## 1 Introduction  
As a result of its benefits in terms of high and intermediate-temperature properties under increased traffic loads, Styrene-butadiene-styrene copolymer (SBS)-modified asphalt binder has attracted extensive attention in recent decades [1]). However, SBS-modified asphalt binder shows higher viscosity than conventional binders, requiring higher mixing and compaction temperatures [2; 3; 4]. Higher temperatures in mixing and compaction are generally associated with more energy consumption during the production process and can introduce more severe aging in asphalt binders. Warm mix asphalt (WMA) techniques have been used to reduce mixing and compaction temperatures during the paving process. WMA additives can decrease the viscosity of asphalt binder without compromising the other physical and mechanical properties [3; 4; 5; 6]. One of the most widely used WMA additives is Sasobit, a type of long-chain aliphatic polyethylene hydrocarbon produced from coal gasification using the Fischer-Tropsch process [4; 7; 8]. According to a study from [PERSON] et al. [9], WMA binder made with Sasobit showed significantly better high-temperature properties and inferior low-temperature properties compared to that made with other WMA additives such as Cecabase, Evotherm and Rediset. In addition, a study by [PERSON] et al. [4] reported that compound-modified asphalt binders with Sasobit and SBS has better fatigue resistance than either the Sasobit or SBS-modified binders. Despite the potential benefits of Sasobit/SBS compound asphalt binder, the properties of bitumen in the field would irreversibly deteriorate under the influence of heat, sunlight, oxygen and the combination of these factors. The oily components, chemical composition and molecular structuring of asphalt would change due to aging. Aging methods can be divided into two main methods: thermal aging and ultraviolet aging. Many standards for conducting thermal aging have been established and can be followed, including the rolling thin-film oven test (RTFOT), thin-film oven test (TFOT) and Pressure Aging Vessel (PAV) [10; 11; 12; 13]. [PERSON] et al. [14] found that ultraviolet (UV) aging shows a more obvious influence on the degradation of SBS copolymers in comparison with PAV aging. With increasing temperatures due to global warming and corresponding decreases in the UV protection layer, the effect of UV radiation on the aging of asphalt has gained more attention from researchers [15]. Based on the amount of UV radiation, a variety of methods have been proposed to avoid the UV-aging of asphalt [16]. Nano materials have been applied in the paving industry in recent years. Among them, Nano-titanium dioxide (Nano-TiO\({}_{2}\)) is a type of photocatalytic material capable of facilitating the reactions of nitrogen oxide and sulfur oxide decomposition due to the effects of ultraviolet radiation. TiO\({}_{2}\) has been used as a coating material for asphalt pavement to eliminate the aging of asphalt materials [17; 18; 19]. [PERSON] et al. [20] pointed out that the resistance to ultraviolet (UV) aging of asphalt binder can be improved significantly by adding nano-TiO\({}_{2}\) at a reasonable dosage. The rheological properties of Sasobit/SBS compound binder modified with nano-TiO\({}_{2}\) after UV aging and PAV aging procedures were investigated by [PERSON] et al. [20]. However, there are few efforts to investigate the combined effects of nano-TiO\({}_{2}\), Sasobit and SBS on the ultraviolet aging resistance of asphalt binder. The aging of asphalt binder is induced by chemical or physicochemical changes in the emissions of ultraviolet radiation during its service life. Currently, assessments of the aging degree of asphalt binder are primarily conducted by measuring certain chemical, physical and rheological indices before and after aging [21]. However, the capability of these indices to characterize modified asphalt binders has been questioned.