Virtual testing of asphalt mixture with two-dimensional and three-dimensional random aggregate structures

This article presents numerical evaluation of mechanical properties of asphalt mixture in dynamic modulus testing. The virtual testing specimen of heterogeneous asphalt mixture was generated with random aggregate structures, fine aggregate matrix (FAM) and air voids. The developed models consider the fraction and spatial distribution of mixture components and coarse aggregate properties such as gradations, aspect ratios and orientations. Both two-dimensional (2-D) and three-dimensional (3-D) finite element (FE) models were developed to predict dynamic modulus and phase angles of asphalt mixture at different loading frequencies. The results from the 3-D FE model were validated with the experimental measurements reported in the literature. However, it was found that the 2-D FE model would underestimate the dynamic modulus and overestimate phase angles. A conversion factor from 3-D volume fraction to 2-D area fraction is proposed to improve the accuracy of the 2-D model, taking dynamic modulus as the indicator. Sensitivity analysis shows that the aspect ratio and orientation angle of coarse aggregates have combined effects on the predicted dynamic modulus. The spatial distribution of coarse aggregates and air voids affects the predicted dynamic modulus depending on their concentrations with respect to the axial loading direction. The investigation of air void effect on dynamic modulus indicates the importance of considering realistic distribution of air voids in the FAM or between FAM and coarse aggregates for virtual testing simulation.