Reclaimed asphalt pavement (RAP) from polymer-modified asphalt pavements often contains a recovered binder that is stiff and brittle, which reduces workability and increases durability risk. Waste cooking oil (WCO) is a promising circular rejuvenator, but its effectiveness remains inconsistent because oil source and degradation state are often not well controlled, particularly in polymer-modified RAP systems. This study introduced a controlled simulated WCO approach and compared four oil sources (Palm, Soy, Olive, and Rice) as rejuvenators for recovered RAP binder and RAP mixtures. Simulated oils were added at 4% and 8% by mass of recovered RAP binder. The simulated WCOs produced clear dosage-dependent softening of the recovered binder. Penetration increased, while softening point and rotational viscosity decreased, indicating partial restoration of binder mobility and improved workability. At the mixture level, the 4% dosage provided the most balanced performance, improving moisture resistance and reducing Cantabro loss compared with the control mixture. Specifically, tensile strength ratio (TSR) increased from 75% to 80.9–83.7%, while Cantabro loss decreased from 19.8% to 13.2–14.6%, showing better cohesion and resistance to particle loss. However, Hamburg wheel tracking (HWT) results revealed strong oil-source dependence, with Soy showing the lowest rut depth and Olive the highest, indicating that excessive softening can reduce deformation resistance. The results demonstrate that controlled simulated WCO can support practical oil-source selection for polymer-modified RAP mixtures. A moderate dosage is more effective because it improves binder restoration and mixture durability without causing excessive softening, while rutting verification remains essential before field application.
Kim et al. (Sat,) studied this question.