# A Rapid Method for the Determination of SBS Content Based on the Principle of Orthogonal Testing
## 3 Results and Discussion  
### Rheological Test Results  
#### 3.1.1 Temperature Scanning Test Results  
The temperature sweep test is carried out on different virgin SBS modified asphalt samples by DSR. The complex shear modulus \(G^{*}\) and phase angle \(\delta\) of three modified asphalt at multiple temperatures are measured to calculate the rutting factor \(G^{*}/sin\delta\). According to the test results, the curves of rutting factor \(G^{*}/sin\delta\) with temperature under different SBS content are plotted, as shown in Figure 1.  
Figure 2 reflects the temperature curves of rutting factor \(G^{*}/sin\delta\) of the three modified asphalt. With the increase of the modifier content, the \(G^{*}/sin\delta\) value of the modified asphalt increases; and as the test temperature increases, the \(G^{*}/sin\delta\) value tends to decrease. This means that the higher the SBS content, the lower the temperature, and the larger the value of \(G^{*}/sin\delta\), indicating that the asphalt is more elastic, the high-temperature flow deformation is smaller, the high-temperature performance is better, and the anti-rutting ability is stronger.  
The high temperature performance index of modified asphalt increases with the increase of SBS content, indicating that the higher the SBS content, the better the high temperature performance of the modified asphalt. This is because SBS polymer and matrix asphalt are two completely different materials. SBS is dispersed as particulates in the matrix asphalt under mechanical force. With a different SBS content, SBS has a different distribution in the asphalt. When the SBS content is small, SBS is scattered as a dispersed phase in the continuous asphalt phase. When the SBS content is high, the SBS dispersed phase forms a network structure in the asphalt. If the SBS content is continuously increased,  
Figure 1: Curves of rutting factor with temperature under different SBS content.  
the asphalt will change phase. Therefore, the larger the content of SBS, the more uniform it is distributed in the asphalt. The formation of a three-dimensional network structure can well limit the movement of the entire molecular system of the modified asphalt at high temperature, thereby improving the high temperature performance of the asphalt.  
According to the SBS content and the calculation results of rutting factor, the fitting curves of \(G^{*}/sin\delta\) value and SBS content at different test temperatures can be drawn, taking 73 \({}^{\circ}\)C, 76 \({}^{\circ}\)C and 79 \({}^{\circ}\)C as examples, as shown in Figure 2. It is obvious that the rutting factor has a good linear relation with the SBS content at different temperatures, which can be used for the calibration of SBS content in modified asphalt. However, the good linear relation is related to temperature. The rutting factor increases linearly with the increase of SBS content at different temperatures, but its growth slope is significantly different. When using this result to determine the SBS content in the modified asphalt, the specific calibration curve at the actual temperature of the asphalt needs to be found. So, this method is not simple. In addition, there is another problem with the determination of SBS content in modified asphalt using a calibration curve based on the rutting factor: this method is susceptible to other modifiers in the asphalt. Due to the high market price of SBS, some modified asphalt manufacturers privately reduce the SBS content and add some cheap modifiers to reduce the cost for personal gain. This makes the rutting factor value of the produced SBS modified asphalt can also meet the requirements of the specification, but its road performance is unknown. In this case, the SBS content measured by the calibration curve based on the rutting factor is qualified with a quite different truth.