# Rheological Characteristics Evaluation of Bitumen Composites Containing Rock Asphalt and Diatomite
## 4 Results and Discussion
### Dynamic Shear Rheometer (DSR) Test  
#### 4.3.1 Temperature Sweep Tests  
The temperature sweep test results are summarized in Figure 3. As expected and seen in Figure 3a, all of the modified bitumens showed higher values of dynamic shear modulus G* as compared to the control bitumen, showing the trend of elastic enhancement as well as the significant improvement in its high-temperature performance. By comparison, the dynamic shear modulus G* was 16% RA+9% diatomite > 13% RA+7% diatomite > 18% RA > 10% mineral filler > petroleum bitumen. For example, at a temperature of 60 \({}^{\circ}\)C, the dynamic shear modulus of 10% mineral filler, 18% RA, 13% RA+7% diatomite, and 16% RA+9% diatomite modified bitumen increased 71.9%, 439.0%, 554.5%, and 2278.6% more than that of the control bitumen, respectively. The dynamic shear modulus G* of the 16% RA+9% diatomite composite-modified bitumen was the largest, and the curve was flatter, indicating that the higher the content of RA and diatomite, the better the sensitivity of modified bitumen. The dynamic shear modulus G* of 13% RA+7% diatomite modified bitumen was similar to that of 18% RA-modified bitumen, which meant that the 13% RA+7% diatomite-modified bitumen reached the dynamic shear  
Figure 2: A SEM image of diatomite. \begin{table}
\begin{tabular}{c c c} \hline \hline \multirow{2}{*}{**Component**} & \multicolumn{2}{c}{**Apparent Viscosity (Pa-S)**} \\ \cline{2-3}  & **135 \({}^{\circ}\)C** & **175 \({}^{\circ}\)C** \\ \hline control & 0.41 & 0.08 \\
18\% RA+0\% diatomite & 2.55 & 0.18 \\
13\% RA+7\% diatomite & 1.84 & 0.25 \\
16\% RA+9\% diatomite & 3.78 & 0.41 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: The rotation viscosity test. modulus of 18% RA modified bitumen, both of which have similar high-temperature performances. These results indicate that RA and diatomic could significantly increase the stiffness of the bitumen. Figure 3b presents the rutting index G*/sin\(\delta\) of petroleum bitumen and four modified bitumens. The trend of the rutting index G*/sin\(\delta\) is overall similar to that of the dynamic modulus. In this study, the rutting index G*/sin\(\delta\) of the 18% RA-modified bitumen and 13% RA+7% diatomite-modified bitumen were extremely close. The rutting index G*/sin\(\delta\) of the 16% RA + 9% diatomite composite-modified bitumen was approximately four times that of the 18% RA-modified bitumen. The rutting index G*/sin\(\delta\) of the 16% RA+9% diatomite-modified bitumen was approximately 10 times that of 10% mineral filler-modified bitumen. The rutting index G*/sin\(\delta\) of the 16% RA+9% diatomite-modified bitumen was approximately 20 times that of the petroleum bitumen,  
Figure 3: The temperature sweep results: (**a**) dynamic shear modulus; (**b**) rutting index; (**c**) phase angle; (**d**) loss tangent; and (**e**) fatigue index. which indicated that both RA and diatomic could significantly increase the rutting performance. Further, the rutting performance improved with a higher RA and diatomic dosage. Phase angle \(\delta\) is the lag of the strain with respect to the stress. The phase angle \(\delta\) for a pure elastic material is 0\({}^{\circ}\), while for a pure plastic material is 90\({}^{\circ}\)[11]. Bitumen is a typical viscoelastic material, so the phase angle \(\delta\) should be between 0\({}^{\circ}\) and 90\({}^{\circ}\). Under periodic loading, the peak strain falls behind the peak stress significantly, forming the phase angle \(\delta\). Figure 3c shows the phase angle test results of petroleum bitumen and four modified bitumens. According to Figure 3c, the phase angle of the bitumen vary from 37\({}^{\circ}\) to 89\({}^{\circ}\), within the theoretical range (0-90\({}^{\circ}\)). Figure 3c shows that a higher temperature results in a longer strain hysteresis, a higher phase angle, and a higher viscosity of bitumen.