Influence of Air Void Distribution on the Moisture Susceptibility of Asphalt Mixes

Abstract

This paper evaluates the relationship between the air void distribution in asphalt mixes and their moisture susceptibility. Asphalt mix specimens were prepared to have different air void distributions through using two different gradations, using two different compaction angles in the Superpave gyratory compactor, and trimming the specimens at different locations. An x-ray computed tomography system was used to capture the internal structure of the specimens, and image analysis techniques were used to quantify the air void distribution and connectivity. Specimens in unconditioned (dry) and moisture-conditioned (wet) states were subjected to dynamic loading, and damage was evaluated using a crack growth index based on fracture theory. The parameters required for the crack growth index were obtained from mechanical and surface energy tests. The analysis results clearly demonstrate the influence of air void distribution on moisture susceptibility. Consequently, the analysis method presented in this paper can be used to evaluate alternative mix designs and internal structures, even when the same materials are used, in order to optimize the resistance to moisture damage.