Recycling Waste Oils for Green Rejuvenation of Aged Crumb Rubber Modified Asphalt: Composite Evaluation Index and Mechanistic Insights

Recycling waste oils as rejuvenators is a key approach to achieving sustainable maintenance of asphalt pavements. However, the rejuvenation efficacy boundaries and microscopic mechanisms regarding deeply aged crumb rubber modified asphalt (CRMA) remain unclear. In this study, four typical rejuvenators, including tall oil, waste cooking oil, aromatic oil, and naphthenic oil, were selected to rejuvenate CRMA with varying aging durations ranging from PAV 20 to 100 h. The asphalt was characterized across multiple scales before and after rejuvenation. To overcome the limitations of single-indicator evaluation, this study innovatively constructed a comprehensive rejuvenation index (CRI) evaluation model based on infoScore screening, principal component analysis (PCA), and the entropy weight method. The results indicate that tall oil, with its rich resin acid content, exhibits the best compatibility and dispersing ability with aged asphalt. Its comprehensive rejuvenation efficiency significantly outperforms that of waste cooking oil, aromatic oil, and naphthenic oil. Furthermore, a physical rejuvenation threshold for CRMA was identified at PAV 60 h. Within this threshold (below PAV 60 h), rejuvenation is primarily dominated by physical solvation and peptization, with highly reversible performance. Once the threshold is exceeded (above PAV 60 h), simple addition of waste oil for physical dilution approaches the practical limit of its rejuvenation capability, the effectiveness of the rejuvenator decreases markedly and gradually reaches a plateau. This study not only quantifies the rejuvenation potential of different waste oils but also reveals the limits of physical rejuvenation strategies in coping with deep chemical aging, providing a theoretical basis for decision-making in the recycling of waste rubberized asphalt pavements.