Bio-Oil Rejuvenation: Mechanistic Insights into the Storage Stability and Compatibility of Aged Asphalt Binders

To promote the green recycling of aged asphalt and improve its service performance and storage stability, three types of bio-oil-based rejuvenators were prepared using castor oil, gutter oil, and soybean oil as base oils, with the addition of plasticizers, penetrants, and wetting agents. Based on the respective optimum dosages, the effects of these rejuvenators on the compatibility and storage stability of rejuvenated asphalt binder were evaluated systematically. A series of characterization techniques, including softening point difference, segregation index (SI), Cole–Cole plots, bending beam rheometer (BBR) testing, gel permeation chromatography (GPC), and fluorescence microscopy (FM), was employed for comprehensive analysis. The results indicate that castor oil– and gutter oil–based rejuvenators exhibit no noticeable phase separation under long-term high-temperature storage, demonstrating significantly better compatibility and storage stability than the soybean oil–based rejuvenator, and also have markedly enhanced low-temperature cracking resistance of the rejuvenated asphalt binder. Although Cole–Cole plots can partially reflect rheological behavior, their strong sensitivity to test temperature limits their effectiveness in accurately characterizing the intrinsic compatibility between rejuvenators and aged asphalt binders. Gel permeation chromatography and fluorescence microscopy analyses further confirm that castor oil– and gutter oil–based rejuvenators effectively restore the molecular structure of aged asphalt at the molecular scale and achieve uniform dispersion within the asphalt matrix, resulting in excellent structural stability. These findings demonstrate that bio-oil-based rejuvenators, particularly those derived from castor oil and gutter oil, have strong potential for efficient and sustainable rejuvenation of aged asphalt.