Understanding the role of particle rotation in asphalt mixture compaction by tracking coarse aggregate movement

Abstract

Compaction is one of the most critical steps in asphalt pavement construction. Understanding the compaction mechanism is essential to improving field and laboratory compaction. Recent studies have transformed from macro- to meso- scale to characterize the compaction process from the perspective of the internal mixture. It has demonstrated that rotation is a critical motion for particles in a confined particulate structure, whereas how particle rotation influences the compaction process in a particulate media is still unclear. This study employs a particle size microelectromechanical systems (MEMS) sensor, SmartRock, and discrete element modeling to track particle movement of asphalt mixture in Superpave gyratory compaction (SGC) for three typical gradation types (dense-graded AC, gap-graded SMA, and open-graded PFC). Results confirm that the particle’s relative rotation could characterize SGC compaction as a two-stage process divided by transition cycle N. Such stage characteristics could be fundamentally related to the mixture’s packing features at the particle scale. The N value decreases in the order of PFC, SMA, and AC with the increase in the Coarse Aggregate (CA) ratio, which indicates that mixtures with a stronger aggregate structure (such as PFC) will be harder to stabilize under compaction loading. The particle relative rotation transition cycle N could be used as a particle-scale index to characterize the internal structure during compaction. Further, in SGC discrete element model, particle rotation was found to be critical in affecting the particle’s horizontal translation and, ultimately material’s densification, which further explains the compaction mechanism of particulate materials.