## 3 UV Aging Law of Asphalt
### Analysis of Test Results
#### 3.2.2 Rheological Properties of Asphal  
The dynamic shear rheometer (DSR) developed by the Strategic Highway Research Program comprehensively considers the influence of loading condition and temperature  
Figure 10: The mass loss rate of asphalt with different UV irradiation time.  
Figure 9: The ductility loss rate of asphalt with different UV irradiation time (the test temperature of base asphalt is 10 \({}^{\circ}\)C while that of SBS modified asphalt is 5 \({}^{\circ}\)C).  
on asphalt performance, and determines the complex modulus (G*), Phase Angle (\(\delta\)), and Rutting Factor (G*/Sin \(\delta\)) that were used to evaluate the high-temperature performance of the asphalt. In this paper, the dynamic shear rheometer was used to test the rheological properties of asphalt under different UV irradiation times (0 h, 48 h, 96 h, 144 h, and 196 h). The irradiation intensity was 157.5 W/m\({}^{2}\), and the test temperature range was 40-76 \({}^{\circ}\)C. G*, \(\delta\), and G*/sin \(\delta\) of asphalt were measured. Figure 11 shows the G* and \(\delta\) of different asphalts under different UV irradiation times and temperatures. Figure  
Figure 11 shows that the G* increased and \(\delta\) decreased with increasing UV aging time. The elastic component of the asphalt response became more dominant and the viscous component less dominant with UV aging. Figure 12 shows that the longer the UV irradiation time, the bigger the G*/sin \(\delta\) of asphalt at the same scanning temperature. Relevant studies show that G*/sin \(\delta\) can be used to evaluate the rutting resistance of asphalt, and the higher the value is, the better the rutting resistance of asphalt will be [13, 14, 15]. Of course, the change in anti-rutting performance was only one of many performance changes. The magnitude of the change also indirectly indicates the aging effect of UV on asphalt. In fact, in addition to the anti-rutting performance, the durability and anti-fatigue performance of asphalt are also  
Figure 12: G*/sin\(\delta\) of different asphalts under different UV irradiation times and temperatures: (**a**) 50\({}^{\beta}\); (**b**) 70\({}^{\beta}\); (**c**) 90\({}^{\beta}\); (**d**) 110\({}^{\beta}\); (**e**) SBS I-C; (**f**) SBS I-D.  
very important, and relevant research reports show that ultraviolet radiation is not conducive to the durability and anti-fatigue performance of asphalt [13; 15].  
By comparing the change law of G*/sin \(\delta\) of different asphalt after UV irradiation, it is not difficult to find that the higher the asphalt grade, the smaller the G*/sin \(\delta\) value at the same scanning temperature, and the worse the high-temperature performance. This law was applicable to any scanning temperature in the process of the experiment. In terms of G*/sin \(\delta\) values, SBS modified asphalt was much higher than base asphalt under the same UV irradiation time and scanning temperature, indicating that the high-temperature performance of SBS modified asphalt under the same UV irradiation condition was much higher than that of base asphalt.  
By summarizing the rheological properties of asphalt in the process of UV radiation, it can be concluded that UV radiation changes the proportion of viscous components and elastic components in asphalt. The specific performance is that the proportion of viscous components decreases and the proportion of elastic components increases, which leads to the change in the asphalt's high-temperature resistance to permanent deformation. With the increase in UV radiation, the magnitude of the change is greater.