TRANSPORTATION RESEARCH BOARD NATIONAL RESEARCH COUNCIL TRANSPORTATION RESEARCH BOARD 1976 Officers HAROLD L. MICHAEL, Chairman ROBERT N. HUNTER, Vice Chairman W. N. CAREY, JR., Executive Director
Executive Committee HENRIK E. STAFSETH, Executive Director, American Assn. of State Highway and Transportation Officials (ex officio) NORBERT T. TIEMANN, Federal Highway Administrator, U.S. Department of Transportation (ex officio) ROBERT E. PATRICELLI, Urban Mass Transportation Administrator, U.S. Department of Transportation (ex officio) ASAPH H. HALL, Federal Railroad Administrator, U.S. Department of Transportation (ex officio) HARVEY BROOKS, Chairman, Commission on Sociotechnical Systems, National Research Council (ex officio) MILTON PIKARSKY, Chairman of the Board, Chicago Regional Transportation Authority (ex officio, Past Chairman 1975) WARREN E. ALBERTS, Vice President (Systems Operations Services), United Airlines GEORGE H. ANDREWS, Vice President (Transportation Marketing) Sverdrup and Parcel GRANT BASTIAN, State Highway Engineer, Nevada Department of Highways KURT W. BAUER, Executive Director, Southeastern Wisconsin Regional Planning Commission LANGHORNE BOND, Secretary, Illinois Department of Transportation MANUEL CARBALLO, Secretary of Health and Social Services, State of Wisconsin L. S. CRANE, President, Southern Railway System JAMES M. DAVEY, Consultant B. L. DEBERRY, Engineer-Director, Texas State Department of Highways and Public Transportation LOUIS J. GAMBACCINI, Vice President and General Manager, Port Authority Trans-Hudson Corporation HOWARD L. GAUTHIER, Professor of Geography, Ohio State University FRANK C. HERRINGER, General Manager, San Francisco Bay Area Rapid Transit District ANN R. HULL, Delegate, Maryland General Assembly ROBERT N. HUNTER, Chief Engineer, Missouri State Highway Commission PETER G. KOLTNOW, President, Highway Users Federation for Safety and Mobility A. SCHEFFER LANG, Assistant to the President, Association of American Railroads BENJAMIN LAX, Director, Francis Bitter National Magnet Laboratory, Massachusetts Institute of Technology DANIEL McFADDEN, Professor of Economics, University of California HAROLD L. MICHAEL, School of Civil Engineering, Purdue University THOMAS D. MORELAND, Commissioner, Georgia Department of Transportation J. PHILLIP RICHLEY, Vice President (Engineering and Construction), The Cafaro Company RAYMOND T. SCHULER, Commissioner, New York State Department of Transportation WILLIAM K. SMITH, Vice President (Transportation), General Mills
NATIONAL COOPERATIVE HIGHWAY RESEARCH PROGRAM Transportation Research Board Executive Committee Subcommittee on the NCHRP HAROLD L. MICHAEL, Purdue University (Chairman) ROBERT N. HUNTER, Missouri State Highway Commission HENRIK E. STAFSETH, Amer. Assn. of State Hwy. and Transp. Officials NORBERT T. TIEMANN, U.S. Department of Transportation HARVEY BROOKS, National Research Council W. N. CAREY, JR., Transportation Research Board
Project Committee SP 20-5 RAY R. BIEGE, JR., Kansas Dept. of Transportation (Chairman) VERDI ADAM, Louisiana Department of Highways Topic Panel on Lime-Fly As/i-Stabilized Bases and Subbases JACK FREIDENRICH, New Jersey Department of Transportation DAVID GEDNEY, Federal Highway Administration H. FABER, National Ash Association EDWARD J. HEINEN, Minnesota Department of Highways A. GUTSCHICK, National Lime Association BRYANT MATHER, USAE Waterways Experiment Station R. L. HANDY, Iowa State University THOMAS H. MAY, Pennsylvania Department of Transportation E. B. McDONALD, South Dakota Department of Transportation THEODORE F. MORF, Consultant R. E. OLSEN, Federal Highway Administration EDWARD A. MUELLER, Jacksonville Transportation Authority W. C. ORMSBY, Federal Highway Administration ORRIN RILEY, Howard, Needles, Tammen & Bergendofi R. SCHWARTZ, Illinois Department of Transportation REX C. LEATHERS, Federal Highway Administration J. W. GUINNEE, Transportation Research Board ROY C. EDGERTON, Transportation Research Board Consultants to Topic Panel Program Staff J. BARENBERG and M. R. THOMPSON, University of Illinois K. W. HENDERSON, JR., Program Director DAVID K. WITHEFORD, Assistant Program Director HARRY A. SMITH, Projects Engineer LOUIS M. MACGREGOR, Administrative Engineer ROBERT E. SPICHER, Projects Engineer JOHN E. BURKE, Projects Engineer HERBERT P. ORLAND, Editor R. IAN KINGHAM, Projects Engineer PATRICIA A. PETERS, Associate Editor ROBERT J. REILLY, Projects Engineer EDYTHE T. CRUMP, Assistant Editor NATIONAL COOPERATIVE HIGHWAY RESEARCH PROGRAM SYNTHESIS OF HIGHWAY PRACTICE 3'7
LIME-FLY ASH-STABILIZED BASES AND SUBBASES
RESEARCH SPONSORED BY THE AMERICAN ASSOCIATION OF STATE HIGHWAY AND TRANSPORTATION OFFICIALS IN COOPERATION WITH THE FEDERAL HIGHWAY ADMINISTRATION
AREAS OF INTEREST: PAVEMENT DESIGN CONSTRUCTION AIR TRANSPORT
TRANSPORTATION RESEARCH BOARD NATIONAL RESEARCH COUNCIL WASHINGTON, D.C. 1976 NATIONAL COOPERATIVE HIGHWAY RESEARCH PROGRAM NCHRP Synthesis 37
Systematic, well-designed research provides the most ef- Project 20-5 FY '74 (Topic 6-06) fective approach to the solution of many problems facing ISBN 0-309-02510-9 highway administrators and engineers. Often, highway L. C. Catalog Card No. 76-45297 problems are of local interest and can best be studied by highway departments individually or in cooperation with Price: $480 their state universities and others. However, the accelerat- ing growth of highway transportation develops increasingly complex problems of wide interest to highway authorities. These problems are best studied through a coordinated program of cooperative research. In recognition of these needs, the highway administrators Notice of the American Association of State Highway and Trans- The project that is the subject of this report was a part of the portation Officials initiated, in 1962 an objective national National Cooperative Highway Research Program conducted by the Transportation Research Board with the approval of the Governing highway research program employing modern scientific Board of the National Research Council, acting in behalf of the techniques. This program is supported on a continuing National Academy of Sciences. Such approval reflects the Governing basis by funds from participating member states of the Board's judgment that the program concerned is of national impor- tance and appropriate with respect to both the purposes and re- Association and it receives the full cooperation and sup- sources of the National Research Council. port of the Federal Highway Administration, United States The members of the technical committee selected to monitor this Department of Transportation. project and to review this report were chosen for recognized scholarly competence and with due consideration for the balance The Transportation Research Board of the National Re- of disciplines appropriate to the project. The opinions and con- search Council was requested by the Association to admin- clusions expressed or implied are those of the research agency that performed the research, and, while they have been accepted as ister the research program because of the Board's recog- appropriate by the technical committee, they are not necessarily those nized objectivity and understanding of modern research of the Transportation Research Board, the National Research Coun- practices. The Board is uniquely suited for this purpose cil, the National Academy of Sciences, or the program sponsors. Each report is reviewed and processed according to procedures as: it maintains an extensive committee structure from established and monitored by the Report Review Committee of the which authorities on any highway transportation subject National Academy of Sciences. Distribution of the report is ap- proved by the President of the Academy upon satisfactory comple- may be drawn; it possesses avenues of communications and tion of the review process. cooperation with federal, state, and local governmental The National Research Council is the principal operating agency of agencies, universities, and industry; its relationship to its the National Academy of Sciences and the National Academy of Engineering, serving government and other organizations. The parent organization, the National Academy of Sciences, a Transportation Research Board evolved from the 54-year-old High- private, nonprofit institution, is an insurance of objectivity; way Research Board. The TRB incorporates all former HRB activities but also performs additional functions under a broader it maintains a full-time research correlation staff of special- scope involving all modes of transportation and the interactions of ists ,in highway transportation matters to bring the findings transportation with society. of research directly to those who are in a position to use them. The program is developed on the basis of research needs identified by chief administrators of the highway and trans- portation departments and by committees of AASHTO. Each year, specific areas of research needs to be included in the program are proposed to the Academy and the Board by the American Association of State Highway and Trans- portation Officials. Research projects to fulfill these needs are defined by the Board, and qualified research agencies Published reports of the are selected from those that have submitted proposals. Ad- NATIONAL COOPERATIVE HIGHWAY RESEARCH PROGRAM ministration and surveillance of research contracts are responsibilities of the Academy and its Transportation are available from: Research Board. Transportation Research Board The needs for highway research are many, and the National National Academy of Sciences Cooperative Highway Research Program can make signifi- 2101 Constitution Avenue, N.W. cant contributions to the solution of highway transportation Washington, D.C. 20418 problems of mutual concern to many responsible groups. The program, however, is intended to complement rather (See last pages for list of published titles and prices) than to substitute for or duplicate other highway research programs. Printed in the United States of America.
PREFACE There exists a vast storehouse of information relating to nearly every subject of concern to highway administrators and engineers. Much of it resulted from research and much from successful application of the engineering ideas of men faced with problems in their day-to-day work. Because there has been a lack of systematic means for bringing such useful information together and making it available to the entire highway fraternity, the American Association of State Highway and Trans-, portation Officials has, through the mechanism of the National Cooperative Highway Research Program, authorized the Transportation Research Board to undertake a continuing project to search out and synthesize the useful knowledge from all pos- sible sources and to prepare documented reports on current practices in the subject areas of concern. - This synthesis series attempts to report on the various practices without in fact making specific recommendations as would be found in handbOoks or design manuals. Nonetheless, these documents can serve similar purposes, for each is a compendium of the best knowledge available concerning those measures found to be the most successful in resolving specific problems. The extent to which they are utilized in this fashion will quite logically be tempered by the breadth of the user's knowledge in the particular problem area.
FOREWORD This synthesis will be of special interest and usefulness to design, construction, materials, and maintenance engineers seeking technical information on the use B ' tall of lime-fly ash—aggregate materials for stabilized pavement bases and subbases. Transportation Detailed iinformation is presented on the materials, mixture properties, selection Research Board of proportions, construction procedures, and pavement behavior and performance. Applications and limitations for the use of lime-fly ash—aggregate materials in pavement construction are outlined. Administrators, engineers and researchers are faced continually with many highway problems on which much information already exists either in documented form or in terms of undocumented experience and practice. Unfortunately, this information often is fragmented, scattered, and unevaluated. As a consequence, full information on what has been learned about a problem frequently is not assembled in seeking a solution. Costly research findings may go unused, valuable experience may be overlooked, and due consideration may not be given to recom- mended practices for solving or alleviating the problem. In an effort to resolve this situation, a continuing NCHRP project, carried out by the Transportation Research Board as the research agency, has the objective of synthesizing and reporting on common highway problems—a synthesis being identified as a composition or com- bination of separate parts or elements so as to form a whole greater than the sum of the separate parts. Reports from this endeavor constitute an NCHRP report series that collects and assembles the various forms of information into single concise documents pertaining to specific highway problems or sets of closely related problems.
In recent years, energy and environmental considerations have brought about an increased interest in the use of lime and fly ash in pavement construction. A well-developed technology now exists for the stabilization of bases and subbases with these materials. However, lime-fly ash—aggregate materials are sometimes not used 'when they might because technical information has not been conveniently available. This report of the Transportation Research Board describes current tech- nology for construction of stabilized bases and subbases using lime-fly ash—aggre- gate materials. Typical specifications for mixing and placing the materials are described. To develop this synthesis in a comprehensive manner and to ensure inclusion of significant knowledge, the Board analyzed available information assembled from numerous sources, including a large number of state highway and trans- portation departments. A topic panel of experts in the subject area was established to guide the researchers in organizing and evaluating the collected data, and to review the final synthesis report. This synthesis is an immediately useful document that records practices that were acceptable within the limitations of the knowledge available at the time of its preparation. As the processes of advancement continue, new knowledge can be expected to be added to that which is now at hand.
3 CHAPTER ONE Introduction
4 CHAPTER TWO Materials Lime Fly Ash Aggregates and Soils Lime-Fly Ash Reactions
10 CHAPTER THREE Mixture and Mixture Properties Range of Composition Engineering Properties of Lime-Fly Ash-Stabilized Materials Factors Influencing LFA Properties
24 CHAPTER FOUR Pavement Behavior and Performance Pavement Behavior Pavement Performance
41 CHAPTER FIvE Selection of Mixture Proportions Approach to Mixture Proportioning Laboratory Test Procedures Quality Criteria
45 CHAPTER SIX Construction Procedures Central Plant Operations Mixed-in-Place Operations Sealing and Surfacing LFA Layers Construction Season Specifications for Mixing and Placing LFA Mixes
52 CHAPTER SEVEN Applications and Limitations
55 APPENDIX A Availability of Lime and Fly Ash in the United States
57 APPENDIX B Proposed Cutoff-Date Procedures for Construc-. tion with LFA Mixes
58 APPENDIX C Typical Specificatiois for Lime-Fly Ash—Aggre- gate Base/Subbase Course
63 APPENDIX D State of Illinois—Special Provision for Pozzolanic Base Course, Type A ACKNOWLEDGMENTS This synthesis was completed by the Transportation Research Iowa State University; Eugene B. McDonald, Materials and Board under the supervision of Paul E. Trick, Assistant Director Soils Engineer, South Dakota Department of Transportation; for Special Projects. The Principal Investigators responsible Robert E. Olsen, Highway Engineer, Office of Development, for conduct of the synthesis were Thomas L. Copas and Federal Highway Administration; W. C. Ormsby, Research Herbert A. Pennock, Special Projects Engineers. This synthesis Chemist, Office of Research, Federal Highway Administration; was edited by Deborah K. Farmer. Donald R. Schwartz, Engineer of Physical Research, Bureau Special appreciation is expressed to Ernest J. Barenberg and of Materials and Physical Research, Illinois Department of Marshall R. Thompson, Professors of Civil Engineering, Uni- Transportation. versity of Illinois, who were responsible for the collection of John W. Guinnee, Engineer of Soils, Geology,• and Founda- data and the preparation of the report. Valuable assistance in the preparation of this synthesis was tions, Transportation Research Board, assisted the Special provided by the Topic Panel, consisting of John H. Faber, Projects staff and the Topic Panel. Executive Director, National Ash Association; Kenneth A. Information on current practice was provided by many Gutschick, Manager, Technical Services, National Lime Asso- transportation agencies. Their cooperation and assistance was ciation; Richard L. Handy, Professor of Civil Engineering, most helpful. LIME-FLY ASH-STABILIZED BASES AND SUBBASES
SUM MARY Technology for stabilizing aggregates with lime and fly ash has been increasing dur- ing the past 20 years. Many state and federal agencies now include this paving material in their specifications. However, because this technology is not widely known, many agencies with sources of lime and fly ash do not make extensive use of these materials. Factors that are likely to influence the future use of lime-fly ash aggregates (LFA) are: Increase in use of coal for fuel. Low energy requirements for producing LFA mixes. New technology for LFA use. Widespread availability of lime and fly ash. Most commercially available hydrated limes are suitable for LFA mixes. In addition, some by-product limes can be used. Although there are differences in the properties of these limes, most of them can be used in LFA mixtures, but each lime source should be validated before approval for use. Fly ash is the fine residue that results from the combustion of coal; it is col- lected from flue gases. It has been estimated that the U.S. fly ash production will approach 40 million tons (3.6 x 107 metric tons) annually by 1980. Fly ashes are pozzolans with little cementitious value but in the presence of moisture will chemi- cally react with calcium hydroxides at ordinary temperatures to form compounds with cementitious properties. "Dry" fly ash is taken directly from the precipitator or from dry storage. Fly ash stockpiled in the open requires the addition of water to prevent dusting. As a result of alkalies present in some fly ashes, dampened fly ashes may set up and require crushing and screening before use. Fly ash is also stored in slurry ponds, and may segregate during settlement causing the final product to be more variable. The physical and chemical properties of fly ash are highly variable. Some of these are: Shape (spherical, solid, or hollow). Glass content. Composition (silica and aluminum plus carbon; and oxides of iron, calcium, magnesium, and sulfur). Size (1mto 80 /Lm). Color (gray, tan, black). Agencies usually cite ASTM Specification C 593 in their specification for fly ash. The quality of a lime-fly ash-stabilized mixture is highly dependent on the 2 aggregates used; crushed stone, gravel, and granular sands produce better mixes than silts. (Fine-grained clays are not normally used with LFA mixtures.) Other factors that affect the stability and strength of the LFA mixture include: gradation, plasticity index, liquid limit, soundness, compactive effort, and curing. Generally, the lime-plus-fly ash content of a mixture ranges from 12 percent to 30 percent with lime-to-fly ash ratios of 1:3 to 1:4 being common. Critical engineering properties of LFA mixtures include: strength (compres- sive, flexural, and shear), modulus of elasticity, Poisson's ratio, fatigue, autogenous healing, volume changes, and durability. These properties are influenced by the constituent materials (lime, fly ash, aggregate, and soil) and by proportions, processing, compaction, and curing (time, temperature, and moisture). Test data on full-scale and model pavements correlated with theoretical analy- ses confirm that the load distribution characteristics of pavements with layers of LFA mixes are essentially those of a slab. The ultimate strength of LFA slabs under static load has been shown to far exceed the strength predicted by elastic slab theory. The stiffer LFA layers distribute the load over large areas of the subgrade by the slab action, thus transmitting low vertical stress to the subgrade. The primary factors affecting the performance of LFA pavements are: load- ing and the interrelationships between load, slab thickness, and material strength; durability of the LFA material as related to the environment in which it must serve; quality of construction, including uniformity of the final product; and subsurface drainage of the pavement system. Performance of LFA pavements has been studied using: scale models in lab- oratory and quasi-laboratory conditions, short-term evaluation of full-scale pave- ments with vehicle loading under simulated service conditions, and performance of pavements in service for a number of years under normal traffic. One objective of the studies of LFA performance has been the identification of structural coefficients to be used in designing LFA pavement systems. Distress in LFA pavements is normally surface cracking caused by excessive loads on the pavement and deterioration of the LFA material, which is often the result of excess moisture and inadequate density (particularly near the pavement edge). Two types of construction-related distress have been observed on LFA pave- ments. One type occurs when the material becomes saturated before setting and shoves under traffic. This is corrected by reshaping and compacting the unstable layer and permitting it to dry. A more harmful type of distress is caused when con- struction traffic causes cracks in partially set LFA material. Under favorable curing conditions these cracks will reheal, but with a reduction in the ultimate strength of the pavement. Exact proportions of lime, fly ash, and aggregate are included in LFA mixtures to satisfy specific requirements. For a given set of materials, several proportions may provide mixtures of satisfactory quality. Advantages of using LFA mixtures in pavement construction include ease of construction and the ability to use conventional construction equipment. The essen- tial construction requirements are thorough mixing, uniform spreading, and com- paction to a high density. LFA materials can be blended or mixed on the roadbed or in a central plant. Compacted layers of LFA materials should be sealed as soon as possible. 3
LFA materials are most effective when used under proper conditions and within specified limitations. Some general guidance is offered:
LFA materials can be used for a wide range of pavement systems from low volume to heavy volume. LFA materials can be used as a base or subbase for flexible pavements, or as a subbase for rigid pavements. The key to good performance with LFA materials is good mixture selection and sound construction techniques. Durability is the single most important consideration in the performance of LFA materials, especially in areas of cyclic freezing and thawing and where use of deicing salt is heavy. Procedures are required for establishing cutoff dates for late-season con- struction with LFA materials. High relative density is critical for high strength and durability.
CHAPTER ONE INTRODUCTION
The technology for stabilizing aggregates with lime and fly Use of LFA materials has increased in recent years be- ash has been growing at a significant pace during the past cause of concern for energy resources and the environment. 20 years. The state of -the art in this technology has de- Currently, more than 35 million tons of fly ash are disposed veloped to the point that lime-fly ash—aggregate (LFA) of annually in an environmentally acceptable manner. As materials are included in many state and federal agency more utilities are forced to shift from gas and oil to coal as specifications as a conventional type of paving material. a source for fuel, quantities of fly ash will increase. In addi- Despite the development of the technology, its acceptance tion, because LFA mixes generally require only 2 to 5 per- has not been universal. In several areas of the country, cent lime, the total energy used in the production of LFA substantial quantities of LFA materials are used annually mixes is very low. These two factors along with a well- in the construction of pavement bases and subbases, but in developed technology should make an attractive case for the expanding use of LFA mixes. other areas with excellent resources of lime and fly ash, the Lime and fly ash are not locally available in all areas of materials are not used extensively. There are, no doubt, a the United States. The distribution of lime and fly ash is number of reasons for this, including the fact that the tech- widespread enough, however, that LFA materials could be nology for use of this material is not widely known in the produced in most areas of the country with local materials profession. One of the primary functions of this synthesis and reasonable haul distances of only one, of the compo- is to summarize the current state of the art on LFA nents. Appendix A shows the availability of lime and fly materials in a readily available format. ash around the country.
Lime and fly ash can be used to stabilize aggregates and quicklime (CaO) and dolomitic quicklime (CaO + MgO) soils to produce acceptable quality base and subbase ma- are produced by calcining calcitic and dolomitic. limestone, terials. 'the characteristics of the lime, fly ash, and aggre- respectively. By the controlled addition of water to quick- gate or soil being stabilized significantly influence the qual- lime, three types of hydrated lime can be produced: high- ity and properties of the stabilized material. Thus, it is calcium, Ca(OH) 2; monohydrated dolomitic, Ca(OH) 2 -I- important to carefully evaluate and consider all of the MgO; and dihydrated dolomitic, Ca(OH)2 + Mg(OH) 2. various mixture components (lime, fly ash, and aggregate Only hydrated high-calcium and. monohydrated dolomitic or soil) and their interactions. limes are used in lime-fly ash stabilization. Quicklimes are not used. For a comprehensive consideration of lime and LIME the lime production process, consult Boynton (1). Typical In general, the term lime refers to oxides and hydroxides properties of commercial varieties of quicklime and hy- of calcium and magnesium, but not to carbonates. There drated limes are summarized in Table 1. are various types of lime commercially available. Calcitic By-product lime also provides a source of lime that is
TABLE 1 PROPERTIES OF COMMERCIAL LIMES * Quicklime
Constituent (percent) High Calcium Dolomitic
CaO 92.25 - 98.00 55.70 - 57.50
MgO 0.30 - 2.50 37.60 - 40.80
CO2 0.40 - 1.50 0.40 - 1.50
S12 0.20 - 1.50 0.10 - 1.50
Fe203 0.10 - 0.40 0.05 - 0.40
A1203 0.10 - 0.50 0.05 - 0.50
H20 0.10 - 0.90 0.10 - 0.90
Specific Gravity 3.2 - 3.4 3.2 - 3.4
(J/kg) Btu/lb J/kg) Specific heat at Btu/lb 11 100 F (38 C) '0.19 (440) 0.21 488)
Bulk Density, pebble lime £ (kg/rn3) 2f (kg/rn3) 55-60 (880-960) 55-60 (880-960)
High Monohydrated - Dihydrated Calcium Dolomitic Dolomitic Ca(OH)2M9(OH)2 Principal constituent. Ca(OH)2 Ca(OH)2MgO 2.4 - 2.6 Specific gravity 2.3 - 2.4 2.7 - 2.9 Btu/lb (/kg) Btu/lb (J/kgl Btu/lb (/kg) Specific heat at 0.29 (675) 100 F (38 C) 0.29 (675) 0.29 (675) (kg/rn3) f. (kg/rn3) Bulk density (kg/rn3) f 25-35 (400-560) 25-35 (400-560) 30-40 (480-640) "rhomiri limp Facts." Bulletin 214 (3rd ed.), National Lime Association (1973). often suitable for use in stabilization. This type of lime is Mechanical moisture in hydrated lime usually available from various manufacturing processes. (as-received basis) Two types of by-product limes commonly available are: maximum percent ...... 4 (a) that collected from the draft of the calcining process The sieve analysis of the lime residue shall be as in lime production operations (flue dust), and (b) the by- follows: product of acetylene gas production from calcium carbide. By-product lime may be a very economical source of lime; MAXIMUM PERCENT however, these limes may be nonuniform in quality (2). SIEVE RETAINED Although many by-product limes may be similar to virgin No. 4 (4.75 mm) 0 limes in terms of chemical composition, other important No. 30 (600 14m) 2.5 properties may be considerably different. For example, No. 100(l50m) 15 commercial hydrates generally are more finely divided and have higher specific surfaces than carbide limes. Pennsylvania Department of Transportation A new form of lime for stabilization has recently been Lime shall meet the requirements of ASTM Designation developed in the Chicago area. The material is a by-product C 207, Type N, Sections 2, 3(a), 6, and 7(a) and shall hydrate produced by hydrating a mixture of flue dust and be capable of producing a mixture meeting Pennsylvania normal quicklime. Although the by-product hydrate is not aggregate-lime-pozzolan mixture requirement. chemically equivalent to normal commercial hydrated lime, it has been successfully used in lime-fly ash stabilization. Ohio Department of Transportation By-product hydrate is less expensive and more readily available in the Chicago area. Hydrated lime shall meet the requirements prescribed in There is some concern as to whether calcitic lime, standard specification for Hydrated Lime for Masonry,
Ca(OH) 2, or monohydrated dolomitic lime, Ca(OH)2 + ASTM C 207, Type N for chemical composition, residue, MgO, is the more effective lime for use in lime-fly ash sampling, inspection and methods of test. (Sections 3.1, 2, stabilization. Studies indicate that monohydrated dolomitic 4, and 5 are not relevant to the intended usage.) lime is more effective than high-calcium lime (3, 4), but both limes produce long-term strengths of approximately Federal A via tion Administration equal magnitude. Other investigators (4, 5, 6) have found that high-calcium lime gives higher strengths, especially at The lime shall meet ASTM Specification C 207, Type N, low lime contents. Thus, it can probably be concluded that Sections 2 and 3(a) when sampled and tested in accordance either high-calcium or monohydrated dolomitic lime is, in with Sections 6 and 7. The above requirements may be general, satisfactory for use in lime-fly ash stabilization. waived if it is demonstrated that a mixture of comparable Laboratory testing may be used to indicate the effectiveness quality and reliability can be produced with lime and/or of any of the lime types, but it should be emphasized that fly ash which do not meet the above criteria. the quality of the fly ash has a much greater influence on the lime-fly ash pozzolanic reaction than does lime type. FLY ASH It can be stated that most types of lime (exclusive of Fly ash is "the finely divided residue that results from the dihydrated dolomitic) are. appropriate if a quality lime-fly combustion of ground or powdered coal and is transported ash-stabilized product meeting strength, durability, and eco- from the boilers by flue gases" (ASTM Specification C nomic criteria can be obtained. Appropriate quality con- 593). Fly ash is collected from the flue gases by either trol testing should be conducted during the course of a mechanical or electrostatic precipitation devices. project to ensure the quality and uniformity of the lime Large quantities of fly ash are produced in the U.S. Past being incorporated into the LFA mixture. Typical lime and future fly ash production trends, as presented by specifications are summarized in the following section. Brackett (8), are shown in Figure 1. Fly ash is a pozzolan and is defined as "a siliceous or Lime Specifications for Lime-Fly siliceous and aluminous material, which in itself possesses Ash—Aggregate Mixtures little or no cementitious value but which will, in finely di- Illinois Department of Transportation vided form and in the presence of moisture, chemically react with calcium hydroxide at ordinary temperatures to The lime, either high-calcium or dolomitic hydrate, shall form compounds possessing cementitious properties" (7). comply with the requirements of ASTM C 207, Hydrated Fly ash is available in different conditions. "Dry" fly ash Lime for Masonry Purposes, Type N, with the following is taken directly from the precipitator or from dry storage. modifications: If the fly ash is stockpiled in the open atmosphere, it is Total calcium and magnesium oxides normally conditioned by adding water to prevent dusting. (nonvolatile basis) Some conditioned stockpiled fly ashes may develop ce- minimum percent ...... 90 mentitious materials and "set up" in the stockpile. If the Calcium oxide in hydrated lime (as-received basis) fly ash has set up, crushing and screening may be re- maximum percent ...... 5 quired prior to use in stabilized mixtures. In some instances Magnesium hydroxide (as-received basis) the collected fly ash is slurried into storage pond areas and maximum percent ...... 5 must subsequently be reclaimed from the pond for use. ashes produced in plants where the SO2 emission control processes use lime or limestone may also contain signifi- cant amounts of calcium or magnesium oxides and other 400 60 products. It may also contain selenium. 0 (12) reports that most fly ashes contain more a Brackett C 0 than 85 percent of alumina, silica, iron oxide, and magnesia 300 with the percentage of any one constituent varying over a E wide range of values, depending upon the character of the 0 particular ash being characterized. The broad ranges of fly 200 :: ash composition are also evident from the studies of
U) Minnick (13), Vincent et al. (14), and Watt and Thorne z g 100 3° (9). a -j 0 According to Bràckett (12), the size of fly ash particles 0 U 0. varies from 1 to 80 microns (3.94 X 10 to 3.15 X 10 0 20 in.) The carbon particles tend to be concentrated in the larger sizes (12, 13). Specific surface values for fly ash are quite variable but are generally in the range of 2 000 to 10 8 000 cm2/g (8,800 to 35,000 in.2/oz). Fly ash is usually light gray in color, but can vary from 0 light tan through shades of gray to black. The tan color is 1950 1955 1960 1965 1970 1975 1980 usually associated with the presence of iron oxide; darker Figure 1. Coal consumption and ash production (8) colors are indicative of carbon or, in some cases, magnetic iron oxide or magnetite (12).
Fly Ash Specifications for Lime-Fly Ash—Aggregate Fly ash particles are predominantly spherical, solid or Mixtures hollow in nature, and amorphous. British studies (9) of seven different fly ashes indicate that the glass content (amorphous material) ranges from 71 to 88 percent. Illinois Department of Transportation Minnick (10) indicated that the amorphous components The pozzolan, prior to dampening thereof to alleviate the of fly ash are the main components involved in the lime-fly dust problem, shall comply with the requirements of ASTM ash pozzolanic reactions. C 593. The maximum loss on ignition, determined in ac- Fly ash particles are primarily composed of silica and cordance with the procedures of ASTM C 311 shall be alumina. Secondary ingredients are carbon and oxides of 10 percent. The tests prescribed by .this specification shall iron, calcium, magnesium, and sulfur. Oxides of sodium, be performed at the option of the engineer. At the time potassium, titanium, manganese, and phosphorus may also of mixing the pozzolan shall be, when dry sieved, in a finely be present. Table 2 gives typical ranges of values for the divided condition, as follows: chemical composition of fly ash. Manz's data (11) for sev- eral United States lignite fly ashes indicate that substantial MINIMUM PER- quantities of calcium oxide (20 to 40 percent) and mag- SIEVE CENT PASSING nesium oxide (5 to 10 percent) are typically present. Fly ½inch(12.Smm) 100 /8 inch (9.5 mm) 95 No. 10 (2.00 mm) 75
TABLE 2 The moisture content of dampened pozzolan shall not exceed 35 percent. TYPICAL COMPOSITION OF FLY ASH
Principal Constituents Percent Pennsylvania Department of Transportation Si02 28-52 Pozzolan shall meet the requirements of ASTM Designa- tion C 593 and shall be capable of producing a mixture A1203 15-34 meeting Pennsylvania aggregate-lime-pozzolan mixture Fe203 3-26 requirements.
CaO 1-10 Ohio Department of Transportation MgO 0-2 Fly ash shall meet the requirements of ASTM C 593, with so3 0-4 the exception of Section 7 for plastic mixes. The maximum loss on ignition shall be 10 percent as determined in Loss on Ignition 1-30 accordance with ASTM C 311. Federal Aviation Administration The gradation in the table sets limits which shall deter- The fly ash shall meet ASTM Specification C 593, Section mine the general suitability of the aggregate from a source 3.2, when sampled and tested in accordance with Sections of supply. The final gradations selected for use shall be 4, 6, and 8. An exception is noted that the water-soluble within the limits designated in the table, and shall also be fraction shall not be determined. The above requirements well graded from fine to coarse and shall not vary from may be waived if it is demonstrated that a mix of com- high to low limits on subsequent sieves. parable quality and reliability can be produced with lime In addition to the gradations given in the table, clean and/or fly ash which do not meet the above criteria. sands and sand-sized materials such as boiler slags can be used. Also, if the aggregate has a substantial portion (75 AGGREGATES AND SOILS percent) passing the No. 4 (4.75-mm) mesh sieve, the gradations in the table can be waived and the aggregate The quality of a lime-fly ash-stabilized product depends to gradation adjusted with the fly ash and fines contents to pro- a large extent on the material being stabilized. High-clay- duce the maximum dry density in the compacted mixture. content fine-grained soils are less desirable for stabilization with lime-fly ash than are silts and more granular sands, gravels, and crushed stones. LIME-FLY ASH REACTIONS A wide range of aggregate types and gradations have The reactions that occur in the lime-fly ash—water system been used successfully including sands, gravels, crushed to form cementitious materials are complex. However, stones, and several types of slag. Aggregates should be of several studies provide basic information pertaining to the such gradation that, when mixed with lime, fly ash, and reactions. water, the resulting mixture is mechanically stable under Minnick (10) presents an illustrative list of reactions, as compaction equipment and capable of being compacted in follows, and acknowledges that other reactions are also the field to a high density. The aggregate should be free possible. from deleterious organic or chemical substances that may 1120 interfere with the desired chemical reaction and should I. RO—*R(OH)2 consist of hard, durable particles, free from soft or dis- integrated pieces. 11,0; CO, RO )RCO3 +H20 Aggregate mixtures with greater fines contents have gen- erally produced materials of greater durability than coarser Co2 R(OH)2 —p RCO3 + H2O grained mixtures. However, mixtures with coarser aggre- gate gradations are generally more mechanically stable. HzO R(OH), + SiO,—*xROySiO2 •zH2O Although laboratory studies have demonstrated the feasi- 1120 bility of stabilizing fine-grained soils (4, 6), lime-fly ash is R(OH)2 + Al,O3 —+xROyAl,O,zH2O not commonly used to stabilize such materials. Such con- siderations as (a) the difficulty of incorporating lime and 11,0 R(OH)2 + AI,O, + Si02 —xROyAl,O3 zSiO,•wH20 fly ash with these materials under field conditions, (b) the 11,0 low-level strength development (as compared to stabilized R(OH), + SO3-- + Al,O -p granular materials), (c) the increased lime-plus-fly ash xRO yAl2O3 zRSO wH, 0 content requirements, and (d) the.use of alternate stabiliz- ing agents, have hindered the widespread use of lime-fly ash Note: R = Ca or Mg or combinations of these ions. stabilization of fine-grained soils. Based on his own studies as well as others documented in Lime-fly ash stabilization specifications vary substantially the literature, Minnick (10) indicates that the major ce- regarding the properties of the materials to be stabilized. menting compounds formed in lime-fly ash mixtures are ASTM C 593, which is widely used, does not consider probably calcium silicate hydrates and possibly ettringite. aggregate or material properties [gradation, plasticity index Low-sulfate sulfoaluminate may also be formed. (P1), soundness, etc.] at all, but rather specifies mixture The amorphous glassy materials in fly ash are the con- quality as evaluated by cured strength and durability. stituents that react to form complex silicates and aluminates Specifications used by some agencies consider aggregate (10, 15, 16, 17). The strength developed as a result of the gradation and quality. The specifications currently used by lime-fly ash reaction is dependent on the quantity of ce- Illinois, Pennsylvania, and Ohio are summarized in Table 3. menting materials produced (18). Mullite may also be an Specifications used by the Federal Aviation Administration important reactant. For a given lime-fly ash composition, can be found in the next section. increased quantities of pozzolanic reaction products are pro- duced by extending the curing time and/or increasing the FAA Aggregate Gradation Requirements curing temperature. The effects of curing time and tem- A wide range of aggregate gradations are permitted with perature on the strength development of a typical lime-fly these base materials provided appropriate mix design pro- ash—aggregate mixture are shown in Figure 2. cedures are followed. If the maximum particle size in the The pozzolanic reactivities of fly ashes are quite variable. aggregate exceeds 0.75 in. (19.0 mm), the aggregate shall Several studies have considered the relation between fly ash meet the gradation requirements given in Table 4 when properties and pozzolanic reactivity (14, 15, 19). The fol- tested in accordance with AASHTO T 11 and T 27. lowing factors are indicative of good pozzolanic reactivity: 8
Increased percentage of fly ash passing the No. 325 material being stabilized. Soil-lime reactiàns that may Oc- (45.m) sieve (14) or increased surface area (15, 19) cur are catiOn exchange, flocculation/agglomeration, and a Increased Si02 (14, 15), Si02 -4- R203 (14), and soil-lime pdzzolañiC reactioh SiO2 + A1203 (15) contents. Cation exchange and flcculation/ agglOnitation reactions Low carbon content (14) or loss on ignition (19). take place quite rapidly and cause decreased plasticity of the Increased alkali contents (19). fines and some "immediate" strengthening. The plasticity reduction improves workability and allows äsièt mixing Minnick et al. (19) emphasize that "ho single test On with rriatërials that áontain substantial quantities of plastic fly ash will predict the performance of that material in fines. compositionS in Which it is used," but that "it is far more Reaction products from the soil-lime pozzolanic reaction preferable to combine factors or develop multiple factors contribute to the dèvelopmènt of the cemntitious matrix in in making performance piedictions" thestabilized mixture. Similar secondary soil-lime reactions In addition to the primary rection between the linie and have been noted for soil-cerhent mixtures 6ontaining "linie- the fly ash, the lime may also react With the "fines" in the reactive" fines.
TABLE 3 AGGREGATE SPECIFICATIONS FOR LIME FLY ASH MIXTURES
Sieve % Passing
IllinOis. Pennsylvania PJii.2. 2" (50.0 mm) 100 100 100
1 1/2 (38.1 ni-n) 100 - 1" (25.0 mm) 9d-1 00 --- - 75-iO6
3/4" (19.0mm) - 52-100 70-100 - 1/2" 02.5 mm) 60-100 - - 50-85 3/8" (9.5 mm) - 36-70 5-100 -
No. 4 (4.75 fluli) 4040 24-0 4580 35-60 No. 8 (2.36 n) - - 1545
No. 16 0.18 mm) -. 10-30 25•-50 10-35
No. 40 (45 urn) 0-25
Nd. 50 000 jim) - --- .-._-- 3-18
No. iÔO (150 lAm) - -- 620 - No. 200 (75 jim) 0-10 (Gravel) 0i0
0.-15 (Crushed StOne & Slag)
b) Othér.Typtcal Requfrements .. Illinois Penn Ohio FAA Sodium Sulfate Soundness (AASHTO - T104) <25% < 20% <15% <12% Los Knge1s Abrasion (AASHTO - 196) <45%. < 55% Platicit$' Index < 9 < 6 - < 6 Liquid Limit < 25
REQUIREMENTS FOR GRADATION OF AGGREGATE FOR THE PLANT-MIX BASE COURSE
Sieve designation Percentage by weight passing sieves (square openings) 4 B C 2'! (50.0 m) 100 - - 1-1/2" (38.1 mm) - 100 - 1" (25.0 mm) 55 - 85 70 - 95 100 3/4" (19.0 mm) 50 - 80 55 - 85 70 - 100 No. 4 (4.75 nirn) 40 - 60 40 60 40 - 65 No. 40(425iirn) 10-30 10-30 - 15-30 No. 200(75 m) 5 - 15 5 - 15 5 - 15
I -I I . •'- --• 16001— I?OF 00°F 1400 ----. - I2D £ i00 70"F
0 I I 010 20 30 90 .60 70 80 90 100 110
Curing Time. days Figure 2. Eflects of curing temperature and curing time on the compressive strength development of an LF4 mixture (22). 10
MIXTURE AND MIXTURE PROPERTIES
RANGE OF COMPOSITION and curing conditions. Many of the properties vary for a given mixture depending on curing conditions. Thus, it is The composition of a lime-fly ash—aggregate (LFA) mix- necessary to define mixture curing conditions (time, tem- ture can be defined by designating the total amount of lime perature, moisture) when reporting mixture property data. plus fly ash and the lime-to-fly ash ratio. Lime and fly ash contents- are generally designated as a percent by dry weight Compressive Strength of the total mixture (i.e., 4 percent lime, 16 percent fly ash, 80 percent aggregate). Unconfined compressive strength is frequently used to eval- Lime-plus-fly ash contents depend on many variables, but uate the quality of cured LFA mixtures. A general range generally range from 12 to 30 percent. Fine-grained soils of typical strengths for various LFA mixtures is given in generally require higher percentages of lime plus fly ash and Table 5. Barenberg (22) states that standard ASTM C 593 requirements for well-graded aggregates generally fall at the curing [7 days at 100 F (38 C)] develops mixture com- lower end of the range. Aggregates of angular shape and pressive strengths ranging from about 500 to 1200 psi rough surface texture require larger quantities of lime plus (3400 to 8300 kPa). ASTM Procedure C 593-69 requires fly ash than rounded and smooth aggregate particles. a minimum compressive strength of 400 psi (2800 kPa) for Lime-to-fly ash ratios vary substantially, but the range is lime-fly ash used in paving-type mixtures. generally from 1:10 to 1:2 with ratios of 1:3 to 1:4 being Compressive strength development continues in LFA mix- common. Factors that tend to increase the lime requirement tures for a substantial period following placement. Figure 3 are (a) greater fines content [minus No. 200 (-75 sm)], shows core strength data for a typical LFA mixture con- (b) increased P1, and (c) increased pozzolanic reactivity of structed in Chicago (23). the fly ash. Lime-fly ash mixture proportions can not be established Shear Strength based on an analysis of the properties of the lime, fly ash, The shear strength of LFA mixtures has not been exten- and material to be stabilized. Proportions are determined sively considered. Unconfined compressive strength data using laboratory-based mixture design procedures (see for typical mixtures indicate that shear strength failures are Chapter Five) using the component materials to be in- not likely for normal pavement applications. corporated into the field mixture. -
ENGINEERING PROPERTIES OF LIME-FLY ASH- STABILIZED MATERIALS Strength I Many properties must be considered in lime-fly ash mixture development L I - proportion selection and pavement structural analysis. LFA 2nd and 3rd __ mixture properties vary depending on lime and fly ash char- years acteristics, mixture proportions, stabilized material, density, L7 Strength j deve/opmen /200 summer TABLE 5 1 RANGES OF COMPRESSIVE. STRENGTH FOR THE mont LIME-FLY ASH-STABILIZED MATERIALS Is winter 800 28 Day Immersed b Material Compressive Strength / Initial strength psi (kPa) 400 development Gravels 400-1300 (2800-9000) Sept construction
Sands 300- 700 (2100-4800) 0 Silts 300- 700 (2100-4800) / /0 /00 /000 /0,000 Clays 200- 500 (1400-3400) Age in days Figure 3. Compressive strength development of lime-fly ash- Crushed Stones and Slag 1400-2000 (10,000-14,000) stabilized mixture in Chicago area (23). 11
Typical shear strength data (24) for lime-fly ash—gravel 400 mixtures (lime-plus-fly ash contents of 13.5 to 18 percent, 4 S//ne lime-to-fly ash ratios of 1:2.5 to 1:3.5) indicate that angles /4 5 fly ash of shearing resistance varied from 49° to 53° and cohesions 82 5 grovel ranged from 55 to 128 psi (380 to 880 kPa). Mixture 320 curing was equivalent to 28-day moist-sand curing at -S approximately 70 to 75 F (21 to 24 Q. 'I
Flexural Strength 240
The flexural strength of LFA mixtures is substantially lower than the corresponding compressive strengths. Similar trends have been noted for other cementitious-stabilized /60 materials such as soil-cement or soil-lime mixtures. Laboratory test procedures similar to ASTM D 1635-63 - 3.6 SI/me can be used to evaluate the flexural strength of LFA mix- tures. Figure 4 illustrates typical flexural strength-cure time 36.4 % fly ash relations for two mixtures. 60.0 5 slop The ratio of flexural strength to compressive strength for most LFA mixtures is between 0.18 and 0.25. A value of 20 percent of the compressive strength is a conservative engineering estimate of the flexural strength of LFA mix- 0 20 40 60 80 /00 tures (22). Age in days Split-tensile and double-punch procedures have also been Figure 4. Flexural strength development of typical lime-fly proposed for evaluating the tensile strength of stabilized ash-stabilized mixtures (laboratory curing) (23). materials (25, 26). The tensile strengths determined by these procedures are approximately one-half the flexural strengths. LFA mixture pavement response and perform- /250 ance studies indicate that the mixtures can sustain repeated flexural stresses that are greater than the split-tensile or double-punch strength of the mixtures. Thus, the double- punch and split-tensile strength data are of limited value in /000 pavement analysis and design procedures. Mix: Modulus of Elasticity 750 I 45//me /4%fly ash According to Ahlberg and Barenberg (23) the elastic 82% grovel moduli for LFA mixtures are different depending on ( whether the modulus is determined from compressive or flexural testing procedures. They indicate that the flex- 500 ural modulus is somewhat lower than the compressive modulus. 2./x106 Flexural moduli values are recommended for pavement 250 design calculations (23). A moment-curvature plot for a typical LFA mixture is shown in Figure 5. Ahlberg and Barenberg (23) indicate that flexural moduli for granular LFA mixtures range from 1.5 X 106 to 2.5 X 106 psi (10 X 106 to 17 X 106 kPa) after a reasonable curing time. 40 80 /20 /60 200 LFA mixtures containing greater fines contents generally (Eb t 45 have lower moduli values. Curvolure, ) x ,o 6 LFA mixture moduli values increase as mixture strength increases. Figure 6 illustrates the development of compres- Figure 5. Moment-curvature relationship for lime-fly ash— aggregate mixture (23). sive strength, flexural strength, and flexural modulus for the LFA mixture used in an extensive University. of Illinois test• track study (23). Studies using "pulse. velocity" evaluation Poisson's Ratio procedures (27) for laboratory and field conditions also suggest increasing moduli values with the development of Poisson's ratio of a material usually varies with the intensity mixture strength. Figure 7 illustrates the relation between of the applied stress. However, this ratio usually remains unconfined strength and pulse velocity for 14 different soils relatively constant at stress levels below about 70 percent ranging from AASHTO classes of A-i-a to A-S. of the ultimate stress. Figure 8 is a plot of Poisson's ratio 12 6 /200 I I Compressive strength -.,L...
Modulus of elasticity
±a,stngth 7. 0 0 '/0 20 30 40 50 Specimen age, days, ambient conditions Figure 6. Effect of curing (approximately 73 F) on the engineering properties, of a lime-fly ash— aggregate mixture (82 percent aggregate, 14 percent fly ash, 4 percent lime) (23).
2000 - 100
0 0 0 80
0 0 ' 60 j1200 -- 0 0 0 0 40 I ®0 00 iaoc -i---
0 20 L 0
0 0 0 0 '.1 .2 .3 .4 100 poissonc ratio y 0 0 2OO 4,000 66000 epoo Figure 8. Effect of stress level on Poisson's ratio VsIoatp - ft. Per Sec. for a lime-fly ash—gravel mixture (23). Figure 7. Relationship between cured compressive strength and velocity for lime-fly ash-stabilized soils (27).
versus stress level for a typical LFA mixture (23). The Fatigue Properties value for Poisson's ratio remains relatively constant at about The fatigue properties of LFA mixtures are important in 0.08 for stress levels below approximately 60 percent of pavement design analysis. Because the compressive stresses ultimate strength and then increases at high stress levels, developed in most pavements with LFA mixture layers are reaching a value of approximately 0.3 at failure. small compared to LFA mixture compressive strength, com- Barenberg (22) indicates that for most pavement design pressive fatigue behavior is not considered to be of any calculations, Poisson's ratio for cured LFA mixtures can be consequence. Flexural fatigue is of major importance, taken as between 0.10 and 0.15 without appreciable error, however. 13
The flexural fatigue properties of lime-fly ash—aggregate mixtures have been studied and reported by Ahlberg and McVinnie (28). Results from these tests are summarized Y:X9/6/ogx in Figure 9. The results are presented as a relationship between the ratio of applied stress to the modulus of rupture 75 <7 1 of the material and the number of load applications to failure. All tests were conducted on beam specimens with loads applied continuously at a rate of approximately 450 applications per minute. .50 In analyzing the fatigue properties of LFA mixtures, the ------influence of the strength gain with time must be recognized. Because flexural strength increases with time, the stress level (expressed as a percent of the ultimate flexural strength) 25 decreases. Thus, as the time required to accumulate the number of load applications to failure becomes longer, the number of load applications to failure becomes greater. If the gain in strength is sufficiently rapid or the stress level is small, the probability of the material failing in fatigue is 2 4 /0 10 1010 6 minimized. 1010 l0 x, Number of cycles to failure
Figure 9. Flexural fatigue behavior of lime-fly ash—aggregate Autogenous Healing mixture (28). Autogenous healing refers to the phenomenon by which a crack in a material heals or re-cements itself by a self- o 6.5 generating mechanism. The continuing pozzolanic reaction between lime and fly ash in LFA mixtures provides the potential for autogenous healing. Laboratory tests by Callahan et al. (29) proved that autogenous healing can take place to a significant extent in lime-fly ash—aggregate mixtures. Several cases in which this phenomenon has occurred in the field have been observed. The degree of healing is dependent on the age at which the fracture occurs, the degree of contact of the fractured sur- faces, and the curing conditions. Although it can not be 4% lime expected that healing will occur across wide cracks, autoge- /0 % fly ash nous healing provides the potential for improved durability 86% grovel and fatigue resistance in LFA mixtures. 5.0 IE
LFA mixtures that are properly proportioned, constructed, 4.5 and cured will have a good resistance to "frost heave." /05 115 /25 /35 /45 /55 Dry density, lbs/cu ft Thus, the major volume changes in the LFA mixtures are induced by thermal and moisture changes. Temperature Figure 10. Effect of dry density on thermal expansion proper- and moisture shrinkage may develop sufficient tensile stress ties (30). to initiate cracking in the LFA mixture pavement layer. Miller and Couturier (30) investigated the thermal ex- Durability pansion characteristics of lime-fly ash—aggregate mixtures. Their data indicate that the coefficients of thermal expan- Cyclic freeze-thaw action is the major durability factor that sion for the LFA mixtures ranged from approximately 5 to must be considered for LFA mixtures. The extent of cyclic 7 X 10-6/°F (9 to 13 X 10-6/ *C). Increased dry density freeze-thaw action is dependent on the location of ma- and larger percentages of lime and fly ash tended to in- terial in the pavement structure, geographic location, cli- crease the coefficient of thermal expansion. Figures 10 and matic variability, and pavement system characteristics (32). 11 illustrate the density and lime content effect. Barenberg Cyclic freeze-thaw and brushing tests (ASTM C 593) reports similar values for the coefficient of thermal expan- have been extensively used for evaluating LFA mixture sion for LFA mixtures (31). durability. ASTM C 593 criteria require less than 14 per- There is no published information on moisture-related cent weight loss following 12 freeze-thaw cycles. volume change in LFA mixtures. It is known from field The Iowa freeze-thaw test (33) has also been used to experience that LFA mixtures do exhibit drying shrinkage evaluate the freeze-thaw durability of LFA mixtures. The tendencies. index of resistance, R, is used as a measure of durability.
70 = 100 P Rf (1) PC in which R = index of resistance to freeze-thaw; '. 6.5 I fib P f = unconfined compressive strength following 28 days moist curing at 71 F (22 C), 24 hours immersion \ I in water, and 10 freeze-thaw cycles; and 20% fly as!' PC = unconfined compressive strength of "control speci- 6.0 mens" following 28 days moist curing at 71 F b (22 C) and 11 days immersion in water. For Iowa climatic conditions, it has been proposed that R f should be greater than 80 for stabilized soils (34, 35). 5.5 Recent stabilized materials durability studies at the Uni- versity of Illinois (36) have resulted in the development of /5% 'I a freeze-thaw testing procedure that closely simulates field E conditions. The standard "freeze-thaw" testing cycle de- veloped for Illinois is shown in Figure 12. Typical com- 5.0 ¼ pressive strength—freeze-thaw cycle response data for LFA mixtures are presented in Figure 13. The mixtures were cured 7 days at 100 F (38 C) in accordance with ASTM C 593 prior to freeze-thaw testing. It is apparent from 451 I Figure 13 that the CA-6, Plainfield sand, and CA-10 LFA 0 2 4 6 8 mixtures possess a high degree of freeze-thaw resistance, Lime by weight, per cent and that Ridgeville sand and pit-run gravel mixtures are less durable. Figure 11. Effect of lime content on thermal expansion Dempsey and Thompson (36) have developed general properties (30). relations between the compressive strengths of stabilized materials (including LFA mixtures) subjected to 5 or '10 freeze-thaw cycles and the compressive strengths of the
0 E 12
Time, hrs Figure 12. Standard freeze-thaw cycle for Illinois. 15
'a cured mixtures prior to freeze-thaw testing. The relation- ships for 5 and 10 freeze-thaw cycles are shown in Figures 14 and 15, respectively. It is apparent that freeze-thaw durability resistance is significantly related to cured strength. 1100 In. a follow-up study (37), Dempsey and Thompson demonstrated that the compressive strength of cured stabi- lized materials subject to vacuum saturation provides a bet- ter indication of the 5- or 10-cycle freeze-thaw compressive 1000 strength. The relationship between vacuum saturation and freeze-thaw strength is shown in Figures 16 and 17. ASTM Committee C7.07 has revised ASTM C 593 to incorporate the vacuum saturation testing procedure. The standard 900 freeze-thaw brushing test was deleted from ASTM C 593. In conjunction with the development of improved freeze- thaw evaluation procedures, Thompson and Dempsey ex- s0 tended the residual strength concept (32). Residual strength is the strength of a stabilized material following the equiva- lent of the first winter's freeze-thaw cycles. If the residual strength can ensure the desired level of structural pavement 7OC response and the material displays a projected strength-time history that ensures that the field strength will always be greater than some minimum strength requirement, then satisfactory pavement performance can be attained. The SOC residual strength concept is illustrated in Figure 18. Field experience with LFA mixtures indicates that if the cured material possesses sufficient durability to survive the first SO winter's freeze-thaw cycles, the probability of experiencing durability problems during subsequent years is quite low. The additional curing developed during the summer follow- ing construction and during subsequent summers is bene- 400 ficial in developing additional strength in the LFA mixture. -S.--.
FACTORS INFLUENCING LFA PROPERTIES 300 There are many factors that significantly affect LFA mix- ture properties. Figure 19 illustrates that mixture properties are dependent on the interaction of many variables. The 200 0. variables can be grouped into four categories: materials, 'U Number Of Freeze—Thow Cycles proportions, processing, and curing. Figure 13. Effect of freeze-thaw on the compressive strength of lime-fly ash-stabilized mixtures. Materials
Fly ash, lime, aggregate, and soil characteristics have a strong influence on the ultimate nature of LFA mixture properties. A general discussion of these materials is pre- sented in Chapter Two. There are substantial property variations in all of the ingredients incorporated into an LFA mixture and there is also a wide range in mixture passing No. 4 (4.75-mm) sieve]. Sufficient matrix material quality as evidenced by the typical compressive strength must be present in the mixture to "float" the coarse aggre- data given in Table 5. gate (plus No. 4) to ensure high strength and good dura- bility. If insufficient matrix material is present in the mix- ture, adequate compacted density is not achieved in the Proportions matrix material, even though the over-all LFA mixture density is high. The total quantity of lime plus fly ash and the lime-to-fly The effects of the lime-plus-fly ash content on the ash ratio are the proportioning variables that can be altered strength and durability of an A-3 sand and a pit-run gravel, in LFA mixture proportion selection. It is generally ac- A-1-b(0), are shown in Figures 20 and 21, respectively cepted that when coarse-textured materials are stabilized, (36). Similar data are shown in Figure 22 for a well- the mixture properties are primarily controlled by the graded crushed stone (36). quality of the matrix material [lime + fly ash + fraction Additional data (6) for three fine-grained soils and a 1400 a'
U, 1200 - 83 + 0.94 0 >' U U r 0,91 Significant at a = 0.01 0 1000
LO- I', 800
'-0 - 200 400 600 800 1000 1200 Unconfined Compressive Strength. After Curing, psi Unconfined Compressive Strength After Curing, psi Figure 14. Relationship between after-curing strength and 5-cycle freeze-thaw Figure 15. Relationship between curing strength and 10-cycle freeze-thaw strength strength (all data adjusted to equivalent lid = 2). (all data adjusted to equivalent lid = 2). Unconfined Compressive Strength After Vacuum Saturation, psi Unconfined Compressive Strength After Vacuum Saturation, psi
Figure 16. Relationship between vacuum saturation strength and 5-cycle freeze- Figure 17. Relationship between vacuum saturation strength and 10-cycle freeze- - thaw strength (all data ddjusted to equivalent l/d = 2). thaw strength (all data adjusted to equivalent l/d = 2).
sand are shown in Figure 23. It is apparent that increased The effects of the lime-to-fly ash ratio (6, 24) on corn- lime-plus-fly ash content effects increased cured strength. pressive strength development of typical LFA mixtures are Normal proportioning operations are directed toward shown in Figures 24 and 25. There is generally an appro- achieving a satisfactory quality LFA mixture at a mini- priate lime-to-fly ash ratio that produces adequate strength mum cost. In most situations, lime and fly ash are more development in a given mixture. Even though the fly ash expensive than the aggregate or soil being stabilized. Lime- source remains the same, optimum lime-to-fly ash ratios for plus-fly ash contents are established at the lowest level a mixture vary depending on the characteristics of the ma- consistent with achieving satisfactory mixture quality. terial being stabilized. Factors that normally increase the lime requirement are increased silt and clay contents, and increased plasticity. The additional lime is required to sat- isfy the lime demand of the greater quantity of plastic fines. In general, lime-to-fly ash ratios are set at the lowest possible level consistent with maintaining LFA mixture quality. Lime is the most expensive constituent in an LFA A mixture.
Processing Mixing Residual Strength Maximum effectiveness of lime-fly ash stabilization is achieved when all of the materials are completely mixed. With fine-grained materials, adequate pulverization is needed to minimize the occurrence of clay balls in the mixture.
Time Figure 18. The residual strength concept of freeze-thaw durability. Plainfield Sand
1500 01 Aggregate Totdl quantity of lime and fly ash
0. Pozzolan 1000 Lime . Quantity of lime Ratio .. Water d' of lime 0 Add/ti yes to fly ash
U, Properties of pozzo/onic 500 stabilized g materials Degree =11Mixing , C. I I Type Time 0 10 20 30 Moisture Com pact/on LIME PLUS FLY ASH CONTENT, %
Moisture Density Temperature Note: Lime:fly ash ratio = 1:4 :1 1 Figure 20. Lime-plus-fly ash-content effects on compressive Figure 19. Factors influencing the properties of lime-fly ash- strength development (Plain field sand) (7-day curing at 100 F) stabilized materials (33). (36).
Well-Graded 1500 Crushed Stone
I I 0 10 20 30 0 10 20 30
LIME PLUS FLY ASH CONTENT, % LIME PLUS FLY ASH CONTENT, % Note: Lime:fly ash ratio = 1:4 Note: Lime:fly ash ratio = 1:4 Figure 21. Lime-plus-fly ash-content effects on compressive Figure 22. Lime-plus-fly ash-content effects on compressive strength development (pit-run gravel) (7-day curing at 100 F) strength development (well-graded crushed Stone) (7-day curing (36). atlOOF) (36).
The effects of mixing time on strength development of Small changes in compacted density effect substantial laboratory mixtures have been considered (24). Generally, changes in strength and durability. Similar trends have after a minimal mixing time for achieving an intimate been noted for other forms of cementitious stabilizers mixture, additional mixing does not produce significant (soil-cement, soil-lime). benefits as indicated in Figure 26. More thorough and uniform mixing can be achieved in plant-mix operations Curing than with mixed-in-place procedures. Proper conditions (moisture, temperature, time) are essen- An extensive study of plant-mixed LFA mixture opera- tial for curing LFA mixtures. Without proper curing, ade- tion in the Chicago area (20) indicates that the coefficients quate mixture designs may not perform satisfactorily in the of variation for cured compressive strength (laboratory- prepared specimens of plant-mixed material) range from field. Maintaining adequate moisture in the mixture is essential 7.7 to 18.2 percent with an average of approximately for proper curing. The lime-fly ash pozzcilanic reaction re- 11.5 percent. According to Thompson and Dempsey (32), quires water. If. the compaction moisture content (generally a reasonable range of coefficient of variation for field-mixed around optimum) is approximately maintained in the LFA stabilized materials is 20 to 25 percent; mixture during curing, sufficient water is available for the pozzolanic reaction. Density The lime-fly ash pozzolanic reaction is time- and tem- The compacted density of a given LFA mixture significantly perature-dependent. Figure 29 illustrates the effect of vari- influences the strength and durability of the cured mixture. ous curing temperatures and times on compressive strength Increased density improves strength and durability. The development for a typical LFA mixture (20). The effect effect of density on the strength and durability of typical of temperature on the lime-fly ash pozzolanic reaction is not LFA mixtures is illustrated in Figures 27 and 28. linear. Curing temperatures in excess of approximately 80 F It is apparent that careful consideration must be directed (27 C) accelerate the reaction to a greater extent than do to density in any construction quality control program. lower temperatures (20, 26). Strength development is sub-
Ratio by weight of lime to fly ash In the ni?uv* isl'2
E .!- 400 C- -0 Lime - fly ash soil no. $ t) .9 Lime - fly ash soil no.3 200 - A Lime -fly ash soil no.5 - 9 Lime ffly ash soil no. 8
I I I I I I I 5 10 '15 20 ' 251 30' 35 40 '45 50 01 Amount of lime-fly ash, percen.t by weight of total mixture
Notes: Soil 1 - Clay soil 5 - Sand Soil 3 - Silty Clay Loam Soil 8 Clay Figure 23. Effect of variations in the amount of lime-fly ash on the 28-day conwressive strength of lime-fly ash- stabiiized soils (6).
20 1 I
4 1.4 /.6 1:8 1:10 1.72 1:14 l.'16 l:fd reo Lime to fly Ush ratio
Figure, 24. Effect of lime-to= fly ash ratio on compressive strength of a lime-fly ash—slag mixture (60 percent slag, 40 percent linie plus fly ash) (24). 21
V a) 1600 a) E E 1200 1 0
800 It CsJ 7
0 0:10 1:9 2:8 -3:7 4:6 5:5 (1:4) (1:2.3) (I: 1.5) (1:1) Ratio by weighs Of lime tO fly ash Notes: Soil No. AASHTO. CThssi.fication 2 A-7-5(18) 3 A-4(8) 4 A-6(8) 5 A-?-4(0) 8 A=7-5(15) Figure 25. Effect of lime-tofly ash ratio on compresive strenth devëlbment (28-day curing, 100 ber- cent humidity, 70 F) (6). 22
Each point is the ave?-oge of 8- 2"x 4" specimens.
: . / 2 4 5 Mixing time, mm
Figure 26. Effect of mixing time on compressive strength development for a lime-fly ash-slag mixture (24).
'IOO 98. 96. 94 92 50
Percentage of Maximum Dry Density
Density, as % of Standard Figure 28. Influence of density on the strength and durability of a lime-fly ash-aggregate mixture (36). 90 95 100
H 120' F
70- b II IIn
0 3040506070 OD 90100110
iz Cu,mq Timi, days ::___ Figure 29. Effects of curing time and temperature on the strength development of a lime-fly ash-aggregate mixture strength of lime-fly ash-stabilized mixtures (22, 36). (20).
stantially retarded at low temperatures [less than approxi- If LFA mixtures are used in areas where low tempera- mately 40 F (4 C)]. tures may occur, it is necessary to consider time-tempera- Field curing occurs at varying temperatures. The "degree ture curing effects on fall construction. Adequate curing day" concept (20, 26) can be used to consider "mixed" must be obtained prior to the beginning of cyclic freeze- curing conditions as illustrated in Figure 30. It is important thaw to assure satisfactory field performance (32). If a to note that higher temperature curing data do not produce minimum LFA mixture strength has been established for a the same "strength-degree day" relation as lower tempera- particular situation, curing requirements (temperature-time) must be established accordingly. ture curing. It is emphasized that the strength-degree day relation is Strength development will continue in LFA mixtures after a property of a particular LFA mixture. Fly ash, lime, and the termination of the formal curing period. Figure 3 il- aggregate properties, as well as mixture composition, will lustrates field strength development for a typical LFA mix- influence the temperature-time dependent strength develop- ture constructed in Chicago (23). ment.
I Curing Tip.robwe 100. F A 50F "1 £60F I •10F UT 85F & 700—
D.gr Doys, 400 F Bass Figure 30. Degree day—strength relationships for a lime-fly ash—aggregate mixture (20). 24
CHAPTER FOUR PAVEMENT BEHAVIOR AND PERFORMANCE
PAVEMENT BEHAVIOR indicate any preliminary failure modes or abrupt changes in the load deflection properties of these pavements. Upon Although most pavements with lime-fly ash—aggregate removal of the LFA slabs, however, the bottoms of the slabs (LFA) materials are classified and designed as flexible in the region of the loaded area were severely cracked, pavements, as indicated in Chapter Three, these materials, indicating slab bending failure prior to the shear punchout when cured, can develop moduli values to well over two (23, 39). For the edge load conditions, the failure pattern million psi (14 000 MPa). With moduli values of this mag- is different, and this is reflected by the break in the load nitude, it can be expected that pavements with cured LFA deflection curves in Figure 36b. Failure of the LFA slabs mixes will behave essentially as slabs rather than as "flexi- under edge loadings follows the classical pattern outlined ble" pavements. Test data on full-scale and model pave- by Meyerhof (47). That is, as the load is increased, radial ments confirm that the theoretical load distribution char- cracks initiate at the point of maximum stress, which is acteristics of pavements with layers of LFA mixes are assumed to be directly under the load, and propagate up- essentially those of a slab (23, 39). Because of the rigid ward and outward from the loaded region. With the propa- nature of the material, slabs are susceptible to cracking gation of the radial cracks, there is a redistribution of caused by thermal and moisture changes in the pavements. internal stresses causing an increase in the radial stresses Detailed studies on behavior of LFA pavements are re- at the pavement surface near the point of maximum nega- ported by Ahlberg and Barenberg (23) and Barenberg tive bending. When negative bending stress reaches the (40). In these studies, model pavements from approxi- flexural strength of the LFA, a semicircular crack develops mately 3 to 6 in. (75 to 150 mm) thick were loaded at on the surface near the point of maximum negative stress. different stages of curing with static plate and dynamic The break in the load deflection curves shown in Figure 36b wheel loads. In the plate load tests, surface deflections were is probably the point at which radial cracking initiated determined by measuring the loaded plate deflections, and under the applied edge load. Although the pavement can the deflection basin determined by measuring the pavement carry additional load, this break point in the load deflection surface deflection at points outside the loaded areas. Some curve is probably the load that should be considered as the typical results of these tests are shown in Figures 31 through design ultimate for sustained pavement performance. 34. Figure 31 shows the relative load deflection patterns The ultimate strength of the LFA slabs under static load for an LFA slab compared with conventional flexible pave- has been shown to far exceed the strength predicted by ments. Figure 32 shows the load distribution effects of a elastic slab theory. Figure 37 shows the effect of flexural 4-in. (100-mm) LFA slab compared with a 9-in. (230-mm) strength of the LFA mix on the theoretical and observed conventional flexible pavement. Figure 33 shows a com- strength of the LFA slabs under interior and edge loading parison between typical measured deflection patterns and conditions. Note that the observed ultimate load under the theoretical deflections indicated by Westergaard slab edge loading agrees well with that predicted by the Meyer- theory for interior loading conditions. Figure 34 shows hof theory (47), whereas for the interior loading condition similar data for loads applied near the edge of the slabs. the observed ultimate load is greater even than that pre- The relative deflections of a flexible and an LFA pavement dicted by Meyerhof's collapse load theory. For both edge under a wheel load moving at creep speed are shown in and interior load conditions, the theoretical ultimate load Figure 35. failure condition is nearly two and one half times greater The load deflection characteristics and ultimate load than the corresponding failure load as determined by the carrying capacity of the LFA slabs are a function of the Westergaard theory. Thus, results from the plate load tests amount of curing of the LFA material, as indicated by the clearly show that the behavior of pavement with LFA ma- material's resistance to flexural deformation. The curves in terials is essentially that of a slab, but that the load-carrying Figure 36a reflect the load deflection curves for six 4-in.- capacity of this slab under single static load is likely to be thick (100-mm) LFA slabs tested to failure under inferior significantly greater than predicted by elastic slab theory. loading conditions applied through a 7-in-diameter (175- The reason for the greater load capacity of the LFA slab mm) steel plate. The fiexural strength of the LFA ma- is understandable in light of the known properties of these terial at the time of testing for each pavement is shown in materials. LFA materials, like concrete and other similar the figure. Similar information for two pavements tested paving materials, are assumed to be quite brittle in nature. under edge loading conditions is shown in Figure 36b. Fail- Although the stress-strain curves of these materials in flex- ure in the slabs under interior loads consisted of a shear- ure tests make them appear brittle, carefully controlled tests type cone punching through the slabs. The shape of the show them to have rather poorly defined yield stress levels. load deflection curves for the interior loadings does not Beyond this level, the materials undergo significant plastic 25
20 1 T I • i i i 8,000 8 18 - Natural Subgrade
16 - - 1-3-0 Flexible Pavement
14— 3-6-0 Flexible Pavement V c 4" LFA Pavement 4" Pozzolanic Base 12 - Intcrlor Load 0 No Surface 0 0 Load required to produce a — 10 - - deflection of 0.05" for var- ious pavement systems. All V 0 8 loads applied through a 7-" -a - diameter plate. 3 6— 2,500 2 Surface Base 1,000 2
Natur 1 Sub rade 0 0 0 25 50 75 100 125 150 175 200 11 4- 3 1 Deflection In .001 Inches 6"
Base ThIckness, Inches Figure 31. Comparison of load deflection characteristics of LFA pavements with typical flexible pavements.
P - 8,000 Lbs. A _I_A O..e
I I 1 1 1 I I I I I I I I I I I j 4035 30 25 20 15 10 5 0 5 10 15 20 25 30 3540
Distance from i of Plate, In.
Figure 32. Deflection profiles for an LFA slab and a typical flexible pavement under a static load applied through a 7-in.- diameter plate. 26
Distance From rL Loaded Area in Inches Distance Fro Edge of Slab, Inches n• In ,n an i,n cn 48 32 16 0 16 32 1.8 00 .001
.08 .05C .075
- .16 C .E .ioo 0 -Obsersed 0flectIons .125 / Theoretical Deflections
150 0bsesd Defiact ions .175 Theoretical Defictlo2,
LOAD NO. 5: SURFACE DEFLECTION OF LOAD NO. 3: SURFACE DEFLECTION OF POZZOLANIC PAVEMENT POZZOLANIC BASE UNDER ALONG LINE PERPENDICULAR STATIC LOAD AT INTERIOR TO EDGE OF PAVEMENT, POINT. UNDER STATIC LOAD APPLIED NEAR EDGE.
Distance Froa Loaded Are. In Inches Distance Pro. 04g. of Slab, Inches 0. 10 1.8 32 16 0 16 32 1.8 .000 20 JO 1.0 50 2 Cli. Ce. - .025
- .080 .050
o .160 .101 0 Ki. .125 Obs.rv.d 0.flsction, Th.oretical D.fi.ctIoni
.150 240 Obserned Def iections &25 Cip. .175 _...... _Theoretical Deflection
.200 ELI I po .225 LOAD NO. 6 SURFACE DEFLECTION OF POZZOLANIC PAVEMENT LOAD NO. 4: SURFACE DEFLECTION OF ALONG LINE PERPENDICULAR POZZOLANIC BASE UNDER TO EDGE OF PAVEMENT, STATIC LOAD AT INTERIOR UNDER STATIC LOAD POINT. APPLIED NEAR EDGE.
Figure 33. Typical load deflection patterns for LFA slabs under Figure 34. Typical load deflection patterns for LFA slabs under static plate loads (interior). static plate loads (edge).
flow without apparent gross rupture. During this yielding stress levels in the slab should be kept in the elastic process, there is a concurrent redistribution of stresses (pre-yield) range. within the slab that accounts for the slab's supporting sub- Recent field studies reported by Hirst, Fang, and stantially higher loads than indicated by the elastic slab Schmidt (45) also emphasize the slab behavior of the theory. Although gross rupture does not usually occur at LFA materials. Pavement sections with typical base course initial yielding, microscopic rupture is probably occurring materials, including LFA materials, used by the Pennsyl- within the material mass that, under repeated load applica- vania Department of Transportation (PENNDOT) were tions, may lead to fatigue failure. Thus, for reliable design, evaluated by deflection techniques in these studies. Dyna- 27
Inches from center of axle 18 WE 80 60 40 20 0 20 40 60 80 16 P
C 14 4.8" LFA - — 8" Crushed MtUre : MEN .02 : stonBase
.04 0 -6 Figure 35. Typical base deflection pattern under a moving load.
'1 98 r •
flect and plate load tests were run on a number of pave- 25 50 75 100 125 150 200 225 ment sections, and relative structural coefficients were de- Def1ection,, in 0.001 Inches a. Load Deflection curves for LFA pavements under termined based on the ability of these pavements to resist static load at interior point. deformation due to load. Moduli values for the different base materials were calculated by correlating measured de- flection values with theoretical values from elastic layer mom INNEE theory and finite element methods of analyses. Results from these studies show that the effective modulus for the LFA Eu• base materials is approximately 1,000,000 psi (6 900 MPa). Corresponding structural coefficients calculated from these IFFAE deflection data are in the order of 1.3 to 1.6 compared with 0. values of 0.10 to 0.16 for dense-graded crushed stone bases. .g 5 NOMENI MEN Creep-speed wheel load tests on full-scale airport pave- ments with LFA layers totaling up to 32 in. (800 mm) ME••• No '0 thick, are reported by Yang (49, 50). In these tests, a test 0 vehicle weighing 187,000 lbs (84 000 kg) was used to —J simulate the load from the landing gear of the Boeing 747 4' 0 aircraft. Up to 5,000 passes with the test vehicle were I- made over instrumented test sections of these pavements to 2 evaluate the behavior and performance of the LFA layers. A significant finding from this study is that the use of the LFA material in lieu of a crushed stone as the base material does not significantly reduce the total pavement 0 40 80 120 160 200 240 280 320 surface deformation, but does greatly improve the defor- Deflection,, in Inches mation recovery of the pavement. This is indicated in b. Load deflection curves for LFA pavements under Figure 38. As Yang observed, "The total surface deforma- static loads applied near an edge of the slab. tion is largely contributed by the deformation of the sub- Figure 36. Load deflection behavior of LFA slabs under static grade. However, the longer, smooth deflection configura- loading conditions. tion of the stabilized base (LFA) will produce a more durable and better performing pavement" (50). Because the aircraft loads are large and are distributed over such a large area, the effect of pavement stiffness on total pavement deformation is small. This is because nearly all of the deformations (>80 percent) occurs in the sub- grade. The stiffer LFA layers, however, distribute the load over larger areas of the subgrade, thus reducing the maxi- heavy-duty LFA pavement constructed for the Portland mum vertical stress transmitted to the subgrade as well as Port Authority, Portland, Oregon, for one of their marine the amount of permanent rutting in the pavement. Fig- terminals. Pavements were constructed with up to 20 in. ure 39 shows the permanent rutting trend versus pavement (500 mm) of LFA materials in three layers with a 3.5-in. thickness observed in the Newark Airport pavement studies. (89-mm) asphaltic concrete surface. Approximately six Plate load tests were also run on various layers of a months after placement of the LFA layers, the surface
16 -THEORETICAL ULTIMATE I ' CAPACITY (Meyerhof)l 1 THEORETICAL FAILURE ELASTIC SLAB (Westergaard)
14 OBSERVED FAILURE LOAD - Interior loading oEdgeloading
Al 4 • _____ ______- r 2 Edge-
80 160 240 320 400 FLEXURAL STRENGTH (psi) Figure 37. Compaison between the theoretical and observed Figure 38. Relationship between permanent and rebound defor- load-carrying capacity of LFA pavement slabs. mations observed in the Newark Airport test sections.
TOTAL PAVEI[NT ThIO(1'ESS1 INCHES 035 3J.. 25 20 15 10 5
N1IlBER OF COVERAGES
300 PAVEMENT SECTION " i,,,,i '2 AC S1F, \\\\\\ 1V'i NDER
8" LAYERS OF LCF STABILIZED - -,, 6"j MATERIALS \2000 10 J- 8_\" SUBGRAGE.- I-IYDRAUUc:FILL cDJ
08L_. l..•._...... I• • I I Figure 39. Eflect of pavement thickness on the performance of pavements for the Newark Airport. 29
and succeeding layers were carefully removed and plate TABLE 6 load tests run on the three layers of LFA base material as EFFECTIVE MODULI VALUES OF LFA PAVEMENT well as on the top of the subgrade. Using the elastic layer LAYERS AT PORTLAND PORT AUTHORITY (48) theory, the effective moduli values were determined for each of the three layers (see Table 6) (48). EFFECTIVE Each of the three mixes used in the pavement had dif- LAYER MIX MODULI, PSI (MPa) ferent proportions, and the corresponding compressive strengths at the time of testing were 1,670 psi (11 500 kPa), Top A 580,000 (4000) 560 psi (3 900 kPa), and 1,760 psi (12 000 kPa) for the Middle B 112,000 (770) A, B, and C mixes, respectively. There was no viable ex- Bottom C 630,000 (4 300) planation why mix B was weaker than mixes A and C; the Subgrade Hydraulic fill 43,000 (300) mixes supposedly increased in quality from the top to the bottom of the pavement (i.e., from mix A to Q. Based on the responses of pavements with LFA ma- conditions (23, 39, 41), (2) short-term evaluation of full- terials reported in the literature, it seems reasonable to scale pavements with conventional highway and aircraft conclude that these pavements distribute loads essentially loading under simulated service conditions (43, 45, 49, 50, by slab action. The effect of the slab action on total pave- 52, 53), and (3) evaluation of performance of pavements ment deflection is not consistent, however, because it de- in service for a number of years under normal traffic con- pends upon the manner in which the load is applied. With ditions (40, 54, 55). Each of these types of studies adds the applied loads distributed over very large areas, such as to knowledge of the performance of pavements with LFA with aircraft gear, the effect of the slab action on total mixes and the factors that influence their performance. pavement deflection is much less than when the loads are Performance trends of scale-model LFA slabs under ac- applied over relatively small loaded areas. celerated wheel loadings under laboratory conditions are reported by Ahlberg and Barenberg (23, 39), and Baren- PAVEMENT PERFORMANCE berg (41). Some typical results from these studies are Performance of pavements with LFA materials is affected shown in Figure 40. These results show that because of the by many factors. Some of these can be taken into account strength-gain characteristics of LFA materials with time, if directly in the design procedure, whereas others are more the ratio of applied to ultimate load as indicated by the subtle and need to be considered only as part of the over- Meyerhof theory is less than approximately 0.6 at the time all design approach. The primary factors affecting the per- of initial loading, these pavements do not fail in fatigue. formance of these pavements are: (a) loading and the If, on the other hand, these pavements are severely over- interrelationships between load, slab thickness, material loaded at an early age, the LFA materials crack and de- strength, etc.; (b) durability of the LFA material as re- teriorate under repeated loading. lated to the environment in which it must serve; (c) quality These observations are valid only if the pavements are of construction, including uniformity of the final product; new at the time of initial loading. As the LFA mate- and (d) subsurface drainage of the pavement system. rial becomes more mature with added curing, the rate of In evaluating the performance of paving materials, it is strength gain decreases. For the strength-gain effects to important to keep several factors in mind. All paving ma- completely affect the cumulative fatigue damage at more terials change dimensionally with changes in moisture and mature stages in development, the load-to-ultimate load temperature, and unless the material has enough ductility ratio has to be correspondingly lower as the pavement to absorb these dimensional changes, the pavements crack. matures. Also, for pavements with sufficient maturity to In addition, there is often a great difference between as- have well-developed shrinkage cracks, the ultimate load sumed material properties and properties of materials as calculations have to be based on edge loading rather than actually placed in situ. Many of the factors affecting pave- interior loading conditions. ment performance are interacting, that is, the presence of A review of the performance of LFA pavement in service one factor such as moisture increases or decreases the by Barenberg (40) also shows that pavements that were not effects of other factors such as loading or cyclic freezing overloaded at an early age did not fail in fatigue. In this and thawing. As a consequence, there are many subtleties study 16 pavements, some in service for 16 years or more involved in evaluating the performance of paving materials. at the time of the study, were reviewed for performance As compared to other paving materials, LFA mixes are and general distress. A summary of the pavements evalu- relatively new. Thus, long-term, documented histories of ated in the study is given in Table 7. Based on results of pavement performance with these materials are not gen- this survey, the author concluded that so long as the ulti- erally available. Several pavement performance evaluations mate load capacity of the pavement under edge loading, as have been reported, however, that permit the determination determined from the Meyerhof theory, was 1.5 to 2.0 times of the potential performance of pavements with LFA mixes, the applied load (load ratio of 0.5 to 0.7), the pavements and a few reports are available with actual performance did not fail in fatigue because of repeated traffic loads. evaluations with pavements having up to 16 years of service. Thus, the performance of these materials, insofar as load Studies on performance of pavements with LFA mixes applications are concerned, can be developed around a can be broken into three categories: (1) scale-model test- strength-versus-thickness criterion for various traffic condi- ing of pavements under laboratory and quasi-laboratory tions. 30
LOAD APPLICATIONS (LOG SCALE) io2 103 IO 5, TEST PAVEMENT NO. .-/ WHEEL LOAD gog 4 BASE MATERIAL_2e'zzoL4'wc 3 BASE THICKNESS ~' .1 2 SURFACE MATERIAL SURFACE THICKNESS RATIO 1.00
2 103 104 105 IO TEST PAVEMENT NO. ' -e 5 WHEEL LOAD 4 BASE MATERIAL ,Cbzzc,sa,v,c 3 BASE THICKNESS 2 SURFACE MATERIAL cr> SURFACE THICKNESS 41 41w4 (0
rr,r rin r Or IViILU r/r. v.ou o2 103 r y4 I05 O6 TEST PAVEMENT NO. ff_ WHEEL LOAD- 4 -J BASE MATERIAL 0ZZ044,'c x 3 ww 0 U BASE THICKNESS _ ._•3 5 Z 2 SURFACE MATERIAL /ei4' SURFACE THICKNESS '"ta o RATIO P/P11 0.68 po io o o ic TEST PAVEMENT NO. Al 4 WHEEL LOAD .92O28s BASE MATERIAL_'zze'.o.wc cax 3 5 BASE THICKNESS 2 cr SURFACE MATERIAL ,e,-Qe' (0 SURFACE THICKNESS zVel" RPtIIU 0.56 Figure 40a. Performance trends for LFA pavements under laboratory conditions. 31
PAVEMENT PERFORMANCE TRENDS
LOAD APPLICATIONS (LOG SCALE) 102 I0 I0 _105 _IC 6 TEST PAVEMENT NO. VT-I 5
WHEEL LOAD 3200L65 4
BASE MATERIAL POz.ZOLAIVIC 3
BASE THICKNESS -.0 2 SURFACE MATERIAL IVo#VE
SURFACE THICKNESS - 0 RATIO p/pu 1.95 51()IO 1011 IO io6 TEST FIEMENT NO. WHEEL LOAD 3200 L8 s BASE MATERIAL Ppzzp,wic 3 BASE THICKNESS 2 SURFACE MATERIAL NONE I SURFACE THICKNESS 0 RATIO 0.87
)IO _ 104 10 IC 6 TEST FAVEMENT NO: T-3 WHEEL LOAD 320oL 5 4 /OZZ0 &NI1X BASE MATERIAL 11 4. 3 BASE THICKNESS _4.0" SURFACE MATERIAL NONE SURFACE THICKNESS - I PATTfl DID fl . fl
)' 10' 104 10 106 TEST PAVEMENT NO. 4.. WHEEL. LOAD 3ppL 4x BASE MATERIAL POzojiii/,c >3z BASE THICKNESS . 5.5'f SURFACE MATERIAL 2 SURFACE THICKNESS -
RATIO P/P•J 0.35 0 '4 zZ
Figure 40b. Performance trends for LFA pavements under laboratory conditions.. 32
TABLE 7 SUMMARY OF PAVEMENT SECTIONS AND PAVEMENT CONDITIONS
Pavement Compressive Estimated Thickness Strength Traffic (inches) of Daily Remarks Pozzolanic Base Material (psi)
(n S.- U, L) - a) U S.- •- 4.1 0 a) U I C a) a) C.) 05 Q)5- U Sfl U, 4- E a) ' >s 0 VS 0 10 US U 4- U .0 10 — U — > . us .- a) L. Uw so U' 10 >m L. . 05—U to .- U VS co VS N- ' LI.-U
1 2 7-9 0 1000 2160 8 4000 600 600 Failed along edge for about (8) 30 to 40% of length.
2 2 7-9 0 1000 1925 8 4000 150 10 Trench settlement failure only.
3 1.5 3-12 0 1000 3240 6 2000 75 5 15 to 20% of total (8) . area failed.
4 2.5 8 4.5 1000 1955 1 3000 325 25 SlIght edge distress only.
5 3 6.5- 4-24 1000 2600 5 400 500 200 Slight edge distress only. 11 (10) 2 to 4% of total area failed. 6 1.5 4-13 12 -- 1310 3 3000 150 50 (7)
7 2-3 5-6 0-12 -- 1720 5 ------No distress.
8 1.5 6 4 1165 1310 3 3000 700 100 2 to 3% of total area failed.
9 2 8 0 1150 1200 8 ------No failures. See discussion.
10 2 6 0 1350 1090 .3 ------1 to 2% of total area failedii areas of soft subgrade only.
11 2 10 - -- No 6 5000 300 van- 1 to 2% total area distressed. Cores able See discussion.
12 3 10 - 1705 1700 7 No distress.
13 2 6 - -- 1100 7 2000 200 50 3 to 5% area distress occurre during first year, did not progress.
14 2 8 - 1104 600 7 ------No distress.
15 2.5 8 - 1795 825 7 -- 250 200 Some map cracking % area not indicated.
16 2 8-10 - 740 1800 8 -- 200 150 No distress. 33
Another way of evalüatig the perforriance of LFA In a- TABLE 8 terials is to. consider the structural coefficiéhts that have STRUCTURAL COEFFICIENTS OF LFA been assigned by various design agencies. Such coefficients MATERIALS (23) are developed ardund some short-term evaluations, and then adjusted on the basis of the over-all performance of pave- STRUCTURAL ments in service. Such coefficients have a s'ome.vhat broader QUALITY OF LFA COEFFICIENT (a2 ) connotation than mere sirength, because they reflect the actual performance of the materials in service. Inservice High ' 0.34 performance is a function of durability of the material and Medium 0.28 construction variability as well as the basic material Low 0.20 characteristics. Following the concept developed by the AASHTO Com- mittee on Pavdmént Design froni the results of the AASHO Road Test (51), the structhral capacity of a flexible pave- TABLE 9 ment can be defined by the relationship RANGES OF COMPRESSIVE STRENGTH AND SN = a1D1 + a2D2 + a3D3 (2) MODULUS OF ELASTICITY FOR LFA MATERIALS
in which COMPRESSIVE STRENGTH MODULUS OF [7 DAYS AT 100 F (38 C)], ELASTICITY, SN = the structural number or structural capacity of QUALITY PSI (kPa) PSI X 10 (MPa) the pavement; D1, D2, D3 = thicknesses of the surface, base, and High >1000 (>6900) >500 (>3400) 'subbase; respectively; and Medium 650-1000 (4500-6900) 250-500 (1700-3400) Low 400-650 (2800-4500) 100-250 (690-1700) a1, a2, a3 = material cdefficients, often referred to as structural coefficients.
This relationship indicates that to achieve a specified structural capacity there is an inverse linear relationship between the structural coefficient and the thickness of each TABLE 10 layer in a flexible pavement system. Usually, there are RELATIVE STRUCTURAL qOEFFICIENTS OF FOUR minimum material stEndards associated with the assigned STAILIZED MATERIALS (PENNDOT) coefficients. In addition, a range of coefficients can be used to reflect diffeierit qualities for specific materials. Ahlberg a0 (TEST a2 (cUR- and Barenberg (23) suggest the coefficients for LFA mate- BORE MATERIAL VALUE) RENT USE) rials given in Table 8. Aggregate-cement base 0.55 0.30 No specific limits for compressive strehgth or modulus Aggregate-lime-fly ash base 0.51 0.30 of elasticity were assigned by Ahlberg end Barenberg for Bituminous concrete base 0.51 0.40 the three categories of LFA, but a review of the background Aggregate-bituminous base 0.49 0.30 data suggests the ranges given in Table 9. Note that the modulus of elasticity does not have a 1:1 relationship with compressive strength. Note also that even the lowest quality of LFA must meet realistic durability criteria to be accept- able. and giving satisfactory performance as of mid-1975. Table A field study on the performance of stabilized base ma- 10 gives th relative structural coefficients for the four terials including LFA materials is reported by Dunn (43). stabilized materials as determined from the Pennsylvania Base materials tested included lime-fly ash—aggregate mix- State University test track, and the current values used by tures, cement-treated aggregates, and two grades of bitu- the Pennsylvania Department of Transportation for these minous stabilized aggregates. These materials were tested same materials. All values are based on a standard value of in the test track operated by Pennsylvania State University. a2 = 0.14 for high-quality crushed stone. This test facility is a one-mile-long test loop that is loaded The higher-than-expected values obtained from the test by trafficking the test pavements with standard truck ve- track results can be explained in two ways. In evaluating hicles. Both pavement behavior and pavement performance these coefficients, it must be kept in mind that if any of the were evaluated in this study. stabilized base materials (especially the aggregate-cement Figures 41 and 42 show the performance trends for pave- and aggregate-lime pozzolan bases) are significantly over- ments with LFA mixtures as reported by Dunn (43). loaded, they crack and the continuity of these bases is par- Trafficking on these pavements was started in October 1972, tially lost. Once these bases are severely cracked, there is and required nearly two years to accumulate the million- a rapid loss in serviceability level with continued loading. plus equivalent 18-kip (80-kN) single-axle loads shown in Thus, some minimum thickness standard is required, along the figures. Private communication with supervisors of the with the structural coefficient values, for sound pavement test facility indicates that these sections were still under test design. It is anticipated that, because of the controlled 5r 1— PSI = 3.25 + .0005W PSI = 3.20 + .0005W
0 CtD 0 0, C21 — 0 FRO—T-0 -----Tr 0 PSI '= 3.18+ .0001W PSI = 3.08 + .0002W Lu U) I- LU U) LU 0
1 ____ 0______0 1/4 CPR SIMULATOR Q-- 0 1/4 CAR SIMULATOR p HYBRID CCWUTER p 1r HYBRID CC*'IPUTER 0 P
200 400 600 &JO 1000 1200 o 2W LIW 6W &)J 1(X) 12(X) EQUIVALENT 18—KIP AXLE LOADS X iü 1073 EQUIVALENT 18—KIP AXLE LOADS X
Figure 41. Pavement performance curves for Section 3; 2.5-in. AC surface, 8-in. LFA Figure 42. Pavement performance curves for Section 12; 2.5-in. AC surface, 8-in. LFA base, and 8-in, granular subbase. base, and 8-in, granular subbase. 35 loading, the test pavements were never overloaded. Thus, TABLE '11 the high apparent structural values compared with the RELATIVE STRUCTURAL COEFFICIENTS USED BY crushed stone. SEVERAL STATES FOR LFA BASE MATERIALS The quality control employed during the construction process could also account for the high structural values. STATE COEFFICIENT, a, No specific data are available on the quality control used Illinois 0.28 in construction of the test pavements, but it seems likely Michigan 1: 1 with black base that because this is a test facility, the level of quality con- Ohio 0.25-0.30 trol would be greater than in normal pavement construc- Pennsylvania 0.30 tion. Because most stabilized materials are more sensitive to variations in product quality than the unbound aggre- gates, it follows that the stabilized materials in the test pavements would give better relative performance than in TABLE 12 normal use conditions. APPROXIMATE MIX PROPORTIONS USED IN THE Typical structural coefficients recommended by several NEWARK AIRPORT PAVEMENT states are given in Table 11. Direct comparisons of these values are not totally valid, because each agency uses INGREDIENTS, % slightly different values for the crushed stone base mate- MIX DES- rials, which are normally considered to be the standard. IGNATION LIME CEMENT FLY ASH SAND STONE However, the values shown provide a general indication of A 3.6 0.9 12 53.5 30 the relative performance of the LFA materials under normal B 3.2 0.8 14 82 0 service conditions. C 2.8 0.7 14 82.5 0 Based on the structural coefficients used by most agen- cies and the results of short-term evaluations, the perform- ance of LFA mixes of intermediate quality compares favor- ably with that of cement-treated aggregates having a 7-day compressive strength of 700 psi (4 800 kPa) or greater. The critical factor in the performance of both LFA and cement-aggregate mixtures is achieving density of the ma- terial in place. In this respect, the advantage lies with the LFA because there is usually a longer time period between MIXA mixing and setting during which density can be achieved. El inch AC Surface With cement-aggregate mixtures, all densification must be accomplished within two hours, and preferably within a much shorter time; but with most LFA mixes, delays of several hours do not affect the compactability of the ma- terial unless it is allowed to dry to below optimum moisture content. This is not a general rule, however, because some fly ashes are so reactive that special handling may be re- quired. Each particular combination of materials used Critical Runway and L 30 inch LFA should be checked for reactivity and rate of reactivity be- Taxiway Areas fore decisions are made on the allowable lead time prior to completion of the compaction process. To thoroughly understand the potential and the limita- tions for LFA materials, it is necessary to review the per- formance and distress of several heavy-duty pavements in service. Some potential problems and causes for these prob- lems can be illustrated through a review of the performance and distress of several highway pavements. With proper de- sign and construction control, pavements with LFA mate- CIIbCIUIflUIIflUJ CV I 111.11 LtI rials have the potential to provide a high level of perform- inch AC ance; with improper design and control during construction, the potential of this materialmay not be realized. The base and subbase for runways, taxiways, and apron areas at Newark Airport were constructed with LFA ma- terials. Figure 43 shows some typical cross sections of the pavement sections for various airport facilities. Mix pro- portions and properties of the cured mixes used in the con- Typical struction are given in Table 12. Quality control during the construction was provided by the Port Authority of New Figure 43. Typical cross sections used at Newark Airport.
York and New Jersey and is generally higher than achieved TABLE 13 in normal highway pavement construction. COMPOSITION OF LIME-FLY ASH MIXES USED IN The projected compressive strength of these materials PORTLAND MARINE TERMINAL varies from around 1,000 psi (6900 kPa) after one year to in excess of 2,000 psi (14 000 kPa) after approximately PROPORTION (%) three years. Cores taken from these pavements after one to two years in place are well in excess of the 2,000 psi MIX MIX MIX COMPONENT projected ultimate strengths. A B C At the time of the latest evaluation,* some of the run- Hydrated lime, ASTM Type N 3.3 3.0 3.0 ways and taxiways had been in service for slightly over five Portland cement, ASTM Type I 1.1 1.0 1.0 years. At that time, the only significant distress in the pave- Fly ash 6.6 6.0 6.0 ments was some shrinkage cracks in the shoulder area where Inorganic silt 8.0 10.0 10.0 an insufficient number of contraction joints was provided, Aggregate 25.0 10.0 - and one crack because of subgrade settlement in an area In-place fill sand 56.0 70.0 80.0 where an old drainage ditch existed prior to the construc- tion. The airport facility engineers for several major airlines using Newark Airport indicate that they are satisfied with the performance of the pavements. They generally agree (48). Cores taken from the pavements after less than six that despite the aforementioned minor cracking distress, the months of service show that the strengths exceed the pro- pavements at Newark Airport are smooth with a high ser- jected strengths of the materials. viceability rating and show excellent performance trends. After more than one year of service, the pavements at the It should be noted that contraction joints as illustrated in marine terminal showed only isolated cracks in two loca- Figure 44 were placed at 150- to 200-ft (46- to 61-m) tions. These cracks are believed to be because of non- intervals on the runways and taxiways. In some instances, uniform settlement of the hydraulic fill placed over the en- the asphaltic concrete (AC) surface was partially sawed tire site before the pavements were placed. It is significant through, directly over the joints in the LFA base, and in to note that Portland has a mild climate with only moderate other instances no saw cuts were made and the AC was ranges in moisture and temperature. No shrinkage cracks allowed to crack in a random manner. The sawed joints were observed in these pavements. Figure 47 shows the were sealed as soon as possible, whereas the random cracks condition of the runway and taxiway extensions at the were not sealed until later when they had fully developed. Portland Airport after almost one year of service. These random cracks have caused the maintenance engi- neers some concern, but apparently have notcaused any structural damage or loss of performance in these pave- ments. Heavy-duty LFA pavements have also been recently Runway II completed by the Portland Port Authority of Portland, _I or Oregon. Figure 45 is a cross section of two of the pave- _fraxiwyj A 4 A II II ments constructed by the Portland Port Authority. Joint Spacing = 150 The marine terminal pavement has been in service for I over a year with no significant problems. This pavement covers over 40 acres (162 000 m2) and is used as temporary storage for containers during transfer from Ship to land transportation. These containers, which weigh up to 40 tons Random crack (36 000 kg) each, are stacked up to three containers high Sawed and Ffiled not Filled with only a few inches between stacks. A transtainer, as I- shown in Figure 46, is used to transport these containers AC from one location to another. Normal wheel load for the 2 wide 2' wide kerf f IX loaded transtainer is 50,000 lb (220 000 N), but under un- kerf filled foam usual loading and wind conditions, individual wheel loads B filled can go as high as 100,000 lb (440 000 N). Composition of the LFA materials used in the Portland Marine Terminal is mix given in Table 13. Projected compressive strengths of these materials vary C-MIX UNJOINTED I ' C-MIX UNJOINTED from approximately 800 psi (5 500 kPa) after three months, to in excess of 2,000 psi (14 000 kPa) after three years Alternate Joints Section A-A * Private communication with airline facility engineers, Newark Airport personnel, and personal observations by Dr. E. J. Barenberg. Figure 44. Jointing system used at Newark Airport.
2" AC surface 8" Mix A 6" Mix B 6" Mix C Runway
Shoulder Pavement 3" As halt Concrete&
,, I 6 LCF ZB 8" LCF - B 8"LCF-C
x 1½" Saw-cut Contraction Joint with Rubber Asphalt Filler
Asphalt Concrete i LCF - A 1" Closed-Cell Polyethylene or LCF - B Rubber Foam Filler @ 200 ft C.C.
LCF - B
LCF - C
Detail of Expansion Joint
Figure 45. Typical cross sections used in the LFA heavy-duty pavements at Portland, Ore., for the marine terminal and airport. 38 1hfl
- -: - -
Figure 46. Transtainer and storage bins at the Portland, Ore Figure 47. Pavemnemzt at Portland International Airport con- Marine lernitnal with LFA pavements. structed with LFA materials showing (a) a pavement Overview (1/IC! (b) a traverse joint.
l'erformance of pavements with LFA materials, as well A section of the pavement surface was removed along the as other paving materials, in pavements in Lake County, transverse crack as shown in Figure 48. Density readings Illinois, were evaluated by Hazarika (44). The primary were taken with a nuclear gauge near the pavement edge thrust of this investigation is to make an economic analy- and at approximately the center of the wheelpath [25 ft sis of the life-cycle costs of different pavement systems and (7.6 rn) from edge]. The measured densities are shown in to evaluate ways of decreasing life-cycle costs through elimi- Figure 48. Note that there is a significant difference be- nation of the distress that causes the loss in serviceability. tween the density near the pavement edge and that in the In the course of his investigation, Hazarika (44) opened wheelpath. several pavements with LFA materials to determine the The distress on Winchester Road (Fig. 49) is similar to cause of the distress. Figures 48; 49. and 50 show the type that on Everett Road except that there is no heave and no and extent of distress at three of these locations. A few alligator cracking along the transverse crack. Density read- observations on the type of distress at these locations are ings for this investigation were taken at three locations: instructive. near the pavement edge, in the wheelpath, and between the At the Everett Road location (Fig. 48), the distress con- wheelpaths. Cores were also taken at these locations where sisted of alligator cracking along the pavement edge and the condition of the LFA material permitted. Core strength along either side of a transverse crack. The material along and density readings are shown in Figure 49. the transverse crack had heaved or tented to a significant As with the Everett Road analysis, there is a significant degree. clitference between the density of the LFA material near
Sketch of Test Site with Distress: Sketch of Test Site with Distress: Section along ' N transverse crack - - Sketch of Test Site with Distress: heaved. upi to 211: I Core Locations Also Locations for I • I Density Measure - -.
ç 0 -
-. 14 Edge Slightly Location YORKHOUSE ROAD Faulted Down Year Constructed 1963 Plan View Plan View Age When Investigated 9 years ADT (average daily traffic) Location I EVEREU ROAD Location WINCHESTER ROAD Initial 400 Year Constructed 1962 Year Constructed 1963 Intermediate 800 Age When Investigated 10years Age When Investigated 9 years Final 650 ADT (average daily traffic) ADT (average daily traffic) Initial 300 ... Initial 400 Location Moisture Dry Intermediate 450 Intermediate 2300 1080: Content Density Final 600 Final (%) •(pcf) 111.0 Location Moisture Dry Location Moisture Dry Compressive Pvmt Edge 8.2 131.9 Content Density Content Density Strength Wheelpath 7.7 Lane Ctr. 7.6 131.9 (%) (pcf) (%) (pcf) (psi) Pvmt Edge 8.4 113.8 Pvmt Edge 7.1 123.6 Notes: Curve superelevated - pave- Wheelpath 7.3 134.4 Wheelpath 127.9 < 2000 ment badly cracked along lower edge. Lane Ctr. Lane Ctr. 6.8 136.4 4500 Upper lane very little cracking - at time of opening test section, Notes: pavement badly heaved across Notes: alligator cracking along both there was a very high percentage of width along transverse crack - possibly pavement edges, north edge slightly semi-truck traffic. due to expansion of AC layer. faulted down, LFA base. yéry&wet. .
Figure 48. Distress pattern on Everett Road. Figure 49. Distress pattern on Winchester Road. Figure 50. Distress pattern on Yorkhouse Road 40 the pavement edge and that found further in from the pave- terial between wheelpaths compared to the material in the ment edge. This difference in density is reflected in the wheelpath are less obvious. Speculation on this phenome- strength of the cores removed from the pavement. Near non leads to two possible causes: (a) the pattern of the the edge where density was very low, no cores could be rollers and other compaction equipment during construc- taken because the LFA was badly disintegrated. At the tion, and (b) the rolling of construction equipment on the locations in and between wheelpaths, the core strengths layers of LFA material prior to its setting up. The pat- reflect the measured densities of the material at these terns of the compaction equipment used in the construction locations, with the higher strength cores also having the of the pavements investigated are not known; thus no fur- higher densities. ther conclusions can be reached concerning this potential The investigation on Yorkhouse Road (Fig. 50) was on cause. Construction traffic on this type of construction does a superelevated curve. At this location, all of the distress not generally follow the final wheelpaths of the pavement. was along the lower edge of the pavement and consisted of It is likely that such traffic produces added densification in alligator cracking that extended to approximately the mid- areas other than the final pavement wheelpaths. point of the lower lane. Density readings for the three Use of the compacted LFA layers by the construction locations are shown in Figure 50. equipment is normal for the type of construction procedures It is noted that in all three locations, the density along used with LFA materials. Although this practice has been the edge was much less than in the wheelpath or between successful and economical, it does involve certain inherent the wheelpaths. Data on the densities from these three dangers. Two types of distress have been observed from locations (plus four additional locations) are summarized these operations. One type of distress occurs when the LFA in Table 14. These data clearly show the effect of inade- material becomes saturated before setting up. If the ma- quate compaction of the LFA material along the edge of terial does not have adequate internal stability, the unset these pavements. LFA begins to shove and rut like a poorly graded aggregate. The types of distress observed during this investigation This distress is immediately observable and can be cor- suggest that three factors are involved in the pavement dis- rected by reshaping and recompacting the pavement layer tress. The distress is due primarily to deterioration of the and allowing it to cure before additional use is permitted. LFA material. This deterioration is, in turn, the direct re- A more subtle and perhaps more harmful type of distress sult of excess moisture in the base material and inadequate can occur when heavy construction equipment runs on LFA density of the LFA, especially along the pavement edge. As materials that are partially set up. This damage is particu- illustrated by the data from Winchester Road, when ade- larly harmful because it occurs after the initial set, and even quate density is achieved, LFA materials develop and main- with the autogenous healing, the damage significantly re- tain a high level of strength. Conversely, it can be shown duces the ultimate strength of the material. This type of that reductions in the compacted density result in signifi- damage is also more harmful because it is usually not ap- cantly lower strength and sharply reduced durability for parent on the layer surface during construction, especially these materials. if the LFA layer is sealed and surfaced immediately. This The pavement edge is usually inadequately compacted second type of damage occurs when the material is placed and, therefore, is of low density because of (a) the lack of over soft supporting soils and heavily loaded trucks, or side restraint during rolling or (b) the lack of adequate other heavy pieces of construction equipment, are permitted rolling along the edges. The different methods of compac- on the partially set up layers. tion and ways to achieve uniform densities to the pavement The discussion on performance of pavements with LFA edge are discussed further in Chapter Six, Construction materials has been directed primarily at, their use as base Procedures. and subbase materials. These materials have also been used Causes for the difference in densities of the LFA ma- as the base layer in pavement shoulders for both rigid and flexible pavements. The performance of LFA materials as the base layer in shoulders is somewhat spotty; some instal- lations show good performance whereas in other installa- TABLE 14 tions the performance is far less favorable. DENSITY OF LFA MATERIAL AT THREE PAVEMENT A review of the installations in which the LFA material LOCATIONS did not give good performance as a shoulder material re- veals that the same factors that cause poor performance in DENSITY AS the pavement section proper also affect its performance in DRY DENSITY (PCF) PERCENT the shoulder. The biggest single cause for distress in the OF WHEEL- shoulder is durability of the LFA material. This, in turn, STD. PATH is greatly affected by such factors as improper compaction LOCATION OF TEST AVE. DEV. DENSITY adjacent to the pavement edge and segregation of the LFA Near pavement edge 122.42 9.1 91.0 adjacent to the pavement drainage edge. This lack of dura- Centerline of bility near the pavement edge produces a surface distress in wheelpath 134.8 6.6 100.0 the shoulder near the pavement edge, which in turn allows Between excessive water to infiltrate the shoulder near the pavement wheelpaths 130.0 7.5 96.0 edge. This water, often saturated with salt, causes an ad- 41 vanced rate of disintegration in the LFA shoulder base layer affected by the same factors that affect the performance of (46,55, 56). pavements with other stabilized materials. Thus, the pri- Although the potential for distress appears greater when mary factors affecting the performance of pavements with using LFA materials for shoulder base construction, the suc- LFA materials are durability, proper thickness design con- cessful use of this material in some locations indicates that sistent with the expected loading, and material strength de- it has the potential for this type of application. During velopment. Pavements with LFA materials are no more shoulder construction, high-quality construction techniques sensitive to these factors or to construction anomalies than should be used to ensure uniform density throughout (es- are pavements with other types of paving materials. It can pecially near the pavement edge) and to prevent segrega- be concluded, therefore, that with proper attention to for- tion of the LFA material due to overhandling. It is also mulation of these mixes, design of appropriate pavement important to design shoulders in a manner that permits sections, and proper control during construction, LFA ma- adequate drainage of infiltrating water. terials have the potential to provide pavements with ex- The performance of pavements with LFA materials is cellent performance records.
CHAPTER FIVE SELECTION OF MIXTURE PROPORTIONS
Proportions of lime, fly ash, and aggregate (soil) should be sufficient matrix material to "float" the coarse aggregate. selected so that a mixture can be used for a designated pur- Lime-plus-fly ash contents in excess of the amount required pose. In most instances, quality requirements for the mix- for maximum dry density produce systems in which the ture components are specified as indicated in Chapter Two coarse aggregate [plus No. 4 (>4.75 mm)] is floating in of this synthesis. a matrix of lime plus fly ash plus aggregate fines. The mixture proportions selected must (a) possess ade- Many agencies use compacted dry density (ASTM C 593) quate strength and durability for the designated use (gen- to determine the approximate amount of lime plus fly ash to erally as a base or subbase layer), (b) be easily placed and incorporate into the mixture. Moisture-density curves are compacted, and (c) be economical. For a given set of ma- developed for several mixtures with varying lime-plus-fly terials, several proportions can provide lime-fly ash—aggre- ash contents. The lime-to-fly ash ratio is constant at some gate (LFA) mixtures of satisfactory quality. predetermined value. A plot is then prepared showing the relationship between maximum dry density and lime-plus- APPROACH TO MIXTURE PROPORTIONING fly ash content. The peak of the density—lime-plus-fly ash curve corresponds to the condition in which the voids in the For a given set of materials (lime, fly ash, and aggregate), aggregate are filled with lime plus fly ash plus aggregate the factors that can be varied in the mixture selection proc- fines [minus No. 4 (<4.75 mm) fraction]. ess are the amount of lime plus fly ash and the ratio of It is desirable and conservative to have lime-plus-fly ash lime to fly ash. The blending of materials creates more suit- contents in excess of the amount required to develop maxi- able gradations that can be stabilized with lime plus fly ash mum dry density. LFA mixture quality may drop off rap- to produce superior quality LFA mixtures (compared to the idly when lime-plus-fly ash contents are less than the If more suitable stabilizing of unblended materials) (58). amount required for maximum dry density. and economical LFA mixtures can be obtained by blend- Figure 51 shows a typical maximum dry density—lime- ing procedures, various blended gradations may be appro- plus-fly ash content response for an A-3 (0) material. Ma- priately considered in the mixture selection process. terials that are well graded in the range of ± 1-in. (25-mm) maximum size through the No. 200 (75-Lm) sieve do not Lime.PIus.FIy Ash Content require large quantities of lime plus fly ash in order to It has been found (57, 58) that the quality of cementitious achieve maximum dry density. Figure 52 indicates that for stabilized mixtures (strength and durability) is related to a well-graded crushed stone and a pit-run gravel, lime-plus- the quality of the matrix material. It is possible to achieve fly ash contents in excess of 10 percent decrease maximum a high compacted density in the matrix material, thereby dry density. It is apparent that the original gradations of improving its strength and durability, only if there is the material to be stabilized significantly influence the lime-
125 I plus-fly ash content requirement for developing maximum dry density. Poorly graded materials with smaller maxi- mum sizes require substantially more lime plus fly ash than Plainfield Sand better graded materials with larger maximum size. A-3 (o) Cl) LO Lime-to-Fly Ash Ratio 120 Ul The proper lime-to-fly ash ratio must be determined based I- 'I, on laboratory data. This ratio does not necessarily remain constant for a given lime and fly ash. Characteristics of the 4- 0 material to be stabilized, such as fines content and plasticity, CL also affect the lime requirement. Increased fines content (0 115 and plasticity require more lime for the same fly ash content. Lime: Fly Ash = 1:4 Once an approximate lime-plus-fly ash content has been established, a series of mixtures with constant lime-plus-fly ash content and varying lime-to-fly ash ratio can be pre- pared. Mixture compressive strength following a designated 110 curing period [perhaps 7 days at 100 F (38 C) for the c 10 is 20 ASTM C 593 procedure] can be used to determine the % Lime Plus Fly Ash appropriate lime-to-fly ash ratio. Figure 51. Effect of lime-plus-fly ash content on maximum coin pacted dry density (Plain field sand). Mixture Designation After the approximate lime-plus-fly ash content and lime-to- fly ash ratio have been determined, it is necessary to further evaluate mixture quality. Such factors as cured compressive strength, durability, and rate of strength development (time- temperature-strength relation) may be of interest. If the preliminary mixture is not satisfactory, other mixtures with 145 different lime-plus-fly ash contents or lime-to-fly ash ratios should be evaluated. After the lime and fly ash content requirements have been Crushed Stone established for a mixture based on the laboratory testing data, the final lime content is designated. A 0.5 percent increase in lime content is generally sufficient to offset the 140 • N construction variability (lime content variation) associated with typical mixture production procedures. In some instances, a less structured approach to selection of mixture proportions may be used. Ranges of lime-plus- fly ash and lime-to-fly ash ratio mixtures are considered and mixture proportions established based on an analysis of l35— strength and durability data. This procedure is usually less efficient.
LABORATORY TEST PROCEDURES Pit-Run Gravel Several different laboratory test procedures are used in de- 130— veloping lime-fly ash—aggregate (LFA) mixture proportions and evaluating LFA quality. Some of the more widely used procedures are considered in the following sections. Lime: Fly Ash = 1:4
Moisture-Density Test Procedures
1251 I 1 I I 1 1I Moisture-density tests are conducted in the usual manner 0 5 10 15 20 25 30 35 with the exception that compactive effort varies. Table 15 gives the compactive efforts specified by various procedures and agencies. The Proctor mold, 4.0 in. (100 mm) in % Lime Plus Fly Ash diameter by 4.6 in. (117 mm) in length, is used in all of the Figure 52. Effect of lime-plus-fly ash content on maximum procedures. coin pacted dry density (crushed stone and pit-run gravel). It is important to note that compacted density has a very 43 substantial effect on the cured strength and durability of TABLE 15 LFA mixtures. Quality criteria developed for one type, of MOISTURE-DENSITY TEST PROCEDURES compaction should not be indiscriminately applied to LFA * mixtures prepared in accordance with a different compac- Agency Procedure Compactive Effort tion procedure. - ASTM C 593 10/18/3/25
Compressive Strength Federal Aviation FAA 1611 10/18/5/25 Administration Compressive strengths of cured LFA mixtures are used to Illinois DOT 10/18/3/25 evaluate mixture quality and to characterize engineering be- - havior. Factors of interest in compressive strength testing Ohio DOT ASTM C 593 10/18/3/25 are sample size, compaction procedure, and curing condi- Pennsylvania DOT PTM 106 5.5/12/3/25 tions (time-temperature). *hammer weight, lbs / hammer drop, inches / Standard-size specimens [4.0 in. (100 mm) in diameter by number of layers / blows per layer 4.6 in. (117 mm) in length] are most widely used. Aggre- gate particles larger than 0.75 in. (19 mm) are scalped and discarded. For fine-grained soils and sandy materials, 2-in.- diameter (50-mm) specimens have also been used. The University of Illinois procedure (36) uses a 2-in.-diameter, 4-in.-long specimen. The Iowa State procedure (59) uses a 2-in.-diameter, 2-in.-long specimen. It is important to note that the length-to-diameter ratios vary for the different pro- cedures. Direct comparison of the strength data developed from by Thompson and Dempsey (60) and MacMurdo and specimens of different sizes is difficult. The use of a cor- Barenberg (20), are required to characterize field curing rection factor based on length-to-diameter ratio (for exam- conditions. The Pennsylvania Department of Transporta- ple per ASTM C 42) should be considered in making such tion (61) has used extensive field temperature data to de- comparisons. velop a procedure for predicting field curing temperatures Standard-size compressive strength specimens are pre- from air temperature data. pared using the same compactive effort specified in the In order to correlate field curing to LFA strength de- moisture-density testing procedure and thus vary, depending velopment, it is necessary to establish a strength—degree-day on agency requirements. In the University of Illinois pro- relationship for the mixture. Temperature ranges used to cedure (36), the mixture is compacted in three layers using establish the strength—degree-day relationship should be a 4-lb (1.8-kg) hammer (full-face compactor) with a 12-in. similar to those expected in the field environment. The (300-mm) drop. The number of blows per layer is varied importance of the curing temperature on strength develop- to produce the desired compacted density (normally per ment is obvious from Figure 29. ASTM C 593). Field curing conditions are quite variable. This varia- General correlations (59) for the Iowa State specimen bility must be considered in developing cure time recom- indicate that for one lift, double-ended compaction, 10 mendations for field conditions. Industry-sponsored studies blows (5 on each end) of a 5-lb (2.3-kg) hammer with a at the University of Illinois indicate that for all curing con- 12-in. (300-mm) drop approximates standard Proctor den- ditions in Illinois (Chicago, Springfield), the standard de- sity, and 20 blows (10 on each end) of a 10-lb (4.5-kg) viation for accumulated curing degree days (based on an hammer with a 12-in, drop approximates modified Proctor analysis period from October 15 to November 30) is ap- density. proximately 75 degree days, 40 F base (42 degree days, 4 C base). It is essential to maintain closely controlled curing con- ditions for LFA mixtures. Both time and temperature sig- Durability Tests nificantly influence LFA mixture strength development. Curing conditions should be indicated when strength data Three procedures have been predominantly used for eval- are presented. uating the freeze-thaw durability of LFA mixtures. Many agencies (Illinois DOT, Pennsylvania DOT, FAA) The freeze-thaw brushing procedure, formerly included in ASTM C 593, is basically modeled after the soil-cement use ASTM C 593 curing conditions [7 days at 100 F (38 C) procedure (AASHTO T 136). Thompson and Dempsey in a sealed container]. In several of the Iowa State studies, (60) indicate that the temperature conditions used in the curing conditions were 70 to 74 F (21 to 23 C) for various ASTM C 593 procedure are unrealistic and do not simu- time periods ranging from 7 to 28 days. late field conditions. The "weight loss" factor determined It is possible to predict the strength development of a in the ASTM procedure has no physical significance in lime-fly ash—aggregate (LFA) mixture under field curing terms of basic engineering properties (strength, stiffness, conditions. Extensive field temperature studies (preferably etc.). with a theoretical heat flow model), such as those described Dempsey and Thompson (36) developed automatic 44
TABLE 16 QUALITY CRITERIA
Minimum Compressive Strength Maximum Weight Agency psi (kPa) Loss, % *
ASTM C 593 400 (2800) 14
Illinois DOT 400 (2800) 10
Ohio DOT 400 (2800) 10
FAA 400 (2800) 14
Pennsylvania DOT Not specified 14
*12 cycles of freeze-thaw
Illinois Mean Winter Temperoture ( December, January, February Note All Temperotures Are In ° F
Illinois Durability Zones 350 Northern Zone Region I Districts 2, 3,8 4 Central Zone Districts 586 Southern Zone Districts 7, 8,89
Figure 53. Mean Winter temperature data and freeze-thaw durability zones for Illinois. 45 freeze-thaw testing equipment that accurately simulates field weight loss criteria are specified by ASTM C 59 3-69, Illi- conditions. Compressive strength after freeze-thaw cycling nois DOT, and the Federal Aviation Administration, as (5 to 10 cycles) is used to characterize LFA mixture given in Table 16. The Pennsylvania Department of Trans- durability. portation has a durability requirement, but no strength cri- The vacuum saturation test procedure proposed by teria. The vacuum saturation strength requirement re- Dempsey and Thompson (37) is a rapid technique (ap- cently incorporated into ASTM C 593 specifies a minimum proximately one hour). The vacuum saturation procedure vacuum saturation strength of 400 psi (2800 kPa). The produces an excellent correlation (Figs. 16 and 17) be- Illinois DOT is also currently considering a vacuum satura- tween the compressive strengths of vacuum saturation tion strength requirement. specimens and freeze-thaw (Dempsey-Thompson technique) Thompson and Dempsey (32) advocate the use of the specimens. ASTM C 593 has been revised to use the residual strength approach for establishing freeze-thaw vacuum saturation procedure for durability evaluation durability criteria. The approach emphasizes that a sliding purposes. scale of quality should be specified depending on the field service conditions anticipated for the mixture. For exam- ple, little freeze-thaw action occurs in an LFA mixture layer QUALITY CRITERIA course in southern Illinois, but many freeze-thaw cycles The acceptability of LFA mixtures is determined by apply- occur in a base course constructed in Chicago. In fact, it ing selected quality criteria. Most mixture proportion pro- has been proposed that Illinois be divided into three sepa- cedures include both strength and durability criteria. rate zones, as shown in Figure 53, for the purpose of estab- Minimum cured compressive strength and maximum lishing stabilized mixture durability criteria.
Among the advantages for use of LFA mixtures in pave- CENTRAL PLANT OPERATIONS ment construction are the ease of construction and the fact that conventional construction equipment can be used to Blending of Components mix and place the materials. The major requirements for Figure 54 shows a schematic layout of a typical plant used the effective use of LFA materials are that the ingredients in the blending of LFA mixtures. The main components of be thoroughly mixed, that the mixture be spread uniformly these plants are: to the proper thickness with a minimum of manipulation, and that it be compacted to a high relative density. This can Aggregate hopper with belt feeders. be accomplished with construction equipment normally Fly ash hopper with a belt feeder and controls. found on a pavement construction site (i.e., spreader box, Lime storage tank with an intermediate feed hopper grader, rollers, water truck, etc.). Although the required and a feed control device. construction procedures are well known to pavement con- Water storage tank with a calibrated pump. tractors, it is emphasized that poor construction techniques Continuous or batch-type pugmill for blending the can result in reduced pavement performance and a final components. product with low reliability. Surge hopper for temporary storage of blended LFA. The blending of lime-fly ash—aggregate (LFA) materials can be done either in place on the roadbed using rotary Figures 55 and 56 show various plants set up to produce mixers and similar equipment, or in a central plant. Plant LFA materials. These plants vary in capacity from small blending is recommended where economically feasible be- portable units, capable of being transported over the high- cause of the greater control over the quantity of ingredients way system and set up without special equipment, to large added and the production of a more uniform mix. permanent plants. The portable plants are designed to pro- 46
Figure 54. Schematic diagram of typical plant layout for LFA mixes. .
duce about 100 tons (90 000 kg) of LFA mix per hour set up in the stockpile. These must be recrushed before use whereas the larger, permanent plants are capable of pro- in LFA mixes. Hammer mills and roll mills have beenued ducing up to 600 tons (540 000 kg) per hour. effectively to crush the set-up fly ash. In addition to the equipment, described, the operator The pugmill mixing plants described in the preceding needs front-end loaders, tractors, and similar equipment to chapters are normally the type used to blend LFA materials. charge the aggregate and fly ash hoppers and to maintain However, central-mix concrete plants have been used suc- an orderly plant site and plant operation.. cessfully for this purpose. Adequate mixing time must be Lime is stored in silo tanks as shown in the figures. It provided in the central-mix plant to ensure thorough blend- is delivered in pneumatic transports that are also used to ing of the constituents: charge the silos with the lime as shown in Figure 57. The storage capacity for lime needed at each plant depends on Hauling the plant production capacity, the reliability of the delivery schedules, and time lag between ordering and delivery of LFA mixtures blended in a cental plant can be hauled to the lime. the road site in conventional, open-bed dump trucks. If Fly ash is normally stored in open stockpiles as shown in haul distances are long, or if drying of the material enroute Figure 58. Fly ash stored in this manner must be condi- poses a problem, provisions should be made to cover the tioned with sufficient water to prevent dusting (usually 15 trucks with tarpaulins or other suitable cover to prevent to 20 percent residual moisture content). During dry loss of moisture or the scattering of dust along haul routes. weather, the stockpile surfaces must be kept moist, or the Sufficient trucks should be made available so that 'all equip- stockpile must be covered to prevent surface dusting. The ment, such as the mixing plant spreaders, rollers, etc., can conditioned fly ash is charged into the feeder hopper with operate at a steady, continuous pace rather than on a a front-end loader or other arrangement. Some fly ashes stop-and-go basis. 47