Mechanistic insights into restoring severely aged asphalt using sustainable rejuvenators from molecular to macroscopic scales

This study presents a multiscale investigation into the rejuvenation mechanism of thermally oxidatively photochemically aged asphalt through integrated experimental characterization, molecular dynamics (MD) simulations and quantum chemical (QC) calculations. Four environmentally friendly rejuvenators, epoxidised soybean oil (ESO), waste cooking oil (WCO), waste engine oil (WEO) and naphthenic oil (NO), were evaluated for their efficacy in restoring the physicochemical properties of severely aged asphalt. The experimental results demonstrate that the addition of these rejuvenators effectively reduces the viscosity of aged asphalt by more than 90% (at a 0.1 s⁻¹ shear rate), rebalances the SARA fraction by replenishing aromatic components (increasing the aromatic content by 34% to 56% Compared to coupling aged asphalt) and shifts the molecular weight distribution toward smaller species, thereby improving the workability and flexibility. Quantum chemical analyses reveal that non-covalent interactions, predominantly dispersion forces, govern the molecular-level compatibility between rejuvenators and aged asphalt, with minimal electrostatic contributions. Notably, the epoxy groups of ESO undergo a ring-opening reaction with the carboxylic acids in aged asphalt, forming hydroxy ester bonds, thereby facilitating the chemical integration between the ESO and the components of the aged asphalt. MD simulations further elucidate that rejuvenator diffusivity and solubility parameter matching are key determinants of compatibility and interfacial blending efficiency. This work provides a mechanistic foundation for designing sustainable, high-efficiency rejuvenators, promoting the circular economy in asphalt pavement recycling by enabling deeper material recovery and longer service cycles.