Assessing the performance of castor oil as a rejuvenator in asphalt concrete mixtures containing reclaimed asphalt pavement

Abstract

This study investigated the use of castor oil as a rejuvenator in asphalt concrete (AC 14) mixtures containing Reclaimed Asphalt Pavement (RAP), with the aim of improving sustainability and cost-efficiency in road construction. The research was conducted in three phases: characterization of RAP materials, evaluation of asphalt mixtures incorporating RAP and rejuvenator, and an economic cost-benefit analysis. Laboratory tests in Phase 1 established that the RAP used contained 4.46% aged binder and conformed to aggregate gradation standards. In Phase 2, various mixtures were prepared with RAP contents of 0%, 15%, 30%, 45%, and 60%, and rejuvenator dosages ranging from 0% to 15% by mass of the aged binder. The optimum mix was identified as one containing 30% RAP with 12% castor oil rejuvenator, yielding the highest stability and satisfactory volumetric properties based on Marshall design criteria. In Phase 3, a comparative cost analysis between a RAP-based mix and a fully virgin mix revealed that the use of RAP and rejuvenator reduced the material cost by UGX 15,220 per ton of asphalt, representing a 5.2% savings. These results demonstrate that castor oil is a viable rejuvenator for RAP, capable of restoring aged binder performance while reducing reliance on virgin materials and lowering project costs.