## 7 Low-Carbon Green Development of Asphalt Mixtures
### Recycled Material
#### 7.1.1 Recycled Asphalt  
Reusing milling material from old asphalt pavement in the construction of new roads can significantly reduce waste disposal, which typically consumes land resources. This practice minimizes the need for mining new materials, conserves energy, and facilitates the recycling of materials.  
The reutilization of milling material derived from old asphalt pavement offers numerous environmental benefits. It not only alleviates the land requirements associated with waste disposal but also reduces the need for extracting new materials. This approach conserves energy and promotes material recycling while minimizing overall environmental impact. [PERSON] et al. [71] conducted a study analyzing the environmental benefits of using recycled asphalt pavement. Their research demonstrated that when recycled asphalt pavement (RAP) is mixed with new asphalt, it can decrease carbon emissions by up to 6.8%. Furthermore, the combination of RAP and warm mix asphalt (WMA) technology has resulted in a 12% reduction in CO\({}_{2}\) emissions and a 15% decrease in energy consumption throughout the road's life cycle. [PERSON] et al. [72] also demonstrated the substantial benefits of combining recycled asphalt pavement (RAP) with warm mix asphalt (WMA) in mitigating CO\({}_{2}\) emissions. This approach not only enhances the sustainability of asphalt mixtures but also contributes to the overall reduction in the carbon footprint associated with road construction and maintenance. Furthermore, [PERSON] et al. [73] investigated the carbon emissions associated with the construction of foam asphalt cold-recycled pavement. Their findings revealed that when producing 1 ton of asphalt mixtures, the foam asphalt cold regeneration technology significantly curtails energy consumption, saving 28.984 kg of standard coal and resulting in a decrease of 71.206 kg in CO\({}_{2}\) emissions. This is a remarkable 47.1% reduction compared to the emissions generated during the production of asphalt-stabilized gravel, highlighting the significant energy-saving benefits of this technology. [PERSON] et al. conducted a comprehensive evaluation of the sustainability of recycled asphalt pavements (RAPs) from three key perspectives: cost, energy, and environmental impact. The study found that, particularly in the context of thin asphalt overlays, the use of RAP represents a more economically efficient and environmentally feasible alternative [74].  
The combination of 100% recycled asphalt with crumb rubber and waste engine oil (WEO) is considered the most environmentally friendly type of asphalt. This mixture results in a 49% reduction in carbon dioxide (CO\({}_{2}\)) emissions, a 97% reduction in volatile organic compounds (VOCs), a 97% reduction in nitrogen oxides (NOx), a 22% reduction in methane (CH\({}_{4}\)), and a 39% reduction in sulfur dioxide (SO\({}_{2}\)) emissions. The production energy consumption of the R100-CRM-x-WEO mixture is 52% lower than that of the original mixture, with 99% of the materials derived from buried waste, significantly improving environmental quality [75]. Additionally, the use of recycled asphalt as a base layer can reduce phosphorus compound emissions in water by 45 g/m\({}^{3}\), outperforming hot mix asphalt (HMA). In terms of ecotoxicity and human non-carcinogenic toxicity, the indicators for the CMRAJ mixture are 60% lower than those for HMA. The incorporation of recycled asphalt pavements (RAPs), non-conforming fly ash (OFA), and food waste bio-oil (FWBO) further reduces environmental impacts [76]. In summary, the introduction of sustainable asphalt mixtures and innovative material combinations not only effectively reduces the emissions of various pollutants but also promotes the widespread application of environmentally friendly asphalt, significantly enhancing the environmental benefits of road construction.