Revealing Mechanisms of Aging and Moisture on Thermodynamic Properties and Failure Patterns of Asphalt-Aggregate Interface from the Molecular Scale

Abstract

The primary purpose of this study was to reveal the effect of aging and moisture on the failure behavior of asphalt binder–aggregate interfaces from thermodynamic properties and the molecular scale and to provide ideas for improving the service life and weather resistance of materials. A 12-component asphalt binder model, an oxidation-aged asphalt binder model, three types of aggregates (i.e., SiO2-, CaO-, and Al2O3-based) models, and corresponding confined asphalt-aggregate models in dry or wet conditions were developed using Materials Studio version 2019 software. Thermodynamic parameters that characterize interfacial failure behavior, including surface free energy, cohesive work, and adhesion work between asphalt binder (unaged and aged samples) and aggregates were obtained by molecular dynamics simulations. A pull-off test was simulated using molecular dynamics to analyze asphalt-aggregate failure patterns and mechanisms. Five tensile rates were applied in tensile simulations of asphalt-SiO2 aggregate, and bond strength at various temperatures was investigated. The findings suggested that oxidative aging reduces thermodynamic properties such as the surface free energy and cohesive energy of asphalt binders but enhances the potential and nonbond energy of asphalt binders. The ranking of the adhesion between unaged asphalt binder and various aggregates is as follows: SiO2>CaO>Al2O3. Oxidative aging has a distinct influence on the adhesion properties of the aforementioned asphalt binder–aggregate interfaces. Furthermore, outcomes for debonding energy and energy ratio (ER) value in the asphalt-CaO aggregate system exhibited the best water stability. Increasing tensile rate caused the failure patterns of the asphalt-aggregate mixes to change from adhesive failure damage between asphalt and aggregate to cohesive failure within the asphalt binder. Temperature had a nonnegligible impact on bond strength at the asphalt-aggregate interface.