Investigation on internal structural properties of asphalt mixtures subjected to loading using image analysis

Abstract

ABSTRACT 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. In past decades, increasing interest has been shown in the use of image analysis techniques for characterising 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 laboratory-produced specimens and field-core specimens. Uniaxial compression tests were conducted to apply different loading levels to the laboratory-produced 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 ISI and loading levels were plotted and their slopes were determined for all laboratory-produced asphalt mixes. Results suggest that under a given load application, the type of asphalt binder is a critical factor influencing the rutting performance of asphalt mixture.