Two-Scale Discrete Element Modeling of Gyratory Compaction of Hot Asphalt

This paper presents a discrete element model for simulations of the compaction process of hot mixed asphalt (HMA). The model is anchored by the concept of a fine aggregate matrix (FAM), which consists of the binder and fine aggregates. In the simulation, the coarse aggregates are explicitly modeled as composite particles. Meanwhile, the FAM is considered as the thick coating of the coarse aggregates with complex constitutive laws. Interparticle interactions include influences of (1) particle properties via Hertz-Mindlin relations; and (2) FAM properties via lubrication relationships. The lubrication relationships include a variable for viscosity for which we derive normal and tangential rate-dependent forms using rheology theory of dense granular-fluid systems, verified reasonable for our systems with the discrete element simulations and experiments with FAM. We assimilate these elements into gyratory compaction simulations of HMA of different aggregate size distributions. We compare these with experiments and find that this model is capable of capturing the measured effects of grain size distribution on the overall compaction behavior of HMA. We conclude by highlighting the advantages of this discrete element model for HMA compaction problems.