Effect of coarse aggregate morphology on the mechanical properties of stone matrix asphalt

The aim of this study is to examine the effects of morphological characteristics of coarse aggregates on the rutting and fatigue performance of stone matrix asphalt (SMA). A total of twenty-two coarse aggregate fractions were analyzed, and different aggregate blends were used to prepare different SMA mixtures following the job-mix formula in Virginia State. Specimens from eight types of SMA mixtures, with three replicates each, were tested for rutting resistance with an asphalt pavement analyzer (APA). Six types of the SMA mixtures were tested for fatigue resistance with a modal mobile load simulator (MMLS) in conjunction with a portable seismic pavement analyzer (PSPA). Rut depth obtained from the APA and seismic modulus difference obtained during MMLS trafficking were linked to morphological characteristics of coarse aggregates. Statistical analysis showed that flatness ratio and elongation ratio had no measurable influence on rut depth. The regression analysis demonstrated that rut depth increased with the increase of sphericity, angularity and texture, which indicates that rutting resistance of SMA can be improved by using more equi-dimensional and angular coarse aggregates with rougher texture. However, angularity and texture were found to have little influence on seismic modulus difference. Sphericity was shown to have a negative influence on seismic modulus difference, and flatness ratio was shown to have a positive effect on seismic modulus difference, which indicated that using more spherical and less flaky coarse aggregates reduces the degradation of stiffness, resulting in improved fatigue performance of SMA mixtures. The performance results suggest that flat and elongated aggregates should be used only in limited amounts.