Interfacial bonding mechanisms and physicochemical evolution at the reclaimed asphalt pavement aggregates-cement interface

The performance of cement-stabilized reclaimed asphalt pavement (CSRAP) mixtures is closely related to the structural evolution and bonding behavior of the interfacial transition zone (ITZ). This work explores the elemental distribution characteristics, elastic modulus, and molecular interaction mechanisms between reclaimed asphalt pavement (RAP) and cement in the ITZ from a multi-scale perspective. SEM-EDS analysis and nanoindentation testing indicate that the ITZs formed at the natural aggregate/cement and RAP/cement interfaces gradually densify with curing time. However, the aged asphalt film inhibits the cement hydration reaction and reduces the elastic modulus of the ITZ. EDS analysis indicates that as curing time increases, the Ca/Si ratio and spatial distribution of hydration products in the ITZ undergo continuous changes, which gradually transform from low-density C-S-H to high-density C-S-H. Molecular dynamics simulations revealed the interaction mechanism between C-S-H and RAP, indicating that surface interfacial bonding constitutes a thermodynamically spontaneous process primarily governed by van der Waals forces. The asphalt film restricts Ca 2+ migration, transforming multi-layer adsorption into single-layer enrichment, thereby weakening interfacial bonding. This study investigates the physicochemical properties and molecular bonding mechanisms of RAP/cement ITZ, providing a theoretical basis for optimizing interfacial structures and enhancing the performance of cement-stabilized reclaimed asphalt pavement materials.