ABSTRACT XUE, LEI. Investigation on the Debonding Potential of Geosynthetic-Reinforced Asphalt Pavements. (Under the direction of Dr. Y. Richard Kim). Asphalt overlays are widely used by highway engineers as a quick and reliable rehabilitation technique to treat distressed pavements. These freshly prepared overlays often crack within no-time under the repeated vehicular loading and temperature fluctuations caused by day to night changes and seasonal variations. The phenomenon of crack propagation through the new overlay from the existing cracks in the underlying pavement structure is known as reflective cracking. Many interlayer reinforcement techniques are employed to mitigate reflective cracking, but geosynthetics products are gaining attention nowadays due to their ease in installation, low cost, and wide availability. However, proper bonding between adjacent asphalt layers is a significant concern that allows the pavement structure to act monolithically in resisting vehicular and thermal loads. A weak bond between the layers and the geosynthetic product which meets the necessary tensile requirements for paving could eventually end in premature failure following a reduction in the service life of asphalt pavements. Therefore, the proper selection criterion for geosynthetic products to meet the different pavement conditions need utmost emphasis. The evaluation of interface bond strength is considered a quick and easy way to measure the debonding resistance. In this study, the monotonic shear test was performed using Modified Asphalt Shear Tester (MAST) under different confining pressures and temperatures on geosynthetic reinforced and unreinforced specimens. Thereby, with the aid of the time-temperature superposition principle, the shear bond strength prediction models were developed. These models rank the bonding and cracking potentials of geosynthetic products in pavement structure by predicting the shear strength at the layer interface and comparing against the typical pavement stress conditions mimicked using a three-dimensional finite element software package for moving load analysis, FlexPAVE™ version 1.1. According to MAST results, the presence of any type of geosynthetic products at any testing conditions reduces the interface shear strength (ISS) and increases the chances of debonding. The geosynthetic-reinforced specimens are categorically classified into two based on the shear strength mastercurves. Paving composite#1 (PC#1) and paving grid (PaG) display the higher shear strength among the geosynthetic-reinforced specimens, while paving mat (PM), paving fabric (PF), and paving composite#2 (PC#2) show lower shear strength in comparison to the former category. The effect of the tack coat application rates on the ISS was determined using the statistical tool, Analysis of Covariance (ANCOVA). The statistical analysis suggests that the tack coat application rate of PM and PF have a significant effect on ISS. Further to which the Tukey’s honest significance or Tukey’s HSD analysis shows significant effect on ISS of PM and PF when the tack coat application rate changes from dry to optimum. Also, a similar significant effect on PF’s ISS is found when the application rate changes from optimum to wet, but not for PM. For the same type of geosynthetic-reinforced specimen, the shear strength decreases with an increase in temperature. Note that the effect of geosynthetic types on the ISS is evident at the low temperature (23C) but is nullified at the high temperature (54C). The increase in confining pressure from 172.37 kPa (25 psi) to 482.63 kPa (70 psi) results in an increase in ISS of PC#1 and PM. Maximum shear ratio analysis using FlexPAVE™ shows that the highest debonding potential among the simulation conditions in this study occurs in thick overlay structure, high temperature, low speed, thin overlay thickness. Consequently, the selection criterion for geosynthetic paving products that are safe against debonding is proposed. The recommended ISS testing condition is at 50C, 5.08 mm/min (0.2 in./min) actuator displacement rate, and 275.8 kPa (40 psi) confining pressure. The minimum required shear strength for the geosynthetic- reinforced specimen at this condition is 305 kPa (44 psi) for acceptance. © Copyright 2020 by Lei Xue All Rights Reserved Investigation on the Debonding Potential of Geosynthetic-Reinforced Asphalt Pavements by Lei Xue A thesis submitted to the Graduate Faculty of North Carolina State University in partial fulfillment of the requirements for the degree of Master of Science Civil Engineering Raleigh, North Carolina 2020 APPROVED BY: _______________________________ _______________________________ Dr. Y. Richard Kim Dr. Cassie Castorena Committee Chair _______________________________ Dr. Shane Underwood ii DEDICATION To Zhang Chunjie and Liu Zhaoquan, amor vincit omnia. iii BIOGRAPHY Lei Xue was born and grew up in Tibetan Plateau, Qinghai, China. He enjoyed his childhood and teenage life with his family. After graduation from Xining No.2 senior high school, he moved to Beijing. He received his bachelor’s degree in Transportation Engineering and Law from Beijing University of Technology. During his senior year, he decided to apply to North Carolina State University for the Master’s in Civil Engineering under the advice of Dr. Richard Kim. iv ACKNOWLEDGMENTS I would like to express my gratitude to my advisor Dr. Richard Kim, for his valuable guidance, support, and encouragement. A sincere thank you to my committee members Dr. Cassie Castorena and Dr. Shane Underwood. I would like to express my thank to Dr. Castorena for her support during my 2020 fall semester. I would also like to thank lab manager Ernie Song for cultivating a good laboratory environment. I would like to extend my thanks to the research group members and my friends. I would like to express my thank to Dr. Nithin Sudarsanan. It is my pleasure to work with you. I always impressed by your passion and enthusiasm for research. This dissertation finished during the COVID-19 globe pandemic. I would like to thank Chi Tian for her patience and love. I would like to thank my family, Liu Yu, Xue Yanxiang, and Niu Shuqing, for your unweaving love and encouragement. v TABLE OF CONTENTS LIST OF TABLES ........................................................................................................................ vii LIST OF FIGURES ..................................................................................................................... viii 1. INTRODUCTION .................................................................................................................. 1 1.1 Background ...................................................................................................................... 1 1.2 Research Objectives ......................................................................................................... 1 1.3 Thesis Organization.......................................................................................................... 2 2. LITERATURE REVIEW ....................................................................................................... 3 2.1 Reflective Cracking .......................................................................................................... 3 2.2 Function of Geosynthetic ................................................................................................. 4 2.2.1 Reinforcing ............................................................................................................... 4 2.2.2 Stress Relieving ........................................................................................................ 4 2.2.3 Water Barrier ............................................................................................................ 4 2.3 Debonding Problem.......................................................................................................... 5 2.4 Factors Influencing the Bonding ...................................................................................... 5 2.4.1 Tack Coat Type ......................................................................................................... 5 2.4.2 Tack Coat Application Rate ...................................................................................... 6 2.4.3 Curing Time .............................................................................................................. 7 2.4.4 Surface Texture ......................................................................................................... 7 2.5 Test Methods .................................................................................................................... 7 2.5.1 Ancona Shear Testing Research and Analysis (ASTRA) Device ............................ 9 2.5.2 Louisiana Interlayer Shear Strength Tester (LISST) .............................................. 10 2.5.3 Sapienza Direct Shear Testing Machine (SDSTM) ................................................ 10 2.5.4 Advanced Shear Tester (AST) ................................................................................ 11 2.5.5 Modified Asphalt Shear Tester (MAST) ................................................................ 12 2.6 Bonding of Geosynthetic-Reinforced Interlayer ............................................................ 14 2.7 Critical Summary ........................................................................................................... 16 3. EXPERIMENTAL PLAN ...................................................................................................