## 4 Conclusions  
In this research, the morphology characterization, chemical composition, and phase composition of the five aggregates were first studied. The five asphalt binder--aggregate systems' water susceptibility was assessed using the engineering approach for assessing the resistance of asphalt mixtures to water damage. Their pertinent characteristic parameters were determined. Then the water susceptibility of the five asphalt binder--aggregate systems was evaluated comprehensively by using the fuzzy comprehensive evaluation method. Finally, sensitivity analysis of the aggregate characteristic parameters was carried out by a random forest analysis model, so as to achieve the optimal screening of the aggregate characteristic parameters.  
1. During sensitivity analysis of each parameter of the aggregate properties using the random forest analysis, the SiO\({}_{2}\) content of the aggregate had the highest importance, and the roughness had the highest importance for the morphology characterization. The water susceptibility of the asphalt binder--aggregate system could be expressed by the SiO\({}_{2}\) content and roughness of the aggregate characteristic parameters.
2. The morphology characterization of the aggregates was analyzed by binarizing the SEM photographs of different aggregate materials, and it was found that the surface texture of the limestone samples was the most developed. Among them, the fractal dimension of granite was similar to that of limestone, which indicated that the surface roughness of the aggregates in this study was not directly related to their lithology.
3. The chemical element and compound composition combination of the aggregates was completely random due to the environmental influence during rock formation, and the chemical composition of the same rock varied for different places of origin and layers. However, the composition of the main minerals of the same rock was largely the same.
4. Using different aggregate compositions and the fuzzy comprehensive evaluation analysis approach, the water susceptibility index of the asphalt binder--aggregate system was investigated. The results showed that, whereas limestone had the best resilience to water damage, granite had the weakest.  
Conceptualization, S.C.; methodology, P.L.; software, X.N.; validation, Z.Y.; formal analysis, M.S. All authors have read and agreed to the published version of the manuscript.  
Figure 11: Relative importance.  
**Funding:** This research was funded by [National Natural Science Foundation of China, Industry Support and Guidance Project by University and College in Gansu Province] grant number [52268070, 2020C-13].  
**Institutional Review Board Statement:** Not applicable.  
**Informed Consent Statement:** Not applicable.  
**Data Availability Statement:** Data will be made available on request.  
**Acknowledgments:** The authors gratefully acknowledge the financial supports by the National Natural Science Foundation of China (52268070), Industry Support and Guidance Project by University and College in Gansu Province (2020C-13). Our deepest gratitude goes to the anonymous reviewers for their careful work and thoughtful suggestions that have helped improve this paper substantially.  
**Conflicts of Interest:** The authors declare no conflict of interest.