A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Transportation Engineering

Thesis (Ph.D.) - Asian Institute of Technology, 2020

Asphalt concrete is a heterogeneous material consisting of asphalt binder, aggregates, and air voids; spatial distributions and interactions of these components affect the performance of the material past decades, increasing interest has been shown in the use of image analysis techniques for characterizing the internal structure and performance of asphalt mixtures; however, the influence of load applications is still lacking. In this study, a 2-D imaging analysis was used to evaluate the changes in asphalt concrete microstructure due to loading of lab-made specimens and field-core specimens. Uniaxial compression tests were conducted to apply different loading levels to the lab-made specimens, while field-core specimens were subjected to different levels of accumulated traffic load. Results indicate that mixture microstructural properties, including number of aggregate contacts, total contact length, and internal structure index (ISI), significantly decreased with increased strain levels resulting from increased loading levels, whereas average contact orientation and vector magnitude did not change significantly with deformation. Relationships between ISIs and loading levels were plotted and their slopes were determined for all lab-made asphalt mixes. Results suggest that under a given load application, the performance grade of asphalt binder is a critical factor influencing the rutting performance of asphalt mixture.