Investigating the Potential of Untreated and Treated Waste Cooking Oil for Rejuvenation of Aged Asphalt Binder

Aging of asphalt increases its hardness due to oxidation, which challenges the incorporation of higher recycled asphalt (RA) content. Waste cooking oil (WCO) is gaining attention as a rejuvenator to incorporate higher RA content in new pavements. The study evaluated the potential of WCO as a rejuvenator before and after transesterification. Rheological tests, such as frequency-temperature sweep and multiple stress creep recovery (MSCR) were conducted to assess the performance characteristics of different rejuvenated binders. Chemical tests, including asphaltene extraction, free fatty acids, transesterification, Fourier-transform infrared spectroscopy (FTIR), and nuclear magnetic resonance (NMR) were performed to corroborate the rheological findings. Based on the investigation, a new method is proposed to determine the optimum dose of WCO for binders incorporating RA, considering viscosity and rutting. The results indicated that the optimum WCO content before treatment was on average 7.03%, which was reduced to 5.73% after transesterification. This is credited to the reduction of free fatty acids by 81.7% in treated WCO after transesterification, resulting in enhanced diffusion characteristics between treated WCO and recycled asphalt pavement (RAP). The rejuvenated binder had a 49.33% lower carbonyl index (CI) than RAP and an 18.35% higher CI than unaged viscosity-graded (VG) 30, respectively, validating the potential of WCO as a rejuvenator. ANOVA analysis of asphaltene content showed no significant difference between the rejuvenated binders with their corresponding optimum WCO and unaged VG 30 contents. Overall, transesterification of WCO could be a potential solution to improve the diffusion characteristics for enhanced rejuvenation. Reclaimed asphalt can be processed and used as a component in the production of new hot-mix asphalt. It commonly is mixed with virgin asphalt binder, aggregates, and other additives to create a sustainable asphalt mixture. The inclusion of RA reduces the demand for virgin materials such as asphalt binder and aggregates, thus decreasing the environmental impact of asphalt production. The current practice permits a lower quantity of RA in asphalt mixtures due to its higher stiffness. The utilization of WCO as a rejuvenator can restore the properties of RA binder to a considerable extent. It also will result in higher RA incorporation and a sustainable solutions including, reduction in inappropriate disposal and multiple-time utilization of WCO. Hence, the utilization of RA with WCO as a rejuvenator is a novel solution for sustainability.