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Moisture-induced interfacial weakening remains a critical barrier to the durability of asphalt mixtures incorporating recycled concrete aggregate (RCA), primarily due to the presence of residual mortar. To address this issue, this study investigates the coupled macroscopic and molecular mechanisms governing asphalt/RCA interfacial degradation under moisture exposure. Marshall residual stability and freeze-thaw splitting tests were conducted on asphalt mixtures with 40% RCA replacement, stratified by mortar coating rate. Pull-off tests further quantified adhesion loss with increasing water immersion time. To elucidate the underlying mechanisms, molecular dynamics simulations were employed to model water-infiltrated asphalt/RCA interfaces and to analyze water transport, interfacial structural evolution, and weakening mechanisms. Results showed that higher mortar content significantly decreased residual strength and increased moisture sensitivity. After 48 hours of immersion, asphalt stripping on mortar exceeded 30%, compared to less than 20% on limestone aggregates. Simulation results indicated that water penetration at the asphalt/RCA interface altered the distribution of asphalt components and promoted stable hydrogen bonds between water and the RCA surface components, which in turn weakened the interface, particularly the asphalt/C-S-H interface. These findings confirm that moisture-induced adhesion loss at the asphalt/RCA interface is driven by both macro-scale mortar effects and micro-scale water-surface interactions. This study provides a multi-scale understanding of moisture-induced interfacial deterioration and offers theoretical guidance for improving the water resistance of RCA-based asphalt mixtures.
Hu et al. (2025) studied this question.