Adhesion and moisture-induced debonding mechanisms at asphalt–recycled concrete aggregate interfaces: molecular dynamics and quantum chemistry insights

Recycled concrete aggregate (RCA) offers a sustainable way to reuse waste concrete in asphalt pavements, but weak bonding between asphalt and adhered cement mortar increases moisture susceptibility. This study investigated the mineral-specific adhesion and moisture-induced debonding mechanisms at asphalt–RCA interfaces. Molecular dynamics simulations and quantum chemistry calculations were combined to examine wetting, adhesion and dynamic separation on calcium silicate hydrate (CSH), ettringite (AFt), monosulfate (AFm) and SiO₂ surfaces. Mean contact angles ranged from 118.3° to 137.4° for asphalt and from 16.8° to 39.0° for water. Dry adhesion energy followed AFt > CSH > SiO₂ > AFm and was dominated by van der Waals interactions. Interfacial water displaced asphalt fractions and reduced adhesion. With a 4 Å water layer, adhesion energies decreased to 29.6–34.7 mJ/m²; AFm retained 37.4% of its dry adhesion energy, whereas AFt retained 20.7%. Water also reduced the adhesion-energy change during dynamic separation. Resins and aromatics were the major contributors to adhesion energies, while quantum chemical descriptors identified potential interaction sites. These findings link mineral surface chemistry and water redistribution to asphalt adhesion and debonding, providing molecular-level insight for RCA pretreatment and moisture-durability improvement.