## 4 Conclusions  
Under the action of temperature-humidity coupling cycles, with the increase in cycle times, the physical indicators of SBS-modified asphalt mastic change are mainly manifested as increased shear strength, decreased ductility, insignificant changes in the softening point, decreased viscosity, and the increased activation energy of asphalt viscosity flow. This indicates that under the temperature-humidity coupling cycle environment, the macroscopic performance indicators of SBS-modified asphalt mastic deteriorate, manifestinging phenomena such as decreased flowability and increased brittleness.  
When the same temperature-humidity coupling cycle times are applied, the aging phenomenon of SBS-modified asphalt mastic becomes more pronounced with a larger temperature difference in the cycling range; under the same temperature difference conditions, SBS-modified asphalt mastic cycled at higher temperature ranges exhibits more significant changes in high-temperature shear strength and ductility. Therefore, special attention should be paid to the service status of asphalt pavements in regions with large temperature differences, such as Xinjiang and Tibet, in actual environments.  
The results of the DENT test show that with the increase in temperature-humidity coupling cycle times, the failure deformation and CTOD value of SBS-modified asphalt mastic decrease, and the peak load increases, indicating that the temperature-humidity coupling cycle weakens the mid-temperature fracture resistance of SBS-modified asphalt mastic.  
The FITR test results indicate that under temperature-humidity coupling cycles in different temperature ranges, there is no carbonyl absorption peak at 1700 cm\({}^{-1}\), possibly due to the mild environment for carbonyl generation; the sulfoxide index, which characterizes the aging of SBS-modified asphalt mastic, increases, while the isoprene index decreases, and the greater the temperature difference in the cycling interval, the more pronounced the changes. The increase in temperature-humidity coupling cycle times and temperature differences exacerbates the aging of SBS-modified asphalt mastic to varying degrees, and the FITR test results are consistent with the macroscopic performance results.  
**Author Contributions:** Conceptualization, C.M.; methodology, C.M. and Y.S.; software, C.M. and B.T.; validation, C.M. and B.T.; formal analysis, C.M.; investigation, Y.F.; resources, W.Z.; data curation, Y.S.; writing--original draft preparation, C.M. and Y.S.; writing--review and editing, W.Z.; visualization, Y.F.; supervision, W.Z. and B.T.; project administration, C.M. and Y.S.; funding acquisition, C.M. All authors have read and agreed to the published version of the manuscript.  
This research received no external funding.  
**Data Availability Statement:** The raw data supporting the conclusions of this article will be made available by the authors on request.  
**Conflicts of Interest:** Author [PERSON] was employed by the company Road & Bridge South Engineering Co., LTD. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.