Interfacial adhesion mechanisms of asphalt mastic-aggregate systems incorporating salt-storage materials: experimental and molecular dynamics investigation

Understanding the influence of salt-storage materials on asphalt mastic–aggregate interfacial adhesion is essential for improving the durability of anti-icing asphalt pavements. This study systematically investigated the macroscopic and microscopic adhesion behavior of asphalt mastic incorporating NaCl-based salt-storage materials using contact angle measurements, atomic force microscopy (AFM), and molecular dynamics (MD) simulations. Results indicate that replacing mineral filler with salt-storage material disrupts the molecular organization of asphalt components, leading to a 33.8–49.2% reduction in surface free energy, decreased adhesion work with aggregates, and increased stripping work. AFM observations revealed pronounced microstructural evolution, characterized by intensified aggregation of polar components and increased development of ‘bee-like’ structures, which corresponded to weakened nanoscale adhesion. Furthermore, MD simulations indicate that the interfacial interaction between NaCl and asphalt is substantially weaker than that of CaCO₃ or SiO₂ systems, rendering the NaCl-asphalt more vulnerable to moisture-induced debonding and mechanical loading. Within the trilayer interfacial system, while CaCO₃ promotes favorable molecular rearrangement and thermodynamic stability, the substitution with NaCl induces localized component enrichment under physical confinement, thereby undermining interfacial stability. Overall, incorporation of NaCl-based salt-storage materials compromises phase homogeneity and interfacial bonding within asphalt systems, which may adversely affect long-term pavement durability.