## 1 Introduction  
Asphalt binder is frequently utilized in hot mix asphalt (HMA) for binding the aggregates mass. Regardless of the global use of asphalt as a binder, its cost is comparatively high. The increased urbanization and surging demand of paved roads led to the need for enhancing asphalt binder intrinsic properties, exclusively the resistance for rutting and thermal cracking. Thermally induced cracking of flexible pavements is critical in cold regions [1], such as South Korea. As the pavement structure tends to shrink under low temperature conditions [2], tensile stresses are developed resulting in cracks or failure. Therefore, asphalt modification is needed as it fundamentally effects the properties of bituminous mixtures. Recently, more attention has been given to improving performance of asphalt binder by modifying it with polymers, resulting in improved engineering properties of asphalt [3; 4; 5; 6; 7]. At low temperatures, a decrease in viscosity of the binder is intended to avoid making asphalt too stiff and losing cohesion with aggregates. The viscosity of asphalt can be manipulated by changing the oil fraction in asphalt colloidal system [8]. Engine oil is a by-product of petroleum refining which provides lubrication to rotating bearings and pistons in automobile engines. After being used by vehicles, it gets contaminated with impurities and toxic chemicals like Polycyclic Aromatic Hydrocarbons (PAHs) [9]. Thus, the final waste product, known as Waste Engine Oil (WEO), may cause serious damage to the environment and organic life if it is dumped without proper treatment [10; 11]. There is a thriving interest in the pavement industry to utilize waste materials and de-escalate the use of natural resources; this is also cost effective as compared to utilizing new materials. South Korea generated about 370 million liters of waste oil in 2012 [12]. This substantial amount of waste oil is mostly consumed as fuel or re-sold after refining. Chemically, the molecular structure of engine oil is similar to asphalt binder [13; 14], therefore waste engine oil can be considered a compatible modifier for asphalt cement [15]. With the increased traffic volume, production of waste engine oil has increased many folds in recent years. Therefore, it is imperative to use the waste engine oil in partial replacement of asphalt binder which will also reduce the cost of Hot Mix Asphalt (HMA) or Reclaimed Asphalt Pavement (RAP). [PERSON] et al. [16] investigated the potency of different rejuvenators on aging and fatigue cracking resistance. They concluded that paraffinic oils were most suitable to rejuvenate the aged RAP binders without adversely compromising the rut resistance. Research conducted by [PERSON] et al. [17] claimed that waste engine oil with a 12% dose significantly improved the low temperature cracking susceptibility of RAP mixture. A considerable loss of volatiles during RTFO aging was observed during mass loss test which indicates an increased aging susceptibility. Based on the results by [PERSON] et al. [18], modifying asphalt binder with 0-10% of used lubricating oil enhanced the critical cracking temperature to about 2 \({}^{\circ}\)C but high temperature PG grade was compromised. [PERSON] et al. [19] studied the use of cooking oil as a bitumen rejuvenator. Their research proved that modification of a 40/50 penetration grade aged asphalt binder with 4% waste cooking oil decreased its viscosity to an unaged 80/100 penetration grade condition. [PERSON] et al. [20] found that a decrement in optimum asphalt content improved fatigue resistance of the mixture and an increased concentration of carbonyl functional groups in asphalt binder after waste engine oil modification. This increase in carbonyl groups left the asphalt binder susceptible to oxidative aging. Oil inclusion also reduced the stiffness at low temperatures but elastic recovery of binder at high temperatures was undermined. [PERSON] et al.