## 7 Low-Carbon Green Development of Asphalt Mixtures
### Recycled Material
#### 7.1.2 Recycled Shredded Rubber  
Crumb rubber, a recycled material derived from discarded tires, has the potential to become a sustainable asphalt pavement when mixed with asphalt mix through both wet and dry processes. This innovative approach to waste material utilization offers a promising future for sustainable road construction. [PERSON] et al. (2017) investigated the environmental impact of utilizing crumb rubber (CR) particles as a polymer additive to enhance asphalt performance. Their findings revealed that recycling waste tire rubber can significantly reduce carbon dioxide (CO\({}_{2}\)) emissions by 71.9% compared to landfilling or incineration. When adding 2% CR to the asphalt mixtures, the resulting reduction in carbon emissions is 23.20%. These findings emphasize the importance of recycling waste materials and the potential of sustainable asphalt pavements. Furthermore, [PERSON] et al. (2018) investigated the performance of crumb rubber-modified asphalt in 1-ton asphalt mixtures. As illustrated in Table 2, their findings revealed that this sustainable pavement material resulted in a reduction in carbon emissions ranging from 18% to 36%, while also achieving energy savings between 15% and 87%. These impressive figures demonstrate the significant environmental benefits of using recycled tire rubber in asphalt mixtures. [PERSON] et al. (2019) compared the performance of elastic rubber modified asphalt with SBS modified asphalt, specifically focusing on their respective energy-saving and emission reduction capabilities. The results of their study revealed that the detrid rubber modifier can significantly reduce energy consumption by 86.24-89.50% and CO\({}_{2}\) emissions by 89.5%. This finding highlights the potential of using the CR modifier as a sustainable replacement for SBS modifier in asphalt mixtures. [PERSON] et al. modified warm mix asphalt with different levels of crumb rubber (10%, 15%, and 20%) and demonstrated that 10% crumb rubber-modified asphalt exhibited optimal rutting, moisture sensitivity, and fatigue resistance, and a 22% increase in tensile strength ratio relative to the 10% specimen ([PERSON] et al., 2018). The reduction in emissions and optimization of performance can be primarily attributed to the balance between the physical properties of crumb rubber materials and their chemical interactions. On the one hand, the incorporation of crumb rubber enhances the elasticity and crack resistance of asphalt, thereby improving the durability and lifespan of the pavement. On the other hand, the characteristics of rubber contribute to the reduction in asphalt volatility at elevated temperatures, leading to decreased emissions of volatile organic compounds (VOCs) and other pollutants. Consequently, the synergistic effects of this material achieve a favorable balance between environmental benefits and performance enhancement. However, the scarcity of shredded rubber, an important renewable resource in the recycling of end-of-life vehicles, has become increasingly pronounced. This scarcity not only arises from the inherent limitations of the resource and the challenges associated with its recycling, but is also profoundly influenced by factors such as the recycling rates of old vehicles and variations in legislative frameworks across countries. Increasing the recycling rates of end-of-life vehicles can significantly increase the supply of shredded rubber. However, notable disparities in the legislation, technological capabilities, and policy incentives related to end-of-life vehicle recycling among different countries result in inconsistent recycling rates. Countries such as those in Europe have established relatively sophisticated recycling systems, implementing a series of effective policies and regulations to promote the recovery of waste tires ([PERSON] et al., 2018).