains)

N = Allowable number of load repetitions

Vb = Percentage of bitumen in the asphalt mixture, by volume

Smix = Asphalt modulus (MPa)

RF = Reliability factor for cemented materials fatigue; refer to Table 4-6 for appropriate values

Table 4-6: RF for asphalt materials fatigue criteria

Reliability Level 80% 85% 90% 95% 97.5% RF 4.7 3.3 2.0 1.0 0.5

4.2.2.10 Permanent deformation in asphalt Permanent deformation in an asphalt layer results from instability in the asphalt mixture. Austroads’ design process for flexible pavement structures excludes permanent deformation in the asphalt layer because a reliable prediction model is not available and modelling becomes excessively complicated when considering temperature changes (6). 4.2.2.11 Comparison to actual traffic To complete the M-E pavement design process, a designer compares the allowable axle load repetitions that were calculated for each distress to actual traffic repetitions (refer to Chapter 2, Pavement Design Components, for methods to collect actual traffic data). If predicted loads exceed Page 54

04- NEW PAVEMENT DESIGN FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL actual loads, a designer can accept the design used for the trial section; if actual loads exceed predicted loads, however, a designer must revised the design. 4.3 Rigid pavement thickness design This section specifies a number of coefficients and variables related to environmental conditions that serve as standard values for typical UAE projects. Whenever a design requires variation from these values, design engineers must stay within the bounds established by the 1993 AASHTO Guide for Design of Pavement Structures (4), justify the variance, and document the variations in a pavement design report.

The following sections describe the process for determining the necessary rigid pavement thickness in a pavement design. 4.3.1 Empirical pavement design An AASHTO road test in Ottawa, Illinois provided the basis for calculating required concrete pavement depths. AASHTO developed models that related pavement performance, vehicle loadings, embankment strength, and pavement structure. Design engineers apply the 1993 AASHTO model to calculate required depth, the minimal necessary depth of concrete pavement to carry the mixed vehicle loads, based on the roadbed soil, while providing satisfactory serviceability during the design period (4).

Design engineers obtain equivalent single axle load value (18-kip ESALs) from surveys of actual traffic survey or from planning offices based on patterns of land use. Refer to section 4.5 of this chapter for a simple example for calculating the accumulated 18-kip ESALs for a mixed traffic.

Truck equivalency factors are approximately fifty percent (50%) higher for rigid pavements than for flexible pavements. Design engineers can also use an actual axle load survey to estimate truck equivalency factors. 4.3.1.1 1993 AASHTO design equation This section outlines the elements used in the design equation specified in the 1993 AASHTO Guide for Design of Pavement Structures (4). Figure 4-5 shows the equation.

This equation determines the following unknown value:

 DR = Required depth of concrete pavement, in inches

Input to this equation includes the following variables:

 ESALD = Accumulated 18-kip equivalent single axle loads over the life of the project.

 ZR = Standard normal deviate from the normal distribution table for design reliability (R). This equation does not include a reliability factor, (%R), which is replaced by the corresponding standard normal deviate. 2  KG = Modulus of sub grade reaction (lbs/inch /in)

Input to this equation includes the following constants:

 SO = Standard deviation.

 PI = Initial serviceability.

 PT = Terminal serviceability.  ΔPSI = Change in serviceability.  S'c = Concrete modulus of rupture (psi) Page 55

04- NEW PAVEMENT DESIGN FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

 EC = Concrete modulus of elasticity (psi)

 CD = Drainage coefficient.  J = Joint transfer factor. 

Figure 4-5: 1993 AASHTO design equation for rigid pavement 4.3.1.2 Design procedure To design a new rigid pavement, an engineer must know the history of successful construction and performance with concrete pavements in the area and perform the following steps.

1. Determine the base types (asphalt Base, treated permeable base, or special select embankment soils).

2. Determine the traffic load forecasts (ESALS). 3. Evaluate concrete material properties, which are generally constant for design purposes, including the following:

• Concrete modulus of elasticity (EC).

• Concrete modulus of rupture (S'C).

Page 56

04- NEW PAVEMENT DESIGN FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

4. Determine what type of subgrade drainage system is required. If the area lacks a strong history of successful construction and performance using special select soils under concrete pavements, use the other base types. 5. Calculate the pavement thickness using the design formula above with all input parameters outlined in Section 4.3.1.1. As an alternative, apply the design chart in Appendix B to determine pavement thickness. 6. Develop remaining pavement design details, including the following:

• Embankment and drainage details • Joint details • Shoulders details • Pavement drainage

Because pavement design details are as important as the design of the pavement depth, designers must focus adequate attention on these details. 4.3.2 Supplemental procedures for rigid pavement design and rigid joint design This section describes additional procedures for rigid pavement design and rigid joint design. This information is based on Part II of the 1993 AASHTO Guide for Design of Pavement Structures (4) and alternative design procedures that resulted from a National Cooperative Highway Research Program project (NCHRP Project 1-30), with modifications that are based on the results of a verification study conducted using the long-term pavement performance (LTPP) database. 4.3.2.1 Define an effective modulus of subgrade reaction (k-value) In pavement design calculations, the modulus of subgrade reaction (k-value) is a measurement of the stiffness of subgrade soils that lay on top of the finished roadbed soil or embankment upon which the base course, concrete slab, or both will eventually be constructed. The k-value represents the subgrade (and embankment, if present); it does not represent the base course. The base course is a structural layer of the pavement combined with the concrete slab; its thickness and modulus are important design inputs to determine the required slab thickness. (Refer to Section 4.3.2.2 for guidance in determining required slab thickness.)

The latest AASHTO design equation uses only the elastic k-value, the measurement of soil on top of the subgrade or embankment. Previous versions of the 1993 AASHTO Guide for Design of Pavement Structures (4) incorporate the gross k-value, which represents not only elastic deformation of the subgrade under a loading plate, but also substantial permanent deformation. Only the elastic component of this deformation represents the response of the subgrade to traffic loads on the pavement. Recent AASHTO tests focused extensively on the elastic k-value test as the main subgrade test. When AASHTO used the elastic k-value in structural analysis of pavements, they determined that slab stresses computed with a three-dimensional finite element model were approximately equal to those measured in the field under full-scale truck axle loadings at creep speed. These results justify the use of the elastic k-value in pavement design.

To determine the k-value input required for this design method, an engineer should perform the following steps.

1. Select a subgrade k-value for each season, using any of the three following methods:

a) Correlations with soil type and other soil properties or tests. b) Deflection testing and back calculation (highly recommended). c) Plate bearing tests. Page 57

04- NEW PAVEMENT DESIGN FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

2. Determine a seasonally adjusted effective k-value. 3. Adjust the seasonal effective k-value to account for the effects of a shallow rigid layer, if present. 4. Adjust the seasonal effective k-value to account for the effects of an embankment above the natural subgrade, if present.

AASHTO’s design methodology requires the mean k-value, not the lowest value measured or some other conservative value. Do not apply any additional adjustment to the k-value for loss of support. Because substantial loss of support existed for many road sections involved in AASHTO tests, the AASHTO model already reflects such effects. 4.3.2.2 Determine required structural design Engineers should determine slab thickness for the mid slab loading position, because this is the critical fatigue damage location for doweled pavements. Mid slab loading causes most cracks to start at the edge of the slab. If the transverse joints are doweled, designs should apply this calculated slab thickness. If the joints are not doweled, make a design check to determine whether the joint loading position causes a more critical stress at the top of the slab. Make another design check to ensure joint design adequacy with respect to faulting.

Determine or otherwise obtain appropriate values for the following:

 Estimated ESALS (W18) for the performance period in the design lane  Design reliability (%R)

 Overall standard deviation, SO  Design serviceability loss, PSI = PI – P2  Effective (seasonally adjusted) elastic k-value of the subgrade, psi/inch

 Concrete modulus of rupture, S’C psi

 Concrete elastic modulus, EC psi  Joint spacing, L, inches

 Base modulus, Eb, psi (section 2.3.3)  Slab/base friction coefficient, f

 Base thickness, Hb , inches  Effective positive temperature differential through concrete slab, TD, OF  Lane edge support condition:

a. Conventional lane width (12 ft [3.7 m]) with free edge. b. Conventional lane width (12 ft [3.7 m]) with tied concrete shoulder. c. Wide slab (for example, 14 ft [4.3 m]) with conventional traffic lane width (12 ft [3.7 m]).

Refer to Glossary for definitions of many of these input parameters for the AASHTO design equation.

Figure 4-6, Figure 4-7, Figure 4-8, and Figure 4-9 provide more details about the design equations for rigid pavement as given by the Supplement to the AASHTO Guide for Design of Pavement Structures, Part II for rigid pavements (31).

Page 58

04- NEW PAVEMENT DESIGN FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

Figure 4-6: Design equations for rigid pavement (part 1)

Page 59

04- NEW PAVEMENT DESIGN FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

Figure 4-7: Design equations for rigid pavement (part 2)

Page 60

04- NEW PAVEMENT DESIGN FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

Figure 4-8: Design equations for rigid pavement (part 3)

Page 61

04- NEW PAVEMENT DESIGN FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

Figure 4-9: Design equations for rigid pavement (part 4)

Refer to Appendix C for related tables. 4.3.3 Joint details Highway pavements generally require longitudinal and transverse joints, based on the dimension of slabs. These joints vary depending upon pavement requirements. Options include expansion joints, contraction joints, isolation joints, thickened edge joints, and construction joints, among others. Providing a joint layout in designs can show how non-standard joint geometries avoid discontinuities that can lead to random cracking.

For details, refer to section 3.3, Rigid Pavement Joint Design, in the 1993 AASHTO Guide for Design of Pavement Structures (4).

Page 62

04- NEW PAVEMENT DESIGN FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

4.3.3.1 Joint sealing To keep incompressible materials out of the joint and to minimize the inflow of water, all joints must be sealed, to the extent possible, out of the subgrade. Because totally sealing pavement joints against water infiltration is not possible, however, a good subsurface drainage system is essential. For concrete-to-concrete joints, use silicone sealant material. For concrete to asphalt joints, use of self-levelling silicone or hot pour sealant material. 4.3.3.2 Transverse (contraction) joints Transverse joints are perpendicular to the centreline of the roadway. They prevent uncontrolled cracking. Most transverse joints are sawed contraction joints. 4.3.3.3 Dowel bars The placement of dowel bars across transverse joints reduces stresses and deflections. Dowel bars also help ensure adequate load transfer, reducing the potential need to pump the subbase material. Dowel bars are inserted into the concrete parallel to the centreline of the roadway and the surface of the pavement. Table 4-7 shows the required width of dowel bars based on the depth of the slab into which they are inserted.

Table 4-7: Required Pavement Dowel Bar

Slab Depth (in cm) Diameter (in cm) 20 2.5 23 – 27 3.2 ≥ 28 3.8

Dowel bars should be spaced 30 centimetre (cm) apart from each other, unless otherwise indicated due to some special reason. Dowel bars should be 45 cm long. Using a dowel bar basket, place dowel bars before the concrete pouring operation. 4.3.3.4 Traverse joint spacing Transverse joint spacing should not exceed 4.5 meter (m) or twenty-four times the slab thickness, whichever is less. 4.3.3.5 Longitudinal joints Longitudinal joints, which are often tied with rebar to maintain the aggregate interlock between slabs, prevent uncontrolled cracking of slabs. They should not be spaced greater than 4.5 m apart from each other. If a lane is wider than 4.5 m, place a longitudinal joint in the centre of the lane. Common wide lanes include ramps and weigh stations. 4.3.3.6 Tie bars Generally, longitudinal joints are tied together by deformed reinforcing steel tie bars, which tightly bind adjacent lanes or shoulders. Although the direct assistance to load transform that tie bars provide is not significant, they do improve aggregate interlock. Number 13 rebars (Metric) have a nominal diameter of 13 mm and are 64 cm long. Number 16 (Metric) rebars have a nominal diameter 16 mm and are 75 cm long. For the best results, space number 13 bars no more than 60 cm apart and number 16 rebars no more than 95 cm apart. Apply the required depth and free edge distance values to determine where to place tie bars along a longitudinal joint.

Page 63

04- NEW PAVEMENT DESIGN FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

4.3.3.7 Expansion joints Expansion joints enable concrete to safely expand when incompressible materials infiltrate into the joints and during periods of extreme temperature change. Expansion joints also support areas with abrupt changes in geometry (such as "T" intersections, bridges, ramps and terminals) or immovable structures (such as parking areas, toll plazas, buildings, bridge approaches, and slabs). Expansion joints also support areas with concrete curbs, traffic separators, manholes, and drainage structures (such as grates and inlets). 4.3.3.8 Construction joints Construction joints provide a clean transition from one concrete pouring operation to the next, especially where fresh concrete abuts old concrete. Construction joints can be longitudinal joints, transverse joints, or a combination of the two. Transverse construction joints, which are formed through the use of a header, are doweled. Longitudinal construction joints are often tied together through the insertion of rebar. 4.3.4 Mechanistic-Empirical pavement design In addition to AASHTO’s methods, as described in their Guide for Design of Pavement Structures (4), pavement designers can apply a newer M-E method. Austroads, the association of Australian and New Zealand road transport and traffic authorities, describes an M-E pavement design method in their Guide to Pavement Technology, Part 2: Pavement Structural Design (6). Austroads’ method is based on the USA Portland Cement Association’s Thickness Design for Concrete Highway and Street Pavements, 1984 (EB109P) (20), with revisions to suit local conditions. In this method, base and subbase layers are not bonded.

Applying a M-E method, designers base their analyses of rigid pavement on a principle of liquid foundations, an assumption that the mechanical pressure between a slab and its subgrade at any point is proportional to the deflection at that point, independent of deflections at any other points. M-E pavement design requires application of the following parameters:

 Predicted traffic volumes; refer to Chapter 2, Pavement Design Components, for details on how to obtain this information.  Subgrade strength in terms of California Bearing Ratio (CBR); refer to Chapter 3, Pavement Materials, for details on how to obtain this information.  Flexural strength of a concrete slab; refer to Chapter 3, Pavement Materials, for details on how to obtain this information.

Concrete thickness also depends on the type of joint reinforcement adopted for a slab. Thickness design uses analytical models and field testing of pavements with typical spacing between joints and thickness ranges. 4.3.4.1 Rigid pavement types This section focuses mainly on one type of rigid pavement, jointed plain concrete pavement (JPCP). JPCP can be either dowelled, with 4.5 m spacing between joints, or un-dowelled, with 4.2 m spacing between joints. JPCP includes longitudinal joints to limit a slab’s width to maximum of 4.3 meters.

Page 64

04- NEW PAVEMENT DESIGN FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

Rigid pavement requires a subbase layer under the concrete slab to provide uniform support and sufficient resistance to traffic and environmental conditions. Austroads recommends using a stabilized subbase layer of either cement or treated asphalt (6). Table 4-8 indicates the minimum sub base thickness based on the estimated future traffic.

Table 4-8: Minimum subbase thickness for rigid pavements

Design traffic Sub base Thickness (mm) Up to 106 125 mm Up to 5 * 106 150 mm Up to 107 170 mm Greater than 107 200 mm

4.3.4.2 Parameters for thickness design This section describes the three main parameters that designers using the M-E method need to determine pavement thicknesses.

Strength of Subgrade M-E pavement designers use CBR to assess the strength of materials in a sub grade down to 1 meter below the subbase. Refer to Chapter 3, Pavement Materials, for details on sub grade strength testing and characterization. If the top 1 meter of material in a subgrade shows different

CBRs, use Equation 4-10 to determine an equivalent subgrade strength (CBRE).

Equation 4-10: Equivalent subgrade strength where:

th  CBRi is the CBR value of i layer th  hi is the thickness of i layer (m)

 ∑hi is taken to a depth of 1.0 m.

The following conditions apply to the use of this equation:

 Layers of thickness less than 200 mm must be combined with an adjacent layer. The lower CBR value must be adopted for the combined layer.  It is assumed that higher CBR materials will be used in the upper layers. The formula is not applicable where weaker layers are located in the upper part of the subgrade.  The maximum CBR from the use of this formula is 15%.

Traffic Methods for estimating design traffic are explained in details in Chapter 2, Pavement Design Components. An equivalent single axle load (ESAL) is the standard unit for design traffic for rigid pavement. A rigid pavement’s design traffic value reflects a cumulative number of ESALs, applied at each axle group load for each axle group type, over a pavement’s design life period.

Page 65

04- NEW PAVEMENT DESIGN FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

Strength of concrete slab For thickness design of concrete pavement, M-E pavement designers use the flexural strength (modulus of rupture) of concrete as the concrete strength. Refer to Chapter 3, Pavement Materials, for details on concrete strength characterization, which has a minimum flexural strength of 4.5 MPa at 28 days.

Project reliability To determine concrete slab thickness, a designer multiplies axle group loads by a load safety factor (LSF). Refer to Table 4-9 to determine an LSF based on project reliability. Refer to Table 4-1 to determine project reliability.

Table 4-9: Load safety factor for rigid pavements

Reliability Level 80% 85% 90% 95% 97.5%

LSF 1.15 1.15 1.20 1.30 1.35

4.3.4.3 Thickness design The following distresses impact the thickness of concrete slab for a rigid pavement:

 Flexural fatigue cracking of the pavement base  Subgrade or subbase erosion, which results from repeated deflections at joints

Thickness design for rigid pavement requires information on axle group types, the distribution of each axle group types, and the number of repetitions of each axle type or load combination throughout a pavement’s design life. Designers should round a calculated base thickness up to the nearest 5 mm. Any thickness so derived serves as a minimum value and is referred to as a pavement’s design base thickness.

A designer uses an assumed or estimated concrete slab thickness to determine the allowable axle load repetitions and estimate fatigue and erosion damage over a pavement’s design life period. A designer compares a pavement’s allowable axle load repetitions to its design traffic. If either fatigue or erosion damage exceeds 100%, designer shall increase the design thickness and repeat this process.

Fatigue cracking distress Designers can use Equation 4-11 or Equation 4-12 to calculate allowable load repetitions (Nf) for a given axle load. Designers shall use Equation 4-11 when stress (Sr) is greater than 0.55.

Equation 4-11: Allowable axle load repetitions when stress (Sr) is greater than 0.55

Designers shall use Equation 4-12 when stress is from 0.45 to 0.55.

Page 66

04- NEW PAVEMENT DESIGN FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

Equation 4-12: Allowable axle load repetitions when stress (Sr) is from 0.45 to 0.55

Equation 4-13: Stress (Sr)

Where:

Se = Equivalent stress (MPa)

fcf = Design characteristic flexural strength at 28 days (MPa)

P = Axle group load (kN)

LSF = Load safety factor (refer to Table 4-9)

F1 = Load adjustment for fatigue due to axle groups

= 9 for single axle with single tire (SAST)

= 18 for single axle with dual tires (SADT)

= 18 for tandem axle with single tire (TAST)

= 36 for tandem axle with dual tires (TADT)

= 54 for tridem axle with dual tires (TRDT)

= 72 for quad axle with dual tires (QADT)

Nf is infinite (or, more commonly, unlimited) when Sr is less than 0.45.

Designers can apply Equation 4-14 to determine equivalent stress (Se) and erosion factor (F3), using the coefficients a to j, as shown in Table 4-10 and Table 4-11.

Equation 4-14: Equivalent stress and erosion factors

Where:

Page 67

04- NEW PAVEMENT DESIGN FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

a, b, c, d, e, f, g, h, i, j are coefficients in Table 4-10 and Table 4-11.

D = Thickness of concrete base (mm)

Ef = Effective design CBR (%)

Table 4-10: Coefficients for prediction of equivalent stresses

Without concrete shoulders Concrete shoulders

Axle group type Axle group type SAST & TRDT & SAST & TRDT & Coefficient SADT TADT SADT TADT TAST QADT TAST QADT a 0.118 0.560 0.219 0.089 -0.051 0.330 0.088 -0.145 b 125.4 184.4 399.6 336.4 26 206.5 301.5 258.6 c -0.2396 -0.6663 -0.3742 -0.134 0.0899 -0.4684 -0.1846 0.008 d 26 969 44 405 -38 -10007 35 774 28 661 4418 1408 e 0.0896 0.2254 0.168 0.083 -0.0376 0.165 0.0939 0.0312 f 0.19 19.75 -71.09 -83.14 14.57 2.82 -59.93 -61.25 g -352174 -942585 681381 1215750 -861548 -686510 280297 488079 h -0.0104 -0.0248 -0.0218 -0.012 0.0031 -0.0186 -0.0128 -0.0058 i -1.2536 -4.6657 3.6501 5.2724 1.3098 -1.9606 4.1791 4.7428 j -1709 -4082 2003 4400 -4009 -2717 1768 2564

Table 4-11: Coefficients for prediction of erosion factors for un-dowelled slabs

Without concrete shoulders Concrete shoulders

Axle group type Axle group type TRDT SAST & TRDT & SAST & Coefficient SADT TADT SADT TADT & TAST QADT TAST QADT a 0.745 1.330 1.907 2.034 0.345 0.914 1.564 2.104 b 533.8 537.5 448.3 440.3 534.6 539.8 404.1 245.4 c -0.2071 -0.1929 -0.1749 -0.2776 -0.1711 -0.1416 -0.1226 -0.2473 d -42419 -43035 -35827 -36194 -44908 -44900 -32024 -15007 e 0.0405 0.0365 0.0382 0.0673 0.0347 0.0275 0.0256 0.0469 f 27.27 26.44 0.64 15.77 20.49 16.37 -9.79 8.86 g 1547570 1586100 1291870 1315330 1676710 1654590 1150280 518916 h -0.0044 -0.0039 -0.006 -0.0084 -0.0038 -0.0032 -0.0052 -0.0075 i -1.4656 -1.4547 1.0741 -1.2068 -1.3829 -0.9584 2.1997 1.5517 j -1384 -1344 50 -625 -913 -765 469 -599

Erosion distress

Designers shall use Equation 4-15 to calculate the allowable load repetitions (Ne) for a given axle load.

Page 68

04- NEW PAVEMENT DESIGN FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

Equation 4-15: Allowable axle load repetitions for erosion distress

Where:

F2 = Adjustment for slab edge effects

= 0.06 for base with no concrete shoulder

= 0.94 for base with concrete shoulder

F3 = Erosion factor (obtained by applying Equation 4-14)

F4 = Load adjustment for erosion due to axle group

= 9 for single axle with single tire (SAST)

= 18 for single axle with dual tires (SADT)

= 18 for tandem axle with single tire (TAST)

= 36 for tandem axle with dual tires (TADT)

= 54 for tridem axle with dual tires (TRDT)

= 54 for quad axle with dual tires (QADT)

Axle load inputs and load safety factors have no set limits, however, advises caution when using allowable loadings calculated with values of (4.5*P*LSF/F1) or (4.5*P*LSF/F4) that exceed 65 kN. 4.3.4.4 Minimum slab thickness Table 4-12 shows minimum allowable thicknesses for concrete slabs, based on traffic levels.

Table 4-12: Minimum concrete slab thickness

Traffic Level < 107 < 5 * 107 > 5 * 107 Slab Thickness (mm) 150 200 250

4.3.4.5 Dowels bars Refer to section 4.3.4.3 for details on dowel bars. 4.3.4.6 Tie bars Refer to section 4.3.4.6 for details on tie bars.

Page 69

04- NEW PAVEMENT DESIGN FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

4.4 Interlocking pavers design

4.4.1 Introduction The use of interlocking paver blocks for pavement surface is the oldest type of pavement structure. Nowadays interlocking paver blocks are used successfully in residential and commercial applications, especially at intersections and turns. The advantage of the paver blocks is the high abrasion and skid resistance, as well as it require no curing time. Also, the paver blocks does not exhibit deformation or surface cracking compared to the asphalt surface in hot climate. Paver blocks can be reused after any maintenance work. 4.4.2 Principle of paver blocks The principle of interlocking pavers is that each paver block interlocks with the adjacent block and should not be allowed to move independently. There are three types of movements: vertical, rotational and horizontal. Vertical movement is prevented through the shear transfer of loads to the surrounding blocks. Rotational movement is limited by the pavers being of sufficient thickness and placed closely together. The horizontal movement is prevented through the laying patterns that disperse braking, turning and acceleration forces. The most effective laying pattern is the Herringbone patterns that offer greater structural capacity and resistance to lateral movements. It is also important to give almost attention to the direction of the pattern with respect to the traffic direction. It is recommended to use 45° angle to the pavement axes to obtain better interlocking. 4.4.3 Construction procedure Typically, interlocking paver blocks are laid on top of unbound compacted base and subbase aggregate layer. Specifications and construction procedure for base and subbase layers under paver blocks is similar to those required for flexible asphalt pavements. After finishing the base layer, bedding sand layer is screeded in an even layer, typically, 50 mm. The pavers are placed on the smooth bedding sand according to the required pattern. Then the pavers are vibrated with a high frequency plate vibrator, which forces sand into the bottom of the joints of the pavers and begins compaction of the bedding sand. Sand is then spread and swept into the joints and the pavers are compacted again until the joints are filled. 4.4.4 Structural design procedure The interlocking paver blocks load distribution and failure modes are similar to flexible pavements. Accordingly, 1993 AASHTO Guide for Design of Pavement Structures (4) procedure is used. For heavy duty pavements such as ports and airports pavements are covered in Interlocking Concrete Pavement Institute (ICPI) manuals: Port and Industrial Pavement Design for Concrete Pavers and Airfield Pavement Design with Concrete Pavers. 4.4.4.1 Design factors The four factors that are considered for flexible pavements are also considered for the paver blocks. These factors are environment, traffic, subgrade strength and pavement materials. The design factors are estimated and obtained similar to the flexible pavements as described in Chapter 2 Pavement Design Components” and Chapter 3 ”Pavement Materials” of this Manual.

After estimating the design factors the steps explained in section 4.2.1 and the 1993 AASHTO chart Figure 4-1 shall be used to estimate the required SN.

The final step is to use the required SN and the material properties of the paver blocks and the bedding sand to calculate the thickness of the aggregate base and subbase layers. The typical Page 70

04- NEW PAVEMENT DESIGN FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL paver block thickness is 80 mm and 25 to 50 mm for the bedding sand. Tests had shown that after initial trafficking, the interlocking between the blocks increases and the layer stiffens. The measured modulus for the paver block and sand bedding reaches about 3,000 MPa which is equivalent to that of the asphalt concrete layer. Accordingly, the AASHTO layer coefficient for the 130 mm paver blocks and sand bedding will be taken as 0.44 as given in Table 4-3. The sand bedding gradation should follow ASTM C 33 as shown below in Table 4-13

Table 4-13: Gradation for bedding sand

Sieve Size Percent Passing 9.5 mm 100 4.75 mm 95-100 2.36 mm 80-100 1.18 mm 50-85 0.600 mm 25-60 0.300 mm 10-30 0.150 mm 2-10 0.075 mm 0-1 For example, a 2 million ESAL will require SN of 3.18 which can be achieved with 80 mm paver block, 50 mm sand bedding and 200 mm aggregate subbase for a total SN of 3.20 ((8/2.54)*0.44+(5/2.54)*0.44+(20/2.54)*0.14).

The structural design of the interlocking paver blocks has lower impact on the pavement performance compared to the construction procedure. It is very critical to emphasize the importance of the construction procedure and quality, such as gradation of bedding sand, blocks laying pattern, vibration/compaction of blocks and bedding sand and filling the joints with sand. These factors if not considered correctly will cause dislocation of blocks and formation of holes in the pavement surface, even if the structure design was safe. 4.5 Empirical pavement design example This section provides an example for an empirical flexible pavement design using the 1993 AASHTO Guide for Design of Pavement Structures.

The example is a 4 lane highway that will link Adu Dhabi Island to Al Ain. The soil is mainly characterized as A-3 Silty-Sand soil with a CBR of 10%. The traffic study shows that the current one way Average Annual Daily Traffic (AADT) is about 1700 vehicle with 60% Buses and trucks (Classes 4 to 13). Flexible pavement is recommended for this road. However, two scenarios will be used to compare the most economical option of the two. The first option is to use typical multi layer structure with aggregate granular base layer. While, the second option is to use a deep strength structure, which includes cement stabilized base layer.

The following are the required inputs for the pavement design. 4.5.1 Environment The ground water table (GWT) along the roadway is deep and will not impact the moisture content of the subgrade layer. Accordingly, no correction is need for the subgrade modulus.

Page 71

04- NEW PAVEMENT DESIGN FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

4.5.2 Traffic Traffic is very important and requires accurate data. A traffic survey was conducted in a nearby existing road. Both vehicle count and vehicle classification was conducted in the survey in addition to an axle load survey. The following parameters are taken for the pavement design:

 Vehicle Classifications: From the traffic survey it was found that the traffic is divided into different vehicle classes as given Table 4-14. The AADT per vehicle class is shown in the third column. The truck traffic from this would be the summation of the vehicle counts from class 4 to class 13. This would yield an Annual Average Daily Truck Traffic (AADTT) of 1700*0.6= 1020 vehicle per day.  Axle load distribution: the Axle load survey gave the percentage of axle load distributions for each of the single, tandem and Tridem axles, as shown in Table 4-15,  Table 4-16Table 4-16, and Table 4-17, respectivel.These loads were used to calculate the EALF as given in Equation 2-9. The standard axle load from Table 2-3 for the single, tandem and Tridem axles were 80, 135 and 181 kN, respectively. Also, the power used in the calculation is 4 for the empirical design method as given in Table 2-4. The EALF for each load group is given in the third column. The EALF is then multiplied by the percentage of this axle load to obtain the individual truck factor (TF) as shown in the fourth column. The individual values are then summed up to obtain the total TF for each axle. The total TF for all axles types summation of the three values i.e. 0.3069+0.7984+1.2914 = 2.3967.  Design life: 20 years  The growth rate was taken to be 6.5%. Using a linear growth factor (GF) as given in Equation 2-7 will give a GF of 2.3.  The lane factor (LDF) and direction factor (DF) were both taken as 100% i.e. 1. The previous parameters are used to calculate the total equivalent single axle load (ESAL) as given in Equation 2-11. ESAL = 1700*0.6*2.3967*2.3*1*1*20*365 = 41,046,106.

Table 4-14: Vehicle classification distribution

Vehicle Class Percentage of Total Traffic AADT 1 0 0 2 10 170 3 30 510 4 1 17 5 30 510 6 6 102 7 2 34 8 5.5 93.5 9 13 221 10 2.08 35.36 11 0.3 5.1 12 0.06 1.02 13 0.06 1.02 Total 100 1700

Page 72

04- NEW PAVEMENT DESIGN FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

Table 4-15: Single axle load distribution Equivalent Axle Axle Load (KN) Percentage (%) Load Factor TF (EALF) Single 13.34 5.26 0.0 0.0000 17.79 3.235 0.0 0.0001 22.24 5.211 0.0 0.0003 26.69 5.151 0.0 0.0006 31.14 6.235 0.0 0.0014 35.59 8.435 0.0 0.0033 40.03 9.899 0.1 0.0062 44.48 11.163 0.1 0.0107 48.93 10.061 0.1 0.0141 53.38 8.144 0.2 0.0161 57.83 6.266 0.3 0.0171 62.28 4.755 0.4 0.0175 66.72 3.667 0.5 0.0177 71.17 2.967 0.6 0.0186 75.62 2.267 0.8 0.0181 80.07 1.818 1.0 0.0182 84.52 1.364 1.2 0.0170 88.96 1.031 1.5 0.0158 93.41 0.791 1.9 0.0147 97.86 0.541 2.2 0.0121 102.31 0.417 2.7 0.0112 106.76 0.29 3.2 0.0092 111.21 0.206 3.7 0.0077 115.65 0.243 4.4 0.0106 120.10 0.144 5.1 0.0073 124.55 0.084 5.9 0.0049 129.00 0.079 6.8 0.0053 133.45 0.04 7.7 0.0031 137.89 0.1 8.8 0.0088 142.34 0.042 10.0 0.0042 146.79 0.024 11.3 0.0027 151.24 0.017 12.8 0.0022 155.69 0.011 14.3 0.0016 160.14 0.01 16.1 0.0016 164.58 0.008 17.9 0.0014 169.03 0.008 19.9 0.0016 173.48 0.007 22.1 0.0015 177.93 0.009 24.5 0.0022 Total 100 0.3069

Page 73

04- NEW PAVEMENT DESIGN FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

Table 4-16: Tandem axle load distribution

Axle Load Percentage Equivalent Axle Load TF (KN) (%) Factor (EALF) Tandem 26.69 7.572 0.0 0.0001 35.59 7.496 0.0 0.0004 44.48 6.8 0.0 0.0008 53.38 6.618 0.0 0.0016 62.28 7.128 0.0 0.0032 71.17 6.75 0.1 0.0052 80.07 6.608 0.1 0.0082 88.96 6.499 0.2 0.0123 97.86 6.441 0.3 0.0178 106.76 5.657 0.4 0.0221 115.65 5.021 0.5 0.0270 124.55 4.818 0.7 0.0349 133.45 4.556 1.0 0.0435 142.34 3.799 1.2 0.0470 151.24 3.206 1.6 0.0505 160.14 2.496 2.0 0.0494 169.03 2.039 2.5 0.0501 177.93 1.509 3.0 0.0455 186.83 1.054 3.7 0.0387 195.72 0.826 4.4 0.0365 204.62 0.77 5.3 0.0406 213.51 0.543 6.3 0.0340 222.41 0.395 7.4 0.0291 231.31 0.309 8.6 0.0266 240.20 0.277 10.0 0.0278 249.10 0.212 11.6 0.0246 258.00 0.127 13.3 0.0169 266.89 0.12 15.3 0.0183 275.79 0.108 17.4 0.0188 284.69 0.058 19.8 0.0115 293.58 0.044 22.4 0.0098 302.48 0.039 25.2 0.0098 311.38 0.038 28.3 0.0108 320.27 0.027 31.7 0.0086 329.17 0.012 35.3 0.0042 338.06 0.012 39.3 0.0047 346.96 0.006 43.6 0.0026 355.86 0.01 48.3 0.0048 Total 100 0.7984

Page 74

04- NEW PAVEMENT DESIGN FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

Table 4-17: Tridem axle load distribution

Equivalent Axle Axle Load Percentage Load Factor TF (KN) (%) (EALF) Tridem 53.38 29.409 0.0 0.0022 66.72 6.9 0.0 0.0013 80.07 5.725 0.0 0.0022 93.41 5.212 0.1 0.0037 106.76 3.423 0.1 0.0041 120.10 3.376 0.2 0.0065 133.45 4.24 0.3 0.0125 146.79 3.318 0.4 0.0144 160.14 5.169 0.6 0.0317 173.48 3.728 0.8 0.0315 186.83 6.634 1.1 0.0753 200.17 4.2 1.5 0.0628 213.51 3.268 1.9 0.0633 226.86 3.073 2.5 0.0758 240.20 2.864 3.1 0.0888 253.55 1.955 3.9 0.0753 266.89 1.252 4.7 0.0592 280.24 1.071 5.7 0.0615 293.58 1.12 6.9 0.0775 306.93 1.312 8.3 0.1085 320.27 0.812 9.8 0.0796 333.62 0.32 11.5 0.0369 346.96 0.318 13.5 0.0429 360.31 0.41 15.7 0.0644 373.65 0.461 18.2 0.0837 387.00 0.097 20.9 0.0203 400.34 0.056 23.9 0.0134 413.68 0.083 27.3 0.0226 427.03 0.017 31.0 0.0053 440.37 0.132 35.0 0.0463 453.72 0.045 39.5 0.0178 Total 100 1.2914

4.5.3 Materials Flexible pavement structure can be composed of several layers such as the subgrade, granular base/subbase, cement stabilized base and asphalt concrete layer. In the following section the modulus of each possible layer will be estimated using the models given in Chapter 3 of this manual. 4.5.3.1 Subgrade layer The subgrade layer resilient modulus (Mr) is calculated from CBR test results. As given in the heading of the example, the subgrade soil in the road area is predominately A-3 Silty-Sand soil

Page 75

04- NEW PAVEMENT DESIGN FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL with a minimum CBR of 10%. Equation 3-1 is used to estimate the Mr of the subgrade layer. The subgrade Mr is an essential input into the 1993 AASHTO design equation.

Mr = 1500*10= 15,000 psi. = 100 MPa 4.5.3.2 Aggregate base layer According to Abu Dhabi Roads Material Specifications, the aggregate base layer material should satisfy a minimum CBR of 65%. If this value is assumed to be achieved in the site during construction, then the Mr for the base layer would be calculated from Equation 3-2.

Mr = 2555*65^0.64 = 36,953 psi = 255 MPa.

Figure 3-1 is then used to estimate the layer coefficient for the granular base layer (a2) which is yield to be 0.13. 4.5.3.3 Cement stabilized base layer The CTB layer is used as a deep strength layer in such cases that heavy traffic is expected to use the pavement structure. The cement stabilized layer will increase the load carrying capacity of the pavement structure without the need to increase the total thickness of the pavement structure. Figure 3-3 can be used to obtain the layer coefficient based on unconfined compressive strength after 7 days of the CTB material. Test results from project using CTB provided a unconfined compressive strength of 900 psi or a modulus of 850,000 psi (5,860 MPa). This value will yield a layer coefficient of 0.24. 4.5.3.4 Asphalt concrete layer The aggregate gradation and binder content in Abu Dhabi mix design specification differ for different AC layer types mainly, surface course and base course. This difference in gradation and binder content will provide a different modulus for each layer. However, in the empirical design the same modulus is assumed for all AC layers. In the empirical pavement design the AC materials is assumed to have a resilient modulus of 3.1 GPa (450,000 psi) which will yield a layer coefficient value of 0.44. In some cases when an open graded friction course or an existing asphalt layer is used in the pavement structure the modulus value can be reduced to 300,000 psi which reduces the layer coefficient to 0.35 as given in Figure 3-5. For this example, the common a1 value of 0.44 will be used. 4.5.4 Structure design The traffic and material are the main inputs for the pavement structure design. However, additional inputs are required according to the 1993 AASHTO guide procedure. The additional inputs are as follows for Rural Roads:

 Reliability level (%) = 99.9 % as given in Table 4-1 for Rural Roads.  Standard normal deviate = -3.09052 for the 99.9 % reliability  Initial serviceability = 4.2  Terminal Serviceability = 3.0  Overall standard deviation = 0.45

In addition to:

 ESAL = 41,046,106  Subgrade Mr = 15,000 psi  Base Mr = 36,953 psi Page 76

04- NEW PAVEMENT DESIGN FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

 CTB Mr = 850,000 psi  Layer coefficient for AC a1 = 0.44  Layer coefficient for aggregate base a2 = 0.13  Layer coefficient for CTB base a2 = 0.24

Equation 4-1 is then used to calculate the required structure number (SN) at the top of the subgrade (SN2) and base layer (SN1).

The required SN2 is equal to 6.93, while, SN1 is equal to 5.18. SN1 is obtained by using the MR of the base layer as the input to the 1993 AASHTO equation.

Option 1 using aggregate granular base:

The total thickness of the AC layer = SN1 * 2.54 / a1 = 5.18 * 2.54 /0.44 = 30.5 cm i.e. 31 cm. This can be divided into 6 cm surface course and 25 cm base course. Then, actual SN1 = 5.37.

The thickness of the base layer = (SN2 – SN1)* 2.54 /a2 = (6.93 – 5.37)*2.54 /0.13 = 30.5 cm i.e. 35 cm. This can be divided into 15 cm granular base layer and 20 cm granular subbase layer.

Total SN = (31*0.44+35*0.13)/2.54=7.16, which exceeds the 6.93 required from the 1993 AASHTO equation.

Option 2 using cement stabilized base:

In case of using the CTB, a new SN1 could have been obtained to reduce the AC thickness. However, in this example the AC thickness is kept the same at 31 cm, and makes the modification in the base layer thickness.

The thickness of the base layer = (SN2 – SN1)/a2 = (6.93 – 5.37)*2.54 /0.24 = 16.51 cm i.e. 17 cm of a CTB base layer.

Total SN = (31*0.44+17*0.24)/2.54 = 6.98, which exceeds the 6.93 required from the 1993 AASHTO equation. 4.5.5 Cost analysis There are two options for the pavement structure design for the given road, the first option has a total thickness of 66 cm and uses the aggregate as a base. While, the second option has a total thickness of 48 cm and it uses CTB. These two options yield a cost difference in its construction as well as maintenance frequency over the life of the pavement. The initial construction cost will be considered here for this example, while for maintenance cost and users cost due to maintenance can be check in the example in LCC analysis Chapter 9 of this manual.

The AC cost will be the same since the AC thickness was kept constant. The cost of the 30 cm of the aggregate base costs 50 AED per unit area. The cost of the 17 cm of CTB is 40 AED per unit area. The total area of the project is 10 km with 4 lane road (10*1000*4*3.65 = 146,000 square meter). Accordingly, the expected cost saving in only the initial construction cost is 10*146,000, which is about 1.5 million AED. 4.6 Mechanistic-Empirical pavement design example The same data used for the empirical flexible pavement design example is used for the M-E example. The traffic will be the same for about 41 million ESALs. The modulus of different materials need to estimated for the M-E method. Finally, the structure design using linear elastic

Page 77

04- NEW PAVEMENT DESIGN FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL software will be used to estimate the strains at different locations. Only the option with aggregate base will be used for this example.

The M-E design requires the assumption of a pavement section before conduction the analysis. If the assumed section satisfies the traffic requirement then the section can be used if it did not then the layer thickness can be revised and the analysis should be rerun. Since the empirical example is being used, then the design section from the empirical example will be used as the initial section for the M-E example. 4.6.1 Climate For the M-E design procedure the Mean Annual air temperature (MAAT) need to know to estimate the WMAPT. The average WMAPT for Abu Dhabi Emirate is 43.5 °C. However for Abu Dhabi Island, the MAAT calculated value in Table 2-2 is 30.6 °C and the WMAPT is 44.2 °C. The 43.5 °C will be used for this example. 4.6.2 Materials In the following section the modulus of each layer will be estimated using the models given for the M-E design as explained in Chapter 3 of this manual. 4.6.2.1 Subgrade layer The subgrade layer resilient modulus (Mr) is calculated from CBR test results. The subgrade soil in the road area is predominately A-3 Silty-Sand soil with a minimum CBR of 10%. Equation 3-1 is used to estimate the Mr of the subgrade layer.

Mr = 1500*10= 15,000 psi. = 100 MPa 4.6.2.2 Aggregate base layer The aggregate base layer material should satisfy a minimum CBR of 65%. If this value is assumed to be achieved in the site during construction, then the Mr for the base layer would be calculated from Equation 3-2.

Mr = 2555*65^0.64 = 36,953 psi = 255 MPa. 4.6.2.3 Asphalt concrete layer The asphalt surface course and base course have different mixture specifications and uses different binder types. Table 4-18 shows the material properties for each layer. For asphalt layers the binder and asphalt mixture modulus is required, these modulus values can be estimated using Table 3-4, Figure 3-6 and Figure 3-7 as shown in Table 4-18. 4.6.3 Structure design The traffic and material are the main inputs for the pavement structure design. These inputs are input in a linear elastic analysis program such as KENLAYER to calculate the strains at critical locations as shown in Figure 4-4 4-4. The critical locations are mainly the bottom of each asphalt layer for fatigue cracking and the top of the subgrade for permanent deformation.

Figure 4-10 4-10 shows the output file for the linear elastic analysis with the critical locations.

The strains obtained from the linear elastic analysis are then used in conjunction with Equation 4-7 for the permanent deformation and Equation 4-9 for asphalt fatigue cracking to calculate the allowable number of load repetitions before failure.

Page 78

04- NEW PAVEMENT DESIGN FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

Table 4-19 shows the critical strains from the analysis and the corresponding allowable number of axle repetitions. The allowable axle repetitions are then compared to the expected traffic that is estimated at 41 million ESAL. From the table it can be seen that the assumed pavement section is very safe and over designed. The most critical location is the asphalt fatigue cracking at the bottom of the asphalt base course layer, with 100 million repetitions.

The difference between the empirical and M-E design can be related to the use of the actual stiffness of each layer especially, the asphalt layer. In the empirical method the layer coefficient was the same for both asphalt layers. While, the estimated modulus values from the nomographs gave a modulus for the base course half of that for the surface course.

Table 4-18: Asphalt material properties for M-E design

Surface Course Base Course Binder Pen 40/50 Binder Pen 60/70 T1 = 15.6 C Pen = 17 T1 = 15.6 C Pen = 25 T2 = 14.0 C Pen = 43 T2 = 14.0 C Pen = 64 A = 0.033 A = 0.043 PI = 1.326 PI = -0.5101 T800pen = 63.5 C T800pen = 50.38 C WMAPT = 43.5 C WMAPT = 43.5 C Binder S = 5 Mpa Binder S = 1 Mpa Binder by wt = 3.9% Binder by wt = 3.5% Binder by Volume (Vb)= 8% Binder by Volume (Vb)= 7% Air voids % = 6% Air voids % = 6% Aggregate Volume = 86 % Aggregate Volume = 87 % Mix Modulus = 3000 Mpa Mix Modulus = 1800 Mpa

Table 4-19: Calculated strain and N for M-E design

Smix Vb Strain N AC Surface Layer 3000 8 4.74E-05 1,712,553,784 AC Base Layer 1800 7 8.92E-05 102,951,808 Subgrade 5.48E-04 404,913,284

Page 79

04- NEW PAVEMENT DESIGN FIRST EDITION -DECEMBER 2016

PAVEMENT DESIGN MANUAL

Figure 4-10: Linear Elastic Analysis Results for the M-E Example

Page 80

04- NEW PAVEMENT DESIGN FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

5 REHABILITATION DESIGN

5.1 Purpose and scope This chapter provides methods and guidance for pavement design engineers to rehabilitate flexible and rigid pavements. Pavement engineers shall ensure that designs are in accordance with the client’s policies, procedures, standards, and guidelines, as well as good engineering practices.

Pavement rehabilitation is primarily a matter of sound application of acceptable engineering criteria and standards. Whilst the standards contained in this manual provide a general basis for uniform rehabilitation practices for typical pavement situations, this manual does not provide precise rules for all possible situations.

Design procedures incorporated into this document are based on the 1993 AASHTO Guide for Design of Pavement Structures (4) and the Guide to Pavement Technology, Part 2: Pavement Structural Design (6) from Austroads. This manual applies AASHTO’s empirical design methodology and Austroads’ M-E design methodology.

This chapter discuss flexible pavement rehabilitation and rigid pavement rehabilitation, with descriptions on how to apply the empirical method and M-E method for each type.

This chapter also outlines overlays that designers can use to remedy functional or structural deficiencies of existing pavements. A pavement’s deterioration can help designers determine whether it has a functional or structural deficiency.

Functional deficiencies that adversely affect highway users include poor surface friction and texture, hydroplaning and splash from wheel path rutting, and excess surface distortions (such as potholes, corrugation, faulting, blowups, settlements, and heaves).

Structural deficiencies such as inadequate thickness, cracking, distortion, and disintegration, arise from conditions that adversely affect the load-carrying capability of the pavement structure. Several types of distress are not directly caused by traffic loads, but become increasingly severe under traffic. Distress can become so severe that it detracts from a pavement’s load carrying capability.

Pavement rehabilitation sometimes includes the placement of maintenance overlays and surface treatments that serve as preventive measures to slow the rate of deterioration. 5.2 Overlay feasibility To determine the feasibility of any overlay, a designer shall consider the following factors.

 Availability of adequate funds for construction of the overlay. Funding is basically a constraint.  Construction feasibility of the overlay, including the following factors:

• Traffic control • Availability of materials and equipment • Climatic conditions • Construction problems such as noise, pollution, subsurface utilities, overhead bridge clearance, shoulder thickness, and, in the case of limited right-of-way, side slope extensions • Traffic disruptions and user delays

Page 81

05-REHABILITATION DESIGN FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

 Required future design life of the overlay. Many factors will affect the life of an overlay, such as the following.

• Existing pavement deterioration (specific distress types, severities, and quantities) • Existing pavement design, condition of pavement materials (especially durability problems, and subgrade soil) • Future traffic loadings • Local climate • Existing subgrade situation

A designer shall consider all of these factors and specific site conditions to determine the suitability of an overlay. 5.3 Important considerations in overlay design Designers of overlays shall consider the following factors:

 Pre-overlay repair  Reflection crack control  Traffic loadings  Drainage  Rutting in AC pavements  Milling AC surfaces  Recycling existing pavement  Need for structural or functional overlay  Overlay materials  Shoulders  Durability of PCC  Overlay joints for PCC  Overlay reinforcement for PCC  Overlay bonding and separation layers for PCC  Overlay design reliability and overall standard deviation  Pavement widening  Potential errors and possible adjustments to thickness 5.3.1 Pre-overlay repair A deteriorated pavement is an existing pavement that has visible and invisible distress or damage at the surface. Invisible damage may be detected by various methods. Depending on the type of distress, an engineer may chose to repair damages before placing an overlay on an existing pavement. A design shall consider factors such as performance and cost tradeoffs when choosing the type and scope of an overlay. 5.3.2 Reflection crack control Reflection cracks are common causes of deterioration in an overlay. With accurate calculations, a designer can reduce the amount and severity of reflection cracks. Different types of materials affect reflective cracking differently.

Page 82

05-REHABILITATION DESIGN FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

5.3.3 Traffic loadings Designing an overlay requires knowledge of traffic loading, in 18-kip ESALs, over the design life of the overlay. Designers use approximate flexible pavement or rigid pavement equivalency factors to estimate ESALs. 5.3.4 Drainage Designers should evaluate the impact of drainage on an existing pavement to determine how anticipated drainage will influence an overlay’s performance. An overlay’s performance can be improved by reducing poor drainage and removing excess water, which improves base and subbase strength by reducing erosion. 5.3.5 Rutting in Asphalt Concrete pavements A designer shall determine the cause of rutting before designing an AC overlay. Overlays are not appropriate for pavement with severe rutting, which can create instability. Milling removes rutted surfaces and any underlying rutted asphalt layers. 5.3.6 Milling Asphalt Concrete surfaces Milling removes a portion of a pavement’s surface, typically improving the performance of an AC overlay by removing cracks and hardened materials. A rehabilitation crew shall perform milling on severely rutted and distorted pavement before placing an overlay. 5.3.7 Recycling existing pavement Designers may consider recycling a section of an existing AC layer, which is a common practice. 5.3.8 Need for structural or functional overlay Functional overlays rectify functional deficiencies. Structural overlays add sufficient thickness to a pavement to enable it to carry anticipated traffic. 5.3.9 Overlay materials Designers shall consider specific loading, climatic conditions, and underlying pavement deficiencies when selecting and designing overlay materials. 5.3.10 Shoulders Overlays for shoulders should match any overlays for corresponding traffic lanes. To select the thickness and material for an overlay on a shoulder, consider the amount of traffic that is anticipated to use the shoulder and the shoulder’s condition. If a pavement is in good condition, designers may limit shoulder rehabilitation to patching only deteriorated areas before overlaying the shoulder to match the grade of traffic lanes. If a shoulder has severely deteriorated and patching will not be cost-effective, rehabilitation crews shall remove and replace it. 5.3.11 Durability of PCC A PCC slab’s durability affects the performance of AC and bonded PCC overlays. If “D” cracking or reactive aggregates are present in a slab, designers should anticipate continuing deterioration and design the overlay to prevent progressive deterioration of the underlying slab.

Page 83

05-REHABILITATION DESIGN FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

5.3.12 Overlay joints for PCC Factors to be considered when designing special joints of bonded or unbounded jointed concrete overlays include joint spacing, depth of saw cut, sealant reservoir shape, and load transfer requirements. 5.3.13 Overlay reinforcement for PCC Jointed and continuously reinforced concrete overlays require sufficient reinforcement to hold cracks together. 5.3.14 Overlay bonding and separation layers for PCC A bonded overlay must remains intact with the existing slab. Unbounded overlays must be constructed so that the separation layer prevents reflection cracks in the overlay. 5.3.15 Overlay design reliability and overall standard deviation

Varying the reliability level used to determine a structural number (SNf) or thickness (Df) of existing pavement produces overlay thicknesses that vary by 6 inches or more. Based on field testing, DMAT recommends using a reliability level of 95 percent to provide a consistent thickness. Different types of overlay have different standard deviations and varying levels of uncertainty, which do not match those characteristics of new pavement. 5.3.16 Pavement widening When widening a lane or adding an additional lane, designers shall take the following functional and structural factors into consideration:

 An overlay and corresponding widening should have the same service life to avoid rehabilitations at different times.  Materials, thickness, reinforcement, and joint spacing for a widened shoulder should match those of existing pavement, although a widened shoulder can have a shorter joint spacing.  Crews should use deformed bars to securely tie and anchor a widened PCC section to an existing PCC slab.  Crews may place reflection crack relief fabric along a longitudinal widening joint.  An overlay’s thickness should match that of the traffic lanes.  Designers should determine necessary positions for longitudinal drainage. 5.3.17 Potential errors and possible adjustments to thickness One or more of the following factors can cause errors in the thickness of an overlay:

 Pavement deterioration may be caused by factors that are not associated with traffic loads. If a calculated thickness is less than or equal to zero, structural improvement is not needed. For functional deficiencies, an overlay should have the least constructible thickness that is still sufficient to remedy the problem.  Designers may need to modify calculations to satisfy agency procedures, applying the following typical inputs and outputs:

• Overlay reliability design level, R

• Overall standard deviation, So

Page 84

05-REHABILITATION DESIGN FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

• Effective slab thickness and structural number adjustment factors • Design subgrade resilient modulus and effective k-value • Other design inputs that require correction 5.4 Pavement evaluation for overlay design Designers shall evaluate a pavement’s entire length before deciding on an overlay type and design. Such evaluation requires a designer to divide pavement into smaller uniform sections, perform functional and structural evaluations, and estimate existing conditions. Chapter 11 provides more information on the pavement evaluations methods and data analysis. 5.4.1 Design of overlay along project The following two approaches for designing overlay thickness for a project are available:

 Uniform section approach: A designer divides a project into sections with relatively uniform designs and conditions and considers each uniform section independently from others. A designer obtains inputs for overlay design from each section to represent each section’s average condition. Using each section’s mean inputs, a designer determines a single overlay thickness for the entire length of each section.  Point-by-point approach: A designer uses specific points along a uniform design section to determine the overlay thickness, determining all of the required calculation input data for each point. Factors such as deflection, thickness, and condition commonly vary from point to point. This approach requires more effort for the design procedure, although field work for both is relatively similar. Based on the point by point overlay thicknesses, a designer can either divide the project into sections with different overlay thicknesses or determine one thickness that is sufficient for use throughout the whole project. A designer may investigate sections with high thicknesses to determine whether they warrant more extensive repair. 5.4.2 Functional evaluation of existing pavement This section describes optional solutions for functional deterioration.

 Possible remedies for surface friction and hydroplaning include the following:

• For all pavement types, designers may use a thin overlay that is suitable for the level of traffic to repair inadequate micro and macro texture in pavement through polishing surfaces. • For AC-surfaced pavement, milling may be necessary to remove the bleeding material, prevent further bleeding through the overlay, and eliminate rutting caused by poor friction. Designers may use an open-graded friction course or an overlay thickness that is sufficient for the level of traffic. • For AC-surfaced pavement, designers may need to take additional corrective action to remedy rutting that has resulted from hydroplaning and wheel path splashing.

 Possible solutions for surface roughness include the following:

• For all pavement types, designers can correct long wavelength surface distortions, heaves, and swells by levelling an overlay with various thicknesses. • For AC-surfaced pavement, designers can repair deteriorated areas to their full depths and apply a thicker AC overlay that integrates a reflection crack control treatment to treat roughness from deteriorated transverse cracks, longitudinal

Page 85

05-REHABILITATION DESIGN FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

cracks, and potholes. Conventional overlays are only temporary remedies, lasting only until cracks reflect through. • For AC-surfaced pavement, repairing roughness caused by ravelling of the surface may require a thin AC overlay and, possibly, milling the surface to remove deteriorated material and prevents debonding. If stripping caused the ravelling, crews should remove the entire layer to prevent further stripping under the overlay. • For PCC-surfaced pavement, designers can apply rigid materials to a pavement’s full or partial depth to repair roughness caused by spalling, potholes, and faulting of transverse and longitudinal joints and cracks. Because spalling is an indication of poor load transfer and drainage, such defects may need to be rehabilitated first.

 Refer to Table 5-1 for primary causes and solutions for rutting.

A designer may apply preventive overlays, such as thin AC and various surface treatments to a pavement surface to slow the rate of deterioration. Preventative overlays are also options for pavements with no current deformation, but for which deterioration is anticipated.

Designers require sound engineering knowledge and experience to ensure that overlay designs address functional problems and prevent their recurrence. Refer to Chapter 8, Flexible Pavement Maintenance, for more information on surface treatments.

Table 5-1: Causes and solutions for rutting

Cause of Rutting Layer(s) Causing Rut Solution Total pavement thickness inadequate Subgrade Thick overlay Unstable granular layer due to Base or subbase Remove unstable layer over saturation thick overlay Unstable layer due to low shear Base Remove unstable layer or strength thick overlay Unstable AC mix (including stripping) Surface Remove unstable layer Compaction by Traffic Surface, base, Surface milling and/or subbase levelling overlay Studded tire wear Surface Surface milling and/or levelling overlay

5.4.3 Structural evaluation of existing pavement Any condition that reduces the load-carrying capacity of a pavement is structural deterioration. Different types of pavement have different structural capacity.

 Flexible pavement – SN (structural number)  Rigid pavement – D (slab thickness)  Existing composite pavement (AC or PCC) – equivalent slab thickness

Although there isn’t a specific method for evaluating structural capacity, effective capacity considers the existing pavement in addition to how materials behave in the future. Client would recommend one of the following three optional assessment measures to determine effective structural capacity:

1. Structural Capacity based on visual survey and materials testing 2. Structural Capacity based on non-destructive deflection testing (NDT) 3. Structural capacity based on remaining life

Page 86

05-REHABILITATION DESIGN FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

These measures do not offer similar estimates due to the uncertainties involved; therefore, the engineer should use all measures and chose the best estimate based on judgment. 5.4.3.1 Structural capacity based on visual survey and materials testing Rehabilitation designers shall base structural capacity based on a visual survey and testing of materials, as outlined in this section.

 A visual survey is the most important factor, starting with a review of all available information regarding the design, construction, and maintenance of the pavement. Designers should create a detailed inventory of the types, amounts, severity levels, and locations of distresses, including the following main types of distress that indicate structural deficiencies.

• AC-surfaced pavements have the following common types of distress: . Fatigue or alligator cracking in wheel paths, which require patching and structural overlays . Rutting in the wheel paths . Transverse or longitudinal cracks that develop into potholes . Localized failing areas where the underlying layers are disintegrating and causing a collapse of a pavement’s AC surface. Such distress requires investigation to determine extent. A designer can repair PCC to the full depth of each defect to remedy PCC slabs with failures that are not extensive. Extensive failures, however, require reconstruction of a structural overlay. • PCC-surfaced pavements have the following common types of distress: . Deteriorating (spalling or faulting) transverse or longitudinal cracks. Designers must repair such defects to their full depths. . Designers must repair corner breaks at transverse joints or cracks to each defect’s full depth. . Localized failing areas where the PCC slab is disintegrating and causing spalls and potholes, a full depth repair is required. . To remedy localized punchouts, primarily in continuously reinforced concrete pavement (CRCP), a designer must repair each defect to its full depth and apply a structural overlay.

 A drainage survey identifies moisture related problems in pavement and locations where improvements need to be made for overlays.  A coring and materials testing program identifies causes behind distresses and determines material thicknesses and conditions. A testing program should determine how the existing pavement compares with similar materials and how old and new materials will react. 5.4.3.2 Structural capacity based on NDT Although NDTs provide an immense amount of data and analysis quickly, with reasonable levels of effort and costs, such analysis is sensitive to unknown conditions. Therefore, only experienced personnel shall perform NDTs.

NDTs offer the following analysis and functions for flexible pavement:

 Roadbed soil resilient modulus  Estimate of effective structural number SNeff of pavement structure.

Page 87

05-REHABILITATION DESIGN FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

NDTs offer the following analyses and functions for rigid pavement:

 Load transfer efficiency at joints and cracks  Effective modulus of subgrade reaction (k-value)  Modulus of elasticity of the concrete which provides estimate of strength

Designers may also use NDTs to quantify variability along a project due to deflection, and to divide the project into smaller sections of similar structural strength. Back calculation enables designers to estimate resilient modulus values for different pavement layers.

Designers can use the following equation to obtain a pavement’s effective structural number.

SNeff = a1 * D1 + a2 * m2 * D2 + a3 * m3 * D3

Equation 5-1: Effective structural number

Where

SNeff = effective structural number of the existing pavement D1, D2, D3 = thickness of existing pavement layers a1, a2, a3 = layer coefficient of different layers m2, m3 = drainage coefficients for base/ subbase layers 5.4.3.3 Structural capacity based on remaining life To determine a pavement’s remaining life, designers must know the actual amount of traffic a pavement has carried, the amount of traffic that it was designed to support, and the level of traffic at which it was expected to fail. Calculations express traffic amounts as a number of 18-kip ESALs. Equation 5-2 shows how to calculate a pavement’s remaining life.

Equation 5-2: Remaining life

Where

RL = Remaining life, percent

Np = Total traffic to date, ESAL N1.5 = Total traffic to pavement “failure”, ESAL

Equation 5-3 shows how to calculate the condition factor (CF).

Equation 5-3: Condition factor

Where

SCn = pavement structural capacity after Np, ESAL SCo = original Pavement structural capacity Page 88

05-REHABILITATION DESIGN FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

Equation 5-4 shows a calculation to estimate a pavement’s existing structural capacity.

Equation 5-4: Estimate of pavement structural capacity

Where

SNeff = effective structural number SNo = original structural number

A designer can use pavement design equations or nomographs, as described in Chapter 4, New

Pavement Design, to estimate N1.5, remaining life. AASHTO recommends 1.5 failure present serviceability index (PSI) and 50% reliability (4). When a pavement has a negative remaining life

(the traffic to date, NP, exceeds the expected traffic load for failure, N1.5), an engineer shall either use a minimum value of 0.5 for CF or discard use of the remaining life approach. Errors have the following main sources.

 Limited predictive capability of AASHTO Road Test equations  Large variations in observed performance, even among pavements of identical design  Erroneous estimations of past 18-kip ESAL  Inability to accurately know the amount of pre-overlay repair a pavement has received

If either of the following two tremendous faults arises, designers must account for them in further calculations:

 A pavement with a short or negative calculated remaining life exhibits only minor distress caused by traffic load.  A pavement with a high or very high calculated remaining life exhibits moderate to severe distress caused by traffic load. 5.4.4 Determination of subgrade resilient modulus for a design

Designers may apply the following to determine a pavement’s design subgrade (Mr):

 Laboratory testing  NDT back calculation  Estimation from resilient modulus correlation studies  Original design and construction data

Values for a pavement’s subgrade should be consistent regardless of the method used. Because values obtained by back calculating are relatively higher, designers must adjust the SNf value to be more conservative to avoid poor overlay performance.

Equation 5-5 shows how to back calculate a pavement’s subgrade:

Equation 5-5: Back calculation for subgrade

Where:

Page 89

05-REHABILITATION DESIGN FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

Mr = back calculated subgrade resilient modulus, in psi P = applied load, in pounds d = measured deflection at radial distance r, in inches r = radial distance at which the deflection is measured, in inches

Equation 5-6 uses an adjustment factor, C, which is required if the backcalculated value is less than 0.33.

Equation 5-6: Back calculation for subgrade, with adjustment factor

AASHTO road tests used a subgrade Mr value of 3000 psi, because it was consistent with laboratory tests of soil samples in the site (4). However, data from those tests illustrates that soil is stress dependent and rapidly increases for deviator stresses less than 6 psi. A subgrade deviator is almost always less than 6 psi, resulting in a subgrade’s Mr being much higher than 3000 psi. Back calculation of Mr values from deflection data and Mr values from laboratory tests confirm AASHTO’s findings. Back calculated Mr values are at least three times higher than Mr values from laboratory tests. 5.5 Flexible pavement overlays Thin bituminous overlays, such as slurry seals, sand asphalt, and micro-surfacing, are regarded as non-structural overlays. Structural overlays, however, involve the use of either granular material or asphalt that is at least 40 mm thick. Pavement designs use non-structural overlays to address deficiencies in their functional performance (including shape, ride quality, and surface texture). Generally, pavement designs use structural overlays to address distress and structural deficiencies. While correcting structural deficiencies, structural overlays also correct any functional deficiencies of the same pavements. This section details the design of structural asphalt concrete (AC) overlays on top of existing flexible pavements (AC over AC).

Construction of flexible pavement overlays involves the following tasks:

 Repairing deteriorated areas and making necessary drainage improvements  Correcting surface rutting by milling or placing a levelling course  Constructing widening  Applying a tack coat  Placing an AC overlay 5.5.1 Feasibility AC overlays are not effective to resolve the following conditions:

 Large quantities of highly severe alligator cracking (which requires the complete removal and replacement of the existing surface)  Excessive surface rutting caused by insufficient stability of existing materials  Grave deterioration of an existing stabilized base, which requires extensive repair to obtain uniform support  Infiltration and contamination of a soft subgrade, which requires removal and replacement of an existing granular base Page 90

05-REHABILITATION DESIGN FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

 Stripping in a pavement’s existing AC surface, which should be removed and replaced 5.5.2 Pre-overlay repair Pavement rehabilitation requires that the following types of distress be repaired before crews apply any AC overlay to avoid great reduction in the road’s service life. Table 5-2 describes specific repairs that must be made before crews apply an overlay.

Table 5-2: Repairs needed before overlay

Distress Type Required Repair Alligator cracking  Repair all high-severity alligator cracking.  Repair medium-severity cracking, unless using reflective crack control or paving fabric.  Remove soft subsurface material. Linear cracks  Patch high-severity cracks.  Fill linear cracks greater than 0.25 inch with sand-asphalt mixture or crack filler.  Apply reflective crack control for transverse cracks with significant opening and closing. Rutting  Apply milling or place a levelling course to remove ruts.  Investigate which layer caused any severe rutting. Surface irregularities  Investigate depressions, humps, ad corrugations; apply treatment as necessary, which typically involves removal and replacement.

5.5.3 Reflection crack control Reflection cracks decrease the service life of an AC overlay and require frequent maintenance. Water seeps through cracks in pavement, causing damage. To delay the occurrence and deterioration of reflection cracks, designers may apply pre-overlay repairs such as patching and crack filling. Additional reflection crack control measures include the following:

 Synthetic fabrics and stress-absorbing interlayer provide the following benefits:

• Control low to medium severe reflection alligator cracks • Control reflection of temperature cracks • Retard reflection of cracks under horizontal or vertical movements

 Crack relief layers thicker than 3 inches can controls reflective cracks under greater movements.  Sawing and sealing joints in an AC overlay can control straight cracks in the underlying AC.  Increasing the thickness of an AC overlay reduces bending, shearing, and temperature variations in existing pavement. 5.5.4 Surface milling If milling is to occur before overlay, designers shall use NDT testing to determine a pavement’s effective structural number (SNeff) and reveal the required depth of milling. If the required depth does not exceed the minimum necessary to remove surface ruts, then a designer does not need to adjust the SNeff. If the required depth exceeds the minimum depth needed to remove surface ruts,

Page 91

05-REHABILITATION DESIGN FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL a designer may reduce then SNeff to equal the structural coefficient determined from the condition survey times the milling depth. 5.5.5 Empirical thickness design According to AASHTO’s Guide for Design of Pavement Structures, an overlay’s designed thickness is the difference between the required structural capacity for future traffic and the effective structural capacity of the existing pavement (4). Designers can use Equation 5-7 to calculate the structural capacity of an overlay, which is represented by the structural number (SN).

SNol = aol * Dol = SNf – SNeff

Equation 5-7: Structural capacity of overlay

Where:

 SNol = required structure number of the overlay  SNf = future structure number of the pavement  SNeff = effective structure number of the existing pavement  aol = layer coefficient of the overlay, 0.44 for asphalt  Dol = required layer thickness of the overlay,

Designers shall take the following steps to estimate the required thickness of an overlay:

1. Evaluate the existing pavement design. Collect the thickness, material type, and subgrade soil information from construction records and reports for the existing pavement. 2. Analyse traffic. Estimate the past ESAL in the design lane to determine remaining life, in accordance with the method as explained in section 5.4.3.3, Structural capacity based on remaining life. In addition, predict the future required ESAL as explained in Chapter 2, Pavement Design Components. 3. Conduct a condition survey. Survey the existing pavement to record different distress types and their severities. Refer to Chapter 8, Flexible Pavement Maintenance, for more details on pavement distresses. 4. Perform deflection testing at uniform intervals of 200 meters along the pavement to assess the extent of deterioration in the existing pavement structure. Use FWDs. Apply the results of deflection testing to back calculate the modulus of the existing layers. 5. Perform material core tests. Take core samples of existing pavement to assess the extent and type of cracks in the AC layer. If you did not perform deflection testing (as instructed in step 4), use samples from the subgrade to obtain the pavement’s CBR, which yields the modulus of the subgrade, as described in Chapter 3, Pavement Materials. 6. Determine the pavement’s future structural number, using the following parameters:

• Effective subgrade modulus, which can be estimated either from sample testing, deflection testing, or soil information • Future traffic (as determined in step 2) • Loss in present serviceability index (PSI), as described in Chapter 4, New Pavement Design. • Design reliability, as described in Chapter 4, New Pavement Design.

• Overall standard deviation (So), with a value of 0.45, as described in Chapter 4, New Pavement Design.

Page 92

05-REHABILITATION DESIGN FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

After collecting these inputs, obtain the pavement’s future structure number (SNf) either by solving the AASHTO equation or by using the flexible pavement nomographs shown in Chapter 4, New Pavement Design.

7. Determine the pavement’s effective structural number (SNeff), as explained in section 5.4.3, Structural evaluation of existing pavement, either from non-destructive testing, a condition survey, or calculation of remaining life. 8. Determine the overlay’s required thickness, using Equation 5-8, applying the appropriate values from previous equations in this chapter.

Equation 5-8: Overlay thickness 5.5.6 Mechanistic-Empirical design Austroads based its guidelines for flexible overlays, as given in its Guide to Pavement Technology (6, 32), on a general M-E procedure (GMP). GMP methods are identical to those of the M-E design procedure for new pavements (as described in Chapter 4, New Pavement Design), except for ways to estimate the material properties of existing layers. Asphalt overlay designs are similar to designs for new pavement layers in that both are based on limiting fatigue cracking and permanent deformation.

Austroads’ GMP assumes that existing asphalt layers are completely cracked and have no remaining fatigue life. Using the GMP, designers only consider fatigue cracking of the overlay layer in their analyses.

Overlay design uses the following performance criteria, which are the same as those used for new pavement design:

 Designers evaluate tensile strains occurring under a standard axle load at the base of the proposed asphalt overlay to predict asphalt fatigue.  Designers evaluate vertical compressive strains at the top of a subgrade under a standard axle load to predict permanent deformation.

Overlay design requires knowledge of parameters such as the amount of traffic the pavement was designed to support, past traffic, and design life, as described in Chapter 2, Pavement Design Components. These parameters are similar to those needed for new pavement design. Overlay design also requires the original modulus for the existing pavement materials and subgrade, which designers can back calculate from deflection testing. An overlay shall resist fatigue cracking and reduce permanent deformation in a pavement.

A designer shall divide a stretch of pavement over which overlay will be applied into homogenous sections with relatively uniform deterioration levels and strengths. Designers can use deflection data to identify these sections and to calculate the modulus of existing pavement layers.

Austroads’ GMP requires that designers know the structural composition and conditions of existing pavement, which designers can obtain from construction records and reports or pavement investigation. An existing layer’s design modulus will differ from that of a new asphalt layer, because traffic and environmental effects have caused it to deteriorate. Accordingly, the design

Page 93

05-REHABILITATION DESIGN FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL modulus of an existing asphalt layer shall not exceed 700 MPa, based on the average WMAPT temperature (43.5 °C) for Abu Dhabi Emirates.

After determining all the required parameters, a designer shall use a trial overlay thickness, in accordance with the process explained for flexible pavement in Chapter 4, New Pavement Design, to determine the allowable number of standard axle repetitions for each distress mode. Comparing the allowable axle repetition to the design traffic loading, a designer then decides whether to accept the design or, if the allowable traffic loading exceeds the design, to revise the design with a new overlay thickness. 5.6 Rigid pavement overlays Rigid pavements have a PCC surface on top of a granular layer. Similarly, rigid pavement overlays are overlays that apply PCC as the surface layer on top of an existing pavement. An existing pavement can be either a rigid pavement or a flexible pavement, that is either PCC over PCC or PCC over AC.

In the UAE, rigid pavements have been used mainly for airports, not for highways. Therefore, designers in the UAE do not need a detailed methodology for rigid pavement overlay design. Regardless, this section provides some details on rigid pavement overlays, with references to international manuals.

This section provides details for one empirical method and one M-E design method. 5.6.1 Empirical Design According to AASHTO’s Guide for Design of Pavement Structures (4), pavement rehabilitation requires knowledge of an existing road’s condition and includes the following major steps:

1. Conduct a base data inventory. Collection and collate road inventory data, data on the pavement’s construction, and a maintenance history from secondary sources. 2. Gather the following pavement information:

• Data on surface distresses such as cracks, faults, and blows • Ride quality information, as determined by using a bump integrator or other suitable equipment • Surface and sub-surface drainage characteristics • Pavement deflection, as obtained by FWDs • In-situ modulus of subgrade reaction, CBR, layer thickness, and other parameters • Material characterisations from core and pit tests

3. Perform traffic surveys to obtain classified traffic volume counts, the spectrum of axle loads, roadside development, and growth potentials. 4. Evaluate pavement for the following functional characteristics:

• Homogeneous sections (based on roughness and ride quality) • Homogeneity among sections (based on data analysis) • Damage severity levels • Lane damage factors • Damage types, such as skids

5. Evaluate pavement for the following structural characteristics:

. Pavement deflection (based on analysis of FWD and DCP data) . Homogeneous sections (based on FWD) Page 94

05-REHABILITATION DESIGN FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

. Remaining life . Target design life

6. Design and formulate a strategy, including cost economics, prioritisation, and the following elements:

• A pavement condition table (showing remaining life versus current condition) for homogeneous sections • An alternative rehabilitation programme for each homogeneous section that defines an appropriate approach for each section (whether preventive maintenance, corrective maintenance, repair, or complete reconstruction) • A cost estimate for each programme • A strategy formulation and least cost proposals • Scheduling for alternative strategies • Economic and financial analyses of strategies • A priority strategy for each homogeneous section

7. Implement the rehabilitation and allocate funds, as follows:

a. Allocate budget before rehabilitation. b. Ensure quality control and quality assurance in construction. c. Ascertain the effect of postponing fund allocation. d. Design and formulate strategy, including cost economics and prioritisation.

8. Monitor and evaluate benefits, as follows:

a. After implementing the selected strategy, evaluate pavement for operation in all weather conditions. b. Assess increase in net asset value and reduction in vehicle operation costs. c. Conduct a road user satisfaction survey (feedback) for the quality level of service and increased revenue due to Pavement Management Systems (PMS) implementation. d. Compile data for research and development after the implementation of the strategy. 5.6.1.1 Definition Pavement definitions for rehabilitation projects are the same as those listed in Chapter 4, New Pavement Design, and as referenced in AASHTO’s 1993 Guide for Design of Pavement Structures (4). 5.6.1.2 Design Process This manual focuses on rehabilitation using a bonded or unbounded PCC overlay on an existing PCC slab with the intention of increasing the life of the existing PCC pavements. Based on the condition and remaining life of an existing pavement, a rehabilitation engineer shall decide whether to use a bonded or unbonded overlay.

Each proposed rehabilitation method shall comply with AASHTO’s 1993 Guide for Design of Pavement Structures (4), especially chapter 5, Rehabilitation Methods with Overlays, and the following clauses:

 Clause 5.8: Bonded Concrete Overlays of JPCP, JRCP, and CRCP  Clause 5.9: Unbonded JPCP, JRCP, or CRCP Overlays of JPCP, JRCP, and CRCP

Page 95

05-REHABILITATION DESIGN FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

5.6.1.3 Bonded rehabilitation Generally, bonded overlay thicknesses are lower than unbonded rehabilitation thicknesses.

Designers can use Equation 5-9 to determine the overlay thickness required to increase a pavement’s structural capacity sufficiently to carrying future traffic.

Dol = Df – Deff

Equation 5-9: Thickness to increase structural capacity of overlay

Where:

Dol = Required thickness of bonded PCC, in inches Df = Slab thickness to carry future traffic, in inches Deff = Effective thickness of existing slab, in inches

For a detailed method to determine rehabilitation overlay thicknesses, refer to AASHTO’s 1993 Guide for Design of Pavement Structures (4), especially clause 5.8: Bonded Concrete Overlays of JPCP, JRCP, and CRCP in chapter 5, Rehabilitation Methods with Overlays.

Depending on the condition of a pavement’s existing PCC layer, rehabilitation can combine mechanical and chemical bonding methodologies. Bonded overlays may suffer heavily if adequate pre-overlay repair is not performed to the existing PCC pavement. 5.6.1.4 Unbonded rehabilitation Unbonded rehabilitation, which is easier to construct and generally used when the existing PCC is badly damaged, improves both structural and functional performance.

Designers can use Equation 5-10 to determine the thickness that an overlay requires to increase a pavement’s structural capacity for carrying future traffic.

2 2 Dol = Sqrt (D f – D eff)

Equation 5-10: Required overlay thickness for future traffic

Where:

Dol = Required thickness of bonded PCC, in inches Df = Slab thickness to carry future traffic, in inches Deff = Effective thickness of existing slab, in inches

For a detailed method to determine rehabilitation overlay thicknesses, refer to AASHTO’s 1993 Guide for Design of Pavement Structures (4), especially clause 5.9: Unbonded JPCP, JRCP, or CRCP Overlays of JPCP, JRCP, and CRCP, in chapter 5, Rehabilitation Methods with Overlays.

Unbonded rehabilitation requires a separation layer between the existing and new overlays. Materials in the separation layer should prevent the transfer of reflective cracking from the exiting PCC to the new PCC.

Page 96

05-REHABILITATION DESIGN FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

5.6.2 Mechanistic-Empirical design According to Austroads (6), rigid overlays are either PCC over flexible pavement or PCC over rigid pavement. 5.6.2.1 Rigid overlay over flexible pavements Designing a rigid overlay over a flexible pavement uses the same method designing a new rigid pavement, assuming method in which the existing flexible pavement acts as a subbase. Refer to Chapter 4, New Pavement Design, for details. Designers need to know the condition of an existing pavement to decide which type of concrete overlay to use.

Rigid overlay designs require the following parameters:

 Traffic loads for which the existing pavement was designed, as described in Chapter 3, Pavement Materials, expressed in terms of heavy vehicle axle groups and axle group distribution.  Minimum subbase requirements with an asphalt modulus, per design, of 2,000 MPa at the WMAPT and design speed. If an existing subbase does not meet the minimum requirement, rehabilitation requires the addition of a 50 mm correction layer of dense graded asphalt.  An equivalent CBR, per design, for the subgrade, treating existing pavement layers below the AC layer as part of the subgrade. Designers can use Equation 5-11 to calculate an equivalent CBR for existing layers in any 100 m section of a homogenous pavement.

Equation 5-11: Equivalent subgrade CBR for homogenous 100 m pavement section

Where:

CBRi = CBR value in layer thickness hi ∑hi = taken to a depth of 1.0 meter

Apply the following conditions when using Equation 5-11:

 A rigid overlay must combine any layer with thicknesses less than 200 mm with an adjacent layer, adopting the lower CBR value for the combined layer.  Use materials with higher CBR ratings in the upper layers. Do not apply Equation 5-11 if weaker layers reside in the upper part of a subgrade.  Include filter layers in the calculation.  Equation 5-11 has a maximum CBR of 20%.

Calculating the required thickness of a concrete overlay in accordance with figures given in Chapter 4, New Pavement Design, requires knowing a pavement’s equivalent design subgrade strength and effective CBR. 5.6.2.2 Rigid Overlay over Rigid Pavements Designs for rigid overlays over rigid pavements depend on the condition of the existing rigid pavement. If an existing slab is highly cracked, which can cause reflective cracking, rehabilitation Page 97

05-REHABILITATION DESIGN FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL requires either removing the slab or cracking and seating it. After such rehabilitation, designers shall perform deflection testing to estimate the existing slab’s modulus then follow the design process outlined for a rigid overlay over flexible pavement, as described in section 5.6.2.1.

If the existing pavement is in good condition with few or no cracks, the existing slab can serve as a subbase for the new overlay. Such an overlay design shall follow the same method as new rigid pavement design, as explained in Chapter 4, New Pavement Design.

Page 98

05-REHABILITATION DESIGN FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

6 LOW-VOLUME ROADS 6.1 Introduction A low-volume road (LVR) has relatively low amounts of traffic that travel at low speeds. Most roads in rural areas are LVRs. A LVR in the right location, based on a good plan and design, with effective construction and maintenance is essential for community development, the flow of goods and services between communities, and management of resources. Roads and road construction, however, can create significant soil erosion. Proper planning and design of a road system minimize adverse impacts to water quality. Poorly planned road systems can have high maintenance and repair costs, contribute to excessive erosion, and fail to meet the needs of the communities they support.

This chapter describes types of LVRs and design considerations as applicable to conditions in Abu Dhabi. Other types of LVRs, such as rigid pavement LVRs, are not applicable to Abu Dhabi.

This chapter address LVRs of two major categories:

1. Flexible pavements 2. Aggregate-surfaced roads

Selecting one of these types of roads for a particular project requires assessing several factors, including traffic volume, land use, traffic speeds, and traffic loads.

Designs for LVRs shall be based on standards in the AASHTO Guide for Design of Pavement Structures, 1993 (4), and the specifications in Chapter 4, Pavement rehabilitation. Designers can refer to design charts in Appendix B and alternative design catalogues to simplify the design process. 6.2 Design considerations for LVRs This section describes key factors that designers must consider to select the best type of LVR for client project. 6.2.1 Land use How communities use the lands that surround a project area is a control factor in LVR design. The types of vehicles that are expected to use a road influence the types of surface treatments, the drainage system, and other vital design elements.

In urban areas, local roads in residential communities are considered to be LVRs. Such areas need sections of asphalt concrete pavement or sealed pavement to make driving and riding comfortable. In rural areas, sections of unsealed pavement are sufficient. 6.2.2 Axle loads Many city streets and rural roads, even when classified as LVRs, carry significant levels of heavy vehicle traffic. For many LVRs, heavy traffic is mainly temporary construction traffic that only occurs for a short duration rather than the road’s entire service life. 6.2.3 Traffic volumes Traffic volumes for LVRs should not exceed one million equivalent single axle loads (ESALs). Designs for roads with greater traffic volumes shall follow the design principles outlined in Chapter Page 99

06- LOW VOLUME ROADS FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

5, Rigid Pavement Design. A LVR shall support a minimum ESAL of 10,000. Refer to Chapter 2, Pavement Design Components, for traffic volume estimation details. 6.2.4 Environmental impacts

Roads and streets with low-volume traffic suffer pavement distress more from environmental affects than from traffic loading. Regardless of the sources of distress, however, a pavement’s structure is critical. Even with low traffic volumes, a road with inadequately designed and constructed pavement may suffer premature distress. 6.2.5 Reliability LVR designs shall apply low reliability percentages. Refer to Chapter 4, Pavement Rehabilitation, for reliability specifications for different road categories. Roads with low traffic volumes have a reliability factor of 50%. Designs for roads that require higher reliability should follow the procedures listed in chapter 4 as regular roads. 6.2.6 Drainage systems A road’s location and the drainage of roads, construction areas, and other areas of activity are the most significant factors that can affect water quality, erosion, and road costs. Managing drainage includes controlling surface water and adequately passing water under roads into natural channels. 6.3 Material specifications for pavement structural layers Pavement for a LVR’s structural layer has the same material specifications as regular traffic pavements. Refer to Chapter 3, Pavement Material Characterization, for the appropriate material specifications. 6.3.1 Subgrade evaluation To determine physical and mechanical properties of the existing soil in a project area, a designer shall evaluate the subgrade according to the DMAT Standard Specification Volume 1 for Road Works (1). The subgrade should have a CBR of at least 10%. Soil treatments should be adopted to increase the CBR to 10% according to the specifications. 6.3.2 Unbound granular material A combination of factors directly impacts the quality and strength characteristics that unbound granular materials must have. Unbound granular materials are specifically impacted by the following factors:

 Traffic loading (which encompasses the number of vehicles and types of vehicles in regard to their number of axles and the resulting stress caused by the contact of their tires with pavement)  Climate  Pavement configuration, cross-section, and drainage  Whether the intended use is base or subbase  Strategic importance of the road

For example, marginal or non-standard materials can more successfully be used for LVRs in dry environments than roads with high traffic volumes in wet environments. Pavement designs shall use such materials only after designers have carefully considered the following criteria:

Page 100

06- LOW VOLUME ROADS FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

 Documented performance history of the proposed material  Costs related to standard materials for their entire expected service life  Predicted traffic loading  Climate at the site  Moisture sensitivity of the proposed subgrade  Quality and uniformity of the materials, as verified by laboratory testing  Consequences of poor performance

Designers shall obtain advice from specialists regarding appropriate laboratory characterizations procedures for non-standard materials. Marginal or non-standard materials are generally less stiff (that is, they have lower modulus) and are less durable than standard granular materials. In addition, because the stiffness and strength of a non-standard material are usually more sensitive to moisture content that standard materials, non-standard materials must be thicker than standard materials to provide equivalent subgrade protection. Although both standard and non-standard materials exhibit similar degrees of rutting, the use of the non-standard materials may result in greater rutting of the pavement materials under traffic loading. Therefore, controlling moisture entry into these pavements is a significant design consideration.

The surfaces of pavements with thin bituminous surfacing need higher quality materials. For LVRs base and subbase, the minimum CBR required is 65%. 6.3.3 Asphalt concrete LVRs require asphalt with different properties than asphalt for roads with high traffic volumes. This is especially true for granular pavements with thin asphalt surfacing and for pavements with low traffic loads. Because LVRs are based on performance, mix design and aggregate requirements, they are less restrictive than for roads with high traffic loads.

Asphalts for LVR are generally more flexible and durable and less permeable than those for heavier traffic applications. These properties make such asphalts useful in thinner layers on more resilient pavements and less likely to compact after construction, but make them more susceptible to common distress modes of cracking and ravelling, which are related to the oxidation of the binder rather than vehicle loads.

Asphalt mixes for light traffic applications generally have a lower air void content than asphalts for more heavily trafficked applications. For Abu Dhabi, designers shall follow the general specification for asphalt concrete mixture design with the air voids closer to the lower value of the given range. 6.4 Maintenance strategy for LVRs A local road network, particularly in urban areas, is unlikely to change significantly in alignment or level for many years, remaining aligned and level for perhaps more than 100 years. Given the expected longevity of such roads, designers shall consider a future maintenance and rehabilitation strategy when determining appropriate pavement structures. Such strategies need to reflect both social constraints (such as the impact on local residents in terms of noise and restricted property access) and physical constraints (such as the fixed levels or kerbing) on future work. Pavement levels shall allow for drainage of crossovers and footpath areas. Such constraints may largely determine a practical strategy.

Rural roads require maintenance during active use, after periodic operations have been completed, and after major storm events to ensure that the drainage structures are functioning properly. Heavy rainstorms cause cut slope failures that block ditches, water flow on road surfaces, and erosion to road surfaces and fill slopes. Debris that moves down natural channels during heavy rains can Page 101

06- LOW VOLUME ROADS FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL block drainage structures, causing water to overtop the road and erode the fill. Ruts, washboards, and potholes in the road surface will pond water, weaken the roadway structural section, accelerate surface damage, and make driving difficult. All roads need routine maintenance to remain serviceable with properly working drainage systems. A well-maintained road will reduce road user costs, prevent road damage, and minimize sediment production.

Refer to Chapter 8, Flexible Pavement Maintenance, for maintenance details, including methods to repair damaged asphalt surface roads. Maintenance methods outlined in chapter 8 include patching and surface sealing techniques, such as micro surfacing, fog sealing, and chip sealing.

For a road with an aggregate surface, routine maintenance can involve compacting the surface to regain level surface, patching potholes, and reapplying surface stabilization treatments. 6.5 Sustainability for LVRs LVRs are ideal for sustainable designs and the use of sustainable materials. Although budgets allocated for LVRs are typically not as high as budgets for high-volume roads, LVRs represent a higher percentage of the length of roads within a network.

For many years, gravelling has been the preferred option for surfacing when upgrading from earth roads. Natural gravel materials are usually excavated from borrows pits or quarries and hauled by trucks to be laid on the previously shaped formation or road surface. A gravel road surface can be appropriate and cost effective in many specific circumstances, including the following:

 Sufficient quantities of gravel are available that meets the required surfacing specifications  Haul distances are relatively short  Rainfall is low or moderate  Traffic is relatively low

Even for sections of AC pavement, it is sustainable to use minimum AC pavement section, which is totally controlled by construction factors and is usually used in residential development communities.

Using surface stabilization treatments, such as cement or asphalt, reduces the environmental impact of dust and air pollution. Surface treatments increase the life of a road and reduce the amount of maintenance that is required over its life span.

LVRs can also use sustainable materials such as recycled aggregate material that can be used for base or subbase layers or stabilized aggregate surface layers. 6.6 Pavement design method Anticipated traffic volumes and axle loads govern what pavement structural designs are suitable. Two main types of LVRs are flexible pavements and aggregate pavements. 6.6.1 Flexible pavement Flexible pavements are surfaced with an asphalt concrete layer over granular base and subbase layers. Designing flexible pavement for LVRs is similar to designing pavements to support conventional traffic, except that constraints and factors that govern the design are less restricting.

For flexible LVRs, designers shall use the empirical design method described in AASHTO’s Guide for Design of Pavement Structures, 1993 (4), with the following parameters:

 Anticipated traffic can go up to one million ESALs. Page 102

06- LOW VOLUME ROADS FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

 Traffic speeds associated with LVR can go up to 40 km/hr.  Reliability level for LVRs is 50%.  A LVR has an initial level of service rating of 4.0  A LVR’s minimum terminal serviceability is 2.0.  A LVR’s subgrade has a CBR of 10%.  A LVR has a minimum SN of 2.0.  A LVR has a minimum AC thickness of 60 mm.  Because reliability is 50%, the overall standard deviation will not impact the calculated SN.  A LVR has a granular layer drainage coefficient of 1.0.

Table 6-1 provides layer coefficients for pavement materials.

Table 6-1: Layer coefficients for pavement materials

Pavement Material Coefficient ai Asphalt Concrete 0.44 Aggregate Base 0.14 Soil Subbase 0.11 Treated Base 0.25

To design a flexible LVR, adhere to the following procedure.

1. Calculate the expected traffic volume (ESAL), as described in Chapter 2, Pavement Design Components, for the pavement’s design life. 2. Obtain the CBR for the subgrade as described in Chapter 3, Pavement Material Characterization. LVRs require a minimum CBR of 10%. 3. Use AASHTO’s design chart for flexible pavement design to estimate the required SN. Refer to Appendix B for this chart. 4. If the SN is less than 2, use a value of 2. 5. Obtain the layers thicknesses, applying the SN equation. 6. For proper construction, asphalt layers for LVRs should be at least 60 mm thick.

For the minimum SN of 2, given a minimum asphalt thickness of 60 mm, a LVR’s granular base layer should be at least 200 mm thick. Figure 6-1 shows a cross section diagram of flexible pavement for a LVR.

Asphalt Surface

Aggregate Base

Prepared Subgrade

Figure 6-1: Flexible LVR cross section

Page 103

06- LOW VOLUME ROADS FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

6.6.2 Roads with aggregate surfaces Roads with aggregate granular surfaces are suitable for maximum traffic levels of 100,000 ESAL applications. Maintenance crews can treat aggregate surfaces with cement, lime, or asphalt to reduce environmental effects, increase serviceability life, and reduce road maintenance. The surface stabilization might not add to the structural capacity of the road but will improve functionality and reduce maintenance.

Designs for aggregate surfaced roads comply with the LVR design catalogue in AASHTO’s Guide for Design of Pavement Structures, 1993 (4). Roads with aggregate surfaces require CBRs that are not less than 50% for their aggregate layer.

Three levels of traffic levels (in ESALs), as follows, apply for aggregate surface roads:

 High-level traffic: 60,000 to 100,000 ESALs  Medium-level traffic: 30,000 to 60,000 ESALs  Low-level traffic: 10,000 to 30,000 ESALs

Based on good quality subgrade, with a CBR of 10%, and dry climate such as in Abu Dhabi, aggregate surface layers require the following thicknesses:

 High-level traffic: 250 mm  Medium-level traffic: 200 mm  Low-level traffic: 120 mm

Figure 6-2 shows a typical cross section of an aggregate surface for a LVR.

Aggregate Base

Prepared Subgrade

Figure 6-2: Cross section of an aggregate surface for a LVR

Maintenance crews can stabilize aggregate surface using lime, cement, or asphalt to get the following benefits:

 Control dust emission  Improve quality of rides  Increase pavement life  Reduce required maintenance  Improve poor material to make it suitable as a pavement layer  Waterproof the surface layer

For more details on cement stabilization, refer to Chapter 3, Pavement Material Characterization. A single chip seal or double chip seal application can stabilize asphalt, providing a good surface for a higher ride quality. Refer to Chapter 8, Flexible Pavement Maintenance, for details on chip seal application.

Page 104

06- LOW VOLUME ROADS FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

7 DRAINAGE DESIGN 7.1 General considerations Design engineers provide stormwater management for road projects for the following reasons:

1. Stormwater management for road projects is important from a traffic and public safety standpoint. Removal of stormwater:  From traffic pavement Is imperative for vehicular safety  From pedestrian pavement is important for maintaining public access  Is important to help minimize potential public health and nuisance elements of standing water 2. Road facilities must consider the effects of ground water and provide for the proper collection and removal of it wherever:  Subsurface water levels or flow may cause damage or reduced life to the pavement and the associated structures  High groundwater levels cause detrimental effects upon the adjacent landscaping, an important aspect of the roadway corridor.

The storm water and subsurface drainage designs shall be performed in accordance with the criteria and requirements included in the DMAT Storm Water and Subsurface Drainage Manual (21). 7.2 Drainage design objectives and philosophy Design engineers must incorporate good engineering judgment and keep in mind the legal and ethical obligations of the Owner concerning hydraulic issues.

Drainage facilities must be designed to convey the water across, along or away from the roadway in the most economical, efficient and safest manner without damaging the roadway or adjacent properties. Furthermore, care must be taken to ensure that the roadway construction work do not interfere with or damage any of these facilities.

Design engineers shall also incorporate the Owner’s sustainability goals by protecting and preserving natural resources and other environmental assets, as well as its citizens’ health and safety.

These goals are integrated with other vital interests entrusted to the Owner including the cost- effective delivery and operation of transportation systems and services that meet public needs. 7.2.1 Importance of having good pavement drainage Pavement surface drainage design criteria provides for the removal of surface runoff, which limits ponding and flow depths to levels reasonable for public driving safety and access. At the same time, storm water management facility design will keep flooding or overtopping flows from damaging the roadway fill, pavement, or other structures, while minimising the amount of free water within the pavement structure. Drainage design is concerned with the following primary items:

1. Surface water: Rainfall on the pavement is removed by providing suitable pavement cross and longitudinal slopes, where the pavement runoff is either allowed to sheet flow off of the shoulder (typical for non-kerbed rural roads) or collected by a system of gutters, inlets,

Page 105

07- DRAINAGE DESIGN FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

storm drains and ditches for delivery to an suitable outfall. Hydraulic design of this collection and conveyance system is done in a balanced way such that the overall system provides the necessary capacity for the “design” storm. Design storm is the amount of precipitation that has been determined as a minimum amount that should be removed from the driving lanes for safety of the traffic and is described by its statistical chance of occurring (i.e. 10-yr storm) as predicted from analysis of long term rainfall records.

Surface drainage design is based on the science of hydrology and hydraulics and is usually performed by engineers with speciality experience. Design engineer shall follow the detailed requirements and criteria listed in Chapters 3 and 4 of the DMAT Storm Water and Subsurface Drainage Manual (21).

2. Ground water: Ground water is a particular problem for the pavement design engineer. Saturation of pavement bases and subgrades soften and reduce the strengths of the various pavement structure materials. This and a phenomenon called “hydraulic pumping” will lead to the rapid deterioration of the pavement structure. Hydraulic pumping occurs when wheel loads slightly depress the pavement creating a localised increase in hydraulic pressure in the saturated layers. This causes surges of flow within the pores and voids of the pavement and base courses. This repeated hydraulic pumping moves the material particles, which causes voids and delaminates the various layers. Results of saturated pavement are a shortened pavement life with loss of pavement foundation support and ultimately cracking and potholing of the pavement surface.

Accordingly, the bottom of the pavement aggregate base courses should be located above high water table levels or systems provided to drain the pavement structure. High water levels become a concern where:

 Soil investigations may identify seasonal or permanent high ground water levels. These conditions often occur along the Emirate’s low elevation coastal areas (tidal influence), in sabkha soils and where underlying impermeable soil strata trap the rainfall.

 Existing or project developed landscape irrigation may saturate the soil adjacent to the pavement with excess irrigation, filling the voids of the pavement base layers.

 Project road drainage will collect and convey runoff flows, such as in ditches and culverts, which may cause a water surface that is higher than the pavement layers, thus saturating them.

 Rainfall drains into the underlying pavement layers and if it becomes trapped by the compacted and low-permeable subgrade, it will saturate the material voids in the base and asphalt layers.

Drainage collection and conveyance systems are designed to maintain a maximum safe water surface elevation below the existing or proposed pavement base level by a minimum clearance. This clearance is required to mitigate the effect of soil capillary rise between the free water table surface and the bottom of the pavement structure. This maximum high water level is sometimes called design high water (DHW). 7.2.2 Maintaining the design high water level Maintaining the DHW is achieved by constructing the pavement to appropriate elevations, providing roadside and/or median ditches, or providing subsurface drainage systems per the following summaries: Page 106

07- DRAINAGE DESIGN FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

1. Roadside or median ditch:

In general, roadside or median ditches are relatively shallow trapezoidal channels located along the pavement area to collect runoff from the roadway. They are designed to handle local surface runoff from roadway surfaces and/or to lower water table elevations by intercepting groundwater. Typically, the design of the pavement aggregate base courses will allow groundwater to drain freely to the roadside ditches.

Roadside ditches are sized to maintain the design water surface below the road base course level. The roadside ditch is also designed to operate at stable velocities for the peak design storm flows, discharging to a main channel or storm drain at the outlet.

2. Storm drain system:

Storm drain systems consist of a series of drain pipes connecting various surface inlets, catch basins, and manholes for collecting pavement area runoff and conveying it to a suitable outfall. Most urban area roadways with kerb and gutters will require storm drainage systems, which are also used on embankments, such as approaches to bridges, to protect the side slopes from erosion.

3. Subsurface drains:

The main purpose of subsurface drains is to control water saturation of the pavement base courses, fills behind walls, and reinforced earth fills. Subsurface drains are also used to maintain the groundwater surface at a level that allows for the proper root growing depth of landscape plantings.

Subsurface drains consist of a system of perforated pipes usually buried within a bedding and surround of uniformly graded, free draining aggregate, all wrapped in a geotextile fabric filter material. Subsurface drains will typically outlet to either a roadside ditch or into a storm drain system structure, as appropriate for the situation.

Subsurface discharge depends on the effective hydraulic head and the permeability, depth, slope, thickness, and extent of the soil layers. Solving subsurface drainage problems often calls for specialised knowledge of geology and the application of soil mechanics. The designer should refer to the project geotechnical engineering reports regarding geological and soil parameters.

General requirements for subsurface drainage are discussed in the following subsections. The design engineer shall follow the detailed requirements and criteria listed in Chapter 4 of the DMAT Storm Water and Subsurface Drainage Manual (21). 7.3 Subsurface drainage Subsurface drains shall be used for the following conditions:

1. Subsurface drains for roadways are provided where the pavement aggregate sub-base layers immediately above the subgrade level have no free outlet to the side of the road cross section. This applies to roads built on low permeability soils or with high groundwater tables and is particularly applicable to kerbed roadways in an urban setting.

2. Subsurface drains are placed at locations and depths required to intercept groundwater flowing horizontally into the roadway embankment prism.

Page 107

07- DRAINAGE DESIGN FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

3. Subsurface drains are placed at depths and locations to maintain the free groundwater at a level below the pavement subgrade elevation and/or to provide for landscaping root depth.

4. Subsurface drains are used as hydrostatic pressure relief drains located at the toe of backfill behind retaining walls and face of mechanically stabilised earth fills. Structural designer usually provides the design; however, the roadway or drainage design engineers will need to coordinate the location of the drain outlet for proper discharge. For the design of this type of subsurface drain, refer to DMAT Road Structures Design Manual (10).

Subsurface drains will typically be placed where there are groundwater issues along the following:

 Low sides of pavements  Low sides of the pavement along the inside of a cut roadway section  Low sides of kerbed pavement  Pattern drains under the pavement base courses and in landscaping areas  Along the edge of the pavement where on-site subsurface seepage is evident to intercept the groundwater flow  Along pavement widening where the pavement base course depths are different, creating a water trap in the base courses

Depths of the subsurface drains will be such that the precipitation runoff entering the pavement sub-base layers will rapidly drain out to the low point subgrade level immediately after the storm has ceased. For locations requiring subsurface drainage interception, or areas having a high water table, the subsurface drain level should be such that the free groundwater is maintained below the pavement subgrade level. A minimum clearance depth is also need to minimise saturation due to soil capillary action (fine grain and sabkha soils are more prone to this condition). Ground water and stormwater surface elevations in culverts and roadway side ditches (includes any potential adjacent-to-roadway ponding conditions) shall be no higher than the roadway edge of pavement elevation, minus the pavement layer and aggregate base coarse layer thickness, minus 0.3 metres. All stormwater and ground water drainage facilities shall be design to maintain this minimum clearance below the pavement subgrade level, for roadways in both cut and fill section.

These subsurface drains for groundwater control may also need to address the dual purpose of protecting landscaped areas by placing them to a depth below the required root zone as specified in DMAT Road Landscaping Manual (22).

Subsurface drainage systems can be classified in terms of their location and geometry, typically divided into the following five distinct types:

 Interceptor drains  Longitudinal edge drains  Transverse and horizontal drains  Permeable bases  Deep drains

Each type may be designed to control several sources of moisture and may perform several different functions. In addition, the different types of subsurface drainage systems may be used in combination to address the specific needs of the pavement being designed. The need for, and design data for, placing these subsurface drains shall be addressed as part of the geotechnical investigation of the project corridor. Various types of subsurface drains are described in more detail as follows:

Page 108

07- DRAINAGE DESIGN FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

1. Interceptor drains:

Also known as trench drains, this system primarily intercepts horizontally moving groundwater and is generally used at the following instances:

 The toe of a cut where side slope is stable  The toe of a fill to prevent or limit groundwater inflow into the roadway prism

Depth is such as to intercept the groundwater flow to the bottom of the soil layer that is flowing water, or to the base course clearance level described in Figure 7-1.

2. Edge drains:

Edge drains are provided along the low edge of pavement, just below the subgrade level, to provide an outlet for water in the pavement base courses. A more recent form of the edge drain is the permeable geo-composite edge drain (PGED), also known as fin drains. They consist of a synthetic collector encapsulated within a geo-synthetic filter material, and offer advantages such as economy, narrow trenches, speed, and ease of construction. Several examples of pavement edge drains are shown in Figure 7-2.

Figure 7-1: Typical subsurface drain for draining pavement layers – kerbed road section

Page 109

07- DRAINAGE DESIGN FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

Figure 7-2: Typical examples of pavement edge drains

3. Traverse and longitudinal drains:

Sometimes called herringbone or pattern drain layouts, these pattern systems primarily reduce a high groundwater level to an acceptable level. They are typically used in flat terrain having either a permanent or seasonal high groundwater table and are usually installed below the roadway prism. Placement is to a depth that maintains the free water surface below the base course clearance levels. These may also be used in landscape areas to control high groundwater due to excess precipitation and irrigation with low underlying soil permeability.

Figure 7-3: General view of pattern drainage

Page 110

07- DRAINAGE DESIGN FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

4. Permeable bases or layer drains:

This system is a permeable aggregate course laid over the top of the prepared roadway subgrade. A layer drain acts as a permeable filter and intercepts surface water that seeps through the road surface. Generally, a geo-synthetic filter fabric is placed at the interface between the permeable layer — including sand, gravel, or aggregate — and the subgrade to prevent intermixing of two dissimilar materials. Oftentimes the lower layer of the aggregate base course will act as this layer, providing a flow path for water to outlet to the lower edge of the pavement subgrade.

5. Deep drains or vertical drains:

These types of drains are similar to the trench drain described in Item 1. They are generally located along the low edges of pavement in areas of high water table at a depth to control the free water surface at the required roadway base clearance. They can also be placed along landscape areas in the medians or side of the road to maintain the water table below the plant rooting depth.

Figure 7-4: Typical vertical/trench drains for lowering groundwater

A typical subsurface drainage system consists of perforated pipe, uniformly graded aggregate pipe bedding or surround, and a filter fabric. Pipe materials generally used are high-density polyethylene (HDPE) and PVC. Pipe perforations should be such that the smaller sized particle of the aggregate material should be larger than the largest size openings, slots, or perforations of pipes.

Filter fabric is required in any permanent subsurface drainage system to prevent fine soil particles from washing into the system. The overall installation consists of a uniformly graded gravel bedding and backfill (pipe surround) wrapped fully in a fine grade geo-textile filter fabric. Filter and perforated pipe surround must be more permeable than the surrounding material to convey water from the adjacent soil to the pipe. 7.3.1 Subsurface drainage design for new pavements The following general steps are involved in designing or planning a subsurface drainage system:

1. Review the geotechnical site investigation reports regarding project groundwater issues.

Page 111

07- DRAINAGE DESIGN FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

2. Prepare the surface drainage design as appropriate for the project. Keep in mind where the surface drainage system may have to act as an outlet for any required subsurface drains.

3. Select the subsurface drain type to match the groundwater condition. Generally, there are three basic groundwater conditions:

a. Groundwater with hydraulic gradient less than the slope of the ground: Typical observations are wet patches or visible outflows on the side of the cut. Interception drains are usually required for these situations.

b. Groundwater that is too close to the surface: Generally observed by collapsing wet spots in flat areas or landscape plant loss. The geotechnical report should identify the permanent or seasonal water levels. Layer drainage coupled with deep drains or trench drains along the low-side edges of pavement are usually required for this condition.

c. Water trapped in the pavement aggregate base course: Provide side of road ditches, longitudinal under drains or pavement edge drains along the low-side base course will provide an outlet for trapped water. This condition is typical of urban conditions with kerb and adjacent paved surfaces. It can also occur at widened areas where the pavement structure design is shallower than the original ground surface. Problems also occur where fill has been placed at the edge of the roadway fill embankment such as often done for agricultural planting or for adjacent to roadway developments.

4. Pavement depths must be known for setting subsurface drain levels.

5. Identify cut-fill lines and locate the transverse drains. Select appropriate locations for subsurface drains, including location of outlets. Where the storm drain system structures are used as outlets for the subsurface drains, the design water surface in the storm drains shall be lower than the invert of the subsurface drain pipe so backflow does not occur.

6. Size the subsurface drain lines in accordance with hydraulic principles. Refer to Sections 4.5.3 and 4.5.4 of the DMAT Storm Water and Subsurface Drainage Manual (21) for criteria and requirements of designing subsurface drains. 7.3.1.1 New roads across sabkhas Low-lying coastal areas and arid regions with shallow water tables are general characteristics of the extensive saline flats called sabkhas. Capillary action is the driving factor for upward movement of brine from groundwater. The static water table shall be controlled to an extent that the structural elements of the roads are not affected by either free water or capillary rise. This can be achieved by using trench under drains parallel to the roadway.

If the roadway is over saturated with fine grained embankments, the height of the capillary rise should be calculated to ensure that the excess water does not enter the pavement layers. As can be expected, the finer the soil, the greater the capillary effect and rise. Gravels are so coarse that there will be negligible capillary effects. Clays have the most capillary rise, which can be a few millimetres in sands to several metres in clays.

Design methods and criteria used to control groundwater free water surface are discussed in Sections 4.5.3 and 4.5.4 of the DMAT Storm Water and Subsurface Drainage Manual (21).

Page 112

07- DRAINAGE DESIGN FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

7.3.2 Subsurface drainage design for rehabilitation projects There are a number of typical locations where subsurface drainage should be used for road rehabilitation projects. These are generally described as follows:

1. Widened roadway section:

The pavement is widened and/or shoulders added; however, the design pavement section may not be the same thickness as the original pavement. In the case where the widened pavement section is different than existing, water in the aggregate base course may be trapped depending on the layer thicknesses and the cross slope direction. For this case, a subsurface sub-base drain should be constructed. Refer to Figure 7-5 for a typical example. This condition can occur for both pavements widened to the outside or to the inside depending on the pavement cross slope direction at the widened locations.

Figure 7-5: Typical subsurface drain for sub-base water removal in widened roadway section

2. Providing drainage for rural roadways that have been filled and landscaped:

Many older roadways in the Emirate were constructed as a fill section where the drainage was designed to simply sheet-flow off the shoulder down the fill slope. However, later, many of the sides and medians of these roads were backfilled with sweet sand, planted, and irrigated. This causes the following problems:

 Roadway surface runoff has no place to drain, so it ponds on the road pavement during periods of rain.  Any water in the pavement layers is trapped and cannot drain rapidly.  Excess irrigation and precipitation raises the groundwater in areas of low permeability and/or otherwise high water table to a level where the base course may be saturated.

Page 113

07- DRAINAGE DESIGN FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

Figure 7-6: Typical example of agricultural fill blocking the pavement surface and subbase drainage

During pavement rehabilitation, an alternative solution for providing drainage in these areas is to create a shallow swale at the edge of pavement shoulder. The swale should have a gravel-type surfacing at least 200 mm thick. A trench drain should be constructed under the swale, along the edge of low-side pavement. Combination of the gravel surfacing and uniformly graded aggregate surround around the subsurface drain pipe will allow for the rapid infiltration and removal of the stormwater runoff. Refer to Figure 7-7 for a typical example.

The bottom of the subsurface drain pipe should be placed to a depth that not only assures the pavement base course will rapidly drain, but also that the groundwater surface is maintained below the minimum DHW clearance level, or to a depth required for maintenance of the landscape plant root zones, whichever is lower.

Figure 7-7: Method for providing pavement drainage where edge of rural roadway has been backfilled and landscaped – typical section

Page 114

07- DRAINAGE DESIGN FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

3. Additional subsurface drainage considerations:

Pavement rehabilitation designs should consist of all work necessary to renew the roadway for the desired life span. The design engineer will need to investigate the existing stormwater drainage and groundwater problems and include repair of any deficiencies in the rehabilitation design.

The required remedies for drainage and groundwater issues will depend partly on the type of rehabilitation project, such as widening, simple resurfacing, total reconstruction, changing type from rural to urban with kerbing, etc., and the type of historical drainage or groundwater problems. For example, where widening involves the revision of a roadway from a rural section, such as a shoulder with sheet flow drainage, to a kerb and gutter section, then the provision of new edge drains would be appropriate for rapid drainage of water that may now be trapped in the pavement base courses. This type of sub-base drainage would also need to be supplemented with a new stormwater system, including kerb inlets and storm drain pipes, which also act as the outlet for the subsurface edge drains.

Alternately, where historical flooding or groundwater problems exist, a geotechnical investigation should be executed. The design engineer will then select the appropriate drainage and/or subsurface drain types and facility arrangements as needed. Subsurface drain types should be selected from the main categories listed in section 7.3, which will be designed in accordance with chapter 4 of the DMAT Storm Water and Subsurface Drainage Manual (21).

Page 115

07- DRAINAGE DESIGN FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

8 PAVEMENT MAINTENANCE 8.1 Introduction This chapter provides guidelines for the selection of consistent, cost-effective, and efficient maintenance strategies to ensure uniform, high-quality maintenance practices. Numerous factors such as expected service life, traffic, weather, soil type, availability of equipment and crews, etc., need to be considered in the selection of the right preservation treatment at the right time to the right pavement.

Please refer to Chapter 11 for details on pavement evaluation data collection and analysis that included function and structural condition surveys. This chapter presents an overview of the purpose, concepts, benefits, and optimum timing for pavement preservation and treatments based on the decision matrix. 8.1.1 Why pavement preservation is important Transportation agencies around the world are concluding that it is no longer possible to “build their way out” of ever-increasing needs for transportation facilities. An aging infrastructure of roadway pavements combined with inadequate resources and rapidly growing traffic volumes indicates a demand for different approaches. Agencies have recognised that times have changed and it is no longer about identifying roads in need of rehabilitation, repair, or reconstruction. One of the current challenges is to extend highway investments by addressing pavement rate of deterioration and functional needs in a pro-active manner, so as to obtain the longest service life from their investment. Timely pavement preservation practices can extend the service life of the existing infrastructure and help in providing better, safer, and more reliable service to users at less overall or LCC (FHWA, 2008). 8.1.2 Purpose of pavement preservation In the simplest terms, the purpose of pavement preservation is to keep pavements in good or near new conditions by applying the right maintenance strategies at the right time to extend pavement life and preserve investments. 8.1.3 Definition Pavement preservation is a program that enhances pavement performance by using an integrated, cost-effective set of practices to extend pavement life, improve safety, and meet motorist expectations. A pavement preservation program consists primarily of three components: preventive maintenance, corrective maintenance, and emergency maintenance. A pavement preservation program does not include pavements that require major rehabilitation or reconstruction. 8.1.4 Preventive maintenance Preventive maintenance is a planned strategy of cost-effective treatments to an existing roadway system and its appurtenances that preserves the system, slows down the future rate of deterioration, and maintains or improves the functional condition of the system (without necessarily increasing the structural capacity). Surface treatments that are less than 50 mm thick are not considered as adding structural capacity.

Preventive maintenance is the most cost-effective preservation program that addresses pavements while they are still in good condition and before the onset of damage. By applying a cost-effective treatment at the right time, the pavement can be restored almost to its original condition. Page 116

08- PAVEMMENT MAINTENANCE FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

Postponement or delay of costly rehabilitation and reconstruction is the cumulative effect of systematic, successive preservation treatments. Preventive maintenance restores the function of the existing system and extends its life by reducing aging and restoring its serviceability, while not necessarily increasing its capacity or strength. Performing a series of successive pavement preservation treatments during the life of a pavement is less disruptive to uniform traffic flow than the long closures normally associated with reconstruction projects. Preventive maintenance treatments include fog seal, microsurfacing, and ultra-thin overlay (less than 50 mm) to improve ride quality and protect the pavement surface. 8.1.5 Corrective maintenance Corrective maintenance is performed after a deficiency occurs in the pavement such as isolated moderate to severe rutting, ravelling, or extensive cracking. This may also be referred to as “reactive” maintenance. Differences between preventive and corrective maintenance are the timing and cost of rehabilitation, as shown in Figure 8-1. Corrective maintenance is reactive; it is performed after a road is in need of repair and therefore costs more. Delays in taking corrective maintenance measures result in even larger costs since defects and their severity continue to increase. Corrective maintenance treatments include crack sealing, isolated machine patches, small pothole repairs, repairing the structure of functional overlays (50 mm or greater), milling, and overlay. 8.1.6 Emergency maintenance Emergency maintenance is performed during an emergency situation such as a blowup, a severe pothole that needs repair immediately, or rutting/shoving of greater than 25 mm. Emergency maintenance is often related to safety and time, with cost not being a primary consideration. Materials that may not be acceptable for preventive or corrective maintenance may be the best choice for emergency situations.

Figure 8-1 shows the timing of different maintenance treatments, and Figure 8-2 shows the benefits of maintenance treatments in extending pavement service life. Both figures are excerpts from the Nebraska Department of Roads Pavement Maintenance Manual (23).

Figure 8-1: Categories of pavement maintenance

Page 117

08- PAVEMMENT MAINTENANCE FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

Figure 8-2: Performance of preventive maintenance treatments 8.2 Pavement management system integration A key to successfully initiating and maintaining a strong pavement preservation program is establishing a pavement management system (PMS) that demonstrates the benefits of different preservation treatments, identifies the long-term needs of the system, and plans multi-year preservation activities. On a network level, the PMS data can be used in preparation of the DMAT’s multi-year needs assessment. At the project level, life-cycle cost analysis is recommended to select the optimum type of preservation treatment based on roadway classification, average daily traffic, loading, and highway speed.

DMAT is currently working towards integrating PMS into the pavement preservation program, which will enable the agency to maintain its current infrastructure in a proactive and cost-effective manner. However, this effort requires considerable coordination with the construction industry, consultants, and researchers to address items such as development of performance models for different maintenance treatments, proper design, construction, and materials. Technology transfer is also required to bring new technology into the region. Although this effort may be cumbersome at first, the outcome will result in millions of AED of future savings for the client. Additional benefits of integrating PMS into the pavement preservation program is achieving sustainability goals by minimising the use of natural resources.

Table 8-1 is an example of an agency customized performance model used to measure the benefit/ cost ratio of different treatments and justify the use of these treatments. This figure is from a study in 2000 conducted by Omar Smadi, Zachary Hans, and Aemal Khattak for the State of Iowa Department of Transportation, as cited in Supporting Preventive Maintenance Programs with Pavement Management by Kathryn A. Zimmerman, P.E., and David G. Peshkin, P.E. (24).

Page 118

08- PAVEMMENT MAINTENANCE FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

Table 8-1: Example of State of Iowa customised preservation treatments

Mean Mean Change No. Of Description Observed in PCI After Observation change in PCI Correction Joint and crack filling with emulsion ACC 2- 1.63 6.33 11 Lane Joint and crack sealing ACC 2-lane pvt. 2.14 6.31 21 Joint and crack sealing ACC 2-lane pvt. 0.50 1.66 2 Joint and crack sealing ACC 4-lane pvt. -1.25 1.48 4

Full Depth patching ACC/PCC 1.08 3.50 23 ACC partial depth patching 1.00 5.72 1 Microsurfacing 2-lane 2.10 4.76 10 Pvt. Fog Seal ACC 2-Lane 1.00 6.47 1

Pvt. Seal coat CRS-2P 2-lane 3.33 5.08 3 Intermittent AC resurfacing (Spot levelling) 5.28 8.60 7 ACC resurfacing 2-lnae 2” deep 5.67 11.41 3 ACC resurfacing 2-lnae 3” deep 8.16 11.03 6

8.3 Flexible pavement distress identification To select the right treatment for the right project at a right time, it is essential to first understand the type and potential causes of distress. This section describes the types and possible causes, and suggests repair strategies for major flexible pavement distresses.

Because pavement distress types and causes of distress are universal, the Washington State Department of Transportation (WSDOT) Pavement Evaluation – Flexible Pavement Distress Manual (25) was used to determine flexible pavement distress types, potential causes, and potential remedies. Information from the WSDOT manual was modified to customise the information for Abu Dhabi’s environmental condition. The WSDOT manual not only discusses types of pavement distress, it also provides an explanation of potential causes and recommendations on how to address pavement distresses. Refer to http://training.ce.washington.edu/WSDOT/.

There are other distress identification manuals used by agencies to collect consistent pavement distress data. Most widely used in the United States is the Distress Identification Manual for the Long-term Pavement Performance Program (26) developed for the Federal Highway Administration (FHWA) as part of a strategic highway research program. Below is the link to this manual, which provides types of pavement distress. However, it does not discuss potential causes and corrective measures. http://www.fhwa.dot.gov/publications/research/infrastructure/pavements/ltpp/reports/03031/ 8.3.1 Type of distresses Each distress discussion includes pictures, a description of the distress, why the distress is a problem, and typical causes of the distress. Table 8-2Table 8-2 lists different distresses considered in this chapter for both flexible and rigid pavements.

Page 119

08- PAVEMMENT MAINTENANCE FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

Table 8-2: Index of pavement distresses

Index of Pavement Distresses Fatigue (alligator) cracking Polished aggregate Bleeding Potholes Block cracking Ravelling Corrugation and shoving Rutting Depression Slippage cracking Joint reflection cracking Stripping Longitudinal cracking Transverse (thermal) cracking Patching Water bleeding and pumping Edge Cracking

8.3.2 Fatigue (alligator) cracking

Close-up fatigue cracking High severity fatigue cracking

Description: A series of interconnected cracks caused by fatigue failure of the hot mix asphalt (HMA) surface (or the stabilised base) under repeated traffic loading. In thin pavements, cracking initiates at the bottom of the HMA layer where the tensile stress is the highest, then propagates to the surface in the form of one or more longitudinal cracks. This is commonly referred to as "bottom- up" or "classical" fatigue cracking. In thick pavements, the cracks most likely initiate from the top in areas of high localised tensile stresses resulting from tire-pavement interaction and asphalt binder aging (top-down cracking). After repeated loading, the longitudinal cracks connect forming multi- sided, sharp-angled pieces that develop into a pattern resembling the back of an alligator or crocodile.

Problem: Indicator of structural failure; cracks allow moisture infiltration; roughness; may further deteriorate to potholes.

Possible causes: Inadequate structural support, which can be caused by a myriad of factors. A few of the more common factors are:

 Decrease in pavement load supporting characteristics

• Loss of base, sub-base, or subgrade support (e.g., poor drainage or spring thaw resulting in a less stiff base) • Stripping on the bottom of the HMA layer (the stripped portion contributes little to the pavement strength so the effective HMA thickness decreases)

 Increase in loading (e.g., more or heavier loads than anticipated in design) Page 120

08- PAVEMMENT MAINTENANCE FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

 Inadequate structural design  Poor construction (e.g., inadequate compaction)

Repair: A fatigue-cracked pavement should be investigated to determine the root cause of failure. Any investigation should involve digging a pit or coring the pavement to determine the pavement's structural makeup, as well as determining whether or not subsurface moisture is a contributing factor. Once the characteristic alligator pattern is apparent, repair by crack sealing is usually ineffective. Fatigue crack repair generally falls into one of two categories:

 Small, localised fatigue cracking indicative of a loss of subgrade support. Remove the cracked pavement area then dig out and replace the area of poor subgrade and improve the drainage of that area, if necessary. Patch over the repaired subgrade.  Large fatigue-cracked areas indicative of general structural failure. Either place a structural overlay over the entire pavement surface or reconstruct the pavement. The overlay option must be strong enough structurally to carry the anticipated loading because the underlying fatigue-cracked pavement most likely contributes little or no strength (15). Another strategy that has gained popularity is full depth reclamation of existing pavement. Full depth reclamation is very cost-effective and sustainable since it uses the in-place base and hot mix. Full depth reclamation operation consists of pulverising the existing base and hot mix in-place to a depth of 150 mm to 300 mm, followed by mixing an additive to the pulverised material such as cement, fly ash, or emulsion; compaction of the stabilised material; curing; and finally, placing hot mix over the stabilised base course. 8.3.3 Bleeding

Bleeding in wheel paths

Description: A film of asphalt binder on the pavement surface. It usually creates a shiny, glass-like reflecting surface (as in the second photo) that can become quite sticky.

Problem: Loss of skid resistance when wet.

Possible causes: Bleeding occurs when asphalt binder fills the aggregate voids during hot weather and then expands onto the pavement surface. Since bleeding is not reversible during cold weather, asphalt binder will accumulate on the pavement surface over time. This can be caused by one or a combination of the following factors:

 Excessive asphalt binder in the HMA (either due to mix design or manufacturing)  Excessive application of asphalt binder during preservation treatment such as fog seal or chip seal (as in the photos above)

Page 121

08- PAVEMMENT MAINTENANCE FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

 Low HMA air void content (e.g., not enough void space for the asphalt to expand into during hot weather)

Repair: Although the following repair measures may eliminate or reduce the asphalt binder film on the pavement surface, they may not correct the underlying problem that caused the bleeding:

 Minor bleeding can often be corrected by applying coarse sand to blot up the excess asphalt binder  Major bleeding can be corrected on a low volume road by removing excess asphalt with milling or micro-milling followed by a surface treatment or thin or thick overlay depending on traffic and truck volume  Hot-in-place asphalt recycling (HIPAR) or cold-in-place recycling (CIPR) of roadway where there is more than 7 to 10 km of pavement bleeding 8.3.4 Block cracking

Block cracks

Description: Interconnected cracks that divide the pavement into rectangular pieces. Blocks range in size from approximately 0.1 m2 to 9 m2. Larger blocks are generally classified as longitudinal and transverse cracking. Block cracking normally occurs over a large portion of pavement area, but sometimes occurs only in non-traffic areas.

Problem: Allows moisture infiltration; roughness.

Possible causes: HMA shrinkage and daily temperature cycling. Block cracks are typically caused by an inability of asphalt binder to expand and contract with temperature cycles because of:

 Asphalt binder aging  Wrong type of binder used in the mix design of the given environmental condition  Too much air void that accelerated the aging process  Too stiff of a base such as cement-treated or lean concrete base

Repair: Strategies depend upon the severity and extent of the block cracking:

 Low severity cracks (<13 mm wide). Seal cracks to prevent the entry of moisture into the subgrade through the cracks and further ravelling of the crack edges. HMA can provide years of satisfactory service after developing small cracks if they are kept sealed (15).  High severity cracks (>13 mm wide and cracks with ravelled edges). Remove and replace the cracked pavement layer with an overlay. A stress relief layer, a fine mix with high binder

Page 122

08- PAVEMMENT MAINTENANCE FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

content, or a geotextile fabric is required to retard reflective cracking coming through new HMA overlay.  Another strategy that has gained popularity is in-situ CIPR due to its cost-effectiveness and sustainability. In this process, the existing HMA is recycled to a depth of 50 mm to 100 mm followed by an HMA overlay. 8.3.5 Corrugation and shoving

Corrugation Shoving

Description: A form of plastic movement typified by ripples (corrugation) or an abrupt wave (shoving) across the pavement surface. Distortion is perpendicular to the traffic direction. It usually occurs at points where traffic starts and stops (corrugation) or areas where HMA abuts a rigid object (shoving).

Problem: Severe roughness.

Possible causes: Usually caused by traffic action (starting and stopping) combined with:

 An unstable (i.e., low stiffness) HMA layer caused by mix contamination, poor mix design, poor HMA manufacturing, or lack of aeration of liquid asphalt emulsions  Combination of high pavement temperature, over-loaded trucks with high axle loading at the intersections  Excessive moisture in the subgrade

Repair: A heavily corrugated or shoved pavement should be investigated to determine the root cause of failure. Repair strategies generally fall into one of two categories:

 Small, localised areas of corrugation or shoving. Remove the distorted pavement and patch.  Large corrugated or shoved areas indicative of general HMA failure. Remove the damaged pavement and overlay.

Page 123

08- PAVEMMENT MAINTENANCE FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

8.3.6 Reflection cracking

Reflection cracking

Description: Cracks in a flexible overlay of a rigid pavement or existing oxidized flexible pavement. The cracks occur directly over the underlying rigid or flexible pavement joints.

Problem: Allows moisture infiltration; roughness.

Possible causes: Movement of the pavement beneath the HMA surface because of thermal and moisture changes. Generally not load-initiated; however, loading can hasten deterioration.

Repair: Strategies depend upon the severity and extent of the cracking:

 Low severity cracks (<13 mm wide and infrequent cracks). Seal cracks to prevent entry of moisture into the subgrade through the cracks and further ravelling of the crack edges.  High severity cracks (>13 mm wide and numerous cracks). Mill, place a stress relief layer (fine aggregate graded hot mix with high binder content or geotextile fabric), and place an overlay with hot mix. Another strategy that has gained popularity is in-situ CIPR due to its cost-effectiveness and sustainability. In this process, the existing HMA is recycled to a depth of 50 mm to 100 mm followed by an HMA overlay. 8.3.7 Longitudinal cracking

Longitudinal cracking as the onset of fatigue Longitudinal cracking from poor joint cracking construction

Description: Cracks parallel to the pavement's centreline or lay-down direction. Usually a type of fatigue cracking. Page 124

08- PAVEMMENT MAINTENANCE FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

Problem: Allows moisture infiltration; roughness indicates the possible onset of alligator cracking and structural failure.

Possible causes:

 Poor joint construction or location. Joints are generally the least dense areas of a pavement; therefore, they should be constructed outside the wheel path so that they are only infrequently loaded. Joints in the wheel path, such as those shown in photos three through five (from left to right) above, will general fail prematurely.  A reflective crack from an underlying layer.  HMA fatigue, which indicates the onset of future alligator cracking.  Top-down cracking.

Repair: Strategies depend on the severity and extent of the cracking:

 Low severity cracks (<13 mm wide and infrequent cracks). Seal cracks to prevent entry of moisture into the subgrade through the cracks and further ravelling of the crack edges. HMA can provide years of satisfactory service after developing small cracks if they are kept sealed (26).  High severity cracks (>13 mm wide and numerous cracks). Remove and replace the cracked pavement layer with an overlay. Geotextile fabric may be used directly over the crack to retarded reflective cracking in the overlay. 8.3.8 Patching

Failing patch Patch over localised Utility cut patch distress

Description: An area of pavement that has been replaced with new material to repair the existing pavement. A patch is considered a defect no matter how well it performs.

Problem: Roughness.

Possible causes:

 Previous localised pavement deterioration that has been removed and patched  Utility cuts

Repair: Patches are themselves a repair action. They can only be removed from a pavement surface by an overlay (structural or non-structural).

Page 125

08- PAVEMMENT MAINTENANCE FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

8.3.9 Polished aggregate

Polished Aggregate

Description: Areas of HMA pavement where the portion of aggregate extending above the asphalt binder is either very small or there are no rough or angular aggregate particles at the pavement surface.

Problem: Decreased skid resistance.

Possible causes: Repeated traffic applications. Generally, as pavement ages, the protruding rough, angular particles become polished. This can occur quicker if the aggregate is susceptible to abrasion.

Repair: Apply a skid-resistant treatment such as slurry seal, microsurfacing, or an overlay.

8.3.10 Potholes

Pothole from fatigue cracking Pothole

Description: Small, bowl-shaped depressions in the pavement surface that penetrate through the HMA layer down to the base course. They generally have sharp edges and vertical sides near the top of the hole. Potholes are most likely to occur on roads with thin HMA surfaces (25 to 50 mm) and seldom occur on roads with 100 mm or deeper HMA surfaces (26).

Problem: Roughness (serious vehicular damage can result from driving across potholes at higher speeds); moisture infiltration.

Page 126

08- PAVEMMENT MAINTENANCE FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

Possible causes: Generally, potholes are the end result of alligator cracking. As alligator cracking becomes severe, the interconnected cracks create small chunks of pavement, which can be dislodged as vehicles drive over them. The remaining hole after the pavement chunk is dislodged is called a pothole.

Repair: Remove and reconstruct 3 m on either side of the affected area. 8.3.11 Ravelling

Ravelling due to loss of fine aggregate From segregation

Description: Progressive disintegration of an HMA layer from the surface downward as a result of aggregate particles being dislodged.

Problem: Loose debris on the pavement; roughness; water collecting in the ravelled locations resulting in vehicle hydroplaning; loss of skid resistance.

Possible causes: There are several possible causes:

 Loss of bond between aggregate particles and the asphalt binder as a result of:

• A dust coating on the aggregate particles that prevents the asphalt binder to bond with the aggregate. • Aggregate segregation. If fine particles are missing from the aggregate matrix, then the asphalt binder is only able to bind the remaining coarse particles at their relatively few contact points. • Inadequate compaction during construction. High density is required to develop sufficient cohesion within the HMA.

Repair: A ravelled pavement should be investigated to determine the root cause of failure. Repair strategies generally fall into one of three categories:

 Small, localised areas of ravelling. Remove the ravelled pavement and patch.  Large ravelled areas indicative of general HMA failure. Remove the damaged pavement and overlay.  Low severity. Apply a surface treatment such as fog seal or microsurfacing.

Page 127

08- PAVEMMENT MAINTENANCE FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

8.3.12 Rutting

Rutting from mix instability

Description: Surface depression in the wheel path. Pavement uplift (shearing) may occur along the sides of the rut. Ruts are particularly evident after a rain when they are filled with water. There are two basic types of rutting: mix rutting and subgrade rutting. Mix rutting occurs when the pavement surface exhibits wheel path depressions as a result of compaction/mix design problems. Subgrade rutting occurs when the subgrade exhibits wheel path depressions due to loading. In this case, the pavement settles into the subgrade and ruts causing surface depressions in the wheel path. This is the most predominate type of distress in Abu Dhabi, especially at the intersections.

Problem: Ruts filled with water can cause vehicle hydroplaning, which can be hazardous because ruts tend to pull a vehicle towards the rut path as it is steered across the rut.

Possible causes: Permanent deformation in any of the pavement layers or subgrade usually caused by consolidation or lateral movement of the materials due to traffic loading. Specific causes of rutting can be:

 A combination of high pavement temperature, overloaded trucks, and stop-and-go action at the intersections.  Insufficient compaction of HMA layers during construction. If it is not compacted enough initially, HMA pavement may continue to become more dense under traffic loads.  Subgrade rutting (e.g., as a result of inadequate pavement structure).  Improper mix design or manufacturing (e.g., excessively high asphalt content, excessive mineral filler, and an insufficient amount of angular aggregate particles).

Repair: A heavily rutted pavement should be investigated to determine the root cause of failure (e.g., insufficient compaction, subgrade rutting, poor mix design, or studded tire wear). Slight ruts (<8 mm deep) can generally be left untreated. Pavement with deeper ruts should be levelled and overlaid with a rut-resistance mix.

Page 128

08- PAVEMMENT MAINTENANCE FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

8.3.13 Slippage cracking

Slippage cracking

Description: Crescent or half-moon shaped cracks generally having two ends pointed into the direction of traffic.

Problem: Allows moisture infiltration; roughness.

Possible causes: Braking or turning wheels can cause the pavement surface to slide and deform. The resulting sliding and deformation is caused by a low-strength surface mix or poor bonding between the surface HMA layer and the next underlying layer in the pavement structure.

Repair: Removal and replacement of affected area.

8.3.14 Stripping

Core hole showing stripping at the bottom Fatigue failure from stripping

Description: The loss of bond between aggregates and asphalt binder that typically begins at the bottom of the HMA layer and progresses upward. When stripping begins at the surface and progresses downward, it is usually called ravelling. The photo on the right shows the surface effects of underlying stripping.

Problem: Decreased structural support; rutting; shoving/corrugations; ravelling; or cracking (alligator and longitudinal).

Possible causes: Bottom-up stripping is very difficult to recognise because it manifests itself on the pavement surface as other forms of distress including rutting, shoving/corrugations, ravelling, or cracking. Typically, a core must be taken to positively identify stripping as a pavement distress. Possible causes include: Page 129

08- PAVEMMENT MAINTENANCE FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

 Poor aggregate surface chemistry.  Water in the HMA causing moisture damage.  Overlays over an existing, open-graded surface course. (Past experience has shown that these overlays will tend to strip.)

Repair: A stripped pavement should be investigated to determine the root cause of failure (i.e., determine how the moisture entered the pavement). Generally, the stripped pavement needs to be removed and replaced after correction of any subsurface drainage issues. 8.3.15 Transverse (thermal) cracking

Transverse Crack

Description: Cracks perpendicular to the pavement's centreline or lay-down direction, usually a type of thermal cracking.

Problem: Allows moisture infiltration; roughness.

Possible causes: Several causes are possible:

 Shrinkage of the HMA surface due to low temperatures or hardening of the asphalt binder  Reflective crack caused by cracks beneath the surface HMA layer  Top-down cracking

Repair: Strategies depend on the severity and extent of the cracking:

 Low severity cracks (<13 mm wide and infrequent cracks). Seal cracks to prevent entry of moisture into the subgrade through the cracks and further ravelling of the crack edges. HMA can provide years of satisfactory service after developing small cracks if the cracks are kept sealed (26).  High severity cracks (>13 mm wide and numerous cracks). Remove the cracked pavement layer, place a fine-graded hot mix stress relief or a geotextile fabric over the transverse crack, and place an overlay.

Page 130

08- PAVEMMENT MAINTENANCE FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

8.3.16 Edge cracking

Edge cracking

Description: Longitudinal or crescent shaped cracks usually within 0.6 m of the pavement edge, adjacent to an unpaved shoulder.

Problem: Allows moisture infiltration; roughness; indicates possible onset of alligator cracking and structural failure.

Possible causes: Overloading at the edge of the pavement; shear failure; or erosion of the shoulder.

Repair: Strategies depend on the severity and extent of the cracking:

 Low severity cracks (<13 mm wide and infrequent cracks). Seal cracks to prevent entry of moisture into the subgrade through the cracks and further ravelling of the crack edges.  High severity cracks (>13 mm wide and numerous cracks). Widen the roadway and re- grade drainage ditches to ensure positive drainage exists. 8.4 Pavement preservation treatments

8.4.1 Introduction This section provides a list of potential preservation and rehabilitation treatments that can be used by the client. For various reasons, including the local contractor’s availability and the relatively small size of the road network, some of these treatments are not implemented at this time. However, the intent of this section is to provide a complete list of preservation treatments that can potentially save the client millions of AED in future pavement rehabilitation.

Figure 8-3 shows a pavement performance curve and a list of preservation or rehabilitation tools that can be used to extend pavement life.

Page 131

08- PAVEMMENT MAINTENANCE FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

Figure 8-3: Pavement preservation and rehabilitation tool box 8.4.2 Treatment selection To effectively manage the existing pavement infrastructure, the selection of the right maintenance strategy at the right time is the most important decision that client personnel can make. Appropriate maintenance strategy will be influenced by the type, severity, and extent of the pavement surface distresses, as well as the structural and roughness condition of the pavement. Photos included in section 8.3 described the type of various distresses and potential causes of distress. It should be noted that in addition to the type of pavement distress, choosing the right treatment also depends on the extent or frequency that the distress occurs. Some of the treatments may be most applicable when very little distress is present or distresses are localised, typically less than 10 percent of the surface area. If the extent is described as “Frequent”, “Extensive”, or “Complete”, the distress affects more than 25 percent of the pavement surface and occurs more or less evenly throughout the section. Pavement with more than 10 percent, but less than 25 percent distress may need to be further evaluated to determine the rate of deterioration to ensure the right treatment is applied. Furthermore, the time of surveying the pavement condition distress to the time when the maintenance treatment is applied is extremely important since the pavement may have deteriorated to a point where the specified maintenance treatment may no longer be valid at the time of construction. 8.4.3 Cause of pavement distress It is very important that the cause of pavement distress is identified to ensure the right strategy is applied. Cause of pavement distress can be divided into two categories: load and/or environment. To effectively select the right treatment, it is important to identify the type and cause of distress and whether it is load- or environmental-related. 8.4.3.1 Environmental-related Some of the flexible pavement distresses that are normally environmental-related include transverse cracking, random/block cracking, and ravelling/weathering. Others such as edge cracking, longitudinal cracking, and distortion may be due to either environmental or loading influence.

Page 132

08- PAVEMMENT MAINTENANCE FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

8.4.3.2 Load-related Some of the distresses commonly associated with loading include alligator cracking, longitudinal cracking in wheel paths, and rutting. Preventive maintenance will not correct most load-related distresses. 8.4.4 Flexible pavement maintenance decision matrix Table 8-3 shows a flexible pavement decision matrix that includes a list of potential preservation and rehabilitation strategies recommended for each pavement distress type. This table can be used as a guideline to determine the right preservation/rehabilitation strategy. As mentioned earlier, it is important that the decision on the type of treatment is based on expected future service life, traffic, projected rate of deterioration, and initial and life-cycle cost analysis. When several alternatives are viable, it is important to conduct life-cycle costs to determine the best alternative for the given roadway.

Table 8-4 shows a numbered list of common preservation and rehabilitation alternatives. These numbers correspond with the numbers in the “Low”, “Moderate”, and “High” columns in Table 8-3.

Table 8-5 contains a life-expectancy and cost of each treatment. A unit price for each treatment should be established in the future by the DMAT when these strategies become part of a standard way of doing business.

Table 8-3: Flexible pavement decision matrix

Flexible Low Moderate High Pavement Distresses Occasional Frequent Occasional Frequent Occasional Frequent Alligator 3,1 3,6 6,3,11,4 12 14 or 15+ 13 14 or 15+ 13 cracking Edge 1,2 2,1 2,12 2,12 9+11 9+13 cracking 9+11 or Longitudinal 9+11 or 2,1 2,6,1 2,6 2,6 9+12, 13, 14 cracking 9+13 or 15+13 Random/ block 2,1 2,3 2,6 2,6 9+11 or 9+6 9+7 or 9+11 cracking Ravelling/ 3,1,6 3,6,5 6,4 6,7 6,11,5 6,11 weathering Distortion 1,8,12 12, 1, 8 8,12,2 8,12,6,2 8,11,6,12 8,14,12 Rutting 1 1 8+6 8+6 8+6,10, 11 8,15,11 Excess 1 1,6 1,6,8 6,8 8+6 8+6 or 11 asphalt Transverse 2,1 2 2 2 2,12 2,12 Crack

Page 133

08- PAVEMMENT MAINTENANCE FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

Table 8-4: Pavement treatments

Pavement Treatments 1. Do nothing 2. Crack seal/fill 3. Fog seal 4. Scrub seal (broom seal) 5. Slurry seal 6. Chip seal 7. Microsurfacing 8. Micro-mill 9. CIPR 10. HIPAR 11. Thin hot mix overlay 12. Patching 13. Thick overlay 14. Full-depth reclamation 15. Total reconstruction

8.4.5 Overview of treatment costs The following is an overview of each treatment type and associated cost:

Preventative maintenance treatments – These are low-cost maintenance treatments applied to preserve, retard future deterioration, and maintain or improve the functional condition without significantly increasing structural strength. These treatments could be applied to a pavement over its entire service life. Some of the treatments related to the repair of transverse cracks would be applied later in the life of pavement or as pre-overlay repairs. Preventive maintenance treatments include surface seals applied to address surface deficiencies such as general ravelling, segregation, or fatigue cracking distresses. These treatments could be applied to mid-life pavements to retard future surface or structural deterioration.

Rehabilitation treatments – These are high-cost rehabilitation treatments such as structural overlays or mill and inlay treatments applied to increase structural capacity and restore serviceability and ride. These treatments could be applied to mid-life and late-life pavements. These treatments are selected if they are cost-effective.

Reconstruction treatments – This high-cost treatment (either reconstruction of a portion or of the total base and pavement structure) would be used as a rehabilitation strategy under exceptional circumstances where the existing pavement has completely failed. In this case, the original roadbed may be the cause of reduced serviceability and excessive maintenance cost, and other rehabilitation treatments may provide only very short-term solutions.

Page 134

08- PAVEMMENT MAINTENANCE FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

Table 8-5: Pavement treatment cost and expected life

Treatment *Cost/Square Meter (AED) Expected Life (Years) Crack seal/fill 2.0 3-5 Fog seal 2.0 1-4 Scrub seal 5.5 2-5 Slurry seal 5.5 3-8 Chip seal 4.5 3-6 Microsurfacing 9.0 3-8 Micro-mill (25mm) 2.0 1-4 CIPR 11.0 8-12 HIPAR 18.5 3-6 Thin hot mix overlay(<50 mm) 37 5-8 Patching 92 3-5 Thick overlay (125 mm) 92 8-15 Full depth reclamation and 92 20+ 100 mm overlay Complete reconstruction 185 20+ *Costs are based on reasonable unit prices. Costs of these treatments should be adjusted for the cost in UAE when they are considered for use.

8.5 Preservation treatments This section provides an overview of various flexible pavement preservation treatments. These treatments have been proven by many agencies to be cost-effective and to extend pavement life. Table 8-6 includes a list of common preservation and maintenance treatments.

Table 8-6: Preservation and rehabilitation treatments

Preservation and Rehabilitation Treatments 1. Crack seal/fill 2. Seal Coat: a. Fog Seal b. Scrub seal c. Slurry seal d. Chip seal e. Microsurfacing 3. Profile milling (25mm) 4. Cold in-Place Recycling 5. Hot in-Place Recycling 6. Full Depth Asphalt Repair (Patching)

8.5.1 Crack sealing and filling Crack sealing and filling prevents the intrusion of water and incompressible materials into pavement cracks. Methods vary in the amount of crack preparation required and the types of sealant materials that are used.

Page 135

08- PAVEMMENT MAINTENANCE FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

Crack sealing is the placement of materials into working cracks. Crack sealing requires thorough preparation of the crack and often requires the use of specialised, high-quality materials placed either into or above working cracks to prevent the intrusion of water and incompressible materials. Crack sealing is generally considered to be a longer-term treatment than crack filling.

Due to the moving nature of working cracks, a suitable crack sealant must be capable of:

 Remaining adhered to the walls of the crack  Elongating to the maximum opening of the crack and recovering to the original dimensions without rupture  Expanding and contracting over a range of service temperatures without rupture or delamination from the crack walls  Resisting abrasion and damage caused by traffic

Crack filling is the placement of materials into non-working or low-movement cracks to reduce infiltration of water and incompressible materials into the crack. Filling typically involves less crack preparation than sealing and performance requirements may be lower for the filler materials. According to the Nebraska Department of Roads (23), filling is often considered a short-term treatment to help hold the pavement together between major maintenance operations or until a scheduled rehabilitation activity.

Figure 8-4: Crack sealing operation 8.5.2 Seal coat Asphalt roadway surfaces tend to deteriorate over time as the elements of nature cause the asphalt to become hard and brittle. Deterioration occurs in the form of ravelling or surface cracks. Application of a seal coat can restore the resilient properties of the asphalt surface and prevent further deterioration. Seal coats will not help the load-carrying ability of a roadway. Experience has shown that when proper preparation has been performed in areas scheduled for seal coat-type surface treatments, the life of the surface treatments can be greatly extended and help in reducing life-cycle costs. It is critical that all necessary preparation work, such as crack filling, pothole repair, Page 136

08- PAVEMMENT MAINTENANCE FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL patching, levelling, utility outs, etc., be performed prior to surface treatments being placed. Seal coats commonly used in roadway maintenance are fog seals, scrub seals, slurry seals, and chip seals. Seal coats should not be placed over flexible pavement mixes with a history of moisture sensitivity or stripping problems.

According to the Nebraska Department of Roads (23), a type of seal coat selected should be dictated by the following guidelines and site-specific conditions. 8.5.2.1 Fog seal A fog seal is a light application of a slow-setting asphalt emulsion diluted with water, similar to a tack coat, to an existing surface. It can be diluted in varying proportions up to one part emulsion to five parts water, but in most cases a one-to-one dilution is used. Grades of asphalt emulsion normally used for this purpose are SS-1, SS-1h, CSS-1, or CSS-1h.

A fog seal should be considered for application four years after asphalt overlay. It is important that a fog seal not be applied until sealed cracks have undergone at least two seasons of oxidation. Also, a fog seal should not be applied to any pavement with existing low skid numbers (signed slippery when wet). A fog seal can be a valuable maintenance aid when used for its intended purpose. It is not a substitute for an asphalt surface treatment or other types of seal coats. It is used to renew old asphalt surfaces that have become dry and brittle with age and to seal very small cracks and surface voids. This corrective action will prolong pavement life and may delay the time when major maintenance or reconstruction is needed. Typically, fog seals are used to seal shoulders and dikes, dig outs, and patches. Also, they are used as a flush coat on newly applied chip seals to provide better rock retention, which can assist in preventing broken windshields and other damage to vehicles. Normally, sand is used as a cover material after applying a flush coat. Care should be taken to keep traffic off of the newly sealed surface until the emulsion has broken. According to the Nebraska Department of Roads (23), even though the application is light, special care must be used when going around curves to keep traffic away from the oil, which has a tendency to flow because of the super elevation.

This operation proceeds rapidly, and daily productivity is approximately 5 to 7 lane km per day. 8.5.2.2 Scrub seal (broom seal) Scrub seal is normally an application of polymer modified asphalt that is broomed into the pavement surface followed by a cover of fine aggregate (sand) and a second brooming, which should be rolled with a pneumatic roller. These seals may be used to improve skid resistance, prevent oxidation, and seal hairline cracks against water infiltration. According to the Nebraska Department of Roads (23), a scrub seal may be used effectively to fill cracks in cases of low to moderate non-working cracks, as long as the roadway profile is good.

Page 137

08- PAVEMMENT MAINTENANCE FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

Figure 8-5: Scrub seal application 8.5.2.3 Slurry seal A slurry seal is a mixture of slow-setting emulsified asphalt, well-graded fine aggregate, mineral filler, and water. It will fill fine cracks in the pavement surface, fill in slight imperfections, and provide a uniform colour and texture. It slows down the rate of surface oxidation, but most importantly, it seals the highway, thus preventing the infiltration of water, which is the most frequent cause of pavement failure. Generally, this strategy performs best when 10 percent or less alligator cracking is present. This product may be used as a substitute for traditional “chip seal” and “hot mix” paving methods. Unlike “chip seal,” there are no loose stones or dust to manage.

Normally, slurry seals are not placed if the wheel paths on the surface to be treated have depressions greater than 15 mm, or if the treatment must be placed at night. According to the Nebraska Department of Roads (23), if these two conditions exist, the use of a slurry seal should be evaluated on a case-by-case basis.

Page 138

08- PAVEMMENT MAINTENANCE FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

Figure 8-6: Slurry seal surface 8.5.2.4 Chip seal Chip seal should be used in cases where light to moderate “ravelling” or light to moderate polishing or flushing is occurring.

Chip seals provide skid resistance and seal the roadway. They generally consist of applying asphaltic emulsions or liquid paving grade asphalts (with additives), and then covering them with aggregate and rolling. Chip seals are a very good surface treatment if they are placed correctly. Consideration should be given to placement at non-sensitive areas (e.g., high average daily traffic due to special events) and places with a high percentage of truck traffic. All cracks should be sealed prior to chip sealing, as chip sealing is not a substitute for crack sealing. Also, centerline tabs must be placed before chip sealing.

According to the Nebraska Department of Roads (23), sand/gravel aggregate should be crushed to provide the gradation shown in Table 8-7.

It is important that clean and crushed aggregate with only a small percent passing No. 200 sieve is used for chip seal.

Table 8-7: Chip seal aggregate gradation limits

Sieve Size Percent Passing Target Tolerance 6 mm 100% No. 4 70% +/- 10% No. 10 30% +/- 5% No. 50 5% +/- 5% No. 200 2% +/- 2%

Page 139

08- PAVEMMENT MAINTENANCE FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

Figure 8-7: Chip seal application 8.5.2.5 Microsurfacing

Microsurfacing refers to a mixture of polymer modified asphalt emulsion, mineral aggregate, mineral filler, water, and other additives properly proportioned, mixed, and spread on a paved surface. Microsurfacing differs from slurry seal in that it can be used on high volume roads to correct minor wheel path rutting (<12 mm) and provide a skid-resistant pavement surface.

In quick-traffic applications as thin as 10 mm, microsurfacing can increase skid resistance, provide colour contrast, restore pavement surface, and extend pavement life. Microsurfacing projects are often re-opened to traffic within an hour.

This treatment requires use of modern, continuous-load pavers capable of laying 5 lane km per day for surfacing applications, with minimum traffic delays. As a thin, surface treatment on heavy traffic intersections, microsurfacing does not alter drainage and there is no loss of curb reveal. According to the Nebraska Department of Roads (23), because microsurfacing can be effectively applied to most surfaces at 10 mm or less, more area per ton of mix is covered, resulting in cost- effective surfacing.

Page 140

08- PAVEMMENT MAINTENANCE FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

Figure 8-8: Microsurfacing placement 8.5.2.6 Profile milling Profile milling may be considered as a possible treatment to restore roadway cross sections when wheel rutting is greater than 15 mm. This may be followed up with either a thin surface treatment such as slurry, chip seal, or a thin overlay. Milling may also be used to treat roads with excess asphalt or extreme cases of ravelling.

If rutting is caused by poor materials or a weak base, milling should be considered as a “temporary fix”, since the ruts will likely reappear in one to three years. Also, caution must be used if the surface thickness is marginal for the traffic loading. Determining whether milling is the proper treatment is often a judgment call, considering the severity of the ruts, the cause of the ruts, and the overall condition of the road. According to the Nebraska Department of Roads (23), when wheel rutting is greater than 12.5 mm deep and the asphalt pavement has sufficient thickness, profile milling may be performed to restore roadways with average daily traffic of less than 20,000 and very low percent truck traffic. 8.5.2.7 Cold-in-place recycling CIPR is an eco-friendly pavement rehabilitation process performed without the use of heat to a depth of 50 to 100 mm. This process creates very little pollution because it is a cold process. There is no heat applied to the asphalt, which reduces the noxious fumes that many other processes produce. It is safer for the environment and the workers.

The typical CIPR process involves the following seven steps:

1. Milling. A milling machine pulverises a thin surface layer of pavement, usually from 50 to 100 mm deep. 2. Gradation control. This pulverised material is further crushed and graded to produce the desired gradation and maximum particle size. On some jobs, this step is omitted; however, on other jobs a trailer-mounted screening and crushing plant is used to further crush and Page 141

08- PAVEMMENT MAINTENANCE FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

grade the pulverised pavement. If needed, virgin aggregate can be added to the recycled material. 3. Additive incorporation. Then the graded, pulverised material is mixed with a binding additive (usually emulsified asphalt, lime, Portland cement, or fly ash). On some jobs, this is performed by the milling machine; however, on other jobs, a trailer-mounted pug mill mixer is used. 4. Mixture placement. This pulverised, graded pavement and additive combination is placed back over the previously milled pavement and graded to the final elevation. Mixture placement is most often performed with a traditional asphalt paver (either through windrow pickup or by depositing the mixture directly into the paver hopper). 5. Compaction. This placed mixture is compacted to the desired density. Typical compaction efforts involve a large pneumatic and a large vibratory steel wheel roller. If an emulsion additive is used, rolling is typically delayed until the emulsion begins to break. If a Portland cement or fly ash additive is used, rolling should begin immediately after placement. 6. Fog seal. A fog seal is necessary over CIPR using a Portland cement or fly ash additive not only to delay surface ravelling, but also to provide a curing membrane for the additive to properly set. 7. Surface course construction. The cold recycled mix should be covered with either a thin surface treatment such as chip seal or HMA overlay. The type and thickness of the overlay should be based on future projected traffic.

CIR Train

EMULSION MILLING PUG MILL TANK MACHINE CRUSHER

Use the paver to place the millings

Figure 8-9: CIPR train on a southern California project 8.5.2.8 Hot-in-place asphalt recycling HIPAR is defined as a process of correcting asphalt pavement surface distress by softening the existing surface with heat, mechanically removing the pavement surface, mixing with a recycling agent, possibly adding virgin asphalt and/or aggregate, and replacing it on the pavement without removing the recycled material from the original pavement site.

HIPAR has been used in Canada and Europe. It is now starting to be implemented in the United States. Recycling of existing asphalt returns the pavement to a near-new condition, giving many

Page 142

08- PAVEMMENT MAINTENANCE FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL more years of life at a reduced cost over normal reconstruction processes. Recycling of granular pavements using specialised equipment has led to much better surface finishes and consistently good performance in recent years. The additives used in the process are lime, cement, slag, fly ash, and various blends of these materials.

The pavement surface is heated by infrared radiation and milled in two steps to a desired depth of 20 to 65 mm. The mix of the old asphalt layer can be changed directly by adding virgin asphalt and a new type of asphalt binder or rejuvenator. The two-stage recycling means the sequential heating and removing of two separate layers of asphalt in one continuous operation. Alternatively, working widths are 3.5 m and 4.2 m.

HIPAR technology offers tremendous benefits in terms of cost savings in material and labour, as well as a reduction in duration of the repair activities. Another benefit from HIPAR is that it can turn a traditionally environmentally damaging process into a process having only minimal environmental effects. Materials savings are realised from the reduction in new asphalt and aggregate. Energy savings result primarily from reduced aggregate haul and drying, and asphalt transportation. Cost savings are greatly influenced by length of aggregate haul and distance from the plant to the job site.

Figure 8-10: HIPAR process 8.5.2.9 Full-depth asphalt repair (patching) Full-depth asphalt repair should be considered anytime there is rutting greater than 20 mm, corrugations and shoving, surface depressions, or a series of potholes.

First step of full depth patching is to cut an area 0.5 to 1.0 m larger than the distressed area needing repair by using a wheel cutter or pavement saw. Equipment such as a backhoe, milling machine, or front-end loader is required to remove as much of the pavement as needed. If the subgrade is unstable, re-stabilise it and compact the subgrade to a proper depth using a plate packer. Tack coat should be applied to all the vertical edges and to the base. HMA should be placed directly into the excavated area and a proper roller should be used to adequately compact

Page 143

08- PAVEMMENT MAINTENANCE FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL the HMA. Edges should be compacted first, followed by compaction of the low to the high side of the mat, overlapping approximately 15 to 25 cm with each pass. All compacted patch should match the existing adjacent surface. 8.6 Rigid pavement maintenance Although pavements in Abu Dhabi are mainly HMA, rigid pavement should be considered as a viable alternative for future projects when conducting a LCC. Concrete pavement is used primarily on high-volume roads with a high percent of truck traffic, and in areas where there is a large volume of stop-and-go traffic occurring, such as at intersections. Concrete properties do not change with the rate of loading or ambient temperature as asphalt does; therefore, concrete pavement does not rut under this type of condition. This is extremely important in Abu Dhabi, especially where there is a high volume of truck traffic with many intersections.

This section describes the methods and techniques used to prolong the life of concrete pavement by slowing its deterioration rate. Performance of concrete pavement similar to hot mix asphalt is directly tied to the timing, type, and quality of the maintenance it receives. However, rigid pavements perform and crack differently from flexible pavements. For details on rigid pavement types, refer to Chapter 5, Rigid Pavement Design. For different rigid pavement distresses, refer to the FHWA’s Distress Identification Manual for the Long-term Pavement Performance Program (26).

(http://www.fhwa.dot.gov/publications/research/infrastructure/pavements/ltpp/reports/03031/) 8.6.1 Joint and crack sealing Sealant products are used to fill joints (Figure 8-11) and cracks in order to prevent entry of water or other non-compressible substances. Although most rigid pavement joints are sealed at the time of new construction, the useful sealant life is limited to three to five years for hot pour sealant and eight to 10 years for silicone sealant as stated by the American Concrete Paving Association (www.pavement.com).

Materials used for creak sealing are hot-pour seals, compression seals, and silicone seals. Sealant performance is dependent upon proper joint design and cleanliness.

Crack sealant is typically used on early stage, isolated panel cracks. Extensive or advanced panel cracking is a symptom of a larger problem (e.g., lack of panel support, inadequate structural design, or poor construction) that cannot be addressed by simple crack sealing.

Figure 8-11: Joint sealing

Page 144

08- PAVEMMENT MAINTENANCE FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

8.6.2 Slab stabilisation Slab stabilisation seeks to fill voids beneath the slab caused by pumping, consolidation, or other means. If left untreated, these voids, which are often quite small (on the order of 3 mm deep), may cause other problems such as faulting and corner breaks or cracking, according to the American Concrete Pavement Association (ACPA) Construction of Portland Cement Concrete Pavements, 1995 (27). Voids are typically filled by pumping grout through holes drilled through the slab. 8.6.3 Diamond grinding Diamond grinding (Figure 8-12) is a corrective maintenance process where gang-mounted diamond saw blades are used to shave off a thin, 1.5 to 19 mm top layer of an existing PCC surface in order to restore smoothness and friction characteristics. It is most often used to restore roadway friction or remove roughness caused by faulting, slab warping, and curling. Diamond grinding can reduce pavement roughness (international roughness index) of an older pavement to 1.0 to 2.0 m/km.

Grinding heads are cooled with water creating a slurry composed of ground PCC particles and water. Most of this slurry is picked up by vacuums within the grinding machine and either deposited along the shoulder of the highway or collected in trucks for off-site disposal.

Diamond grinding addresses serviceability problems, but not their root cause, (i.e., it will reduce the roughness on a faulted pavement, but will not address the cause of the faulting).

Figure 8-12: Diamond grinding machine 8.6.4 Patches Rigid pavement patches are used to treat localised slab problems such as spalling, scaling (e.g., reactive aggregate distress, over-finishing the surface), joint deterioration, corner breaks, or punch outs. If the problem is limited in depth, then a partial depth patch may be appropriate, otherwise a full depth patch is recommended. A high-quality patch can be considered a permanent repair, although all patches are treated as a form of pavement distress. Sometimes HMA is used for emergency patches, but PCC should be used for permanent patches. Fast-setting PCC can minimise setting time. 8.6.4.1 Partial depth patch Partial depth patch is used to restore localised areas of slab damage that are confined to the upper one-third of slab depth. Generally, this includes light to moderate spalling and localised areas of Page 145

08- PAVEMMENT MAINTENANCE FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL severe scaling. Partial depth patches are usually small, often only 50 to 75 mm deep and covering an area less than 1 m2.

Partial depth patching process consists of:

 Locating the area to be patched (the patch should be extended beyond the damaged area by 75 to 100 mm)

 Removing the damaged material by sawing and chipping deep enough to remove all of the damaged material

 Cleaning the area to be patched by sand or water blasting to remove loose particles and create a rough texture to which the bonding agent can adhere

 Applying a bonding agent such as a cementitious grout that helps the patch material bond to the original slab

 Place, finish, and cure the new PCC

New PCC should be placed so that the patch elevation is the same as the surrounding slab and finished by working from the centre to the edges in order to push the new material firmly against the existing slab, creating a higher potential for a high-strength bond. 8.6.4.2 Full depth patch Full-depth patches (Figure 8-13) are used to restore localised areas of slab damage that extend beyond the upper one-third of the slab depth or originate from the slab bottom. This includes spalling, punch outs, corner breaks, moderate to severe slab cracking, and localised areas of severe scaling. Corner breaks and punch outs should always be patched to full depth. When deciding between a partial and a full-depth patch for spalling and slab cracking, recognise that joint spalls extending more than approximately 75 to 150 mm from the joint are indicative of possible slab bottom spalling and corner breaks, and slab cracking is indicative of structural inadequacies that cannot be addressed with partial depth patching. These problems should be addressed using a full-depth patch.

Figure 8-13: Full-depth patch preparation

Full-depth patching process consists of:

Page 146

08- PAVEMMENT MAINTENANCE FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

 Locating the area to be patched (if located too close to an existing joint or crack, it should be extended to an existing transverse joint; if it falls on an existing crack, but away from the joint, then it should be extended beyond by 0.15 m)

 Removing the damaged material by isolating the repair area using full depth saw cuts, then lifting out the isolated section

 Preparing the patch area by compacting and drying the subgrade and base material and inserting dowel bars into the holes drilled into the adjacent slab transverse sections to provide load transfer across the patch boundary (replacements longer than 4.5 m require longitudinal tie bars as well)

 Applying a bonding agent such as a cementitious grout that helps the patch material bond to the original slab unless the edge of the patch material is located at the working joint (in this case, the joint should be sawed to re-establish the working crack)

 Place, finish, and cure the new PCC.

New PCC should be placed so that the patch elevation is the same as the surrounding slab. Vibratory screeds are often used to strike off and finish full-depth patches. Any edge of patching material located at the concrete joint should be sawed to re-establish the working crack at the joint.

Page 147

08- PAVEMMENT MAINTENANCE FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

9 LIFE-CYCLE COST ANALYSIS

9.1 Introduction This chapter describes the procedures used to conduct a Life-Cycle Cost Analysis (LCC) for the selection of the preferred pavement alternative for new construction, rehabilitation, or preservation projects.

LCC is an engineering analysis tool that uses economic principles to evaluate long-term investment options. LCC is an integral part of the decision-making process for selecting the preferred pavement types, rehabilitation strategies, and the optimum pavement design life. When feasible, LCC should include both agency and user costs over the service life of the infrastructure. The LCC process helps decision-makers select the preferred alternative based on the lowest cost over the analysis period, while meeting project objectives. Taking into consideration available budget, constructability and maintenance issues, and environmental concerns, the lowest LCC may not ultimately be selected, in some cases.

There are two different approaches to LCC — deterministic and probabilistic. The deterministic approach is the traditional methodology in which the user assigns each LCC input variable a fixed value usually based on historical data and user judgment. The probabilistic approach is a relatively new methodology and accounts for the uncertainty and variation associated with input values. The probabilistic approach allows for simultaneous computation of differing assumptions for many variables by defining uncertain input variables with probability distributions of possible values. The following link to the Federal Highway Administration (FHWA) LCC assessment Web site (28) can be used to obtain the latest advancements in LCC. RealCost software, developed by FHWA, can be used to conduct either deterministic or probabilistic LCC.

http://www.fhwa.dot.gov/infrastructure/asstmgmt/lcca.cfm

Because there is no historical probability distribution of individual LCC input variables at this time, the deterministic LCC approach is used by DMAT. 9.2 LCC process LCC should be conducted as early in the project development cycle as possible. The level of detail in the analysis should be consistent with the level of investment. Generally, the process involves the following steps:

1. Establish alternatives 2. Determine an analysis period 3. Determine a discount rate 4. Determine maintenance and rehabilitation frequencies 5. Estimate costs 6. Calculate LCCs 7. Analyze LCC results 9.3 Establishing alternatives LCC begins with the development of alternative pavement designs that will accomplish the structural and performance objectives of a project. For example, comparisons can be made between flexible versus rigid pavement; hot mix asphalt (HMA) mill-and-overlay versus HMA

Page 148

09- LIFE-CYCLE COST ANALYSIS FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL overlay; and 10-year versus 20-year design life rehabilitation. Each competing alternative must be properly designed to meet the project goals and requirements.

Table 9-1 provides examples of some possible alternatives to consider for new construction, widening, rehabilitation, and pavement preservation projects. This table may be expanded in the future as more rehabilitation tools become available in Abu Dhabi.

Table 9-1: Potential design alternatives for LCC

Pavement Alternative I Alternative II Alternative III Project Type 40-year flexible 20-year flexible New 40-year rigid pavement pavement pavement Remaining service 40-year flexible Widening life of existing 20-year flexible pavement pavement pavement  Cold or hot-in-place recycling and overlay or Rehabilitation Mill and overlay Overlay  Geotextile fabric and overlay Crack sealing and/or Preservation Do nothing Scrub seal and microsurfacing microsurfacing

9.3.1 Determine an analysis period The analysis period is the period of time during which the initial and any future costs for the project alternatives will be evaluated.

The LCC analysis period should be sufficiently long to reflect long-term cost differences associated with the reasonable design strategies. The analysis period should be longer than the pavement design period, as shown in Figure 9-1. As a general rule, the analysis period should be long enough to incorporate at least one rehabilitation activity. Figure 9-1 shows a typical analysis period for a pavement design alternative. Regardless of alternatives, the analysis period used should be the same for all alternatives.

Figure 9-1: LCC analysis period

Table 9-2 provides recommended analysis periods to be used when comparing two alternatives designed with the same or different design lives. For example, a minimum analysis period of 35 Page 149

09- LIFE-CYCLE COST ANALYSIS FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL years should be considered if 10-year and 20-year pavement design life alternatives are compared, or if two different pavement design alternatives with the same 20-year design life are compared. The reason for the 35-year analysis period is to allow for at least one rehabilitation to be performed for each alternative over the analysis period.

Table 9-2: LCC analysis period

Alternative 5-Year 10-Year 20-Year 40-Year Design Life 5-year 20 years 20 years N/A N/A 10-year 20 years 20 years 35 years 55 years 20-year N/A 35 years 35 years 55 years 40-year N/A 55 years 55 years 55 years

The LCC assumes that the pavement will be properly maintained and rehabilitated to carry the projected traffic over the specified analysis period. As the pavement ages, its condition will gradually deteriorate to a point where some type of maintenance or rehabilitation treatment is warranted. Thus, after the initial construction, reasonable maintenance and rehabilitation strategies must be established for the analysis period. 9.3.2 Determine a discount rate A discount rate is the interest rate by which future costs (in constant dollars) will be converted to present value. It is commonly known as a “real discount rate” as it reflects only the opportunity value of time, without including the general rate of inflation. Real discount rates typically range from three to five percent, representing the prevailing interest rate on borrowed funds, less inflation. The most common discount rate used by agencies around the world is four percent. Therefore, a four percent discount rate is used to conduct LCC on client projects. 9.3.3 Determine maintenance and rehabilitation frequencies After the viable project alternatives are selected, the type and timing of future rehabilitation must be determined over the analysis period. This information can be obtained from past project history or based on local experience. A pavement management system is also a good source for determining past pavement performance and frequency of rehabilitation.

Table 9-3 provides suggested values for different rehabilitation and preservation treatments. However, when conducting LCC, expected service life for these treatments should be adjusted based on local experience, existing pavement conditions, future average daily traffic (ADT) and truck traffic, and project information and goals.

Table 9-3: Pavement treatments expected life

Treatment Expected Life (Years) 1) 50 mm overlay 7-10 2) 50 mm mill and overlay 10-15 3) Scrub seal 2-5 4) Slurry seal 3-8 5) Chip seal 3-6 6) Microsurfacing 3-8 7) Micro mill (25mm) 1-4 8) Cold-in-place recycling and overlay 10-15

Page 150

09- LIFE-CYCLE COST ANALYSIS FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

10) Hot-in-place recycling 5-7 11) Thin hot mix overlay (<50mm) 5-8 12) Patching 3-5 13) Thick overlay (125mm) 8-15 14) Full depth reclamation and 100 mm overlay 20+ 15) Complete reconstruction 20+

9.3.4 Estimating costs LCCs include agency costs and user costs. Agency costs include initial costs, annual maintenance costs, and rehabilitation costs. When user costs are calculated for LCC, they should include travel time costs and vehicle operating costs (excluding routine maintenance) incurred by the traveling public.

Figure 9-2 illustrates different costs that should be considered when conducting LCC such as the initial, rehabilitation, and maintenance costs, as well as the remaining service life. It is very important that agency and user costs are not combined and are reported separately. 9.3.4.1 Initial costs Initial costs include estimated construction costs and project support costs (for design, environment, construction administration and inspection, project management, etc.) to be borne by an agency for implementing a project alternative. The DMAT’s Bill of Quantities Manual for Road Projects (3) and Project Cost Estimating Manual (2) should be used when estimating project costs. Initial costs should be calculated using the DMAT’s procedures. 9.3.4.2 Construction costs For each alternative, construction costs should be determined from the engineer’s estimate. Costs for mainline and shoulder pavement, base and subbase, drainage, earthwork, traffic control, time- related overhead, mobilization, supplemental work, and contingencies should be included. Construction costs common to both alternatives, such as bridges, traffic signage, and striping may be excluded if those costs can be separated from the rest of the estimate. If not, then it will be easier to include them. 9.3.4.3 Maintenance costs Maintenance costs include costs for routine, preventive, and corrective maintenance, such as chip seal, fog seal, patching, and thin HMA overlay, whose purpose is to preserve or extend the service life of a pavement over the analysis period.

Page 151

09- LIFE-CYCLE COST ANALYSIS FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

Figure 9-2: Costs to be considered when conducting LCC 9.3.4.4 Rehabilitation costs Rehabilitation costs refer to costs for future rehabilitation or reconstruction activities scheduled to be performed after implementing a project alternative. Rehabilitation costs for a particular activity should include costs for all the necessary appurtenant work for drainage, safety, and other features. 9.3.4.5 User costs Best-practice LCC calls for consideration of not only agency costs, but also costs to facility users. User costs include travel time costs and vehicle operating costs (excluding routine maintenance) incurred by the traveling public. Such user costs typically arise when work zones are imposed for fieldwork, which restricts the normal capacity of the facility and reduces traffic flow. Additional user costs resulting from work zones can become a significant factor when a large queue occurs in one alternative but not in the other. An example difference in user costs between two alternatives is roadway re-paving of high volume road during the daytime versus the nighttime, or using flexible versus rigid pavement for pavement rehabilitation. shows an example of LCC with both agency and user costs. As can be seen from this figure, the user costs are several times higher than the agency costs because of very high ADT and long construction duration. It is important to note that in this example, the rigid pavement alternative has the highest user costs because of longer construction duration and curing time required for concrete pavement.

Page 152

09- LIFE-CYCLE COST ANALYSIS FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

Table 9-4: LCC summary with agency and user costs

Rehabilitation Cost LCC Initial Present Uniform Users Pavement cost Pavement Worth Annual Costs Thickness Million Yr. 10 Yr.20 Yr.30 Strategy Million Cost Billion (AED) (AED) (AED) (AED)

280 mm Complete JPCP over Reconst. 1.84 42,545 72,960 119,012 2.07 104,570 10 100 mm With JPCP GBC 40 mm Complete SMA, 220 Reconst. mm HMA, 1.30 203,169 246,038 92,724 1.85 93,088 6 With HMA 100 mm GBC 40 mm SMA, 130 mm HMA, Mill & Fill 0.83 203,169 246,038 92,724 1.37 69,204 3 25-150 mm profile milling

Of all of the user cost rates, the cost rate assigned to user delay (i.e., the value of time) is by far the most controversial. Table 9-5 shows user costs value based on the research conducted by the National Cooperative Highway Research Program (NCHRP-133) and guidance provided by the Office of the Secretary of Transportation, as well as updated values used by FHWA in its Highway Economic Requirements System Model. The values in this figure were last updated in 1996.

Table 9-5: User cost ($/Vehicle-Hr) based on NCHRP-133 study

Trucks Value of Time Pass Cars Single Unit Combination Value 1970 $3.00 $5.00 $5.00 Factor 8/96 3.928 3.928 3.928 Value 8/96 11.78 19.64 19.64

Table 9-6 shows the suggested values when calculating user costs in the Emirate until local user costs values can be developed. These values were converted from U.S. dollars to UAE AED and are based on the recommendations from FHWA.

Table 9-6: Recommended values of time and value

Vehicle Class Value per Vehicle Hour Passenger Vehicles 48 AED Single-Unit Trucks 73 AED Combination Trucks 88 AED

Page 153

09- LIFE-CYCLE COST ANALYSIS FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

The following equation may be used to determine user costs for different alternatives.

UC= (AVT)[(L/RS) – (L/IS)](ADT)(PT)(CP)

Equation 9-1: User cost formula

Where: UC = User cost (total project costs)

AVT = Average value of time (use values from Table 9-4 or a value determined by a more detailed analysis)

L = Project Length

RS = Reduced speed through construction zone

IS = Initial speed prior to construction zone

ADT = Average daily traffic in current year (only portion of ADT affected by the project

PT = Percent of the traffic affected by the construction project. Perform traffic study to determine percent of traffic using facility during the period.

CP = Construction period in days 9.3.4.6 Remaining capital value Design alternatives should be evaluated over equivalent analysis periods in order to yield fair comparisons of LCC. However, in many cases, one or more alternatives will have service lives that exceed the analysis period. Any service life exceeding the analysis period is known as remaining capital value. Failure to account for differing remaining capital value can result in an economic bias toward one or another alternative when using a LCC analysis. The remaining capital value is calculated by determining the percentage of useful life remaining beyond the analysis period, and multiplying that percentage by the construction cost for that component. The estimate of the remaining capital value at the end of the analysis period is then converted to a present value and subtracted from the initial capital cost. 9.3.4.7 Calculating LCCs Calculating LCCs involves calculation of the total LCCs of each alternative for direct comparison. However, because dollars spent at different times have different present values, the anticipated costs of future rehabilitation activities for each alternative need to be converted to their value at a common point in time. This is an economic concept known as “discounting”.

A number of techniques based upon the concept of discounting are available. FHWA recommends the present value approach, which brings initial and future costs to a single point in time, usually the present or the time of the first cost outlay. The equation to discount future costs to present value is as follows:

Equation 9-2: Future cost discount formula

Where: F = Future cost at the end of nth years Page 154

09- LIFE-CYCLE COST ANALYSIS FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

i = Annual discount rate

n = Number of years

The equivalent uniform annual cost approach is also used, which produces the yearly costs of an alternative as if they occurred uniformly throughout the analysis period. The most common method used to report LCC is the net present value.

Table 9-7 shows discount factors for different discount rates. The future costs can be converted to present value by either using Equation 9-1 or Table 9-7. It is important to note that future cost, F, is the present agency unit price used for the engineer’s estimate.

Table 9-7: Conversion of future costs to present value

9.3.5 Analyze LCC results Analyzing LCC results involve analyzing and interpreting the LCC results of alternative pavement designs. There are many factors from which to choose when beginning the comparison. For example, one of the first things to consider might be the user costs’ proportion comprising total LCCs for the project alternatives. For projects proposed on highway corridors with large traffic volumes, user costs can be significantly greater than agency costs. These user costs for each alternative should be compared to see if one of them has a disproportionately high or low impact on users.

If the lowest agency cost alternative has a disproportionately high user cost impact, this information should be used either to revisit the alternative’s traffic management aspect or to reconsider an alternative that might have somewhat higher agency costs but much lower user costs. The lowest agency cost alternative may not necessarily be the best solution since there are also other factors that should be addressed, such as safety and air pollution, and non-user and business impacts resulting from reduced or restricted traffic. If a higher LCC alternative is selected over a less costly Page 155

09- LIFE-CYCLE COST ANALYSIS FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL alternative, justification for the decision should be explained in the project document. However, for analysis purposes, project alternatives whose LCCs are within 10 percent of each other will be considered to be equivalent, meaning that any one of the alternatives can be considered to have the lower LCC. 9.4 LCC example The following example shows a step- by-step process to determine the lowest LCC and select the preferred alternative

Figure 9-3: Example highway 9.4.1 Project description Table 9-8 gives a summary of the project that is used in the LCC example.

Table 9-8: Project summary

Location Example Highway

Design Traffic Loading 25x106 ESALs ADT 15,000 Type of Facility Major Highway Subgrade Strength CBR = 15 Project Length 50 km Pavement Width 23 m Existing Pavement: Layer and Type Thickness Condition AC Surface 200 mm Fair Aggregate Base 250 mm Good Wheel path rutting: a) >21 mm 10% of length of the project Condition of Existing b) >15mm rutting <20 m- 25% of length Pavement Condition Survey of the project c) <15 mm 65% of length of the project Pavement Evaluation No structural overlay is required based on the Structural Evaluation Falling Weight Deflectometer testing and coring Functional Evaluation Need to address surface rutting

Step 1: Establish alternatives

Page 156

09- LIFE-CYCLE COST ANALYSIS FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

In this example, the project requires rehabilitation or preservation to address rutting caused by a combination of heavy axle loads and high pavement temperature. It is assumed that structural overlay is not required based on the FWD testing, coring, and projected future loading.

Table 9-9 is used to determine several potential rehabilitation and preservation alternatives. The following alternatives are selected based on the extent and severity of rutting on this highway:

 Alternative 1: 50 mm mill and 50 mm HMA Type II Wearing Course  Alternative 2: 50 mm hot-in-place recycling  Alternative 3: Microsurfacing to fill in the ruts

Table 9-9: Potential design alternatives for LCC

Pavement Alternative I Alternative II Alternative III Project Type 40-year flexible 20-year flexible New 40-year rigid pavement pavement pavement Remaining service 40-year flexible Widening life of existing 20-year flexible pavement pavement pavement  Cold or hot-in-place recycling and overlay or Rehabilitation Mill and overlay Overlay  Geotextile fabric and overlay Crack sealing Scrub seal and Preservation Do nothing and/or microsurfacing microsurfacing

Step 2: Determine an analysis period

Using Table 9-10, a 20-year analysis period is selected based on the expected service lives of 10 years or less for the proposed alternatives.

Table 9-10: LCC analysis period

Alternative 5-Year 10-Year 20-Year 40-Year Design Life 5-year 20 years 20 years N/A N/A 10-year 20 years 20 years 35 years 55 years 20-year N/A 35 years 35 years 55 years 40-year N/A 55 years 55 years 55 years

Step 3: Determine a discount rate

A four percent discount rate is used to calculate LCC.

Step 4: Determine maintenance and rehabilitation frequencies

Based on the existing pavement condition, projected future traffic, engineering judgment, and guidelines from Table 9-3, the following values shown in the right column of Table 9-11 were estimated for the expected service lives.

Page 157

09- LIFE-CYCLE COST ANALYSIS FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

Table 9-11: Pavement treatments expected life

Estimated Service Life Treatment Expected Life (Years) for this Project (Years) 1) 50 mm overlay 7-10 2) 50 mm mill and overlay 10-15 10 3) Scrub seal 2-5 4) Slurry seal 3-8 5) Chip seal 3-6 6) Microsurfacing 3-8 5 7) Micro mill(25 mm) 1-4 8) Cold-in-place recycling and 10-15 overlay 10) Hot-in-place recycling 5-7 7 11) Thin hot-mix 5-8 overlay(<50 mm) 12) Patching 3-5 13) Thick overlay (125 mm) 8-15 14) Full depth reclamation and 20+ 100 mm overlay 15) Complete reconstruction 20+

Based on the information gathered in Steps 1 and 3, Table 9-12 was created showing the type and timing of different rehabilitation/preservation over the 20-year analysis period.

Table 9-12: Rehabilitation and preservation alternatives over a 20-year analysis period

Example Highway Rehabilitation and Preservation Alternatives Over a 20-Year Analysis Period Year 0 Year 5 Year 7 Year 10 Year 12 Year 15 Year 17 50 mm mill Micro- Micro- Alt. 1 and fill surfacing surfacing 50 mm hot- 50 mm Micro- Alt. 2 in-place mill and surfacing recycling fill 50 mm hot- 50 mm Micro- Alt. 3 in-place mill and surfacing recycling fill

Step 5: Estimate costs

The unit prices for cold planning and asphalt concrete Type II wearing surface were selected from the DMAT’s reasonable unit prices document, shown in Figure 9-4. For strategies such as hot-in- place recycling and microsurfacing where there are no DMAT unit prices, reasonable unit prices from the United States were used. These unit prices should be verified to prior to use.

Page 158

09- LIFE-CYCLE COST ANALYSIS FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

Figure 9-4: Reasonable unit prices

User costs were not calculated for this project since all three alternatives require very similar traffic control and lane closures. However, it is very important that user costs are included for higher volume roadways when there are heavy traffic interruptions and user costs can be significantly different alternatives.

Step 6: Calculating LCCs

Both present worth and uniform annual costs were calculated for all three alternatives. Table 9-13, Table 9-14, and Table 9-15 each shows a result of LCC for one of the alternatives.

Page 159

09- LIFE-CYCLE COST ANALYSIS FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

Table 9-13: LCC result (alternative 1)

Alternative 1: 50 mm Mill and Fill

Year 0: 50 mm Mill and Fill Year 10: Hot In-Place Recycling Year 17: Microsurfacing

Length Width Total Pavement (meter) (meter) Area (sq. meter) 50,000 23 1,150,000 Unit Price Unit Description (Dh) 50 mm Asphalt Concrete Wearing Course 30.00 Sq. meter AD Unit Prices 50 mm Cold Planing 2.50 Sq. meter AD Unit Prices Microsurfacing 10.00 Sq. meter US Unit Prices Hot In-Place Recycling 25.00 Sq. meter US Unit Prices

Alternative 1: 50 mm Mill and Fill 4% Total Price PW Price Year Description Discount (Dh) (Dh) Factor 0 50 mm Asphalt Concrete Wearing Surface 1.0000 34,500,000 0 50 mm Cold Planing 2,875,000 Initial Construction Cost 37,375,000

10 50 mm HIR 0.6756 28,750,000 19,423,500 Year 10 Cost 19,423,500

17 Microsurfacing 0.5553 11,500,000 6,385,950 Year 15 Cost 6,385,950

20 Two-Year RSL 0.4564 4,600,000 2,099,440 Total Future Rehabilitation Cost PW 61,085,010 UAC 0.07358 4,494,635

Page 160

09- LIFE-CYCLE COST ANALYSIS FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

Table 9-14: LCC result (alternative 2)

Alternative 1: 50 mm Mill and Fill

Year 0: 50 mm Mill and Fill Year 10: Hot In-Place Recycling Year 17: Microsurfacing

Total Width Pavement Length (meter) (meter) Area (sq. meter) 50,000 23 1,150,000 Unit Price Unit Description (Dh) 50 mm Asphalt Concrete Wearing Course 30.00 Sq. meter AD Unit Prices 50 mm Cold Planing 2.50 Sq. meter AD Unit Prices Microsurfacing 10.00 Sq. meter US Unit Prices Hot In-Place Recycling 25.00 Sq. meter US Unit Prices

Alternative 1: 50 mm Mill and Fill 4% Total Price PW Price Year Description Discount (Dh) (Dh) Factor 0 50 mm Asphalt Concrete Wearing Surface 1.0000 34,500,000 0 50 mm Cold Planing 2,875,000 Initial Construction Cost 37,375,000

10 50 mm HIR 0.6756 28,750,000 19,423,500 Year 10 Cost 19,423,500

17 Microsurfacing 0.5553 11,500,000 6,385,950 Year 15 Cost 6,385,950

20 Two-Year RSL 0.4564 4,600,000 2,099,440 Total Future Rehabilitation Cost PW 61,085,010 UAC 0.07358 4,494,635

Page 161

09- LIFE-CYCLE COST ANALYSIS FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

Table 9-15 : LCC result (alternative 3)

Alternative 3: Microsurfacing

Year 0: Microsurfacing Year 5: Hot In-Place Recycling Year 12: 50 mm Mill and Fill

Total Length Width Pavement (meter) (meter) Area (sq. meter) 50,000 23 1,150,000 Unit Price Unit Description (Dh) 50 mm Asphalt Concrete Wearing Course 30.00 Sq. meter AD Unit Prices 50 mm Cold Planing 2.50 Sq. meter AD Unit Prices Microsurfacing 10.00 Sq. meter US Unit Prices Hot In-Place Recycling 25.00 Sq. meter US Unit Prices

Alternative 3: Microsurfacing 4% Total PW Year Description Discount Price (Dh) Factor (Dh) 0 Microsurfacing 1.0000 11,500,000 Initial Construction Cost 11,500,000

5 50 mm Hot In-Place Recycling 0.8219 28,750,000 Year 5 Cost 23,629,625

12 50 mm Mill and Fill 0.6246 37,375,000 Year 12 Cost 23,344,425

20 RSL Cost 0.4564 7,475,000 3,411,590 Total Future Rehabilitation Cost PW 55,062,460 UAC 0.07358 4,051,496

Step 7: Analyze LCC results

Alternative 3 provides the lowest initial cost and LCC over the 20-year analysis period as shown in Table 9-16 and Figure 9-5.

The important conclusion that can be drawn from the LCC is that the lowest LCC was accomplished through use of proactive preservation treatment; microsurfacing, which allowed the agency to delay a more expensive treatment; and mill and fill to year 12.

Page 162

09- LIFE-CYCLE COST ANALYSIS FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

Table 9-16: LCC summary table

LCCA Summary Table 20-Year Analysis Period and 4% Discount Rate

Uniform Present Rehabilitation Initial cost Annual Alternative Worth Alternatives (Dh) Cost (Dh) (Dh)

Alternative 1 50 mm Mill and Fill 37,375,000 61,085,010 4,494,635

50 mm Hot In-Place Alternative 2 - - 61,085,010 Recycling

Alternative 3 Microsurfacing 11,500,000 55,062,460 4,051,496

As can be seen from Table 9-16, Alternative 3 provides a cost savings of over 6M AED as compared to Alternative 1, while providing the travelling public with a high-quality roadway.

LCCA Summary

120,000,000

100,000,000

80,000,000

60,000,000 PW (Dh) Initial Cost (Dh) 40,000,000

20,000,000

- Alternative Alternative Alternative 1 2 3

Figure 9-5: LCC summary

Based on the results of the LCC, Alternative 3 is recommended for this project.

Page 163

09- LIFE-CYCLE COST ANALYSIS FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

10 PAVEMENT MANAGEMENT SYSTEMS 10.1 Overview In addition to selecting materials and determining thickness requirements, pavement designers must also ensure optimum quality and economical maintenance. Designers apply a pavement management system (PMS) to ensure an effective initial design, conduct periodic monitoring, and plan timely maintenance. A PMS provides a comprehensive database of current and historical information on pavement conditions, pavement structures, and traffic. It also provides a set of tools that help pavement designers determine existing and future pavement conditions, predict financial needs, and identify and prioritize pavement preservation projects. Access to and use of a PMS is vital to the success of any pavement design project. This chapter describes the link between pavement design and the use of a PMS. It does not, however, detail methods or guidelines for establishing a PMS.

According to the 1993 AASHTO Guide for Design of Pavement Structures (4), a PMS is “a set of tools or methods that assist decision makers in finding optimum strategies for providing, evaluating, and maintaining pavements in a serviceable condition over a given period of time.” Tools within a PMS include systematic procedures for scheduling maintenance and rehabilitation activities that are related to pavement design.

Because keeping a road in good condition is far less costly than repairing it after it has deteriorated, pavement management systems prioritise preventive maintenance over road reconstruction. According to the DMAT’s Road Structures Design Manual (10), focusing on preventive maintenance over repair reduces costs and ensures better overall condition over a road’s design life. 10.2 Tasks that involve using a PMS Typical pavement design tasks that involve the use of a PMS include the following:

1. Conducting pavement condition surveys: Conducting a pavement condition survey is the first step for PMS development. Such surveys should encompass an entire pavement network to obtain the type and severity of different distresses. Engineers should apply a consistent approach when conducting pavement condition surveys to ensure that resultant data within the PMS is consistent. Periodic follow-up surveys are necessary to keep data in the PMS up to date. 2. Updating and accessing the pavement condition database: A pavement condition database is the backbone of a PMS. This database should include all information related to pavement structures, including general information about each road, layer thicknesses, traffic (design and actual), material properties, maintenance and rehabilitation activates, and known distresses identifies through pavement condition surveys. 3. Applying analysis schemes: An analysis scheme is a computer program that enables users to analyse information in the database. Engineers can apply such programs to evaluate LCCs, determine ways to optimise road performance, and to predict future performance. 4. Applying decision criteria. To make good pavement management decisions, an engineer must apply a complex set of criteria when analysing data in a PMS. Such criteria include construction costs, road user costs, and environmental effects.

Page 164

10- PAVEMENT MANAGEMENT SYSTEMS FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

5. Following implementation procedures. After using a PMS to make decisions, an engineer must follow procedures to implement those decisions. Such procedures are governed by available funds, public benefits, local realities, and other general factors. 10.3 PMS Methodologies When using a PMS, engineers can apply two different pavement management methodologies, focusing on either project or network information. According to the National Cooperative Highway Research Program (NCHRP) Pavement Management Methodologies to Select Projects and Recommend Preservation Treatments (29), engineers can evaluate either project-level information, which influence decisions for the entire pavement network, or network-level information, which will require project-level action. A network-level approach is concerned with policy, plans, and budget for the entire network. A project-level approach focuses on smaller sections of the network, basing decisions on pavement conditions, required maintenance, reconstruction, and rehabilitation activities, and specific cost related to those activities. When applying the project-level approach, engineers study different life cycle cost analyses to compare and evaluate different alternatives.

Variations of these methods include the following:

1. Pavement condition analysis (a project-level approach): Using this method, considered the simplest of the three, a designer aggregates pavement condition information for a project, then selects the most appropriate maintenance strategy. Pavement maintenance projects are then selected based on a network-level budget. Although this method is simple, its effectiveness is limited because it does not consider future pavement conditions. This is a project-level approach, because decisions are first made at the project-level. 2. Priority assessment modelling (a project-level approach): Because it incorporates predicted future pavement conditions, this method is more effective than pavement condition analysis. Using this method, designers apply priority assessment models to consider future predicted conditions and, potentially, evaluate limited conditional (“what if”) scenarios based on network level decisions. A designer’s opportunities to evaluate conditional scenarios, however, is limited, because modelling alternate decisions requires changing project-level data, which is generally very time-consuming. Although more complex than pavement condition analysis, priority assessment modelling is also a project- level approach because engineers still make low-level decisions, such as determining an individual pavement section’s maintenance strategy, before progressing to higher-level decisions, such as defining an overall pavement network strategy. 3. Network optimization modelling (a network-level approach): Using this method, which is considered the most sophisticated, a designer simultaneously evaluates all portions of an entire pavement network to determine the optimum network management strategy. Specific maintenance projects and locations are then selected to meet this strategy. This is a network-level approach, because decisions are first made for the entire network, rather than for specific projects. Such network-level decisions then have a direct impact on all of the projects for the network. 10.4 Network-level pavement management Network-level pavement management uses a systems methodology, combining methods, procedures, data, software, policies, and decisions to produce optimal solutions for an entire pavement network. In essence, a network-level approach uses aggregate data (such as traffic loads, safety statistics, materials inventories, and pavement conditions) to first identify optimum network strategies. Engineers then apply these strategies to make project-level decisions, such as

Page 165

10- PAVEMENT MANAGEMENT SYSTEMS FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL determining maintenance options and selecting projects. A network-level approach requires large amounts of data, accurate aggregation, computer models, and individuals with appropriate training.

Engineers apply network-level approaches to produce optimum solutions for entire pavement networks. Key elements in a network-level approach include the following:

 A system definition. Because a network-level approach optimizes solutions for an entire defined system, optimal solutions require a comprehensive and accurate system definition. Many experts believe that pavement management, to be effective, must reflect the broader transportation infrastructure rather than the pavement network only.  A network model. Engineers make network-level decisions, which influence all decisions, including those for specific projects, based on outputs from a complex simulation model. Such decisions are only as good as the network model. Selection of an appropriate model requires knowledge of inputs, accuracy, sensitivity, assumptions, and calibration.

A purely network-level approach may not always provide sufficient data about individual roadway sections to enable designers to make fully-informed project decisions. Although a network-level approach is powerful and sophisticated, it requires large amounts of data and resources, as well as attention to detail, to ensure effective pavement management.

Refer to the Highway Design and Maintenance Standards Model (HDM-4) (30), developed by the World Bank, as a good example of a network-level PMS. 10.4.1 Advantages of network-level pavement management Network-level pavement management is characterized by top-down logic, system optimization, aggregate data, large data and resource requirements, and sophisticated models. Its chief advantages include the following:

1. Network-level pavement management establishes an optimal solution for the entire network. A network-level approach optimizes the cost-benefit ratio for the entire network, focusing on the overall system rather than any individual project. Project-level approaches can support network-level pavement management by assigning project priorities that are commensurate with network-level programs, decisions, or budgets. However, because projects are already planned before such high-level decisions are made, project-level decisions and priorities may be inconsistent with network-level decisions and priorities, resulting in a system that does not fully meet the requirements of the network as a whole. 2. Network-level methods enable quick and accurate production of conditional scenarios. Engineers use software models based on a network-level approach to adjust top-level budget and policy inputs, then quickly calculate the resulting network-wide effects of these top-level decisions. For example, a designer using a network-level model could calculate how a proposed law to lower axle load limits might affect economic or pavement conditions. A designer could also evaluate long-term network performance under varying levels of funding. Using project-level software, however, is often more laborious than network-level software. To determine how a top-level budget or policy change would impact individual projects, a designer must modify many lower-level inputs. 3. A network-level approach facilitates prioritisation of broad areas of maintenance. Because network-level analysis provides target maintenance treatments and costs, designers can easily and consistently apply such values to individual projects. To obtain the same results with a project-level approach, designers must receive network-level targets before making need project-level decisions. 4. Network-level pavement management enables the use of consistent inputs to scenarios, which ensures consistent comparisons. Using a network-level model, different can model Page 166

10- PAVEMENT MANAGEMENT SYSTEMS FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

different scenarios on the same system. By applying consistent assumptions across all scenarios, a designer can generate outcomes with qualitative and comparative results. With project-level approaches, designers must input such assumptions for individual projects, making comparisons across different scenarios more difficult. Because project-level approaches involve many groups across an agency, communication problems, personal differences, and regional biases can create inconsistent input across different scenarios and different projects. 5. A network-level approach facilitates getting attention from top management. Designers can use network-level software’s ability to evaluate conditional scenarios to easily demonstrate the fiscal importance of pavement management and the implications of various decisions to executive management and key stakeholders. 10.5 Project-level pavement management Project-level pavement management uses a bottom-up methodology that can produce network- level solutions by to combining methods, procedures, data, software, policies, and decisions. In essence, a project-level approach first uses individual section data (such as traffic loads, safety statistics, materials inventories, and pavement conditions) to determine the optimum section maintenance and rehabilitation strategies and to prioritise projects. Pavement managers then make high-level network decisions by selectively including and excluding projects. Project-level decisions, such as maintenance strategies and project prioritisation, drive the overall network solution, which then may or may not be optimized for the entire pavement network. With this method, pavement managers enforce network priorities by including or excluding projects (based on rankings that reflect the strategies for project selection and maintenance and rehabilitation that have already been set) or by relying on the compatibility of project-level decisions with network- level goals.

Most pavement management systems in operation today apply a project-level approach. Many state and local pavement management systems are project-level systems.

Although less able to produce optimum solutions and conditional scenarios than network-level pavement management, the project-level approach is advantageous because it maintains detailed project-level information needed to make project-level decisions. 10.5.1 Advantages of project-level pavement management Project-level pavement management is characterized by the use of simpler models, less data aggregation, fewer data and resource requirements, less reliance on feedback for success, and better understanding. Its chief advantages are as follows:

1. Project-level pavement management relies less on aggregate data than network-level approaches. Such reliance on aggregate data to drive models poses inherent risks. First, the aggregate data, if not carefully chosen, may not accurately represent actual conditions, which can lead to incorrect decisions at the highest level. Second, applying aggregate data to achieve project-level results is sometimes difficult. 2. Project-level methods are applicable with little data. Project-level systems are very useful for smaller agencies that have less need to access large quantities of data. Network-level systems require large amounts of data and resources (such as computers, trained personnel, and advanced algorithms), which smaller municipal agencies may not be able to afford. Additionally, networks managed by smaller municipal agencies may be simple enough that they do not require network-level analysis. Project-level systems, however, are not always useful with limited data. A project-level system can require a significant amount of data, depending on its complexity and the sophistication of its models. Page 167

10- PAVEMENT MANAGEMENT SYSTEMS FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

3. Project-level pavement management facilitates better correlation between network-level and project-level management decisions. Because decisions flow from the bottom up, high- level network decisions, although somewhat limited in scope, are based on low-level project decisions. Network-level pavement management, however, requires translating broad network-level decisions into specific project actions, which can be difficult. 4. Project-level approaches depend less on feedback. Because political sentiment, budgets, pavement conditions, and maintenance and rehabilitation strategies are highly dependent on the local environment, network-level models invariably need calibration based on continual feedback and updates. If this feedback and update process is interrupted or halted (resulting from budget cuts or personnel transfers, for example) a network-level model's utility can quickly degrade. Using network-level models that are not properly calibrated can also produce errors.

Project-level approaches can be simpler and more easily understood, making getting buy-in easier. Network-level approaches typically use sophisticated models that make many generalisations and assumptions.

Page 168

10- PAVEMENT MANAGEMENT SYSTEMS FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

11 EXISTING PAVEMENT EVALUATION This chapter details the evaluation of the condition of the existing pavement for routine monitoring or planned corrective action. Pavement evaluation is the procedure to determine the structural and functional conditions of a road. Structural conditions focus on structural integrity and distresses; whilst, functional condition is concerned with skid resistance, surface texture, and overall riding quality of the pavement.

This section should be used in conjunction with the distress definition detailed in Section 8.3 and the pavement evaluation for overlay design described in Section 5.4, and Chapter 9 of the DMAT’s Geotechnical Investigation and Design Manual Part 2. 11.1 Overview Pavement evaluation is needed to access the current condition of the existing pavement. Investigation outputs will aid the Engineer’s decision on the proper maintenance or rehabilitation strategy to be used. Pavement evaluation procedures shall be conducted by first collecting data through distress surveys, material testing, structural evaluation, and functional testing. Collected data are then analysed using software or manual analyses procedures. Then, the result of the analysis is fed into a PMS, or given to the agency to help decide the proper action to be taken.

Pavement evaluations shall follow these steps:

1. Identify the road properly with kilometre posts, direction, dates, and anything to make the survey referenced easily. 2. Conduct a windshield survey to identify the critical location and extent of the pavement condition. 3. Based on the length of the road, and the available funds, a walking survey or automatic survey can be conducted. 4. Data collected from the distress survey shall then be analysed to identify the main distresses observed and to recommend further testing. 5. If the major distress is cracking, then non-destructive structural capacity testing shall be used to access the pavement layers stiffness. 6. If the major distress is rutting, then trench, cores, and asphalt mixture testing shall be conducted to identify the weak soil that caused the deformation. 7. Roughness and skid resistance testing shall be conducted if the condition survey reported the presence of these distresses in the pavement. 8. Based on the severity levels assigned to each distress, the proper maintenance technique shall be adopted. 9. Maintenance techniques can vary from surface sealing to fixing minor cracks and skid resistance to the removing and replacing portions of the pavement structure.

This section also focuses on the data collection and manual analysis for the pavement evaluation. Data collection is detailed in the first section, whilst the second section will detail the data analysis. Different maintenance techniques are described in Chapter 8, and rehabilitation structural design is detailed in Chapter 5 of this manual. 11.2 Data collection Data collection is the first and most important step of the pavement evaluation. At the time of the survey, the Engineer shall require data to access the pavement condition; and, the detail and

Page 169

11- EXISTING PAVEMENT EVALUATION FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL accuracy of the data collection vary from a visual limited survey to a comprehensive investigation. Different types of pavement condition surveys include the following:

 Distress survey;  Structural capacity using non-destructive or destructive testing;  Roughness testing (ride quality); and  Skid resistance (surface texture).

It is not necessary to have the same detail at each survey; however, it is important to use the same general definitions. It is not necessary to collect all of the data. Some measures, such as structural evaluation, may only be collected at certain projects. Additional measures, such as surface friction, may only be used when a specific problem has been identified. Each type of survey shall be detailed in the following sections. 11.2.1 Distress survey Distress is damage observed along the pavement surface. To determine the type, severity, and quantity of the distress, the Engineer performs distress surveys, which show the type of the developed damage, the severity of the damage, and quantify the extent of the damage.

Distress surveys are conducted automatically or manually. Automated surveys are more accurate and faster, but are also costly. Manual surveys, which vary from a walking survey of the entire or a portion of the read to windshield surveys, require trained Inspectors to conduct the survey accurately. Walking surveys are accurate in accessing the type and severity of the distress but might require road closures for crew safety. Windshield surveys are similar to the automated survey but less accurate because they are conducted by a person in a moving vehicle; however, the windshield survey can be used as a first step to identify locations for walking surveys, especially if the road is long.

In general, the cost, required accuracy, precision, and resolution will decide the type of distress survey to be used. Walking or windshield surveys are extensively used; however, in recent years, more agencies are beginning to move towards automated surveys. 11.2.1.1 Windshield survey procedure Windshield surveys are conducted by an Inspector travelling in a vehicle at approximately 8 km to 20 km per hour. Distresses are visually identified by the Inspector, and the area affected is estimated as a percentage of the road surface. This information is recorded on a data collection sheet, digitizing tablet, or laptop computer as the Inspector travels along the road. 11.2.1.2 Walking survey procedures Walking survey inspections are conducted on selected units that consist of a small segment of the road that is then inspected in detail. Units are usually uniform in size and inspected at random or through a defined sampling procedure.

The Inspector inspects the sample unit by walking the pavement and whilst standing on the shoulder. During this process, each distress type, its severity, and amount present is identified and recorded, and their amounts must correspond to those defined in the distress identification. Quantities and severities are normally estimated using accurate wheel and tape measuring techniques.

Page 170

11- EXISTING PAVEMENT EVALUATION FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

Data may be recorded using a handheld microcomputer, a pen-based computer (electronic clipboard), or a data collection sheet. Total quantities for each distress type and its severity are automatically tallied in the data collection devices.

Manual distress survey procedures are slow, labour intensive, and subject to transcription errors. Consistency between classification and quantification of the distresses observed by different inspectors can also be a problem. Once the data has been summarized and corrected for transcription errors, the only recourse for checking apparent anomalies in the data is a return visit to the field. Safety of field crews is also another concern. 11.2.1.3 Automated distress surveys Vehicles that take photographs or other visual images of the pavement have been developed to speed the field data collection time and provide a permanent visual record of the actual pavement condition. A new class of condition survey vehicles that uses objective measures of the pavement surface to classify and quantify different types of distress is emerging. Current developments in distress survey equipment includes video imaging that takes a picture of a portion of pavement and, by using pattern recognition technology, classifies and quantifies distress directly without the subjective evaluation of human inspectors.

Automated surveys use a high-resolution video camera mounted on a vehicle that captures a video of the road while driving at road speed. These videos are then analysed to measure values of each distress. Additional automated surveys use lasers to map the pavement surface.

Camera resolution is a function of the equipment used to make the image. Precision is a function of the number of measuring devices and the location differences between repeat runs. These equipments need periodic calibration. Additionally, precision and accuracy are functions of the interpretations, the lighting, and the placement of the imaging during repeat runs. Laser-based systems have more precision problems because they view small areas that are combined to give estimated distress information. Figure 11-1 shows the digital survey vehicle, whilst, Figure 11-2 shows a software snapshot used for automated cracking mapping.

For the imaging systems, the images can be affected by shadows and the direction of the sun. Lighting conditions shall be controlled either by enclosing the camera and pavement with fixed lighting or by completing all surveys at night and using fixed lighting. Lights can be set at an angle so that known shadows can be used to help identify crack widths and elevation differences.

Automated distress survey procedures are less subjective than manual surveys. In the simplest form, the images are interpreted manually. Distress identification is still manual; the Inspector identifies, quantifies, and records distress from the image rather than from the pavement surface. This takes the Inspector off the road and reduces traffic interruption, both of which are extremely important for safety on high volume highways, but subjectivity is still present.

Automated analysis of the images is the least subjective system; however, image analysis by automated means has been found to be quite complex. At the current time, any distress information collected and reduced using automated procedures needs to be analysed carefully to determine the accuracy, precision, and resolution.

Page 171

11- EXISTING PAVEMENT EVALUATION FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

Figure 11-1: Digital survey vehicle

Figure 11-2: Automatic crack mapping 11.2.2 Structural capacity Pavement structure is designed to carry traffic loads. Structural analyses determine the pavement load-carrying capacity for current and projected future traffic. Structural capacity of pavements shall be accessed through destructive or NDT. Test selection is based on road category and distress severity under investigation.

Non-destructive deflection testing of the pavement is a simple and reliable method to assist in making this evaluation; however, destructive testing, such as coring and trench studies, may also be used. Pavement structural evaluation is important in the selection of treatments, especially if cracking exists. The selection of which structural capacity test to carry depends on the importance of the roadway, value of the Project, and availability of equipments to conduct the test.

Page 172

11- EXISTING PAVEMENT EVALUATION FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

11.2.2.1 Destructive testing for structural pavement evaluation Forensic and regular evaluations have used trenching and coring during destructive testing to determine the main cause of the pavement failure. Trench and core studies are described in the following subsections.

Trench Studies Trench studies are saw-cut deep enough in the asphalt layers with minimal disturbance to the aggregate base course. Trench dimensions shall be approximately 1 m by 4 m, or as seen suitable to cover the area of investigation. Asphalt layer samples need to be separated by layer, surface, binder, or asphalt base course for analysis of each layer separately. After the asphalt layer is removed and samples collected, aggregate base course tests can be conducted. If needed, after testing and sampling, the aggregate base course can be dug out to access, sample, and test the subgrade soil.

For example, Figure 11-3 shows a picture of a trench cut out for a road section that suffered from severe rutting. The trench was needed to detect the deformation in different layers. It can be seen from the figure that the deformation was mainly in the surface layer. This leads to the conclusion that the asphalt mix design for the surface layer was incorrect. Milling the surface layer and replacing it with a properly designed asphalt surface will fix this pavement failure.

Asphalt Cores Asphalt layers are testing by taking a coring rig and water for cooling. Rigs shall be lowered gradually until they reach the end of the asphalt layer. If there is a chemically treated base layer, the coring should continue in the base to obtain an intact sample. Cores can measure 10 cm or 15 cm in diameter. Figure 11-4 shows a core with a 5-cm asphalt surface and 14-cm base course. Asphalt cores are used to check the thickness of pavement layer and to compare it to the as-build details because the overlay might have been carried out and the asphalt layer thickness was increased.

Core locations are decided based on the extent of the Project. Cores shall be taken from locations that represent the entire pavement at 500-m intervals for long roads.

Figure 11-3: Trench cutout showing severe rutting

Page 173

11- EXISTING PAVEMENT EVALUATION FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

Figure 11-4: Asphalt cores showing surface and base courses

Aggregate base and subgrade soil tests, such as in situ plate load testing. Additionally, field CBR, moisture content, Atterberg limits, and permeability can be conducted on soil samples. Asphalt samples taken from the trench or cores can be used to conduct the following testing:

 Obtain the asphalt layer thickness;  Run extraction test to compare the asphalt mixture to the mix tolerance limits;  Conduct dynamic modulus testing on cylindrical samples to access the asphalt stiffness;  Conduct beam fatigue on beams to access the fatigue characteristics of the asphalt layer;  Conduct repeated load permanent deformation tests for rutting characteristics of the asphalt mixture. 11.2.2.2 Non-destructive testing for structural pavement evaluation NDT provides the overall response of the pavement to external loads. It does not damage the pavement, does not require laboratory test, and is fast. NDT testing relies mainly on collecting surface deflection data. Weaker pavements deflect more than stronger pavements.

Exact location and frequency of structural testing within specified road sections should be carefully determined prior to seeking testing services. Tests shall be limited to locations where distress condition survey and roughness surveys indicate structural problems and areas where overlays are anticipated.

Several NDT devices are available; however, they are not all available in UAE. These NDT devices include the following:

 Benkelman Beam;  Dynaflect;  Road Rater;  Falling Weight Deflectometer (FWD);  Ground Penetrating Radar (GPR);  Rolling Deflectometer;  Seismic Pavement Analyser (SPA); and  Dynamic Cone Penetrometer (DCP).

Page 174

11- EXISTING PAVEMENT EVALUATION FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

All devices, except the GPR and DCP, operate by measuring the pavement response to an imposed force. Responses are generally in terms of surface deflections at one or more points on the pavement. Major differences between these devices include the load levels; the way the load is applied to the pavement, such as steady, vibratory, or impulse; and the number of points at which deflections are measured. GRP uses energy waves to estimate the layers’ thickness. DCP is used on unbound pavement layers to obtain stiffness of the layer. This Project’s NDT will focus on the FWD, DCP, and GPR — each of which are available in the UAE.

Dynamic Cone Penetrometer DCP is a portable device that complies with ASTM D 6951 – 03 and consists of a two-piece rod; the lower rod measures approximately 1-m-long and is fitted with a replaceable cone tip at the penetration end and an anvil at the upper end, which houses a threaded receptacle for attaching the upper rod. The upper rod carries the 17.6-lb. sliding hammer and has a handle for steadying the device during testing. Figure 11-5 shows a picture of the DCP.

The Operator drives the DCP tip into the soil by lifting the sliding mass (hammer) with one hand to the handle then releasing it, whilst the other hand holds the instrument by the handle to maintain an approximate vertical position.

Initial depth readings are made using a measuring stick between the bottom of the sliding mass and a stationary surface, such as a pavement surface or ground level. Total penetration for a set of blows is measured and recorded by an assistant, who will generate a graph of depth versus cumulative blows and shall fit a trend line to the data points for each tested layer. Penetration rates, measured in mm/blow, are determined as the slope of the trend line.

The number of blows in a set can vary. For softer soils, 1 to 3 blows may be a set, whereas for stiffer soils, 5 to 10 blows may be a set. Some soils may be so stiff that little to no penetration is recorded in a given set.

The U.S. Army Corps of Engineers has developed a number of correlations relating rate of penetration to soil stiffness in terms of the CBR. For most applications, the following relationship is adequate for approximating in situ stiffness:

CBR = 292/PR1.12

Equation 11-1: CBR relationship for approximating in situ stiffness

Where: CBR = California Bearing Ratio PR = penetration rate, mm/blow.

This relationship has been further correlated to elastic modulus (E) using the following relationship:

E = 2555 CBR0.64

Equation 11-2: Elastic modulus (E) correlation

Where E = elastic modulus

Page 175

11- EXISTING PAVEMENT EVALUATION FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

Figure 11-5: Dynamic cone Penetrometer Falling Weight Deflectometer FWD is a trailer-mounted device that places a 300-mm-diameter load plate in contact with the highway at each test location. Load columns carry a stack of weights that are dropped to impart a load to the pavement similar to that imparted by a passing dual truck tire set. Seven geophones, spaced away from the load plate at 30-cm increments, measure the surface deflection, generating a deflection bowl. Figure 11-6 shows the FWD device.

Testing intervals are set every 200 m, or at 30 locations per project. Where a divided roadbed exists, surveys shall be taken in both directions — if the Project includes improvements in both directions. Temperature data, collected at the time of testing, is necessary for all flexible pavements because the modulus of bituminous materials is temperature-dependent.

FWD requires the use of computer software for backcalculation of deflection data collected. Software, such as MODULUS 6.0, ELMOD 5.0, and EVERCALC 5.0, is Windows compatible and include analyses and graphing features.

Figure 11-6: Falling weight Deflectometer

Page 176

11- EXISTING PAVEMENT EVALUATION FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

Inputs required for the backcalculation are the raw deflection file, pavement layer thicknesses, layer Poisson ratios, probable layer moduli ranges, and asphalt temperatures at the time of testing. This process works on the assumption that the pavement structure is a linear elastic layered system. Knowing the layer thickness, deflection, and Poisson ratio, the modulus can be approximated. Once a reasonable match is made, the moduli that allow this match are reported as the individual layer moduli.

There are precautions and limitations to the backcalculation procedure that the user must consider. In the end, engineering judgment will be needed to decide on the viability of solutions generated. Advice for using MODULUS 6.0, as reported by the Texas Department of Transportation (http://onlinemanuals.txdot.gov/txdotmanuals/pdm/pavement_evaluation.htm) includes the following:

 Modulus for thin layers cannot be back calculated.  Four is the maximum number of layers for which the modulus can be backcalculated (one of which is always the natural subgrade).  Checks of the MODULUS summary table shall be made to detect outliers that skew the average value reported. Outliers may be the result of full-depth patches, consisting of different pavement structure, or very weak areas.  Shallow bedrock will usually result in the underestimation of the subgrade modulus and over-estimation of the flexible base modulus.  Soft upper subgrade can also lead to high errors in the backcalculation process.

Ground Penetrating Radar GPR is an NDT that pulses electromagnetic radiation into a pavement, instead of using a load pulse. Pulses of radar energy are sent by the system into the pavement and returned reflections are captured from each perceived layer interface within the structure. Returned energy amounts and the time delay between reflections are used to calculate layer dielectrics and thickness. The dielectric constant of a material is an electrical property that is most influenced by moisture content and density. As the density and moisture content go up, the amount of energy reflected increases, and the penetrating ability decreases. Conversely, if the air voids increase, the amount of energy reflected decreases.

GPRs are mounted on a van in a self-contained system that is suspended above the roadway. This allows for uninterrupted data collection at near-highway speeds. Figure 11-7 shows the GPR.

GPR is a valuable tool to the pavement engineer to assist in determining the following:

 Layer thicknesses, section changes, and full-depth patches;  Location and the extent of potential problems, such as elevated moisture levels or stripping in the HMA; and  Location and extent of segregation.

Page 177

11- EXISTING PAVEMENT EVALUATION FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

Figure 11-7: Ground penetration radar 11.2.2.3 Roughness testing Roughness, or ride quality, is a measure of pavement surface distortion along a linear plane or an estimate of the pavement’s ability to provide a comfortable ride to the users. Roughness is often converted into an index, such as the Present Serviceability Index (PSI) or the International Roughness Index (IRI). Pavement roughness is considered most important by the using public, and it is especially important on pavements with higher speed limits.

Roughness can be generated by localised surface or subsurface distress and poor construction quality, including compaction, grade control, and poor bonding of the surface HMA layer to the underlying HMA layer. New or reconstructed pavements shall be as smooth as practical. Roughness will accelerate deterioration. Roughness is important because it affects not only ride quality but also vehicle delay costs, fuel consumption, and maintenance costs.

Roughness equipments range from very simple to very complex techniques. Different techniques are listed below and are arranged from very simple to very complex:

1. Rod and level survey; 2. Dipstick profiler; 3. Profilographs; 4. Response type road roughness meters (RTRRMs); and 5. Profiling devices.

Rod and level surveys provide an accurate profile measurement; however, they take a long time and require road closures, which are not practical for major long roads. To reduce the time and increase accuracy, a dipstick profiler can be used, as seen in Figure 11-8; however, the length of the road needs to be relatively small.

For longer road stretches, Profilographs, which have a sensing wheel mounted to provide free vertical movement at the centre of the frame, may be used. Refer to Figure 11-9, for an example. Deviation against a reference plane, established from the profilograph frame, is recorded on graph paper from the motion of the sensing wheel. Profilographs can detect slight surface deviations or undulations up to approximately 6 m in length.

Page 178

11- EXISTING PAVEMENT EVALUATION FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

Figure 11-8: Dipstick Profiler

Figure 11-9: Profilograph

Roughness can also be measured using the RTRRMs, often-called road meters. RTRRM systems are adequate for routine monitoring of a pavement network and providing an overall picture of the condition of the network.

RTRRMs measure the vertical movements of the rear axle of an automobile or the axle of a trailer relative to the vehicle frame. These meters are installed in vehicles with a displacement transducer on the body, located between the middle of the axle and the body of a passenger car or trailer. Transducers detect small increments of axle movement relative to the vehicle body and the output data consists of a strip chart plot of the actual axle body movement versus the time of travel.

The disadvantage of a RTRRM is that it depends on the dynamics of the particular measurement vehicle, which results in unstable and unrepeatable measurements.

Profiling devices, which range from manual straightedge measure to automatic profilometers, are the most-used roughness techniques. Straightedge measure was improved by mounting it on wheels, which is the profilograph. Examples of automated profilometers include the Automated Page 179

11- EXISTING PAVEMENT EVALUATION FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

Road Analyser Vehicle (ARAN), which is equipped to measure the road profile expressed by the IRI, as seen in Figure 11-10.

Each roughness measuring technique uses a different parameter to detect the road roughness, and there is no correlation between these devices. It is recommended to use the IRI because it is widely used for roughness measurement, as it is fast, accurate, and measured automatically. IRI is computed from longitudinal profiles using an automatic profilometer mounted on a vehicle that operates at traffic speed.

Figure 11-10: Automatic road analyser vehicle 11.2.2.4 Skid resistance Skid resistance is the ability of the pavement surface to provide sufficient friction to avoid skid- related safety problems and it is important on pavements with high speeds. Skid resistance is a function of the micro and macro texture of the pavement surface. It is a measure of the condition of the pavement surface and often can be used to determine the need for maintenance.

To measure skid resistance, an index, referred to as a skid number, shall be used. As the skid number decreases, the surface friction decreases. Low skid numbers are an indicator of accident potential.

Skid resistance is measured with different methods. These methods vary according to measuring technique and they include the following:

 Locked wheel tester;  Mu-Meter;  Spin-up tester;  Laser or image processing; and  Portable devices, such as Keystone or California Skid testers.

Mu-Meters use a triangle frame with three un-braked wheels, a load cell, and a recorder to document the distance and the coefficient of friction, as friction is encountered on the pavement. Test wheel speeds range from 60 km to 160 km per hour. A water delivery system is available to distribute water in front of the two wheels. Laser testers measure only the macro texture and need

Page 180

11- EXISTING PAVEMENT EVALUATION FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL to be adjusted for the micro texture that influences the skid resistance. At the same time, the laser device is more expensive to operate compared to the locked wheel tester; however, the portable devices are relatively cheaper and are less accurate.

On highway pavements, skid measurements are usually made with the locked wheel tester, which is the most common method used. For this method, a trailer is towed, normally at 60 km per hour. Water is applied in front of the test wheels, and the test wheels are locked. The force required to drag a tire that is prevented from rolling over the wet pavement is measured after the test wheel has been sliding on the pavement for a certain distance. Skid numbers (SN = 100 x Friction Factor) are calculated for that part of the pavement. Skid numbers are the standard procedure for evaluating the coefficient of friction between a tire and pavement and its calculation depends on temperature. Figure 11-11 shows the locked wheel tester.

Figure 11-11: Locked wheel tester 11.3 Data analysis After the data collection, the second step in the evaluation is the data analysis. This section will focus on the distresses data collected from the condition survey, roughness data (IRI), and skid resistance data (SN). Structural capacity data are analysed by computer software, as explained earlier to estimate different layers modulus. Existing layer’s modulus, aided by asphalt cores to estimate the layer thickness, can be input in an empirical or M-E design process to design the overlay thickness required, as explained in Chapter 5.

For any distress survey, manual, or automated, the following data analysis procedure is applicable. Sections of the road corridor need to be identified for delineation for uniformity and for comparable attributes. The delineation can follow the method described as “Analysis Unit Delineation by Cumulative Differences,” 1993 AASHTO Guide, Appendix- J (4).

Pavement condition surveys shall be conducted considering the five major distress types covering surface deformation and surface distresses, which are primary responsible symptoms for pavement failures. Different distress types and their main cause are explained in Section 8.3 of these manual, which includes pictures to document the shape of the distress. Table 11-1 lists the five major distresses.

These distress types are indexed for severity level into six levels for better mapping of the problems at site covering from Failed (Level 5) to Excellent (Level 0) condition of the pavement. Pavement condition data shall be collected and the pavement thoroughly investigated for each unit

Page 181

11- EXISTING PAVEMENT EVALUATION FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL of 100 m long and full-lane width for distress types, according to condition rating as defined in Table 11.2

Note that the Severity Levels should be assessed for each 100m lane and then pegged at each kilometre. The most severe location is identified judiciously within 100m lane and is representative for the pavement distress types for the 100m stretch. The kilometre severity level is summed up for the determination of the homogeneous section Severity Level.

The intensity by distress type and severity levels should be calculated as per the criteria listed in Table 11-3. Data are recorded either by mapping, as shown in Figure 11-12, or in a tabular form, as given in Figure 11-13. Tabular forms are recommended for the pavement distress survey because they provide data that are more accurate; however, the mapping shall be easier to use with the windshield survey. Figure 11-14 shows an example of the delineation of a pavement road in both directions.

Considerations for roughness are made by using the IRI limits and severity, as given in

Table 11-4. Similarly, the skid resistance (skid number) severity levels are shown in Table 11-5. These limits shall be considered for all roads as a pavement distress indicator that will trigger maintenance of the pavement surface.

Once all the distresses and its severity levels are obtained, the data can be summarized by using an average called Aggregate Severity Level (ASL), which is calculated using the following equation.

∑ v y v

Equation 11-3: Average Aggregate Severity Level

The ASL can be modified to have a weighted average by giving more emphasis on some distresses over the other as seen applicable by the agency. Using the weighted average and the weights to be given to each distress will be project dependent and shall be approved by the agency before being used. 11.3.1 Delineation methodology This approach, used in the 1993 AASHTO Guide, is a cumulative difference approach that is a relatively straightforward and powerful method for delineating statistically homogenous units. Manual delineation can be done in this Project’s case, but the Engineer has selected to use an analytical method.

This methodology calculates the difference between the cumulative area under a uniform stretch and the overall average cumulative area for the same stretch. Differences between these two areas are called the cumulative difference variable Zx.

Zx is calculated for a discontinuous data of equal testing interval by the following equation:

n nt n x= ai ai ni i=1 i=1

Equation 11-4: Cumulative difference variable (Zx)

Page 182

11- EXISTING PAVEMENT EVALUATION FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

Where: ai = xi *(ASLi-1+ASLi)/2 = average ASLi * xi

xi = interval between measurement (1 km) n = number of i measurement

nt = total number of measurements

Accordingly, the value of Zx can be a positive or a negative value, depending on the difference of the two areas. 11.3.2 Analysis report After finishing the data analysis, a report shall be prepared that includes location, collected distress data, the severity level of each distress, the ASL, NDT test and IRI results, skid resistance test results, and any other relevant data. This report shall include pictures of the surveyed areas and the output results from any analysis software used in the analysis.

Based on the summarized data, the pavement designer shall refer to Chapter 5 to select the appropriate rehabilitation or Chapter 8 for maintenance techniques.

Table 11-1: Pavement distress types

Distress Type S. No. (Functional Response Characteristics Parameters) Deformation 1. Rutting Distress 2. Cracking 3. Ravelling Surface Distress 4. Potholing 5. Edge Break

Figure 11-12: Graphical manual pavement condition survey data collection

Page 183

11- EXISTING PAVEMENT EVALUATION FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

Pavement Evaluation: Manual Pavement Condition Survey Chainage (km) Major Defects Type Remarks: Overall Visual Condition Rating/ Sub Cracking Cracking Cracking Ravelling Edge Break Any Other Rut Depth (mm) Potholes (No.) Location/ Refrenence km Section <3mm (%Area) >3mm (%Area) Type/ Pattern (% Area) (% Length) Information Foto etc.

0.000 0.200

0.200 0.400

… 0.400 0.600

0.600 0.800

0.800 1.000

0.000 0.200

0.200 0.400

… 0.400 0.600

0.600 0.800

0.800 1.000

0.000 0.200

0.200 0.400

… 0.400 0.600

0.600 0.800 0.800 1.000

Figure 11-13: Tabular manual pavement condition survey data collection

Figure 11-14: Example delineation of a roadway

Page 184

11- EXISTING PAVEMENT EVALUATION FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

Table 11-2: Pavement condition rating for different severity levels and threshold levels

Pavement Threshold Level for Repair and Severity Level Condition Rating Maintenance Action Severity Level 5 Failed Severity Level 4 Poor Repair and Maintenance Intervention Level Severity Level 3 Fair

Severity Level 2 Good Minimum Threshold Level

Severity Level 1 Very Good Desirable Threshold Level Severity Level 0 Excellent Table 11-3: Assigned severity levels for pavement condition rating criteria levels

Pavement Distress Type Assigned Severity Level and Sr. No. (Functional Response Pavement Condition Rating Criteria Parameter) 0 – Rut depth < 10mm 1 – Rut depth < 20mm 2 – Rut depth < 30mm 1 Rutting 3 – Rut depth < 40mm 4 – Rut depth < 50mm 5 – Rut depth > 50mm 0 – Cracking Area< 2% 1 – Cracking Area < 5% 2 – Cracking Area < 20% 2 Cracking 3 – Cracking Area < 40% 4 – Cracking Area < 60% 5 – Cracking Area > 60% 0 – Ravelling Area = 0% 1 – Ravelling Area < 1% 2 – Ravelling Area < 2% 3 Ravelling 3 – Ravelling Area < 5% 4 – Ravelling Area < 10% 5 – Ravelling Area > 10% 0 – No. of potholes = 0 1 – No. of potholes = 1 2 – No. of potholes < 5 4 Potholing 3 – No. of potholes < 8 4 – No. of potholes < 10 5 – No. of potholes > 10 0 – % Length = 0 1 – % Length < 0.5 2 – % Length < 1.0 5 Edge Break 3 – % Length < 2.0 4 – % Length < 5.0 5 – % Length > 5.0

Page 185

11- EXISTING PAVEMENT EVALUATION FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

Table 11-4: IRI maximum limits and severity

IRI Maximum limit Severity Comment (m/km)

0.9 – 1.0 0 (Excellent) New Construction Freeway

New Construction Non- 1.1 – 1.3 0 (Excellent) Freeway

1.7 1 (Very Good) Required Level

1.7 – 2.7 2 (Good) Acceptable Roughness

2.7 – 3.0 4 (Poor) Maintenance Required

>3.0 5 (Failed) Maintenance Required

Table 11-5: Skid resistance criteria

Skid Number Severity Level

< 30 5 (Failed)

31 – 34 3 (Fair)

≥ 35 2 (Good) – Heavily travelled roads

≥ 30 2 (Good) – LVRs

Page 186

11- EXISTING PAVEMENT EVALUATION FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

CITED REFERENCES

1. Abu Dhabi Department of Transport. Standard Specifications Volume 1 for Road Works Manual. Abu Dhabi, UAE: Abu Dhabi Department of Transport, 2013, Manual No AD-C-01.

2. Abu Dhabi Department of Transport. Project Cost Estimating Manual. Abu Dhabi, UAE: Abu Dhabi Department of Transport, 2013, Manual No AD-C-03.

3. Abu Dhabi Department of Transport. Bill of Quantities Manual for Road Projects. Abu Dhabi, UAE: Abu Dhabi Department of Transport, 2013, Manual No AD-C-02.

4. American Association of State Highway and Transportation. AASHTO Guide for Design of Pavement Structures. Washington, D.C., USA: American Association of State Highway and Transportation Officials, 1993. 1-56051-055-2.

5. Municipality, Abu Dhabi. Roadway Design Manual. Abu Dhabi UAE : Abu Dhabi Municipality, 2000.

6. Austroads. Guide to Pavement Technology, Part 2: Pavement Structural Design. Sydney, Australia: Austroads Incorporated, 2008. 978-1-921329-51-7.

7. United Arab Emirates, Ministry of Presidential Affairs. National Center of Meteorology and Seismology. [Online] [Cited: June 1, 2011.] www.ncms.ae/english/.

8. Ltd, Shell International Petroleum Co. Pavement Design Manual: Asphalt pavement and overlays for road traffic. London: s.n., 1978.

9. Federal Highway Administration (FHWA). Guide to LTPP Traffic Data Collection and Processing. Mclean, Virginia, USA : Federal Highway Administration, 2001.

10. Abu Dhabi Department of Transport. Road Structures Design Manual. Abu Dhabi : Department of Transport, 2013 Manual No. AD-D-06.

11. Institute, Asphalt. Asphalt Pavements for highways & Streets Manual Series 1 (MS-1). Lexington, KY USA : Asphalt Institute, 2008. 978-1-934154-01-4.

12. ASTM. Standard Test Method for CBR (California Bearing Ratio) of Laboratory-Compacted Soils. (D1883-07e2).

13. ASTM. Standard Test Method for CBR (California Bearing Ratio) of Soils in Place (D4429).

14. American Association of State Highway and Transportation. AASHTO Standard Method of Test for The California Bearing Ratio (AASHTO T-193).

15. ASTM. Standard Test Method for Compressive Strength of Molded Soil-Cement Cylinders. (ASTM D-1633)

16. American Association of State Highway and Transportation. AASHTO Standard Method of Test for Resistance to Plastic Flow of Bituminous Mixtures Using Marshall Apparatus. (AASHTO T- 245)

17. ASTM. Test Method for Resistance of Plastic Flow of Bituminous Mixtures Using Marshall Apparatus. (ASTM D 1559)

Page 187

REFERENCES - INDEX FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

18. American Association of State Highway and Transportation. AASHTO Recommended Practice for Geosynthetic Reinforcement of the Aggregate Base Course of Flexible Pavement Structures. (AASHTO R 50-09)

19. Payne and Dolan Incorporated. Warm Mix Asphalt – a Contractor’s Perspective, a presentation to an AASHTO subcommittee.

20. USA Portland Cement Association. Thickness Design for Concrete Highway and Street Pavements, 1984. (EB109P)

21. Abu Dhabi Department of Transport. Road Drainage Manual. Abu Dhabi, UAE: Department of Transport, 2013. Manual No. AD-D-07.

22. Abu Dhabi Department of Transport. Road Landscaping Manual. Abu Dhabi, UAE: Department of Transport, 2013. Manual No. AD-D-08.

23. Nebraska Department of Roads. Pavement Maintenance Manual. Nebraska Department of Roads. http://www.transportation.nebraska.gov/.

24. Kathryn A. Zimmerman, P.E., and David G. Peshkin, P.E. Supporting Preventive Maintenance Programs with Pavement Management, 6th International Conference on Managing Pavements (2004)

25. Washington State Department of Transportation. Pavement Evaluation – Flexible Pavement Distress Manual. http://training.ce.washington.edu/wsdot/.

26. FHWA: Miller and Bellinger. Distress Identification Manual for the Long-term Pavement Performance Program (Fourth Edition). Federal Highway Administration, 2003. http://www.fhwa.dot.gov/publications/research/infrastructure/pavements/ltpp/reports/03031/

27. American Concrete Pavement Association (ACPA), (1995). Construction of Portland Cement Concrete Pavements. National Highway Institute Course No. 13133. AASHTO/FHWA/Industry joint training. Federal Highway Administration, Department of Transportation. Washington, D.C.

28. Federal Highway Administration (FHWA). Life-cycle Cost Analysis resource page. [Online] http://www.fhwa.dot.gov/infrastructure/asstmgmt/lcca.cfm.

29. National Cooperative Highway Research Program (NCHRP). Pavement Management Methodologies to Select Projects and Recommended Preservation Treatments. Washington D.C.: Transportation Research Board, National Research Council, 1995. Synthesis 222.

30. World Bank. Highway Design and Maintenance Standards Model (HDM-4). [Online] [Cited: 2001] http://www.worldbank.org/transport/roads/rd_tools/hdm4.htm.

31. American Association of State Highway and Transportation. Supplement to the AASHTO Guide for Design of Pavement Structures, Part II-Rigid Pavement Design and Rigid Pavement Joint Design. Washington, D.C., USA: American Association of State Highway and Transportation Officials, 1998.

32. Austroads. Guide to Pavement Technology, Part 5: Pavement Evaluation and Treatment Design. Sydney, Australia: Austroads Incorporated, 2009. 978-1-921551-22-2.

Page 188

REFERENCES - INDEX FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

OTHER REFERENCES

1. Department of Municipal Affairs and Transport. Consultant Management Manual. Abu Dhabi, UAE: Department of Transport, 2013. Manual No. DOT-M-03.

2. Federal Highway Administration (FHWA). Life-cycle Cost Analysis Primer, 2002, available online through the FHWA’s life-cycle cost analysis resource page at http://www.fhwa.dot.gov/infrastructure/asstmgmt/lcca.cfm.

3. Department of Municipal Affairs and Transport . Geotechnical Investigation and Design Manual: Part-2. Abu Dhabi, UAE: Department of Municipal Affairs and Transport, 2016.

Page 189

REFERENCES - INDEX FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

INDEX

A Delineation, 183, 184, 186

AASHTO, xi, xii, xiv, xvi, 2, 6, 8, 18, 23, 25, Department of Transport, i, 1, 189, 190, 26, 30, 34, 35, 39, 40, 42, 44, 45, 46, 47, 191 48, 56, 57, 58, 59, 60, 64, 65, 71, 72, 78, 79, 83, 91, 92, 94, 95, 96, 98, 99, 101, 104, Distress, xiii, xiv, 3, 5, 50, 55, 56, 67, 70, 83, 105, 106, 166, 183, 184, 189, 190, 195, 84, 89, 91, 92, 93, 94, 96, 102, 103, 121, 210, 212 127, 130, 131, 132, 134, 135, 145, 148, 171, 172, 173, 174, 176, 180, 183, 184, Aggregate, xi, xii, xiv, 5, 28, 30, 33, 34, 36, 185 39, 40, 49, 64, 71, 72, 78, 79, 80, 103, 104, 106, 108, 109, 110, 113, 114, 115, 116, E 122, 123, 126, 128, 129, 130, 132, 139, Empirical, xii, xiii, 1, 5, 6, 8, 10, 14, 22, 24, 140, 141, 142, 144, 145, 148, 167, 168, 25, 30, 34, 39, 44, 45, 72, 73, 78, 80, 81, 169, 175 83, 96, 104, 183

Analysis Period, xi, 160 ESAL, xii, xvi, 6, 18, 20, 46, 66, 72, 73, 79, Asphalt 81, 90, 91, 94, 102, 105, 106

base, xi F

concrete, xi, xii, xvi, 33, 48, 78, 80, 103 Fatigue Cracking, xi, xiii, 4, 33, 43, 50, 54, 55, 67, 80, 81, 95, 96, 122, 123, 126, 127, Asphalt treated base, xi, xv, xvi, 30 128, 136

Austroads, xvi, 2, 6, 7, 10, 11, 15, 22, 25, Fog Seal, xii, 119, 124, 129, 139, 144, 153 28, 29, 30, 32, 33, 34, 35, 39, 40, 44, 50, 52, 55, 65, 83, 95, 96, 99, 189, 190 H

Axle, xii, xv, xvii, xviii, 6, 7, 8, 14, 15, 18, 19, Hot Mix Asphalt, xi, xvi, 8, 33, 34, 41, 42, 20, 21, 45, 46, 52, 54, 55, 56, 59, 66, 67, 122, 123, 124, 125, 126, 127, 128, 129, 68, 70, 73, 75, 76, 77, 81, 95, 96, 97, 99, 130, 131, 132, 144, 146, 148, 150, 153, 101, 104, 125, 159, 168, 181 155, 159, 179, 180

B J

Backcalculation, xi, 90, 92 Joint, xii, xiii, xv, 58, 59, 63, 64, 65, 85, 86, 126, 127, 146, 148, 149, 190 C K Cement treated base, xi, xv, xvi, 30, 78, 79 k-value, xiii, xvii, 58, 59, 86, 90, 195 Climatic, xi, 83 L Condition Survey, xiii, 94, 95, 166, 171, 173, 176, 183, 185, 186 Life Cycle Cost, xii, xvii, 1, 2, 3, 4, 44, 45, 79, 118, 146, 150, 151, 152, 153, 154, 155, D 156, 157, 158, 159, 161, 162, 163, 164, 165 Damage, xii, 8, 9, 10, 14, 15, 18, 19, 52, 59, 67, 84, 93, 97, 104, 107, 118, 129, 132, Low Volume Roads, xiii, xvii, 1, 2, 3, 101, 138, 139, 148, 172, 176 102, 103, 105, 106

Page 190

REFERENCES - INDEX FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

M Resilient Modulus, xiv, 8, 9, 23, 24, 25, 28, 34, 35, 45, 46, 78, 80, 86, 89, 90, 91, 92 Maintenance, xii, xiii, 1, 2, 3, 4, 6, 14, 41, 45, 71, 79, 83, 89, 93, 96, 97, 101, 103, 104, Roughness, xiii, xvi, 87, 88, 97, 122, 124, 106, 116, 118, 119, 120, 134, 135, 136, 126, 127, 129, 131, 132, 133, 134, 147, 137, 138, 139, 146, 147, 150, 152, 153, 176, 180, 182, 183, 184 154, 160, 166, 167, 168, 169, 170, 171, 180, 182, 184, 185 Rutting, xiv, 33, 40, 43, 54, 83, 85, 87, 88, 92, 93, 103, 119, 130, 131, 135, 142, 143, Material, xi, xii, xiii, xiv, xv, 1, 2, 3, 6, 7, 8, 22, 146, 158, 159, 171, 175, 176 23, 25, 28, 29, 30, 32, 34, 39, 41, 44, 45, 48, 50, 53, 54, 58, 64, 66, 71, 78, 80, 81, S 85, 87, 88, 89, 92, 93, 94, 95, 102, 103, Serviceability, xi, xii, xiv, xv, xvii, 18, 45, 46, 104, 106, 108, 109, 111, 113, 123, 127, 56, 57, 59, 78, 91, 95, 105, 106, 119, 136, 139, 144, 145, 148, 149, 166, 171, 179 147 Mechanistic-Empirical, xiii, xvii, 1, 6, 7, 8, Slurry seal, vii, xiv, 136, 137, 140, 141, 153, 10, 14, 20, 21, 22, 24, 28, 30, 32, 34, 35, 160 44, 50, 52, 54, 56, 65, 66, 80, 81, 82, 83, 95, 96, 183 SN, xii, xv, xvii, 45, 46, 48, 71, 72, 79, 88, 94, 105, 183 N Strength, xi, xiv, xviii, 8, 10, 30, 32, 33, 39, Nomograph, xiii, 5, 6, 37, 38 40, 45, 48, 56, 65, 66, 68, 71, 72, 78, 85, Non-destructive test, xvii, 88, 89, 91, 94, 88, 90, 100, 102, 103, 119, 123, 131, 136, 174, 176, 177, 179, 185 148

P Structural Capacity, xiii, xiv, 1, 2, 45, 48, 71, 88, 89, 91, 94, 98, 106, 118, 136, 171, 174 Pavement Management Systems, xiii, xvii, 3, 97, 120, 166, 167, 168, 171 Structural Design, xiv, 2, 6, 22, 35, 59, 72, 123, 146, 171 Pavement performance, xi, xiii, xvii, 7, 40, 56, 58, 72, 118, 133, 152 Subbase, xiii, xv, 3, 4, 8, 24, 25, 26, 27, 28, 44, 48, 64, 65, 66, 67, 71, 72, 77, 79, 85, PCC, xi, xvii, 4, 24, 39, 84, 85, 86, 88, 89, 96, 88, 90, 99, 100, 102, 103, 104, 116, 153 98, 99, 121, 147, 148, 149 Subgrade, xi, xii, xiii, xiv, xv, xvii, 3, 4, 7, 8, Permanent Deformation, xi, xiii, 4, 33, 50, 9, 10, 23, 24, 25, 44, 45, 48, 50, 52, 53, 54, 54, 55, 58, 80, 81, 95, 96, 176 56, 58, 59, 64, 65, 66, 71, 72, 77, 78, 79, 80, 84, 86, 90, 91, 92, 93, 94, 95, 96, 97, Present Serviceability Index, xiv, xvii, 45, 99, 100, 102, 103, 105, 106, 108, 110, 111, 46, 59, 91, 95, 180 113, 122, 123, 125, 126, 127, 130, 132, R 133, 146, 149, 175, 176, 179, 195, 196, 197, 198, 199, 200, 201, 202, 203, 204, Rehabilitation, xiii, xv, 1, 2, 3, 14, 25, 83, 85, 205, 206, 207, 208, 209 93, 96, 97, 98, 99, 100, 101, 103, 115, 116, Subsurface, xii, 64, 83, 93, 107, 109, 110, 117, 118, 119, 133, 134, 135, 136, 137, 111, 113, 114, 115, 116, 117, 123, 132, 138, 143, 150, 151, 152, 153, 154, 156, 159, 160, 166, 167, 169, 170, 171, 185 180

Reliability, xiv, 45, 50, 55, 56, 59, 67, 78, 84, 86, 91, 95, 102, 105

Page 191

REFERENCES - INDEX FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

T 84, 85, 86, 87, 90, 91, 94, 95, 96, 97, 98, 99, 101, 102, 103, 104, 105, 106, 107, 108, Temperature, xi, xvii, xviii, 4, 5, 6, 8, 10, 11, 118, 119, 120, 122, 124, 125, 128, 130, 12, 35, 41, 55, 59, 65, 80, 93, 94, 96, 124, 131, 135, 138, 139, 141, 142, 143, 144, 125, 130, 146, 159, 178, 183 146, 152, 153, 154, 156, 157, 158, 160, Traffic, xi, xii, xiii, xiv, xv, xvi, 1, 2, 3, 4, 5, 6, 161, 166, 167, 169, 173, 174, 182, 189 7, 8, 12, 14, 17, 18, 19, 20, 21, 22, 35, 42, W 44, 45, 49, 50, 52, 54, 55, 56, 58, 59, 60, 65, 66, 67, 70, 71, 72, 73, 78, 80, 81, 83, Wearing Course, 5, 33, 40, 49

Page 192

REFERENCES - INDEX FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

APPENDIX A: DEVELOPING EFFECTIVE MODULUS OF SUBGRADE REACTION (K-VALUE)

This appendix provides an excerpt from the 1998 American Association of State Highway and Transportation Officials (AASHTO) Supplement to the AASHTO Guide for Design of Pavement Structures, Part II-Rigid Pavement Design and Rigid Pavement Joint Design (32). It provides details about developing a k-value as a necessary input for the AASHTO design method and equation.

Figure A-1: Developing effective modulus of subgrade reaction (part 1)

Page 193

APPENDIX-A FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

Figure A-2: Developing effective modulus of subgrade reaction (part 2)

Page 194

APPENDIX-A FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

Figure A-3: Developing effective modulus of subgrade reaction (part 3)

Page 195

APPENDIX-A FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

Figure A-4: Developing effective modulus of subgrade reaction (part 4) Page 196

APPENDIX-A FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

Figure A-5: Developing effective modulus of subgrade reaction (part 5)

Page 197

APPENDIX-A FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

Figure A-6: Developing effective modulus of subgrade reaction (part 6)

Page 198

APPENDIX-A FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

Figure A-7: Developing effective modulus of subgrade reaction (part 7)

Page 199

APPENDIX-A FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

Figure A-8: Developing effective modulus of subgrade reaction (part 8)

Page 200

APPENDIX-A FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

Figure A-9: Developing effective modulus of subgrade reaction (part 9)

Page 201

APPENDIX-A FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

Figure A-10: Developing effective modulus of subgrade reaction (part 10)

Page 202

APPENDIX-A FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

Figure A-11: Developing effective modulus of subgrade reaction (part 11)

Page 203

APPENDIX-A FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

Figure A-12: Developing effective modulus of subgrade reaction (part 12)

Page 204

APPENDIX-A FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

Figure A-13: Developing effective modulus of subgrade reaction (part 13)

Page 205

APPENDIX-A FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

Figure A-14: Developing effective modulus of subgrade reaction (part 14)

Page 206

APPENDIX-A FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

Figure A-15: Developing effective modulus of subgrade reaction (part 15)

Page 207

APPENDIX-A FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

APPENDIX B: AASHTO 1993 DESIGN CHART

This appendix provides an excerpt from the 1993 American Association of State Highway and Transportation Officials (AASHTO) Guide for Design of Pavement Structures. It includes the AASHTO design chart for rigid pavement.

Figure B-1: Design chart for rigid pavement (part 1)

Page 208

APPENDIX-B FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

Figure B-2: Design chart for rigid pavement (part 2)

Page 209

APPENDIX-B FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

APPENDIX C: AASHTO SUPPLEMENTAL DESIGN TABLES

This appendix provides an excerpt from the 1993 American Association of State Highway and Transportation Officials (AASHTO) Guide for Design of Pavement Structures. It provides supplemental design tables.

Page 210

APPENDIX-C FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

Figure C-1: Supplemental design tables (part 1)

Figure C-2: Supplemental design tables (part 2)

Page 211

APPENDIX-C FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

Figure C-3: Supplemental design tables (part 3)

Page 212

APPENDIX-C FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

Figure C-4: Supplemental design tables (part 4)

Page 213

APPENDIX-C FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

Figure C-5: Supplemental design tables (part 5)

Page 214

APPENDIX-C FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

Figure C-6: Supplemental design tables (part 6)

Page 215

APPENDIX-C FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

Figure C-7: Supplemental design tables (part 7)

Page 216

APPENDIX-C FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

Figure C-8: Supplemental design tables (part 8)

Page 217

APPENDIX-C FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

Figure C-9: Supplemental design tables (part 9)

Page 218

APPENDIX-C FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

Figure C-10: Supplemental design tables (part 10)

Page 219

APPENDIX-C FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

Figure C-11: Supplemental design tables (part 11)

Page 220

APPENDIX-C FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

Figure C-12: Supplemental design tables (part 12)

Page 221

APPENDIX-C FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

Figure C-13: Supplemental design tables (part 13)

Page 222

APPENDIX-C FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

Figure C-14: Supplemental design tables (part 14)

Page 223

APPENDIX-C FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

Figure C-15: Supplemental design tables (part 15)

Page 224

APPENDIX-C FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

Figure C-16: Supplemental design tables (part 16)

Page 225

APPENDIX-C FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

Figure C-17: Supplemental design tables (part 17)

Page 226

APPENDIX-C FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

Figure C-18: Supplemental design tables (part 18)

Page 227

APPENDIX-C FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

ANNEX 1

General Requirements for the Pavement Design

The following requirements should be fulfilled for road pavement design for Abu Dhabi Emirate projects;

4. General Design Considerations

A. The designed pavement layer thickness should be based on full design calculations (as specified in this manual) and not referring to tables to estimate minimum Asphalt layer requirement for the project. The values of minimum required asphalt layer thickness for different road class addressed in this manual, should be used as a final check after conducting full design calculation as per this manual.

B. As per this manual, Empirical Pavement Design procedure shall be conducted, and design check to be applier using the Mechanistic – Empirical Design Method,

C. In case that an existing pavement to be considered in pavement design, full pavement condition evaluation study is required (as per this manual) to assess the current pavement condition and recommend the required action(s) to be taken to ensure proper utilization of the existing asphalt pavement along the project life,

D. Several pavement design options should be studied and value engineering optimized (Technically, Financially and Environmentally) based on sustainability criteria to achieve the following; . Longer Pavement Service Life, . Less overall Life-Cycle Cost, . Faster and more economical Constructability. . Faster and more sustainable Maintenance Activities, . Saving in raw material, water and energy consumption, . Have Less Carbon Emissions and Less Impact on Natural Environment, . Studying the Utilization of non-traditional solutions (such as Pavement Recycling, Asphalt Mix Additives, Recycled Materials, Design Using Geosynthetics ….) to achieve more sustainable pavement design on project basis

5. Required Basic Related Studies,

A. To review and issue No Objection on pavement design for any project in Abu Dhabi Emirate, an Geotechnical Study (approved by the relevant governmental Engineer / Authority) is a major requirement. The relevant Geotechnical information should be submitted to the Abu Dhabi Emirate relevant authority, then reviewed and an official No Objection should be issued accordingly, attached with conditions (if any), then the accepted geotechnical report, attached with the geotechnical No Objection conditions to be submitted to Road Pavement Design Reviewer for consideration. In some cases (if any) that no need for geotechnical study, or some previous geotechnical information are used in the pavement design, this should be accepted by the relevant governmental geotechnical specialist.

B. Traffic Study of the project area including ; The existing and expected ADT (Average Daily Traffic) or PHV (Peak Hour Volume) and the traffic classification(Composition) of Page 228

ANNEX-1 FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

different traffic vehicles that expected to utilize the project area along the pavement life and Traffic Growth Factor along the road design life (In addition to all other requirements of the project traffic Study as required by Abu Dhabi Emirate relevant Traffic Specialist / Authority). In case of Non – Available Traffic Study, Traffic Estimates should be accepted by the Abu Dhabi Government relevant specialist / Authority.

C. Any other study (or information) that may be required as an input data for Pavement Design Analysis, should be submitted, Reviewed and Accepted by the Governmental relevant Specialist / Authority.

6. Pavement Design Report Contents

The pavement design report (or section in an overall design report) should fulfill (but Not limited to) the minimum standard required contents as follows;

1 Introduction, - Project Information (Location, Area, scope, objective, etc) - Land Use of Project area and adjacent areas, - Road Hierarchy of roads included in project scope,

2 Reference Standards of Pavement Design,

3 Selected values of Reliability (R), Standard Deviation (S0), and Standard normal Deviation (ZR) according to road hierarchy.

4 Design Geotechnical Data,

The following geotechnical data are considered as minimum requirement for pavement design purpose. Further testing and Geo-Physical / Geotechnical requirements that may be required by Abu Dhabi Emirate Geotechnical Specialist to fulfill the Geo-Physical / Geotechnical scope should be fulfilled by the consultant.

- Summary of Approved Project Geotechnical Report Results, - Soil Classification and Selected value of Soil CBR, - Highest Ground Water table, and related recommendations of Geotechnical study, - Soil Resilient Modulus (MR) value, and method of MR calculation, (as per this Manual) - Geotechnical study recommendations that should be adopted in Pavement design (if any),

5 Pavement Layers Material Properties, (As Per this Manual and Abu Dhabi Emirates relevant Standard Specifications). - Mr value of Supporting Soil, - Mr value of Pavement layers, - Layer coefficient (a) for different pavement layers, - Drainage factor of granular base course and sub-base layer.

6 Design Traffic Data, (As Per this Manual and as agreed with the relevant authority design reviewer); - Summary of Approved Traffic Study results, - Selected peak hour traffic volume, - Calculated Average Daily Traffic ADT, Page 229

ANNEX-1 FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

- Traffic Classification percentage of different traffic vehicle types utilizing the project area, - Traffic growth factor along pavement design life, - Truck factor for different types of traffic vehicles, - Selected Traffic Parameters, Directional Distribution factor (Dd), and Lane Distribution factor (Ld),..etc. - Calculation of Predicted number of ESALs equivalent single axle load W18,

7 Pavement Design Calculations, - Calculation of SN for each pavement layer, - Calculation of Pavement layers thickness design options, - Layered – Analysis Check for Each Pavement Layer, - Minimum Asphalt Thickness Check, - Design Calculation Check, using Mechanistic – Empirical Design Method (as per this Manual), - Comparison between different pavement design options (Technically, Financially and Environmentally), - Selected Pavement layers thickness for different design options in the project, showing the bases of selection,

8 Recommendations, - Recommended Pavement Section(s), Considering Standard Drawings and Specifications,

9 After Getting No – Objection on Final Pavement Design for the Project, the consultant is requested to submit the project pavement design data in GIS format. The GIS format to be discussed and agreed with the Abu Dhabi Government related Pavement Design Reviewer and GIS Specialist.

10 Appendices, - Appendix (A), i. Project Location Map & Satellite Image, ii. Land Use Plan (for Different land use inside the project), iii. Road Hierarchy Plan,

- Appendix (B), Pavement Design Drawings, i. Plan showing different pavement types, ii. Pavement structure details for all types of pavement, iii. Construction details, including Tie – Inn, widening, connection details for different types of pavements, and connections between old & new pavements,

- Appendix (C), Traffic Study Data, i. Official Traffic No Objection, and its conditions (if any), ii. Summary of Traffic Volumes, selected for Pavement Design Calculations.

- Appendix (D), Geotechnical Study Data, i. Official Geotechnical No Objection, and its conditions (if any), ii. Plan of boreholes and test pits locations, iii. Soil profile including proposed design level, ground water level and soil layers along project roads,

Page 230

ANNEX-1 FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

iv. Test results of boreholes and test pits, v. Recommendations regarding ground water or road pavement structure.

- Appendix (E), Pavement Design Calculations, i. Detailed calculations of different designed pavement sections, ii. Layered Analysis Check (as per AASHTO-1993, iii. Pavement Design Check, using Mechanistic – Empirical Pavement Design Method (as per this Manual).

7. Quality Assurance of Pavement Design

The following checklist should be followed by the consultant during pavement design of road projects as a part of pavement design quality assurance process, and to be included in the pavement design report submitted to the relevant Abu Dhabi Government Authority – Pavement Design reviewer, for review and acceptance.

Pavement Design Checklist:

No. Item Yes No N Remarks A 1 Existence of Project Basic Information  Project Information (Location, Area,.. )  Land Use of Project area and adjacent areas,  Road Hierarchy, 2 Clear Reference Standards of Pavement Design 3 Basic Input Design Data for each road class  Selected values of Reliability (R),  Standard Deviation (S0),  Standard normal Deviation (ZR) 4 Input Design Traffic Data,  Traffic Study (or Estimate) is Accepted by the relevant Authority/ Engineer?  Summary of Traffic Study results,  Selected peak hour volume(s),  Traffic Classification Percentages,  Calculated Average Daily Traffic ADT,  Traffic growth factor along pavement design life,  Truck factor for different types of traffic vehicles,  Selected Traffic Parameters, Dd, Ld, etc.  Calculation of W18,  Construction Traffic Volume is considered 5 Input Design Geotechnical Data,  Geotechnical Study is No Objected by relevant Authority / Engineer,  Project Geotechnical Report Results,  Selected value of Soil CBR,  Highest Water table condition, and concerned recommendations of Geotechnical study,

Page 231

ANNEX-1 FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

 Soil MR value, and method of MR calculation,  Geotechnical recommendations to be adopted in Pavement design, soil replacement, or road construction.

6 Input Pavement Layers Material Coefficients,  Layer coefficient (a) for different pavement layers,  Drainage factor of granular base course and sub- base layer. 7 Pavement Design Calculations,  Is Pavement Type Selection is justified?  Calculation of required SN for each pavement layer ,  Asphalt Layer(s) Thickness has been minimized,  Layered Analysis Check (AASHTO-1993) Is Done,  Design Check with Mechanistic Empirical Method is Done,  Several Design Options have been studied,  Comparison between design options is conducted,  Pavement Design is Value-Engineering Optimized,  Pavement Maintenance Type and Cost are considered,  Consistency of Pavement Design with Adjacent area,  Longer Design Life or Less Pavement Thickness,  Life Cycle Cost is Calculated and Cost saving is considered,  Constructability of selected design is considered,  Saving in Raw Material, water and energy consumption,  Studying the Utilization of Un-Traditional – Sustainable solutions as (Pavement Recycling, Asphalt Mix Additives, Recycled Materials, Geo- synthetics ….) to achieve more sustainable pavement design on project bases, 8 Attached Drawings & Related Reports ; i. General;  Project Location Map and Satellite Image,  Land Use Plan (for Different land use inside the project),  Road Hierarchy Plan, ii. Pavement Design Drawings,  Plan of different pavement types,  Pavement structure details for all types, including details of soft soil and high water table Page 232

ANNEX-1 FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

conditions,  Construction details, including Tie–Inn details for different types of pavements, iii. Geotechnical Study Data,  Plan of boreholes and test pits locations,  Soil profile including proposed design level, ground water level and soil layers along project roads,  Test results of boreholes and test pits,  Recommendations regarding ground water or road pavement structure.  Detailed calculations of Pavement Design options,

Page 233

ANNEX-1 FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

ANNEX 2

A sample EALF calculation sheet for typical public bus

CALCULATION SHEET No: 1 Rev: 0

Project: WORKED EXAMPLE By:

Check Subject: Load Equivalency Factor Public Bus By: References/Results Design Vehicle - Public Bus

LEF of the vehicle = 2.82

Assumed as typical Public bus GVW = 17,245 kg Man low floor city bus = 38,019 lbs

Estimated 7.25 10.00 Axle w eight (tonnes) 15,972 22,046 Axle w eight (lbs) 15.97 22.05 Axle w eight (Kips) 42% 58% Weight distribution (%) ESAL/veh = 0.62 2.20 2.82 ESAL/veh LEF equation (tab LEF Calcs)

Rev 0 Calculation Sheet (Excel)

Page 234

ANNEX-2 FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

ANNEX 3

ACCEPTANCE CRITERIA FOR MECHANICALLY STABILIZED FLEXIBLE PAVEMENTS USING GEOGRIDS

1. General

1.1 INTRODUCTION

Implementation of sustainability concepts is a major objective for roads and infrastructure projects under the jurisdiction of Abu Dhabi Government. It is more than just employing the right designs and construction techniques. Project function, performance, life cycle cost, quality, safety, technological advancement, optimized energy and raw material consumption as well as minimized impacts on the natural environment and public health are all major considerations of aimed sustainable projects.

The major objective of the application of Geogrids in mechanical stabilization of granular pavement layers is to add structural value to the overall pavement structure, reduce life cycle cost, raw material and energy consumption during construction and minimize carbon emissions, in order to safeguard the environment and public health.

The primary mechanism of the Geogrid contribution in a full depth pavement structure can be summarized as lateral confinement of aggregate particles, increasing the modulus of the aggregate layer, which in turn increases the load-carrying capacity and improves pavement structural performance.

Abu Dhabi experience from actual projects has shown that the use of Geogrid in sustainable pavement design has provided:

 Longer service life and/or reduced required pavement thickness for the same pavement design life.  Reduction of pavement construction costs and life cycle cost.  Reduction in construction time for pavement works.  Reduced risk related to construction quality of pavements.  Savings in raw materials and energy during construction.  Reduced carbon emissions during construction.

However, the application of these benefits is not simply based on the product characteristics of the Geogrid product alone. The effect of the Geogrid on the individual pavement layer in which it is included (i.e. granular base or sub-base material), must be correctly identified and quantified for inclusion in pavement calculations. Combining a stabilization Geogrid with a granular material results in a composite layer known as a “mechanically stabilized layer”, which will have improved performance properties. It has become clear that these performance properties can be quantified from laboratory testing but must be verified by full scale trafficking trials carried out by an internationally recognized testing facility.

The following provides information for pavement designers who wish to use Geogrid products within Abu Dhabi Emirate road pavement projects, as well as guidance on the criteria Abu Dhabi Government relevant authority will use to determine suitability of the Geogrid products selected. Page 235

ANNEX-3 FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

1.2 DEFINITIONS AND TERMINOLOGY

Geogrid – An open grid-like mesh formed of polymer materials with stiff integral junctions or ribs and apertures, sufficiently large to allow strikethrough of soil particles, used to reinforce or stabilize soils.

Interlock - The mechanism by which the stabilization Geogrid and the aggregate interact under applied load. During the placement and compaction of a granular layer over a Geogrid, the aggregate particles partially penetrate into the apertures and abut against the ribs of the Geogrid.

Confinement - The effect of the mechanism of interlock by which the structure of the stabilization geogrid restrains the aggregate particles.

Stabilization - Stabilization is defined as the beneficial consequence on the serviceability of an unbound granular layer via the inhibition of the movement of the particles of that layer under applied load. This is the result of the mechanical effect of confinement on an aggregate layer, resulting from the mechanism of interlock provided by a stiff Geogrid structure.

Stabilization Geogrid - A Geogrid where the specific function of stabilization has been identified and associated with a product line by an independent approvals authority as being distinct from the reinforcement function. The stabilization Geogrid will be defined by specific stabilization-based product characteristics.

Geogrid Product Line - The class of manufactured products that vary by no more than one product parameter (e.g. sheet thickness in the case of punched and drawn Geogrids or number of filaments in the case of woven or knitted Geogrids). All other parameters remain the same with respect to the manner in which the elements associated with the final product are assembled into a stable geometry.

Mechanically Stabilized Layer (MSL) - A composite layer comprising stabilization Geogrids and a defined thickness of granular fill (base or sub-base) having greater serviceability and increased modulus when compared to the equivalent thickness of non-stabilized granular fill. When incorporated into a pavement structure, the MSL provides structural benefits to the whole pavement to allow increased pavement life or reduced pavement thickness.

Modulus Enhancement - The increase in modulus of a MSL, compared to an equivalent non-stabilized layer of equal thickness. Consistent laboratory based methods (such as triaxial testing as per AASHTO T307) for measuring modulus enhancement of the stabilized layer are yet to be finalized. Therefore, laboratory derived methods shall be verified with evidence from field trials where the Geogrid product line proposed has been used to form a MSL and has had standard cyclic plate loading tests (as per AASHTO T294) carried out to evaluate surface modulus values. These should be made available for submission to ADM.

Note: International studies are currently seeking to characterize the stabilized layer enhancement utilizing Resilient Modulus. Characterization of layer enhancement is subject to continuous review and update to include international recognized studies addressing different material characterization methods. Page 236

ANNEX-3 FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

Evaluation of Geogrid Benefits - The contribution of a Geogrid in a pavement structure is variable and influenced by a change of subgrade soil strength, base (or sub- base) strength and thickness, asphalt layer(s) strength and thickness. Therefore, design parameters expressing the Geogrid contribution in the pavement structure should be derived from performance-based evaluation. The improvement offered to the pavement performance by Geogrid materials can be expressed in different ways:

Layer Coefficient Ratio (LCR) - The effect of the stabilization Geogrid on a granular layer, resulting in a MSL whose effect is evaluated and defined by various combinations of pavement layer thickness, aggregate type and subgrade strength. The LCR is dependent on evaluation of a variety of full-scale trafficking trials to allow predicted trafficking performance to be verified with actual trafficking trial data. The LCR can then applied to directly affect the “Structural Number” of the base or sub-base material component of any pavement design case.

Base Course Reduction Factor (BCR) - The percentage reduction in stabilized base or sub-base thickness from the non-stabilized thickness with the same material constituents for the same defined trafficking load.

Traffic Benefit Ratio (TBR) - The ratio of the number of load cycles on a stabilized pavement section to reach a defined trafficking load to the number of load cycles on a non-stabilized pavement section with the same material properties and geometry (layer thicknesses), sometimes referred to as the Traffic Improvement Factor (TIF). The TBR concept can be helpful in quantifying and comparing results of trafficking trials.

TBR values are only relevant to the specific pavement section tested. TBR values derived for one pavement section cannot be applied to a pavement section with differing material properties or geometry. If TBR values are to be used in the evaluation of an Abu Dhabi pavement, they must be derived from full-scale trials based upon the specific pavement materials, geometry and subgrade condition that apply to the project.

1.3 ACCEPTANCE CRITERIA

In order to standardize material and design requirements for utilizing Geogrids in the mechanical stabilization of granular pavement layers of Abu Dhabi roads, the Abu Dhabi Municipality Technical Team developed the first revision of “ADM Approval Process of Geogrid Materials, Utilized in Stabilization/Reinforcement of Base Course (and/or) Sub-base Layers of Flexible Pavements” in June 2012. This included material and design requirements that should be fulfilled by supplier, designer and contractor. This document is under continuous update and development, according to continuous research studies and communications with material suppliers and pavement specialists. Material and design requirements are summarized in the following sections:

It is essential to confirm that a Geogrid material is accepted by Abu Dhabi Emirate and has “Approval for Application” for utilization in the mechanical stabilization of paved roads. In order to be accepted by Abu Dhabi Government, it should comply with both the Material Criteria and Design Procedures. In cases where a material meets only the Material Criteria or Design Procedures but not both, the material is not considered suitable for Abu Dhabi Government “Approval for Application”.

Page 237

ANNEX-3 FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

1.3.1 Verification of Material Characteristics

Technical characteristics of Geogrid materials should be verified and certified by an independent Third Party Laboratory (to be approved by the relevant Abu Dhabi Authority - Material Quality Section), and fulfilling all Abu Dhabi Government regulations and requirements related to Geogrid material properties and performance. The independent third party certificates verifying the technical properties shall be recent (within two years of the date of the Material Submittal).

Previous Geogrid material approvals for similar applications in previous projects are required to be included in a comprehensive material submittal to relevant Abu Dhabi Authority- Material Quality Section for review and approval (previous case studies in the UAE and GCC are preferred).

1.3.2 Full-Scale Accelerated Pavement Testing

The ability for engineers to assess the performance of Geogrids in flexible pavements has been facilitated in recent years with the availability of full-scale accelerated pavement test (APT) facilities, located at a number internationally recognized testing laboratories around the world.

AASHTO document (Ref.: R50-09) provides the most recent advice to pavement designers interested in incorporating Geogrids in their pavements. There is recognition that as pavement design procedures used experimentally derived input parameters which are Geogrid specific, engineers are encouraged to affirm their designs with field verification of the pavement performance. For practical purposes, full-scale accelerated pavement testing is considered acceptable as “Field Verification”.

Therefore, the primary source to quantify the effect of the stabilization Geogrid to be used within the Abu Dhabi pavement design process should be full-scale accelerated pavement testing.

1.3.3 Full-Scale Independent Accelerated Pavement Testing (FS/APT)

These tests are required to evaluate performance of a pavement incorporating the MSL under moving wheel loads and develop design parameters for use in a pavement design.

The proposed supplier shall present evidence of at least two full-scale APT trials.

The APT testing should be carried out by an internationally recognized independent pavement test facility (to be approved by relevant Abu Dhabi Authority) in compliance with NCHRP Report 512 and Synthesis 325. Examples of such facilities are the UK Transportation Research Laboratory, US Corps of Engineers, ARRB Transport Research (Australia) and CSIR Transportek, South Africa. Reference should be made to the accepted facilities detailed in NCHRP Report 512.

The wheel loads shall be equivalent to or exceed an 80kN (18 kip) single axle. Geogrid stabilized sections must be compared with a non-stabilized paved control section. The test must extend to sufficient ESAL’s to provide a realistic indication of whole-life performance. The rutting performance of the sections must be assessed by trenching.

Page 238

ANNEX-3 FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

Design procedures which incorporate the benefit of a particular geogrid line shall require the supplier and/or manufacturer to demonstrate to the design engineer of record that FS/APT results for one or more products within that product line meet or exceed results generated by the design procedure. 1.3.4 Large-Scale Laboratory Testing Whilst the primary source of performance data for Geogrids must be full-scale accelerated pavement testing, large-scale laboratory performance testing can be conducted to demonstrate performance differences between the behavior of an Abu Dhabi previously - approved Geogrid evaluated in full-scale testing, and other products within the same product line, in order to seek Abu Dhabi Government approval for these additional products.

This information can be used to develop design parameters for additional members of a product line from those included in APT and it must be recorded within the independent review and validation report. 1.3.5 Acceptance Criteria of Pavement Design A - General Design Requirements For an acceptable design of a mechanically-stabilized flexible pavement with Geogrid, the following should be followed:

1. Pavement design utilizing Geogrid mechanically stabilized aggregate layers should be based on full and detailed design calculations, conducted by a pavement design specialist, accepted by relevant Abu Dhabi Governmental Authority.

2. The design submission shall include all design steps, geosynthetic benefit verifications and justification including supporting testing results provided by the Geogrid Material Supplier or Manufacturer and fulfilling all required material and design procedures summarized in this document.

3. The design process should assess several options, including conventional design (without Geogrid material) and other options, in order to optimize the most suitable design option for each particular project (case by case basis). 4. Optimization of the most suitable design option should be based on:  Longer service life.  Less overall life cycle cost.  Less expected pavement distresses and better serviceability.  Easier and more sustainable maintenance activities.  Easier and faster construction process.  Saving in construction raw materials, water and energy consumption.  Less carbon footprint.  Any Other design considerations defined by relevant Abu Dhabi Governmental Authority Pavement Design Reviewer.

5. All performance-based evaluations, required to verify Geogrid material contribution in pavement structure, shall contain information that at a minimum must include the specific Geogrid material designation or be properly correlated to other materials within the same product line, with testing as per the reference standards.

6. No proposed equal Geogrid will be accepted based on material index properties or explanations of performance based on these properties.

Page 239

ANNEX-3 FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

7. The items described below must be performed either by, or on behalf of, the Geogrid Material Supplier or Manufacturer, then reviewed and approved by the pavement design specialist.

B - The Use of Proprietary Design Software

Design software is ideally suited for pavement analysis with a variety of programs available from Geogrid manufacturers. ADM encourages the use of this proprietary software, but any software package incorporating design parameters representing the Geogrid performance must be approved by the relevant Abu Dhabi Governmental Authority . Approval will be granted for proprietary software that has been independently evaluated and validated by an internationally recognized pavement design specialist with software development expertise recognized and accepted by Abu Dhabi Government Engineer. Validation shall include the design methodology, design parameters and software functionality.

C - Design Reference Standards

Design of Mechanically Stabilized Asphalt Pavement with Geogrids shall refer to the following references, in addition to any other reference that may be directed by ADM Technical Staff:

1. ADM Roadway Design Manual, 2014. 2. AASHTO R-50: “Geogrid Reinforcement of the Aggregate Base Course of Flexible Pavement Structures” (2009). 3. GMA White Paper: “Geo-synthetic Reinforcement of the Aggregate Base/Sub- base Courses of Pavement Structures” (2000). 4. NCHRP, Report 512: “Accelerated Pavement Testing: Data Guidelines”, TRB (2003). 5. NCHRP, Synthesis 325: “Significant Findings from Full-Scale Accelerated Pavement Testing”, TRB (2004). 6. European Organization for Technical Approvals - Technical Report TR41.

D - General Design Steps

To properly design a mechanically stabilized flexible pavement with stabilization Geogrid, the design steps below should be followed and must be performed either by or on behalf of the geogrid manufacturer/supplier and then reviewed and approved by the ADM project design consultant: Step 1 Design a non-stabilized pavement section as per this manual for the design of flexible pavements. Calculations should be based on defined performance criteria as well as the structural layer parameters, the types of construction materials and associated design parameters and layer thicknesses for the pavement section.

Page 240

ANNEX-3 FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

Step 2 With the same design input parameters for pavement performance and material properties used in Step 1, hand calculations or an approved proprietary design software is to be used to carry out the design of the flexible pavement incorporating the stabilization Geogrid benefit, appropriate to increase life and/or reduce pavement thickness resulting from the enhanced modulus of the resulting MSL.

All design parameters reflecting the performance and contribution of the MSL in a pavement shall be reviewed and validated by an independent internationally recognized pavement design specialist accepted by relevant Abu Dhabi Governmental Authority. See Independent Review and Validation in Section 5.3.6.

Note: TBR values are only relevant to the specific pavement section tested - see definition of TBR in Section 5.2. Step 3 Carry out layered analysis as defined in the AASHTO 1993 method to ensure adequate layer thickness for each pavement component, considering the modified Resilient Modulus of the stabilized road base course to determine the minimum required layer thickness for the stabilized pavement section. Step 4 Conduct life cycle cost analyses of non-stabilized and stabilized pavement sections. Step 5 Evaluate the carbon footprints of non-stabilized and stabilized pavement sections. Step 6 Conduct a study comparing the non-stabilized and stabilized pavement designs described in Steps 1 to 5 above from technical, financial and environmental viewpoints, to assess the overall benefits to the project. This should include:  Expected pavement service life.  Construction cost savings.  Life cycle cost analysis.  Evaluation of the effect on carbon footprint of pavement construction. Step 7 Prepare a performance-based specification detailing the requirements of the selected flexible pavement design. This should include:  Project performance criteria.  Pavement analysis and evaluation.  Conforming design.  Stabilization Geogrid performance-related product characteristics.  Stabilization Geogrid product identification characteristics (for on-site verification purposes).  Stabilization Geogrid durability requirements.  Guidelines for alternative proposals (see note below).

Page 241

ANNEX-3 FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

Note: Submission of alternative proposals incorporating a Geogrid must follow all of the criteria included in this document. No proposal for an alternative Geogrid will be accepted based on product characteristics (material index properties) or explanations of performance based on product characteristics. Proposals shall be accompanied by documented independently reviewed evidence of the associated design along with pavement design calculations by hand or using an approved proprietary software demonstrating performance equivalent or superior to that stated in the performance based specification (from Step 7 above). 1.3.6 Independent Review and Validation An independent review by an internationally recognized pavement engineering services company (approved by relevant Abu Dhabi Authority before review) is required before a Geogrid product can be considered as a qualified product by Abu Dhabi Government or utilized in a design procedure. Refer to NCHRP Report 512. The third party shall be able to demonstrate familiarity with both the role of Geogrids and AASHTO pavement design principles, as well as performance evaluation of pavements. Independent review will examine the design methodology and proposed calculation of stabilization effect, product characteristics, quality assurance procedures and documentation, supporting performance testing and field experience documentation. In a written report, the reviewer shall validate that the design methodology proposed for use with the specific stabilization Geogrid product family is correct, that underlying calculations are supported by appropriate experimental procedures and that the manufacturer’s research supports the protocols and intent of AASHTO R- 50. The review document shall accompany all final design proposals once complete.

1.4 REFERENCES

1. AASHTO Designation: R 50-091: “Geogrid Reinforcement of the Aggregate Base Course of Flexible Pavement Structures”. 2. IB / Derivation Trafficking / 29.01.11: “The Method of Derivation of Traffic Improvement and Equivalent Performance Factors for Tensar TriAx™ Geogrids from Full-Scale Trafficking Trials at TRL”. 3. Derivation of traffic improvement and equivalent performance factors for Tensar TriAx™. 4. US Army Corps of Engineers, Engineer Research and Development Center: “Full Scale Accelerated Pavements Tests, Geogrid Reinforcement of Thin Asphalt Pavements, Phase 1 Interim Report”, Sarah R. Jersey and Jeb S.Tingle (2010). 5. Wisconsin Highway Research Program (www.whrp.org): “Quantifying the Benefits of Geogrids for More Durable Pavements”, No. 0092-07-05 (July 2009). 6. Sarika B. Dhule, S.S. Valunjkar, S.D. Sarkate, S.S. Korrane: “Improvement of Flexible Pavement with Use of Geogrid, Vol. 16” (2011). 7. GMA White Paper: “Geogrid Reinforcement of the Aggregate Base/Subbase Courses of Pavement Structures”, (2000). 8. NCHRP, Report 512: “Accelerated Pavement Testing: Data Guidelines”, TRB (2003).

Page 242

ANNEX-3 FIRST EDITION -DECEMBER 2016 PAVEMENT DESIGN MANUAL

9. NCHRP, Synthesis 325: “Significant Findings from Full-Scale Accelerated Pavement Testing”, TRB (2004). 10. Applied Research Association, ARA “Independent Review and Validation of Tensar’s Modified AASHTO 1993 Pavement Design Procedure and Verification of Spectrapave 4™ Software”, (April 2013).

Page 243

ANNEX-3 FIRST EDITION -DECEMBER 2016