Cracking of the PCC Layer in Composite Pavement A DISSERTATION SUBMITTED TO THE FACULTY OF THE GRADUATE SCHOOL OF THE UNIVERSITY OF MINNESOTA BY PRIYAM SAXENA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY Lev Khazanovich, Advisor December 2011 © Priyam Saxena 2011 ACKNOWLEDGEMENTS I wish to express my sincere thanks to my advisor Dr. Lev Khazanovich for the guidance, cooperation, and continuous support that he provided during my stay at the University of Minnesota. I greatly appreciate his patience and the encouragement he provided to help me focus on the work. I would also like to thank my thesis committee members Dr. Mihai Marasteanu, Dr. Henryk K. Stolarski, and Dr. Douglas M. Hawkins for their help and valuable feedback on this dissertation. The financial support provided by the Minnesota Department of Transportation and the Federal Highway Administration (FHWA) Transportation Pooled Fund Study TPF-5(149) ―Design and Construction Guidelines for Thermally Insulated Concrete Pavements‖ is deeply acknowledged. Special thanks to all my fellow students for making memories that I will cherish forever. Last but not the least, I am most grateful to my husband, Amit for his love and support during this time. I am forever thankful to my loving family. i To my parents ii ABSTRACT An asphalt concrete (AC) overlay of a jointed plain concrete pavement (JPCP) is intended to extend the service life of the existing pavement structure. Also known as composite pavements, such pavements exhibit features of both rigid and flexible pavements. While behavior of rigid pavements is mainly elastic, behavior of asphalt layer is load-duration dependent. At the same time, temperature curling causes non- linear interaction with the foundation. The available models of composite pavement ignore the behavior of the load duration dependent asphalt layer when the composite pavement is subjected to a combination of temperature curling and traffic loads. This research concentrates on the improvement of structural modeling of composite pavements subjected to slow developing temperature curling and instantaneous traffic loads. A finite element (FE)-based model accounting for the viscoelastic behavior of the asphalt layer in composite pavements is developed and verified using comparisons with semi-analytical solutions obtained in this study. In order to maintain compatibility with the Mechanistic-Empirical Pavement Design Guide (MEPDG) framework, a simplified procedure is developed. The procedure uses a different asphalt modulus for curling than for axle loading and determines the total stresses in the pavement as a combination of the stresses from solutions of three elastic boundary value problems. The simplified procedure is compared with the existing MEPDG model for fatigue cracking in AC overlaid JPCP. A framework for the implementation of the proposed model into the MEPDG is also developed. iii TABLE OF CONTENTS List of Tables .................................................................................................................... vii List of Figures .................................................................................................................. viii CHAPTER 1. Introduction ........................................................................................... 1 CHAPTER 2. Literature Review .................................................................................. 5 2.1 MEPDG Fatigue Cracking Model ............................................................................ 5 2.2 Components of Stress Under Temperature Curling .................................................. 8 2.3 MEPDG Rapid Solutions for Predicting Critical PCC Bottom Surface Stresses ... 12 2.3.1 Slab Equivalency Concept ............................................................................... 12 2.3.2 MEPDG Neural Networks for Computing PCC Stresses ................................ 19 2.4 Adoption of the Fatigue Cracking Model for Composite Pavements in MEPDG .. 24 2.5 Asphalt Characterization ......................................................................................... 26 2.5.1 Viscoelastic Behavior of Asphalt Concrete ..................................................... 26 2.5.2 Characterization of Asphalt in the MEPDG .................................................... 28 2.6 Limitations of the Structural Modeling of Composite Pavements in the MEPDG . 31 2.6.1 Use of a Single Dynamic Modulus of Asphalt ................................................ 32 2.6.2 Assumption that the AC Modulus Changes on a Monthly Basis..................... 32 2.7 Existing Computer Programs for Pavement Analysis ............................................ 33 CHAPTER 3. Finite Element Analysis of Composite Pavement Incorporating a Viscoelastic Layer ............................................................................................................. 35 3.1 Viscoelastic Material Representation of Asphalt Concrete .................................... 35 3.2 Development of Finite Element Model for the Analysis of Viscoelastic Slab-on- Grade ............................................................................................................................. 42 3.2.1 Formulation of the Finite Element Model ....................................................... 43 3.2.2 Thermal Loading .............................................................................................. 49 3.2.3 Viscoelastic Analysis ....................................................................................... 50 iv 3.2.4 FE Formulation of the Winkler Foundation..................................................... 53 3.2.5 Assembling the Global Matrix and Computing Stresses Based on the Time- Discretized Viscoelastic Analysis ............................................................................. 56 3.3 Extension of the FE Model to Multi-Layered Composite Pavements .................... 58 3.3.1 Equivalent Single Layer Slab........................................................................... 59 3.3.2 Equivalent Linear Temperature Gradient in the Equivalent Single Layer Slab ................................................................................................................................... 60 3.3.3 Equivalent Linear Creep Strain Gradient in the Equivalent Single Layer Slab ................................................................................................................................... 62 3.3.4 Additional Stresses in the Composite Pavements Due to Non-linear-strain- causing Temperature and Non-linear-strain-causing Creep Strains Components .... 62 3.3.5 Total Stress in the Composite Pavements ........................................................ 64 3.4 Step-by-Step Procedure for Computing the Stresses in the Composite Pavement . 65 3.5 Validation of the Finite Element Model ................................................................. 69 3.5.1 Viscoelastic Plate on Viscoelastic Winkler Foundation .................................. 69 3.5.2 Viscoelastic Plate with Simply Supported Corners ......................................... 75 3.5.3 Verification of the Formulation for Multi-Layered Slabs................................ 78 3.5.4 Sensitivity of the Viscoelastic FE Model to Internal Parameters .................... 85 3.6 Summary ................................................................................................................. 96 CHAPTER 4. Stress Solutions Using the 2-Moduli Approach .................................. 97 4.1 AC Moduli Under Traffic Loads and Temperature Gradients ................................ 98 4.2 The 2-Moduli Approach ........................................................................................ 100 4.3 Stress Computation Procedure Using the 2-Moduli Approach ............................. 102 4.3.1 The First Elastic Problem............................................................................... 102 4.3.2 The Second Elastic Problem .......................................................................... 104 4.3.3 The Third Elastic Problem ............................................................................. 106 4.3.4 Combined Stress ............................................................................................ 106 4.4 Brief Formulation for the FE Model Based on the 2-Moduli Approach............... 108 4.5 Step-by-Step Procedure for Computing the Combined Stresses .......................... 111 v 4.6 Verification of the Combined Stress Obtained Using the 2-Moduli Approach .... 115 4.6.1 Comparison with the Viscoelastic FE Model – Example 1 ........................... 115 4.6.2 Comparison with the Viscoelastic FE Model – Example 2 ........................... 119 4.6.3 Comparison with Simple Addition of the Stresses ........................................ 121 4.7 Comparison of the Stress Solution using the 2-Moduli Approach with the Stress Solution Using the MEPDG Process .......................................................................... 124 4.8 Summary ............................................................................................................... 128 CHAPTER 5. Development of a Framework for Implementation of the 2-Moduli Approach into MEPDG................................................................................................... 129 5.1 Simplification of the Structural System ................................................................ 130