Composite rejuvenator strategy for optimizing the performance of RAP-recycled asphalt mixtures

Asphalt pavement recycling is increasingly recognized as an effective strategy for resource conservation and carbon reduction. This study investigates the deterioration characteristics of aged asphalt and develops a composite rejuvenator composed of bio-oil and DOTP plasticizer to restore binder performance and enhance the pavement properties of RAP-recycled asphalt mixtures. Response surface methodology was used to optimize rejuvenator dosage, after which recycled mixtures with RAP contents of 15%, 30%, 45%, and 60% were fabricated. Binder tests, high- and low-temperature rheological evaluations, rutting tests, moisture stability tests, freeze-thaw splitting, and semicircular bending (SCB) tests were conducted to assess rejuvenation effectiveness. The optimized formulation (M2: 3% bio-oil + 2.5% DOTP) achieved a 93% recovery rate of binder properties and exhibited rheological behavior most comparable to virgin asphalt, showing improved high-temperature stability, enhanced low-temperature relaxation, and increased mixture fracture energy. Grey relational analysis revealed that RAP content exerted the greatest influence on stiffness-related indicators and negatively affected crack resistance, with 30% RAP achieving the best balance among performance metrics. Overall, the bio-oil - DOTP composite rejuvenator effectively improved the high-temperature, low-temperature, and moisture-resistant performance of RAP-recycled asphalt mixtures, providing a practical pathway for promoting sustainable asphalt recycling.