Study on the multiple recycling limit of asphalt binders containing high RAP content based on chemical and rheological properties

Multiple recycling is an emerging strategy to maximize the use of reclaimed asphalt pavement (RAP), yet the evolution of binder performance during repeated rejuvenation and the feasible recycling limit remain unclear. To clarify this, binders extracted from laboratory-aged mixtures containing 60 % RAP underwent five aging and rejuvenation cycles with a bio-based rejuvenator. The optimal rejuvenator dosage was established based on key rheological indicators, followed by a comprehensive evaluation of chemical properties, rheological behavior, fatigue life, and low-temperature cracking resistance. The results demonstrate that key rheological requirements were satisfied without the need to progressively increase the bio-oil dosage. Despite accumulating asphaltenes, multiple rejuvenation cycles maintained colloidal stability and improved oxidative aging resistance. The lowtemperature performance grade (PG) remained stable, while high-temperature performance improved, as Shenoy non-recovered compliance (Snr) decreased by up to 56 % and fatigue life increased by up to 214 % compared to the virgin binder, before both indicators declined in the fifth cycle. All properties, except the creep-rate critical cracking temperature (Tc, m), varied significantly from one cycle to the next. The rise in cracking susceptibility set a practical limit of four recycling cycles. Principal component analysis (PCA) revealed that three cycles provided optimal performance. This work quantifies the recycling limit for high-RAP binders, identifies low-temperature cracking susceptibility as the controlling mechanism, and provides guidance for sustainable pavement practice.