## 5 Conclusions  
Based on macroscopic experiments, microscopic structure observation, and molecular dynamics simulation, this study examined the enhancement effect of SCA modification on the interface performance of RCA and asphalt before and after modification and investigates its underlying mechanism for enhancement. The following findings were made.  
The results of the boiling water experiment and direct tensile experiment indicate that SCA modification significantly improves the interface behavior between RCA and asphalt. The bond between SCA-modified RCA and asphalt is enhanced by two grades, and the tensile strength goes up by 72.2% in dry conditions and 119.7% in wet conditions.  
The observation results of SEM show that SCA modification effectively improves the interface structure defects between RCA and asphalt. Before SCA modification, there are numerous pores on the surface of RCA, resulting in structural defects between the RCA and asphalt interface. After SCA modification, a dense film is formed on the surface of the RCA, effectively filling the pores of the RCA surface mortar and creating a more compact bond at the RCA/asphal interface.  
The results of the molecular dynamics simulations indicate that SCA modification reduces the number of hydrogen bonds formed between C-S-H and water molecules, thereby decreasing the hydrophilicity of the C-S-H surface. SCA modification also improves the interaction energy and water resistance of C-S-H with asphalt. Additionally, SCA molecules can penetrate the asphalt layer to create a dense interfacial transition zone between C-S-H and asphalt. This makes the two substances work better together and reduces the effect of water on the nanoscale structure of the asphalt interface.  
Figure 18: The concentration profiles of SARA components: (**a**) C-S-H/water/asphalt model; (**b**) C-S-H/SCA/water/asphalt model.  
The study findings help us understand the mechanisms of interfacial interactions between asphalt and modified aggregate surfaces and develop more effective interface modifications. In addition, it lays the foundation for the application of RCA/asphal mixtures on road surfaces and for improving the road performance of asphalt mixtures. Future research can consider the influence of SCA modification on the interactions between different interfaces, such as \(\text{SIO}_{2}\)/asphalt, \(\text{CaCO}_{3}\)/asphalt, etc. The interaction mechanism of SCA modification on RCA/asphal interface is explained from a more comprehensive perspective.  
Conceptualization, K.H.; methodology, J.Z.; software, [PERSON]; validation, [PERSON]; formal analysis, [PERSON]; investigation, [PERSON]; resources, [PERSON]; data curation, [PERSON]; writing--original draft preparation, [PERSON] and X.D.; writing--review and editing, [PERSON] and Y.C.; visualization, [PERSON]; supervision, [PERSON] and Q.Y.; project administration, [PERSON] and J.G.; funding acquisition, [PERSON] All authors have read and agreed to the published version of the manuscript.  
This work was financially supported by the Fundamental Research Fund of Natural Science Foundation of China (No. 52208434), the Central Public Welfare Research Institute (No. 2020-9049), Natural Science Foundation of Henan Province (No. 222300420142), Postdoctoral Fund of Henan Province; Science and Technology Project of Henan Province (No. 192102310229), China Postdoctoral Science Foundation (No. 2022M711079), and Young backbone teachers plan of Henan University of Technology (No. 21420156).  
**Informed Consent Statement:** Not applicable.  
**Data Availability Statement:** All data from this study are presented in the paper.  
The authors declare no conflict of interest.