# Study on the Aging Behavior of Asphalt Binder Exposed to Different Environmental Factors
## 3 Results
### Analysis of Outdoor Exposure on the Chemical Composition of Asphalt Binder
#### 3.3.2 Effect of Outdoor Exposure on the Functional Groups of Different Asphalt Binder  
Asphalt binder is composed of numerous molecules, rendering its chemical composition exceptionally intricate. Precisely extracting the composition of asphalt binder remains challenging. Fourier Transform Infrared Spectroscopy (FTIR) can evaluate the type and content of certain functional groups in asphalt binder based on wave numbers and peak shapes in the spectrum. The analysis of functional groups in asphalt binder subjected to various aging modes was conducted using FTIR, and the results are depicted in Figures 13 and 14. As evident in Figures 13 and 14, unaged asphalt binder exhibits a multitude of distinctive peaks. The peak at 2920 cm\({}^{-1}\) corresponds to the antisymmetric stretching vibration of methylene (-CH\({}_{2}\)-), while the symmetric stretching vibration of methylene -CH\({}_{2}\)- appears at 2850 cm\({}^{-1}\). The absorption peak near 1600 cm\({}^{-1}\) is attributed to both the backbone vibration of the benzene ring and the carbon-oxygen double bond. Carbonyl group absorption peaks lie between 1800 cm\({}^{-1}\) and 1650 cm\({}^{-1}\), while sulfoxide group absorption peaks are near 1030 cm\({}^{-1}\). Most absorption peaks below 600 cm\({}^{-1}\) correspond to compounds comprising carbon and other elements. Notable alterations in the intensity of absorption peaks, particularly in the vicinity of 1700 cm\({}^{-1}\) and 1030 cm\({}^{-1}\), were observed before and after asphalt binder aging. The carbonyl and sulfoxide indices serve as common metrics for quantifying the extent of asphalt binder aging. \[CI=\frac{CA}{Cref} \tag{2}\]  
\[SI=\frac{SA}{Sref} \tag{3}\]  
where \(CI\) = Carbonyl index; \(CA\) = Carbonyl characteristic peak area; \(SI\) = Sulfoxide index; \(SA\) = Sulfenyl characteristic peak area; \(Cref\) and \(Sref\) = Reference peak area. Typically, peak areas around 1700 cm\({}^{-1}\) were chosen to represent the carbonyl group and around 1031 cm\({}^{-1}\) for the sulfoxide group. The carbonyl and sulfoxide indices of the unaged asphalt binder and the three naturally aged asphalt binders were calculated using Equations (2) and (3), with the results presented in Table 6. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Binder** & **Modules** & \(A_{\text{C=O}}\) & \(A_{\text{S=O}}\) & \(A_{\text{C-H}}\) & \(I_{\text{C=O}}\) & \(I_{\text{S=O}}\) \\ \hline \multirow{4}{*}{Virgin asphalt binder} & Unaged & 0.289 & 0.754 & 18.244 & 0.0158 & 0.0413 \\  & TFOT & 0.254 & 0.751 & 17.616 & 0.0144 & 0.0426 \\  & O & 0.287 & 1.853 & 18.096 & 0.0159 & 0.1024 \\ \cline{1-1}  & O+UV & 0.296 & 2.490 & 16.760 & 0.0177 & 0.1486 \\ \cline{1-1}  & All & 0.360 & 2.590 & 17.792 & 0.0202 & 0.1456 \\  & PAV & 0.499 & 2.154 & 16.086 & 0.0310 & 0.1339 \\ \hline \multirow{4}{*}{SBS-modified asphalt binder} & Unaged & 0.540 & 0.138 & 17.933 & 0.0301 & 0.0077 \\  & TFOT & 0.061 & 1.140 & 18.201 & 0.0034 & 0.0626 \\ \cline{1-1}  & O & 0.227 & 2.244 & 17.666 & 0.0128 & 0.1270 \\ \cline{1-1}  & O+UV & 0.241 & 1.936 & 17.709 & 0.0136 & 0.1093 \\ \cline{1-1}  & All & 0.2000 & 2.226 & 17.620 & 0.0114 & 0.1263 \\ \cline{1-1}  & PAV & 0.612 & 3.455 & 17.644 & 0.0347 & 0.1958 \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Calculation Results of Carbonyl and Sulfoxide Index. Figure 14: FTIR of SBS modified asphalt binder. As observed in Table 6, both the carbonyl index (\(I_{\text{C=O}}\)) and sulfoxide index (\(I_{\text{S=O}}\)) of the asphalt binder increased following aging in various modes. Generally, the carbonyl index exhibited relatively small changes before and after natural aging, while a notable increase was evident in the sulfoxide index. Notably, O+UV-aging and All-aging had the most significant impact on the sulfoxide index of virgin asphalt binder, surpassing even the effects of PAV aging. All-aging on the carbonyl index of virgin asphalt binder was slightly less than that of PAV aging, accounting for approximately 65.2% of the carbonyl index observed after PAV aging.