Effects of kneading and impact action on the movement of aggregates in asphalt mixtures during compaction

Current studies on the movement of asphalt mixture components and the formation of internal structures during compaction are lacking. Therefore, this article focuses on the effect of compaction and compaction methods on the movement and contact of mixture components. First, models of asphalt mixtures were established based on Xray computed tomography (X-CT) and the discrete element method (DEM). Subsequently, compaction processes of the Marshall and Superpave gyratory compactor (SGC) method were simulated, and the model was verified using monitoring results of the smart rock. Finally, the macroscopic air voids, component contacts, and coarse aggregate trajectories were recorded and analyzed. The results showed that, in the early compaction stages, the compactness of the Marshall specimen increased rapidly, which also led to more resistance. The number of contact points and the contact force inside specimens gradually increased with compaction; however, the rate of this increase was different. The trajectories of coarse aggregates were affected by their location and compaction methods, especially the distance to the impacted side and to the center of the cross-section. An edge effect, namely lower compactness at the edges may also be caused by this difference. The movement of aggregates inside the Marshall specimen mainly occurred in the direction of impact. The kneading effect of the SGC method made aggregate particles move and rotate periodically, and compaction efficiency in the later stages was higher.