# Performance Assessment of Waste Cooking Oil-Modified Asphal Mixtures
## 1 Introduction  
Flexible pavements undergo various types of field distress (e.g., cracking and rutting) [1; 2]. The characteristics of pavement materials (i.e., binder, aggregates, and asphalt mixture) are one of the main factors affecting this distress [3]. Several approaches are investigated to enhance the mixture's performance, including modifying components or implementing new performance assessment tests, specifications, and design approaches. Asphal binder modifiers are additives added to the binder to enhance its resistance to specific distresses (i.e., fatigue cracking, rutting, and thermal cracking) [4]. Although it is an old practice, several concerns encourage the asphalt community to differentiate, implement, and optimize the use of such modifiers, including (1) the increasing demand for using flexible pavements (e.g., high traffic volumes and loads), (2) reduction in crude oil supply, (3) development of new binder specifications (i.e., SuperPave binder specifications), and (4) environmental and economic concerns (i.e., pressure to recycle waste materials) [5]. Researchers investigated numerous types of modifiers, including elastomer (e.g., Styrene butadiene), plastomer (e.g., ethylene propylene diene monomer), anti-strip (e.g., fattyamido amines), hydrocarbons (e.g., paraffinic), antioxidants (e.g., hydrated lime), extenders (e.g., Sulfur), and fillers (e.g., Mineral filler, lime, Portland cement, fly ash) [5; 6; 7; 8]. These modifiers differ in their interacting mechanism and impact on binder performance (i.e., enhancing/declining resistance to cracking/rutting, composition and physical nature, and source (i.e., natural, manufactured, or waste modifiers)). Waste modifiers (i.e., modifiers derived from waste materials) are believed to have several benefits over other modifiers, including (1) they are free or inexpensive, which reduces production expenses of conventional mixtures; (2) they reduce environmental pollution; and (3) they assess in saving the natural resources. Several waste modifiers were proposed, including tire rubber, glass, oil shale ash, polystyrene, medical ash, electric arc furnace dust, rubber seed oil, palm oil, clinker fine, engine oil, dates seed, and vegetable oil [4; 9; 10; 11; 12; 13; 14; 15]. The recycling of Waste Cooking Oil (WCO) has garnered considerable interest. WCO has become one of the major pollutants nationally [16]. It has a low recoverability rate, many metals, viruses, and bacteria, and it is a potential source of soil, water, and air pollution. It has been used in different applications to mitigate its environmental impacts, such as biodiesel, biogas, grease, animal food, soaps, and detergent productions [17; 18; 19]. However, massive amounts are still illegally dumped into landfills [16]. Several researchers explored the applicability of recycling WCO oil into asphalt binders or mixtures. It has mainly been used as a modifier or rejuvenator for virgin and aged binders. Recently, various research studies have documented the state of knowledge of recycling the WCO into asphalt binder and mixture asphalt materials [20; 21; 22; 23; 24; 25; 26]. It was found that WCO was able to affect the physical (i.e., penetration, softening point, viscosity) and rheological (i.e., phase angle [8], complex shear modulus [G*]) properties of asphalt binders. In addition, it influences the mixture performance (e.g., workability, rutting, low-temperature cracking, stability, flow, and creep stiffness). The literature review findings highlight the feasibility of using WCO as an asphalt binder modifier or rejuvenator. It was observed that adding WCO increases the penetration and viscosity, and \(\delta\), while decreasing the softening point and G* of an aged binder. Furthermore, it enhanced rutting and low-temperature cracking, stability, and resistance. However, several concerns have been raised.