## 5 Conclusions  
To enhance the SRNR performance of EAC and clarify the formation mechanism of its surface texture characteristics and their relationship with SRNR performance, this paper investigated the effects of four mix design parameters--water-binder ratio, sand ratio, coarse aggregate volume ratio, and proportion of aggregates > 9.5 mm--on the surface texture characteristics, SRNR performance, and mechanical properties of EAC through orthogonal experiments. The optimal mix proportions for EAC were proposed, and a correlation analysis was conducted between the surface texture characteristics and the SRNR performance. The main conclusions are as follows:  
1. The proportion of aggregates > 9.5 mm is the most significant factor affecting the surface texture characteristics and SRNR performance of EAC. When the proportion of aggregates > 9.5 mm is 70%, both the exposed aggregate depth and the exposed aggregate area ratio of EAC decrease significantly. Therefore, the proportion of aggregates > 9.5 mm should not be too high during mix design.
2. The optimal mix proportions of EAC are as follows: water-binder ratio of 0.43, sand ratio of 31%, coarse aggregate volume ratio of 42%, and proportion of aggregates > 9.5 mm of 50%. Compared with ordinary grooved concrete, the optimal mix proportions of EAC increase the pendulum value by 31.5% and reduce the noise value by 6.48 dB. The frequency range of noise reduction is mainly concentrated between 1.5 kHz and 4.0 kHz, which belongs to the mid-high frequency range that is more sensitive to the human ear.
3. There is a high correlation between noise value and exposed aggregate depth, as well as between pendulum value and exposed aggregate area ratio. Specifically, as the exposed aggregate depth increases, the noise value gradually decreases and stabilizes, showing an inverse exponential function relationship. On the other hand, as the exposed aggregate area ratio increases, the pendulum value first decreases, then increases, and finally decreases again, exhibiting a cubic polynomial relationship.  
EAC has broad application prospects in the field of pavement engineering due to its superior SRNR performance. Future research will employ 3D laser scanning technology and machine learning algorithms [40; 41; 42; 43] to establish the relationship between macroscopic/microscopic surface texture parameters and SRNR performance of EAC, in vestigating the evolution patterns of texture parameters and SRNR performance under different wear levels, so as to provide a reference for the practical engineering application effects of EAC.  
Conceptualization, C.W. and X.Z.; methodology, C.W. and R.L.; software, C.W.; validation, C.W. and R.L.; formal analysis, X.Z; investigation, C.W.; resources, X.Z.; data curation, C.W.; writing--original draft preparation, C.W.; writing--review and editing, X.Z. and R.L.; visualization, Y.L.; supervision, X.Z. and Y.L.; project administration, X.Z. All authors have read and agreed to the published version of the manuscript.  
This work was funded by National Natural Science Foundation of China [grant number 51878077] and the Postgraduate Scientific Research Innovation Project of Hunan Province [grant number CXCLY2022002].  
Not applicable.  
The original contributions presented in this study are included in the article. Further inquiries can be directed to the corresponding author.  
The authors declare no conflicts of interest.