# Aging Characteristics of Rubber Modified Asphalts in Different Environmental Factors Combinations
## 1 Introduction  
Two approaches are generally used to modify asphalts with vulcanized rubber powder, namely, physical and chemical modification. Numerous works have proven that physical modification can enhance the resistances to putting at high temperatures and cracking at low temperatures [1; 2; 3; 4]. Meanwhile, chemical modification, which is dependent on trans-polyoctenamer rubber (TOR), can further improve the workability and high temperature performance [5]. Moreover, rubber modified asphalts are regarded as environmentally friendly owing to their great consumption of waste tires [6]. Accordingly, employing these asphalts into pavement construction has become increasingly popular [7].  
Mastering the aging characteristics of rubber modified asphalts tightly follows their promising prospects. However, comprehensive progress has yet to be achieved in this regard. Some research achievements on asphalt aging can be used for reference. It is confirmed that the aging of asphalt in service is mainly caused by the different environments to which the asphalt is subjected. From a chemical perspective, [PERSON] and [PERSON] have concluded that thermal oxygen induces the formation of carbonyl and sulphoxide groups [8; 9]. [PERSON] proposed that carbonyl area index could be used as achemical indicator to reflect the aging level of asphalt binder [10]. These polar functional groups in asphalt tend to aggregate and form complex and high-weight molecules, which are responsible for the increase in viscosity. Meanwhile, [PERSON], and [PERSON] have held that oxidation is the chief cause of the hardening of asphalt binder, which further leads to the sharp degradation of durability and premature failure in service [11; 12]. According to [PERSON], ultraviolet radiation is also a major cause of asphalt aging that results in the decay of fatigue resistance, increase in creep stiffness, and decline of failure strain [13]. [PERSON] suggested that working temperature of UV aging was under 50 \({}^{\circ}\)C [14]. Furthermore, [PERSON] has proposed that the soluble substance in asphalt is susceptible to escape under rainfall, which also aggravates aging [15]. Therefore, the influences of different environmental factors should be considered to establish a comprehensive description for the aging characteristics of rubber modified asphalts.  
The thin film oven test (TFOT) and pressurized aging vessel (PAV) test have been developed in the laboratory and standardized to simulate the thermal oxidative aging of modified asphalts (the tests also apply to rubber-modified asphalts) [16]. By contrast, the simulation of ultraviolet or water aging has received less attention. Fortunately, a few researchers have offered conversion methods for outdoor irradiation time, and pointed out that photochemical reaction has a significant effect on the surface of asphalt film [17; 18; 19]. In addition, [PERSON] has introduced water molecules into the PAV test to study the asphalt degradation [20]. These suggestions undoubtedly provide inspiration for the design of aging simulations for the two rubber-modified asphalts in this study.