Complementary Rejuvenation of Aged Asphalt by Waste Cooking Oil and Waste Wood Pyrolysis Oil: Experimental Characterization and Molecular Dynamics Insights

To address the difficulty of simultaneously restoring the molecular mobility and structural stability of aged asphalt using a single bio-oil rejuvenator, a dual-source bio-oil composite rejuvenation system consisting of waste cooking oil (WCO) and waste wood pyrolysis oil (WWO) was developed based on the concept of component-specific functional division. According to their compositional characteristics, WCO primarily serves to replenish light fractions and restore molecular mobility, whereas WWO is used to enhance the regulation of interactions among polar components and asphaltene aggregation behavior. Compositional and microstructural characterization, rheological testing, and molecular dynamics simulations were employed to investigate the rejuvenation effectiveness and molecular interaction characteristics of the different rejuvenation systems. The results showed that, compared with aged asphalt, the composite-rejuvenated asphalt exhibited a 33.92% increase in aromatic content, a 32.20% decrease in asphaltene content, and a 22.50% increase in the colloidal stability index, together with fewer surface cracks and improved morphological continuity. The composite system reduced the stiffness of aged asphalt, enhanced its low-temperature stress relaxation capacity, and maintained favorable resistance to permanent deformation at high temperatures. Its creep stiffness at −12, −18, and −24 °C decreased by 41.03%, 51.87%, and 45.71%, respectively. Molecular dynamics simulations further showed that the peak value of the asphaltene–asphaltene radial distribution function decreased by 17.48%, while the fractional free volume increased by 20.00%, indicating suppressed asphaltene self-aggregation and increased molecular mobility within the system. These findings demonstrate that WCO and WWO exhibit functional complementarity in replenishing light fractions, restoring molecular mobility, and regulating asphaltene aggregation, thereby providing a theoretical basis for the component-oriented design of waste bio-oil-based composite rejuvenators.