# A Rapid Method for the Determination of SBS Content Based on the Principle of Orthogonal Testing
## 3 Results and Discussion
### FTIR Test Results  
#### 3.2.1 Analysis of FTIR Test Results  
The infrared spectrum of each sample is obtained by scanning it with an infrared spectrometer. Figure 4 shows the infrared spectrum of matrix asphalt, SBS, rubber oil and SBS-modified asphalt in the wave number region between 500-1400 cm\({}^{-1}\). Comparing the infrared spectrum of matrix asphalt and SBS modifier, it can be found that the methyl  
Figure 3: Calibration curves of SBS content based on (**a**) stiffness modulus \(S\) and (**b**) creep slope \(m\). \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Temperature (\({}^{\circ}\)C)** & **SBS Content** & \(S\)**(MPa)** & \(m\) \\ \hline \multirow{4}{*}{\(-12\)} & 0\% & 125 & 0.420 \\  & 2\% & 102 & 0.417 \\  & 4\% & 109 & 0.409 \\  & 6\% & 103 & 0.387 \\ \hline \multirow{4}{*}{\(-18\)} & 0\% & 387 & 0.287 \\  & 2\% & 256 & 0.329 \\ \cline{1-1}  & 4\% & 232 & 0.314 \\ \cline{1-1}  & 6\% & 209 & 0.298 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: BBR test results. and methylene groups in matrix asphalt produce a characteristic absorption peak near 1377 cm\({}^{-1}\), which is not affected by SBS modifier because SBS does not have this peak. The infrared spectrum of SBS has two strong absorption peaks, one is formed by the out-of-plane rocking vibration of C-H (polystyrene) in benzene ring at 699 cm\({}^{-1}\), and the other is formed by the out-of-plane rocking vibration of trans-butadiene = CHC\({}_{2}\) (polybutadiene) at 966 cm\({}^{-1}\)[25]. Since the SBS modifier is physically compatible with matrix asphalt, the infrared spectrum of SBS-modified asphalt is a simple superposition of that of SBS and base asphalt, where no new peaks appear, or existing peaks disappear [13]. It can be seen from Figure 4 that the modified asphalt retains the SBS characteristic absorption peaks at 699 cm\({}^{-1}\) and 966 cm\({}^{-1}\), as well as a characteristic absorption peak of matrix asphalt at 1377 cm\({}^{-1}\). The absorption peaks of modified asphalt at 699 cm\({}^{-1}\) and 966 cm\({}^{-1}\) can be used to judge the existence of SBS modifier, and the SBS content can be quantitatively analyzed according to the intensity of the absorption peak. Figure 5 is the infrared spectrum of the modified asphalt with different SBS content. The peak area of the absorption peak at 699 cm\({}^{-1}\) and 966 cm\({}^{-1}\) has a certain relationship with SBS modifier content, and the intensity of the three absorption peaks does not affect each other. Therefore, the content of SBS modifier can be quantitatively analyzed based on the ratio of the absorption peak area at 699 cm\({}^{-1}\), 966 cm\({}^{-1}\) and 1377 cm\({}^{-1}\) in the infrared spectrum of the modified asphalt. The absorbance \(A\) is measured by spectral peak area. In this paper, the ratio of characteristic peak area at 699 cm\({}^{-1}\) to that at 1377 cm\({}^{-1}\) is \(A_{1}\), and the ratio of the peak area at 966 cm\({}^{-1}\) to that at 1377 cm\({}^{-1}\) is \(A_{2}\), i.e.,  
\[A_{1}=\frac{\textit{peak area (intensity) at 699 cm}^{-1}}{\textit{peak area (intensity) at 1377 cm}^{-1}}\]  
\[A_{2}=\frac{\textit{peak area (intensity) at 966 cm}^{-1}}{\textit{peak area (intensity) at 1377 cm}^{-1}}\]  
Without any other additives, two kinds of base asphalt (SK70# and Zhongshiyou asphalt) are used to respectively prepare SBS-modified asphalt with the SBS content of 2%, 4% and 6%. Five sets of parallel tests were conducted for each content. By using the OMNIC software reading tool to read the absorbance value the infrared spectrum of these two modified asphalt groups and the two kinds of matrix asphalt is determined. The standard curves of characteristic absorption peak area ratio \(A_{1}\), \(A_{2}\) and SBS content are drawn, as shown in Figure 6.  
Figure 4: Infrared spectrum of SBS, base asphalt, rubber oil and SBS modified asphalt. Regardless of the type of matrix asphalt, the \(A_{1}\) and \(A_{2}\) values at 699 cm\({}^{-1}\) and 966 cm\({}^{-1}\) also increase with the increase of SBS content.