Investigation of Specimen Geometries for the VECD Model and Calibration of the LVECD Program for Fatigue Cracking Performance of Asphalt Pavements

Fatigue cracking is one of the complex distresses that is dependent of pavement structure, asphalt mixture properties and environmental conditions. During the last decades, many asphalt agencies have conducted significant researches to investigate the fatigue cracking characterization. However, fatigue performance is still difficult to predict not only due to models and parameters but also because this phenomenon itself is not well understood.;The key point in fatigue performance prediction is which model to use and how to find the correct parameters for the selected model by using the simplest but the most reliable testing method. The modulus is one of the primary asphalt mixture properties used for the mechanistic performance prediction of asphalt pavements. Dynamic modulus testing is a common method of measuring mixture modulus as a function of loading frequencies and temperatures. Despite the numerous researches that have been carried out to evaluate mixture stiffness, it is still necessary to establish a practical dynamic modulus test method that is compatible with the field cores which are mostly less than a few inches. One of the objectives of this dissertation is to present the results of a ruggedness study of dynamic modulus testing in indirect tension mode to evaluate the factors that are most likely to affect the final results. Specimen thickness, air void content, gauge length, test temperature, and horizontal strain level, that are the critical factors that affect the dynamic modulus of asphalt concrete, were selected for the ruggedness analysis. According to the findings, air void content was found to be a major factor that affects the dynamic modulus values.;To investigate the fatigue life of the pavement, valid cyclic fatigue testing data which truly represents the mixture behavior seems necessary besides the mixture stiffness. With regard to direct tension fatigue testing, one of the common problems that substantially influence the mixture fatigue behavior is the failure at the ends of the asphalt specimens. During testing, it was observed that as more and more material was cut from the top and bottom of the gyratory-compacted specimens, the likelihood of failure in the middle of the specimen greatly increased. Therefore, fabricating shorter test specimens that are cored and cut from taller gyratory-compacted specimens can produce test specimens that have more uniformly distributed air voids such that middle failure occurs within the gauge length of the linear variable differential transformer (LVDT) in direct tension tests. As a part of study, the optimum specimen geometry of 100 mm diameter and 130 mm height was introduced through the experimental testing and numerical simulation.;The Simplified Viscoelastic Continuum Damage (S-VECD) model, a continuum damage mechanics-based model that is known as one of the effective models, has been applied to predict the performance of asphalt concrete mixtures under different loading conditions. Besides, energy-based fatigue failure criterion (GR) has been proved to be able to predict the fatigue life of asphalt concrete mixtures across different modes of loading, temperatures, and strain amplitudes. This dissertation presents the application and calibration of the L&barbelow;ayered V&barbelow;iscoE&barbelow;lastic pavement analysis for C&barbelow;ritical D&barbelow;istresses (LVECD) program which is based on both S-VECD and GR method to evaluate 33 pavement sections from different locations inside the United States, Canada, South Korea, and China. The capability of the LVECD program to capture crack initiation, crack propagation and, the damage in the pavement sections is investigated by comparing the simulation results with the field observations. In this regard, LVECD was found to effectively predict the fatigue cracking propagation in the pavement sections since reasonable agreement was obtained between the program simulations and field observations. Finally, predicted damage-to-field cracking transfer function was developed to correlate the predictive damage to the measured cracking.