## 4 Results Analysis
### Effect of Physical Additives on the Test Accuracy of SBS Content
#### 4.3.2. Mechanism Analysis  
The infrared spectrum of the first group of SBS-modified asphalt at 966 cm\({}^{-1}\), whether it contains added compatibilizers, is shown in Figure 5, and the peak-area test results are shown in Table 5.  
\begin{table}
\begin{tabular}{c c c c c c c} \hline
**Compatibilizer** & **Test Sample** & **A966/(A966 + A1377)** & \
\begin{tabular}{c} **Compatibilizer** \\ **Content** \\ \end{tabular} & **Test Results** &
\begin{tabular}{c} **Actual SBS** \\ **Content** \\ \end{tabular} & **Error** \\ \hline \multirow{4}{*}{1} & First group & 0.1207 & 2.7\% & 3.84\% & 3.89\% & \(-\)0.05\% \\ \cline{2-7}  & Second group & 0.0747 & 2.7\% & 3.84\% & 3.89\% & \(-\)0.05\% \\ \cline{2-7}  & Third group & 0.1139 & 2.7\% & 3.89\% & 3.89\% & 0.00\% \\ \cline{2-7}  & Fourth group & 0.0793 & 2.7\% & 3.93\% & 3.89\% & +0.04\% \\ \hline \multirow{4}{*}{1} & First group & 0.1198 & 3\% & 3.78\% & 3.88\% & \(-\)0.10\% \\ \cline{2-7}  & Second group & 0.0770 & 3\% & 3.98\% & 3.88\% & +0.10\% \\ \cline{2-7}  & Third group & 0.1161 & 3\% & 3.97\% & 3.88\% & +0.09\% \\ \cline{2-7}  & Fourth group & 0.0786 & 3\% & 3.89\% & 3.88\% & +0.01\% \\ \hline \end{tabular}
\end{table}
Table 4: Test results of SBS-modified asphalt with compatibilizer.  
Figure 5: Infrared spectra of SBS-modified asphalt with and without compatibilizer at 966 cm\({}^{-1}\).  
As can be seen from Figure 5, the characteristic peak area at 966 cm\({}^{-1}\) of the modified asphalt with the compatibilizer added is smaller because the addition of the compatibilizer increases the total mass of the SBS-modified asphalt, which is equivalent to diluting the SBS-modified asphalt. The actual content of the agent will be relatively reduced, resulting in a slight decrease in the peak area ratio. The data in Table 5 prove that the addition of compatibilizer did not cause the change of the characteristic peak area at 966 cm\({}^{-1}\), while 966 cm\({}^{-1}\) is the characteristic peak of butadiene, which represents the out-of-plane vibration of trans =CH bond in butadiene. The area of the characteristic peak at 966 cm\({}^{-1}\) did not change, indicating that the trans =C-H bond in butadiene in SBS did not change quantitatively, and there was no change in the chemical bond.  
The components of compatibilizer used commonly are aromatic, saturated, or two mixtures of them, which belong to the four components of asphalt [25]. During the production and storage process of SBS-modified asphalt, the volatilization of saturated and aromatic components will be caused, so using compatibilizer to supplement these two components can slow down the separation of SBS-modified asphalt and matrix asphalt. In Figure 6, the aromatic component in the compatibilizer mainly acts on the polystyrene segment of SBS, and, according to the principle of similar polarity, swelling occurs in the polystyrene microregion. By swelling, the distance between the polystyrene molecular chains will be increased, the molecular force between the segments is reduced, and its motion capacity is enhanced. Because of the intensified movement of polystyrene microdomains, the continuous phase of polybutadiene is more dispersed, the area of SBS increases, and the dispersion of SBS in the asphalt is more uniform, which increases the compatibility of SBS in asphalt. It can be seen from the mechanism of the compatibilizer that the adding of compatibilizer does not cause changes in the chemical bond and molecular structure of the SBS, so the compatibilizer belongs to the physical additive. From the above, it can be concluded that after removing the error caused by the quality of the compatibilizer, the adding of compatibilizer will not cause the change of characteristic peak area and affect the test accuracy.