Experimental and Numerical Analysis on Mesoscale Mechanical Behavior of Coarse Aggregates in the Asphalt Mixture during Gyratory Compaction

Compaction is a critical step in asphalt pavement construction. The objective of this study is to analyze the mesoscale mechanical behaviors of coarse aggregates in asphalt mixtures during gyratory compaction through experiments and numerical simulation using the Discrete Element Method (DEM). A novel granular sensor (SmartRock) was embedded in an asphalt mixture specimen to collect compaction response data, including acceleration, stress, rotation angle and temperature. Moreover, the irregularly shaped coarse aggregates were regenerated in the DEM model, and numerical simulations were conducted to analyze the evolution of aggregate interaction characteristics. The findings are as follows: (1) the measured contact stress between particles changes periodically during gyratory compaction, and the amplitude of stress tends to be stable with the increase of compaction cycles; (2) the contact stress of particles is influenced by the shape of aggregates: flat-shaped particles are subjected to greater stress than angular, fractured or elongated particles; (3) the proportion of strong contacts among particles is high in the initial gyratory compaction stage, then decreases as the number of gyratory compactions grows, the contacts among particles tending to homogenize; (4) during initial gyratory compactions, the normal contact forces form a vertical distribution due to the aggregates' gravity accumulation. The isotropic distribution of contact forces increases locally in the loading direction along the axis with a calibrated internal angle orientation (1.25 degrees) in the earlier cyclic loading stage, then the local strong contacts decrease in the later stage, while the strength of the force chains in other directions increase. The anisotropy of aggregate contact force networks tends to weaken. In other words, kneading and shearing action during gyratory compaction have a positive impact on the homogenization and isotropy of asphalt mixture contact forces.