Influence of air voids on mechanical properties of asphalt mixtures

Air voids play an important role in influencing the performance of asphalt mixtures. This study utilized several mechanical tests to characterize the influence of air void distributions on mechanical properties and response of asphalt mixtures. The overlay tester, Hamburg Wheel-Tracking Test (HWTT), and a repeated tensile test were used to characterize the resistance to fatigue cracking, permanent deformation, and moisture damage, respectively. The overlay test results showed that specimens with more uniform air void distribution had less variability in terms of resistance to fatigue cracking compared with specimens with less uniform air void distribution. Consequently, recommendations were made to improve air void distribution and reduce the test variability. The HWTT results were found to be insensitive to the air void distribution. The repeated tensile test was used to measure material properties that were required inputs to a fracture-based model for the analysis of moisture damage. The repeated tensile test and model results showed that the detrimental effect of moisture was the highest for specimens with the highest percent of air voids. In addition to the characterization of mechanical properties, this study evaluated the effect of temperature distribution in Superpave Gyratory Compacted (SGC) specimens on air void distribution. It was possible to make some minor changes to the compaction procedure in order to improve the uniformity of temperature distribution and, consequently, enhance the uniformity of air void distribution.