# Study on the Aging Behavior of Asphalt Binder Exposed to Different Environmental Factors
## 3 Results
### Analysis of Outdoor Exposure on the Macroscopic Properties of Asphalt Binder  
#### 3.2.1 Effect of Outdoor Exposure on the Complex Modulus of Different Asphalt Binder  
To accurately characterize these viscoelastic properties, rheological methods are commonly employed. A dynamic shear rheometer was used to evaluate asphalt binder's rheological properties, which can objectively reflect high-temperature performance, low-temperature performance, and fatigue performance. The complex modulus is indicative of the asphalt binder's resistance to deformation. Frequency scanning tests were performed on samples. Complex modulus principal curves were obtained with a reference temperature, representing the rheological characteristics of asphalt binder over a broader frequency range (or temperature domain), as illustrated in the figure below.  
Figure 7 illustrates that TFOT aging resulted in an increased complex modulus of asphalt binder. A higher complex modulus indicates a lower proportion of viscous and more elastic components, rendering the asphalt binder harder, more brittle, and resistant to deformation with reduced viscoelasticity. The complex modulus after O-aging closely approximated that after TFOT aging, indicating that O-aging had little impact on the complex modulus. Notably, outdoor exposure at room temperature and atmospheric pressure did not induce significant aging in virgin asphalt binder. O+UV-aging and All-aging had a substantial effect on the complex modulus of virgin asphalt binder, signifying that exposure to light expedited its aging. As shown in Figure 8, the TFOT aging had an insignificant effect, while O-aging led to a notable increase in complex modulus. The effects of O+UV-aging and All-aging were significant on SBS-modified asphalt binder, with All-aging exerting the greatest influence, followed by O+UV-aging. The disparity between All-aging, O+UV-aging, and O-aging hinged on the impact of light as a factor, revealing the significant role of light in asphalt binder's rheological properties.  
Figure 7: Complex modulus master curve of virgin asphalt binder.  
The increase in the complex modulus of SBS-modified asphalt binder was less significant than that observed in virgin asphalt binder under the same aging conditions. This suggests that the addition of the SBS modifier enhances the aging resistance of virgin asphalt binder, with a notable improvement in the aging resistance of the asphalt binder, consequently enhancing its road performance [21]. Specifically, the complex modulus of SBS-modified asphalt binder exhibited a substantial increase following O-aging, whereas O-aging had a comparatively minor impact on the complex modulus of the virgin asphalt binder. This discrepancy highlights that thermo-oxygenation exerts a more pronounced influence on SBS-modified asphalt binder. When subjected to O+UV-aging, the impact on the SBS-modified asphalt binder was less severe than that on All-aging, while O+UV-aging had the most substantial impact on the virgin asphalt binder. The primary distinction between All-aging and O+UV-aging lies in their susceptibility to external factors such as wind, rain, and dust. Generally, it is believed that dust accumulation diminishes the asphalt binder's exposure to outdoor elements, resulting in reduced aging. Notably, All-aging had the most pronounced effect on SBS-modified asphalt binder, suggesting that it is less influenced by environmental factors like wind, rain, and dust.