# A Rapid Method for the Determination of SBS Content Based on the Principle of Orthogonal Testing
## 3 Results and Discussion
### FTIR Test Results
#### 3.2.2 Analysis Impact of Additives Based on Orthogonal Test  
According to the orthogonality table, nine kinds of modified asphalt are prepared by 0.0%, 0.1%, 0.2% sulfur combined with 0%, 2%, 4% rubber oil. Five parallel samples are prepared for each kind of modified asphalt. FTIR test is carried out on each sample, reading the corresponding absorption peak areas and calculating the infrared spectrum \(A\) value as a test index. The test plan is listed in Table 4.  
Figure 5: Infrared spectrum of SBS modified asphalt with different SBS content. Figure 6: Standard curves of \(A\) value with SBS content at different absorbance (**a**) 699 cm\({}^{-1}\) and (**b**) 966 cm\({}^{-1}\). Taking \(A_{1}\) and \(A_{2}\) values as the test indexes, MANOVA is conducted on the orthogonal test results respectively using SPSS21.0, which adopts the system default significance level \(\alpha=0.05\). The results of MANOVA are listed in Tables 5 and 6, which show the calibration model test in ANOVA. The original hypothesis is that the SBS content, sulfur content and rubber oil content in the model have no effect on \(A\) value that is the test index. If the probability \(p\) value is less than the significance level \(\alpha\), it means that the variance model is statistically significant, that is, at least one of the three influencing factors has a significant influence on the \(A\) value. degree of the three factors. Table 5 showed \(F_{\text{B}}>F_{\text{C}}>F_{\text{D}}\), the \(F\) value of SBS content is 376.333, which is much larger than that of sulfur and rubber oil content, and the \(F\) value of sulfur content is also larger than that of rubber oil content. It indicates that the most influential factor for the absorbance \(A_{1}\) value is the SBS content, followed by sulfur content and rubber oil content. 2. \(A_{2}\) value as the test index  
Similarly, as can be seen from the results of MANOVA in Table 6, for the absorbance \(A_{2}\) value, the probability \(p\) values of SBS content, sulfur content and rubber oil content are all close to 0, all significantly less than the significance level \(\alpha=0.05\), which means all these three factors have significant influence on the \(A_{2}\) value. According to the critical value of the 3-factor significance level \(\alpha=0.05\) for the 2 degrees of freedom is \(F_{(2,3)0.05}=19.164\), Table showed \(F_{\text{sbs}}=441.598>F_{(2,3)0.05}\), \(F_{\text{sulfur}}=33.542>F_{(2,3)0.05}\), \(F_{\text{rubber oil}}=9.867<F_{(2,3)0.05}\). Moreover, comparing the \(F\) values of the three factors, it is found that the \(F\) value of SBS content is much larger than that of sulfur content and rubber oil content, and the \(F\) value of sulfur content is also larger than that of rubber oil content. This means that the influence of these three factors on the absorbance \(A_{2}\) value is different, which is the same as the case where the \(A_{1}\) value is the test index. In order of their effect, SBS content is the largest, sulfur content followed, and rubber oil content is the smallest. Furthermore, Using SPSS to remove the effects of other variables, the marginal mean was estimated at different levels of each factor and was shown in Figure 7. Figure 7 illustrated that the A\({}_{2}\) increased when the content of SBS and rubber oil increased, but reduced when the content of sulfur increased. Therefore, at the significance level \(\alpha=0.05\), the three factors of SBS content, sulfur content and rubber oil content have significant influence on the \(A_{1}\) and \(A_{2}\) values, which are the characteristic peak area ratios of SBS-modified asphalt at 669 cm\({}^{-1}\) and 966 cm\({}^{-1}\) in the infrared spectrum. The influencing degree is both: SBS content > sulfur content > rubber oil content. This means under different SBS content, the addition of sulfur and rubber oil will have a significant effect on the accuracy of FTIR test results, and the influencing degree of sulfur is greater than that of rubber oil.