Adhesion recovery of aged asphalt on mineral surfaces induced by reclaimed engine oil bottom: surface free energy and molecular dynamics analysis

Asphalt aging weakens binder cohesion and asphalt–aggregate interfacial adhesion, thereby compromising pavement integrity and durability. This study investigates reclaimed engine oil bottom (REOB) as a rejuvenator for aged asphalt and examines its adhesion recovery mechanism. A REOB-only reclaimed asphalt group (REOB-R) was introduced to distinguish the intrinsic contribution of REOB from the additional effects of SBR and anti-aging agents. Fluorescence microscopy was used to characterize microstructural evolution, while contact-angle-based surface free energy analysis quantified the work of adhesion between asphalt and granite, basalt, and limestone aggregates. Molecular dynamics simulations were further performed to probe molecular redistribution at asphalt–mineral interfaces. The results show that aging markedly reduces adhesion work, whereas REOB-reclaimed asphalt restores interfacial bonding. REOB-R accounts for most of the recovered adhesion deficit, while the fully reclaimed asphalt provides further improvement, confirming the secondary role of auxiliary additives. Simulations reveal that aging drives aromatic fractions away from mineral surfaces, whereas REOB promotes aromatic re-enrichment and strengthens asphalt–mineral interactions. The recovery is most pronounced on limestone, indicating superior compatibility with carbonate minerals. These findings provide a multiscale explanation of how REOB restores adhesion in aged asphalt.