Molecular Dynamics Investigation of Adhesion Mechanisms at the Asphalt-Defective Aggregate Interface: Chloride Erosion, Temperature Effects, and Ion Diffusion Analysis.

The adhesion between asphalt and aggregate significantly influences the durability and lifespan of road structures. This study employs molecular dynamics simulations to investigate the interface behavior between asphalt and aggregates with varying defect sizes under chloride salt solution immersion and ion infiltration (physical erosion without chemical reactions). The interfacial adhesion energy (Eint), relative ion concentration (RC), mean square displacement (MSD), and hydrogen bond count were analyzed to assess the adhesion performance of asphalt at the defective aggregate interface. The effects of chloride concentration and temperature on adhesion were also examined. Results indicate that aggregate surface defects enhance local asphalt adhesion within the defect region, although larger defects reduce the global interfacial adhesion energy normalized by total area: the adhesion energy decreases from -417 kcal/mol (defect-free) to -315 kcal/mol (20 Å) and -277 kcal/mol (30 Å), with a reduction of 24-34%. Additionally, defects accelerate ion diffusion significantly, with diffusion coefficients of water and ions increasing by up to 69%, promoting chloride ion accumulation, which exacerbates erosion physical interface deterioration. Both elevated temperature and chloride concentration further accelerate this degradation physical interface weakening, with high temperatures causing severe interface damage: adhesion energy decreases by about 28% as temperature rises from 290 K to 340 K, and by 15% as NaCl concentration increases from 0% to 20%. These findings offer a theoretical foundation for understanding the adhesion mechanisms of the asphalt-aggregate interface under chloride erosion chloride ion infiltration and physical erosion and provide insights into enhancing chloride resistance to chloride ion infiltration of road materials.