Amphiphilic Bioagents for Cold-Mix Asphalt: Enhancing Asphalt–Aggregate Adhesion and Moisture Resistance via Interfacial Nanostructure Regulation

Cold-mix asphalt that incorporates reclaimed asphalt pavement presents a promising alternative for sustainable roads. However, its durability is compromised by moisture-induced damage caused by acidic bitumen and hydrophilic aggregates. Although previous efforts have addressed moisture susceptibility through mineral treatments, direct reinforcement of the asphalt–aggregate interface has received limited attention. This study proposes a suturing strategy using amphiphilic bioagents produced from waste biomass to enhance adhesion at the asphalt–aggregate interface. Three bioagents were evaluated, and molecular dynamics studies were conducted to investigate the molecular-level mechanism at the interface. The results demonstrate that the bioagents form molecular bridges in which heteroatom-containing groups establish hydrogen bonds with minerals, while aromatic and aliphatic chains interact with the asphalt phase through π–π stacking and van der Waals forces. Surface free energy analysis confirms improved thermodynamic adhesion and reduced debonding potential due to increased Lifshitz–van der Waals interactions. Additionally, the moisture-induced shear-thinning test revealed enhanced interfacial bonding and decreased moisture susceptibility. Among the bioagents tested, the agent derived from pig manure was the most effective because of its nitrogen-rich heterocyclic compounds. This study provides mechanistic insights into bioagent-mediated interface reinforcement for valorizing waste biomass and reclaimed asphalt in sustainable pavement.