Assessment of RAP Refining Duration Based on Bitumen Mastic Removal Efficiency and Preservation of Aggregate Surface Texture to Increase RAP Content in New Asphalt Mixtures

The use of Reclaimed Asphalt Pavement (RAP) in new asphalt mixtures is often limited due to the presence of aged binder, which can compromise the mechanical performance of the road pavements. However, from a sustainability perspective, it is crucial to develop effective strategies for the recovery and reuse of RAP aggregate. One potential approach involves the mechanical treatment of the material to remove the binder coating on the aggregates, producing a refined product suitable for large-scale reuse in new asphalt mixtures. This study investigated the performance of a plant for the mechanical refining of RAP aggregate with the aim of identifying the optimal refining duration and maximizing bitumen mastic removal without causing excessive polishing of the aggregates. RAP was subjected to different processing times in the plant: one with direct flow, and others with 2, 3, and 5 min of refining loop duration, evaluating both residual bitumen content and skid resistance. The results showed that a refining loop duration of 2 min provided the best balance between efficient bitumen mastic removal and preservation of aggregate surface texture.