Formulation Optimization, Multi-Component Compounding Mechanisms, and Regeneration Insights of a Waste Vegetable Oil-Based Bitumen Regenerant

Waste vegetable oil-based regenerants (WVO-Rs) are essential for sustainable asphalt pavements; however, their formulation optimization frameworks remain insufficient, and both the component synergy and the multi-component regeneration mechanism remain unclear. In this study, Response Surface Methodology was employed to optimize the WVO-R formulation by jointly considering the multi-temperature performance and interfacial water stability of the regenerated bitumen. Multi-scale performance tests and quantum chemical calculations were conducted to comprehensively evaluate its regeneration effectiveness and thermal behavior and to elucidate the underlying molecular mechanisms. The results indicate that the formulation optimization framework dominated by multi-temperature rheological properties and interfacial water stability exhibits superior engineering applicability compared with traditional methods, and the optimal WVO-R formulation corresponds to a mass ratio of WVO:DBP:CPR:SCA:ATO = 100:23.6:14.4:1.7:1. The WVO-R achieves optimal comprehensive regeneration at a dosage of 6–8%, exhibiting excellent thermal and storage stability along with uniform mixing. At the molecular level, the WVO-R forms a dynamic and stable molecular aggregate structure by integrating inherently stable components, leveraging the bipolar silane coupling agent to regulate critical polarity mismatches of dibutyl phthalate (DBP), and establishing a synergistic interaction network dominated by dispersion forces, supplemented by localized stacking and hydrogen-bonding interactions. On this basis, Oleic acid further depolymerizes aged asphaltene (AAS) aggregates through hydrogen bonding interactions, DBP enhances the reversible deformation capacity of AAS via π–π stacking effects, and the overall WVO-R components reshape the electronic structural characteristics of AAS to levels comparable to virgin asphaltene by smoothing the surface electrostatic potential gradient and suppressing electronic reactivity. Overall, this study establishes a systematic framework for WVO-Rs that integrates formulation optimization, regeneration performance evaluation, thermal behavior analysis, and molecular-level mechanism elucidation, thereby providing solid theoretical support for the efficient design and engineering application of bio-based bitumen regenerants.