Sustainable asphalt rejuvenation using waste cooking oil: A comprehensive review

Roads serve as a backbone of developing economies; thousands of kilometres of new roads are built every year and old ones are continuously repaired. Due to the large areal extension, maintenance of asphalt pavements generates significant economic, energy, social, and environmental impacts. ‘Rejuvenation’ of reclaimed asphalt pavement (RAP) in roads helps minimize reliance on non-renewable resources; for this purpose, various organic-based rejuvenators have been used in recent times. Waste cooking oil (WCO), which contains light oil components analogous to those of the virgin bitumen, has been proposed as a sustainable product for improving recycling of aged asphalt. The present review study collects state-of-the-art information on asphalt rejuvenation using WCO. It provides insights on the correlations between plant production methods and laboratory studies to manufacture high content rejuvenated RAP mixes. In addition, WCO is comprehensively examined to provide more information about its chemical composition and the changes occurring in its chemical properties at various states of degradation (i.e. virgin and used cooking oil). The effect of WCO on the mechanical, rheological, chemical and microscopic characteristics of the asphalt binder and asphalt pavements behaviour was assessed. This review highlights that the addition of WCO to the asphalt binder improves fatigue and thermal cracking properties of the mix, but at the expense of rutting resistance unless further polymeric modification is achieved. The increase in the acid value of the oil and its moisture content negatively affect the asphalt binder properties. For the asphalt mixtures, an increment in WCO dosage generates an increase in the thermal cracking resistance but reduces rutting, fatigue, and moisture resistance of the pavement. Overall, this review article provides an overview of the positive and negative aspects of the applications of WCO as an eco-friendly asphalt rejuvenator.