Atomic perspectives on the impact of aggregate surface roughness: Unraveling changes in bond strength and failure modes at the bitumen-aggregate interface

This study aims to explore the impact of aggregate surface roughness on bitumen-aggregate interface behavior, a critical factor in asphalt deterioration, under both dry and moist conditions using molecular dynamics simulations. Different roughness levels of aggregate substrates were constructed by functionally segmenting the calcite and quartz mineral base. Static work of adhesion and dynamic tensile stress-strain curves were employed to assess the bonding strength of the interface model. The surface area, free volume at the interface, as well as two modes of failure-cohesive failure and adhesion failure-were employed to investigate the reasons and conditions for the interface failure. Findings demonstrate that moderate roughness enhances adhesion by increasing the contact surface area, while excessive roughness leads to decreased adhesion due to incomplete contact. Moist conditions further reduce adhesion capability as water molecules interfere with the bitumen-aggregate contact, increasing free volume and exacerbating contact issues. Notably, the study introduces novel insights into how increased roughness can counteract moisture's detrimental effects, maintaining damage within the cohesive failure mode. These findings contribute to a deeper understanding of molecular-scale adhesion mechanisms, offering guidance for the design of more durable asphalt mixtures.