Effect of Aggregate and Void Characteristics on Shear Resistance of Asphalt Mixtures

Shear strength plays a critical role in the rutting resistance of asphalt pavements. In this study, a three-dimensional discrete element method (DEM) model was developed in PFC3D to systematically investigate the effects of aggregate and void characteristics on the shear resistance of asphalt mixtures under triaxial loading. The simulation results exhibited excellent agreement with laboratory triaxial tests across varying confining pressures and mixture gradations, confirming the reliability of the DEM approach. Both aggregate and void characteristics were found to exert significant influences on shear deformation. Uniform aggregate distributions and higher friction coefficients enhanced interparticle interlocking, thereby increasing cohesion, internal friction angle, and shear resistance. In contrast, elevated air-void contents or nonuniform void distributions significantly degraded shear performance, whereas a well-distributed void size range (1–4 mm) optimized aggregate skeleton interlocking and load-transfer efficiency. These findings provide micromechanical insights into the mechanisms governing shear resistance and offer practical guidance for designing asphalt mixtures with improved rutting resistance.