Atomic-Scale Mechanism of Bitumen–Aggregate Interfacial Cracking: Insights from Molecular Dynamics Simulation

Abstract

The adhesion failure between the bitumen and aggregates is the main reason leading to the cracking of asphalt mixtures and moisture damage of asphalt pavements, greatly compromising the resilience of the world’s transportation network. Due to the complexity resulting from the multivariable and multiscale characteristics of the behavior at the bitumen–aggregate interface, the origin and evolution mechanisms of failure at this interface are still unclear. Six types of rock-forming minerals were selected as representatives to construct the bitumen–aggregate interface models in this study, and the interface model was subjected to tensile simulation using the molecular dynamics (MD) method. The failure modes of bitumen–aggregate interface models under different loading rates and the impact of aggregate mineralogy on the behavior of interface cracking were investigated. The research results indicate that several debonding modes are displayed by the bitumen–aggregate interface model at varying loading rates. As the loading rate slows down, the failure mode of the interface model gradually transitions from adhesive failure to cohesive failure, with a decrease in interfacial strength at failure and an increase in critical deformation and fracture energy. The exponential cohesive zone model (CZM) provides a relatively accurate fitting for the bitumen–aggregate interface debonding behavior. However, due to the appearance of a clear plateau in the traction-deformation curve of the interfacial model at the intermediate loading rate range (0.0001–0.01 Å/fs), the applicability of the exponential CZM will decrease to a certain extent. Among the six rock-forming minerals aggregate models constructed in this study, two interface models of bitumen–quartz and bitumen–anorthite exhibit weaker adhesion performance than that of other interface models, manifested as lower interfacial strength, critical normal separation, and fracture energy. This study reveals the mechanism of bitumen–aggregate interfacial cracking at the atomic scale and is expected to provide a basis for multiscale forecasting of failure patterns of the bitumen–aggregate interface.