# Anti-Aging Performance and Action Mechanism of Asphalt Modified by Composite Modification
## 4 Conclusions  
Performance grades and rutting factor: The Performance Grade (PG) of OMA and ULMA is PG-70, while LMA has a higher value of PG-76, indicating that the addition of hydrotalcite alone significantly improves the high-temperature stability of asphalt. The rutting factor ranks as LMA > ULMA > OMA, showing that LMA has the best high-temperature rutting resistance, meaning that the single addition of hydrotalcite is more effective in enhancing asphalt's high-temperature rutting resistance.  
Aging resistance: The rate of change in the Carbonyl Index (CI) and Sulfoxide Index (SI) is OMA > LMA > ULMA, suggesting that the composite-modified asphalt has superior aging resistance compared to the hydrotalcite-modified asphalt.  
Compatibility and thermal stability: The UV absorber has the smallest solubility difference with asphalt, indicating the best compatibility and thermal stability. Hydrotalcite shows the largest solubility difference with asphalt, indicating poorer compatibility and thermal stability. The addition of the UV absorber improves the solubility difference of the composite modifier with asphalt compared to hydrotalcite, and as the proportion of UV absorber increases, the solubility difference decreases, significantly enhancing the thermal stability of the asphalt system.  
Free volume fraction: After the addition of the composite modifier, the free volume fraction of asphalt decreases by 2.81%. This indicates that the composite effect of the UV absorber and hydrotalcite better reduces the free volume fraction of asphalt compared to the single addition of hydrotalcite, improving the internal structure stability and aging resistance of the asphalt.  
Diffusion coefficient: The addition of the composite modifier has the greatest impact on the asphalt diffusion coefficient, increasing it by approximately 65.13%. This indicates that the composite effect of the UV absorber and hydrotalcite enhances the diffusion rate of asphalt molecules in the colloidal system, reducing the impact of UV radiation on asphalt molecules during aging and improving the UV aging resistance of the asphalt.  
**Author Contributions:** Z.L.: conceptualization, formal analysis, writing--original draft, methodology, data curation. X.S.: funding acquisition, investigation, writing--review and editing, methodology. H.X.: formal analysis, writing--review and editing. Y.L.: writing--review and editing, visualization. Z.S.: formal analysis, writing--review and editing. Y.Y.: formal analysis, data curation. G.H.: writing--review and editing, data curation. All authors have read and agreed to the published version of the manuscript.  
**Funding:** This research was funded by the Opening Funding Supported by the Key Laboratory of Transport Industry of Road Structure and Material (Research Institute of Highway, Ministry of Transport), Beijing, PRC.  
**Institutional Review Board Statement:** Not applicable.  
Figure 32: Diffusion coefficients of the different types of asphalt and their difference plots.  
**Informed Consent Statement:** Not applicable.  
**Data Availability Statement:** All data collected and analyzed are presented in this published article. Any additional data supporting the results can be made available upon request to the corresponding author.  
**Acknowledgments:** This paper describes research activities mainly requested and sponsored by Opening Funding Supported by the Key Laboratory of Transport Industry of Road Structure and Material (Research Institute of Highway, Ministry of Transport), Beijing, PRC. That sponsorship and interest is gratefully acknowledged.  
**Conflicts of Interest:** Author [PERSON] was employed by the company Shanxi Transportation Holding Group Co., Ltd. The remaining authors declare that the re-search was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.