Optimizing rejuvenator dosage for high RAP content asphalt binders under multiple recycling cycles: A study based on an alternative rheological approach

The widespread use of rejuvenators has enabled the incorporation of 60 % reclaimed asphalt pavement (RAP) into new asphalt mixtures. However, it is uncertain whether rejuvenators can persist in restoring the kernel properties of asphalt binders after multiple recycling processes. This study conducted three cycles of aging and rejuvenation using two bio-based rejuvenators (R1 and R2) and one wax-based rejuvenator (R3), with subsequent aging performed in the laboratory. After determining the rejuvenator dosages based on the Recommendation proposed by RILEM TC-264 RAP TG3, the study assessed dynamic rheological behavior across a broad temperature range, rutting performance, fatigue life, and chemical property changes in the rejuvenated binders. The results indicated that the optimal dosage for R1 and R2 showed a decreasing trend, and the rejuvenated binders still exhibited good high-temperature rutting resistance after three cycles of rejuvenation. The low PG was restored, and due to the cumulative softening effect of the rejuvenators, the fatigue life increased by 146.57 % and 137.83 % under 2.5 % strain, and by 102.17 % and 88.99 % under 5 % strain, respectively. Additionally, the relative content of asphaltenes remained stable, and the chemical aging index (CAI) decreased. In contrast, for R3, despite an increasing optimal dosage, the low PG could not be restored. After three cycles, the relative content of asphaltenes increased by 4.38 % compared to the aged binder, and the CAI also increased. Although bio-based rejuvenators are more suitable for multiple recycling, attention must be paid to their gradually increasing sensitivity to low-temperature cracking and the potential for excessive softening.