Investigation of the possibility of using waste cooking oil as a rejuvenating agent for aged bitumen Majid Zargar, Esmaeil Ahmadinia, Hallizza Asli, Mohamed Rehan Karim Bitumen is a useful and expensive material with high thermal sensitivity. Despite the limited resources, it has been applied in abundance (110 million tonnes annually in the world) in the high-way industry [1]. The ageing of the bitumen during storage, mixing, transport and laying on the road, as well as in service life [2], are the most important problems presented by the use of bitumen in pavements. The main ageing mechanism of bitumen is the loss of volatiles and oxidation, which leads to having higher viscosity and a bitumen that is stiffer than fresh bitumen [2,3]. The ageing problem of bitumen leads to pavement failure, such as surface ravelling and cracking, especially reflective cracking [3]. These problems increase the expense of renovation and the preservation of bituminous pavements. Therefore, highway agencies, due to high demand, high expense, low life cycle, ageing, and lack of sufficient natural resources of bituminous material, have introduced the application of recycled asphalt pavement (RAP) material in hot mix asphalt (HMA) as an economic and environmentally sound solution [4,5]. The investigations illustrated that even though the life cycle of HMA has reached the end, the binder and aggregate from the old HMA are still valuable [6]. The only problem that has limited the application of the RAP (only 15%) is the ageing of bitumen. An increase in the application of a higher percentage of the RAP (till 80%) in the pavement is possible using a rejuvenator [7]. Rejuvenators, which are categorised into rejuvenating agents and softening agents [1], restore the original ratio of asphaltenes to maltenes in oxidised (aged) bitumen binders [8] in order to soften the aged binder and create a broad-spectrum rejuvenation that replenishes the volatiles and dispersing oils while promoting adhesion [3]. In recent years, the use of rejuvenation in RAP materials (for application in HMA mixtures) [5], chip seals, and as rejuvenation seals [3] (this method extends the service life of roads) to rejuvenate the aged bitumen has increased remarkably. In addition, recently, because of the high demand for rejuvenators, the application of waste products as a rejuvenating agent, such as recycled motor oil (RO), have been investigated. Romera et al. [9], in Spain, applied RO and other rejuvenators in recycled HMA mixture. The results of the investigation indicate that by employing RO as a rejuvenating agent the permanent deformation was postponed compared to a sample of the original bitumen. Furthermore, they reported that a mixture of 80% aged bitumen with 20% recycled motor oil as a rejuvenator, obtained exclusively from waste materials, can compete with new 60/70 bitumen in terms of quality [9]. The successful application of motor recycling oil (RO), powered the theory of the application of waste oil, such as WCO, as a rejuvenating agent in bitumen. The novelty of this paper is using the waste cooking oil (WCO) as a rejuvenator in aged bitumen using the bitumen test methods including penetration, softening point, Brookfield viscosity, dynamic shear rheometer and Fourier transform infrared (FTIR) spectroscopy test. The aim of this research is to determine the potential of using waste cooking oil as a rejuvenating agent for aged bitumen binder in order to reduce WCO environmental pollution [10] and the expense of highway renovation. Material and experimental procedure