## 3 Analysis of Test Results
### Changes in Chemical Composition  
The Fourier transform infrared spectrometer was used to test SBS-modified asphalt, limestone powder, and SBS-modified asphalt mastic, and the SBS-modified asphalt mastic after 12 cycles at different cycling temperatures was tested. The test results are shown in Figure 10.  
The SBS-modified asphalt mastic did not produce new characteristic absorption peaks. Its characteristic absorption peak is the superposition of the characteristic absorption peaks of SBS-modified asphalt and limestone powder, indicating that the contact between limestone powder and SBS-modified asphalt is mainly physical adsorption, and no clear chemical reaction occurred. Combined with Figure 10, it can be seen that under the action of temperature and humidity coupling cycles, the chemical composition of limestone powder was stable, while alterations in the characteristic functional groups of the mastic primarily stemmed from changes in the characteristic functional groups of the asphalt. Therefore, the change rate of asphalt characteristic functional groups can be used to characterize the influence of temperature and humidity coupling cycles on the mastic. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Number of Temperature and Humidity** & \(\mathbf{w_{e}}\)/(\(\mathbf{kJ}\cdot\mathbf{m}^{-2}\)) & \(\mathbf{R^{2}}\) & **CTOD/(mm)** \\ \hline
0 & 17.673 & 0.9962 & 17.03 \\
6 & 13.330 & 0.9728 & 11.99 \\
12 & 11.501 & 0.9984 & 9.57 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: DENT results for SBS-modified asphalt mastic under different cycle times. The changes in the carbonyl absorption peak at 1700 cm\({}^{-1}\), sulfinyl absorption peak at 1031 cm\({}^{-1}\), and butadiene absorption peak at 966 cm\(-1\) can be used to characterize the aging degree of SBS-modified asphalt [35; 36]. In accordance with the Lambert-Beer law, the summation of peak areas within the fingerprint region ranging from 2000 to 600 cm\({}^{-1}\) served as the reference point. The carbonyl index (I\({}_{\text{C=O}}\)), sulfifin index (I\({}_{\text{S=O}}\)), and butadiene index (I\({}_{\text{B}}\)) of the mastic before and after cycling were determined using Equations (8)-(10). Subsequently, quantitative analysis was conducted on the alterations in the chemical compositions of the SBS-modified asphalt mastic, both pre- and post-temperature-humidity coupled cycling, with the outcomes presented in Table 6.  
\[\text{I}_{\text{C=O}}=\frac{A_{1700}}{\sum A_{2000\text{-600}}} \tag{8}\]  
\[\text{I}_{\text{B}}=\frac{A_{966}}{\sum A_{2000\text{-600}}} \tag{9}\]  
\[\text{I}_{\text{S=O}}=\frac{A_{1031}}{\sum A_{2000\text{-600}}} \tag{10}\]  
In the above formula, \(A_{2000\text{-600}}\) is the peak area of the asphalt fingerprint region in the range of 2000-600 cm\({}^{-1}\). \[A_{2000\text{-600}}=A_{1600}+A_{1456}+A_{1376}+A_{1162}+A_{1031}+A_{966}+A_{8 61}+A_{810}+A_{744}+A_{722}\] \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Temperature** & **Uncycled** & \(-\)**20\(-\)60 \({}^{\circ}\)C** & \(-\)**20\(-\)40 \({}^{\circ}\)C** & \(0\)\(-\)60 \({}^{\circ}\)C** & \(0\)\(-\)**40 \({}^{\circ}\)C** \\ \hline I\({}_{\text{B}}\) & 0.00686 & 0.00282 & 0.00435 & 0.00385 & 0.00548 \\ I\({}_{\text{S=O}}\) & 0.01632 & 0.03171 & 0.02495 & 0.02454 & 0.02499 \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Calculation results of the characteristic functional group index of the FTIR spectrum of SBS-modified asphalt mastic under different test conditions. Figure 10: FTIR spectra of SBS-modified asphalt, limestone mineral powder and SBS-modified asphalt mastics. Combined with Figure 9 and Table 6, it can be seen that there is no carbonyl absorption peak at 1700 cm\({}^{-1}\) in the SBS-modified asphalt mastic before and after the temperature and humidity coupling cycle. This may be because the experimental environment is relatively mild for the generation of carbonyl under the action of the temperature and humidity coupling cycle, resulting in a small amount of carbonyl generation that is not observed.