Molecular mechanisms and engineering performance of hydrophilic–lipophobic modified asphalt for mitigating oil film contamination

Oil-fouling resistance and moisture stability are crucial for the durability of asphalt pavements in tunnels and service areas, where adhesion failure at the asphalt‒aggregate interface fundamentally compromises long-term performance. This study synthesised a quaternary ammonium salt-type LLL modifier and systematically investigated its interfacial mechanisms through a combination of macroscopic experiments (FTIR spectroscopy, contact angle measurements, fluorescence tracing, moisture stability tests and oil-fouling cleaning tests) and molecular dynamics simulations. The results showed that FTIR confirmed the successful physical incorporation of LLL into the asphalt. At the 4% dosage, the asphalt surface transformed from hydrophobic-oleophilic to hydrophilic-oleophobic, with the surface energy increasing by 620% (13.2 to 95.1 mJ/m²), where 98.0% of the polar component contribution established a high-energy barrier that inhibited oil adsorption. The modified asphalt achieved an immersion residual stability of 91.58% and a freeze‒thaw splitting strength ratio of 86.20%, exceeding high-grade standards. Oil-fouling resistance tests demonstrated a 22.6% reduction in skid resistance degradation after 120 min exhaust gas exposure, a 2.1-fold improvement in cleaning efficiency and a 96.6% BPN recovery. Molecular dynamics simulations revealed dual-interface regulation: LLL formed density-enhanced monolayer adsorption on CaCO₃ surfaces (9.1% interfacial energy increase) and diffusion-promoted multilayer adsorption on SiO₂ surfaces (24.9% increase), both achieving optimal low-mobility-strong-adsorption state at a 15% dosage (diffusion coefficient: 1.02 Ų/ps). These mechanisms provide molecular-scale insights for optimisng asphalt pavement performance in specialised road sections.