Rejuvenation effect of waste cooking oil on the adhesion characteristics of aged asphalt to aggregates

There are many studies on the rejuvenation of waste cooking oil (WCO) on reclaimed asphalt pavement (RAP), focusing mostly on mechanical properties of asphalt mixture while rarely on the adhesion of asphalt to aggregates. In this study, the surface free energy (SFE) method and molecular dynamics (MD) simulation were used to study the effect of WCO on the adhesion of asphalt and aggregate from the macroscopic and nanoscopic levels, respectively. Four types of aggregates (basalt, limestone, granite, and sandstone) and minerals (SiO2, MgO, CaCO3, and CaO) representing aggregates were selected. The SFE of asphalt and aggregate was obtained, then the adhesion work, debonding work, and the energy ratio (ER) were calculated to evaluate moisture susceptibility. Then the asphalt-mineral interface model was built and the adhesion work under dry and wet conditions and interaction energy were analyzed. The results show that from the SFE perspective, WCO can improve the SFE parameters of aged asphalt and its adhesion work with aggregates, whereas the rejuvenation effect decreases with the increase of WCO content. The aging process will increase the debonding work of the interface, resulting in aged asphalt easier stripping from the aggregate. The resistance to moisture damage ranks as basalt > limestone > granite > sandstone. From the SFE perspective, the van der Waals interaction contributes the main component of adhesion work of asphalt with SiO2, MgO, and CaO, while the electrostatic interaction is the main component with CaCO3. Under the wet condition, the adhesion work of the asphalt-SiO2 interface is affected to the smallest extent due to the minimal interaction between SiO2 and water molecules. Combining with the results of the SFE method and MD simulation, WCO plays a rejuvenation effect, improving the resistance to moisture damage. This study can guide the selection of aggregates to make WCO recycled asphalt mixture with sound moisture resistance.