Synergistic hydromechanical mechanism of accelerated nanoscale damage at asphalt mixture interfaces

During their service life, asphalt pavements are often subjected to the coupled effects of traffic loads and water ingress. However, existing studies tend to examine these two factors in isolation, overlooking the fundamental role of hydromechanical coupling in damaging the interface of asphalt mixtures. Furthermore, due to limitations in macroscopic observation methods, traditional testing methods struggle to dynamically capture the synergistic process between tensile cracking and water ingress. To address this, this study employs molecular dynamics simulations to simultaneously model tensile cracking at the interface and the dynamic water ingress process within the same system. It systematically analyzes the evolution of molecular conformations at the interface, the mechanisms of mechanical response, and the patterns of energy changes under various conditions. The results indicate that hydromechanical coupling is not a simple superposition of individual factors, but rather that water generates a wedging force at the crack tip induced by the load; when this force is superimposed on the external tensile force, it causes the interfacial stress to drop sharply after reaching a peak. At the same time, this phenomenon also highlights the issue of overestimating residual interaction energy in the previous three-layer models. The initial water content at the interface is a key factor controlling the failure mode and tensile strength; as the water saturation increases, the interface’s resistance to coupling damage gradually deteriorates. Furthermore, different aggregate types exhibit variations in water adsorption and diffusion behavior. Among them, CaCO₃ demonstrates superior resistance to coupled damage compared to SiO₂ due to its higher interaction energy with asphalt and the “strong adsorption-low diffusion” hindrance mechanism it imposes on water molecules. These findings deepen our understanding of the hydromechanical coupling failure mechanism and provide a reference for the refined design of asphalt mixtures with high resistance to water damage.