Enhancing sustainability via chemistry-informed design of bituminous composites: Unveiling the underlying molecular level mechanisms of moisture-induced damages

Moisture-induced damage at the asphalt binder–aggregate interface is a major factor in the premature failure of asphalt mixtures when exposed to moisture. While studies often relate moisture damage to aggregate types and compositions, this paper highlights the role of asphalt binder's acid value as a major contributing factor to moisture damage. While polar alkane acids in asphalt can improve adhesion in dry conditions, their high acid content exacerbates water-induced degradation at asphalt binder–aggregate interface. This study investigates the molecular-level mechanisms underlying moisture susceptibility, focusing on the role of asphalt's acid value in influencing desorption and water retention at the asphalt–aggregate interface. A combination of laboratory experiments, including contact angle measurements and moisture-induced shear-thinning index (MISTI) tests, and computational methods such as molecular dynamics (MD) simulations and density functional theory (DFT) calculations was employed. Experimental results revealed that binders with higher acid content exhibit increased moisture susceptibility, with contact angles as high as 155° for high-acid binders, a 2.65 % increase compared to neat asphalt binder. MISTI values also showed greater deviation from unity for high-acid binders, indicating weakened interfacial adhesion. MD simulations identified a critical acid content threshold of 8 %, beyond which hexadecenoic acid accumulates at the silica-water interface, forming micelles and disrupting adhesion. DFT calculations quantified the adsorption energy of hexadecenoic acid on silica as −36.7 kcal/mol, significantly higher than most asphalt components (−20.8 kcal/mol), further driving acid migration to interface, hence weakening the interface resistance to moisture damage. These findings emphasize the importance of chemistry-informed design of asphalt mixtures to optimize interfacial binding when exposed to moisture. By minimizing acid value in asphalt, particularly when using modifiers and rejuvenators, the durability of asphalt pavements can be significantly enhanced, reducing moisture-induced damage and promoting sustainable construction practices.