# Rheological Characteristics Evaluation of Bitumen Composites Containing Rock Asphalt and Diatomite
## 4 Results and Discussion
### Dynamic Shear Rheometer (DSR) Test
#### 4.3.2 Frequency Sweep Tests  
The frequency sweep test results are summarized in Figure 4. Figure 4a illustrates the dynamic shear modulus G* of petroleum bitumen and two modified bitumens at a frequency from 1 Hz to 25 Hz. At the same frequency, two modified bitumens show higher values of dynamic shear modulus G* as compared to the control bitumen, indicating that RA and diatomic can significantly increase the high-temperature performance of the bitumen. Further, a higher dosage of the composite modifier of RA and diatomic results in a higher value of dynamic shear modulus G*. As shown in Figure 4b, the rutting index G*/sin\(\delta\) increases gradually with frequency. The rutting index G*/sin\(\delta\) increases faster when the sweep frequency is lower than 5 Hz. Contrastively, the rutting index G*/sin\(\delta\) increases slowly and gradually and tends to be stable when the sweep frequency is higher than 5 Hz. Moreover, a higher dosage of RA and diatomic results in a better anti-rutting performance of the modified bitumen. The results show that the dynamic shear modulus G* and rutting factor G*/sin\(\delta\) of petroleum bitumen are improved by incorporating RA and diatomic, which significantly improves the deformation resistance. In addition, the anti-rutting performance is improved gradually with the higher dosage of RA and diatomic.  
Figure 4c presents the phase angle \(\delta\) of petroleum bitumen and two modified bitumens. It can be seen that the phase angle \(\delta\) overall decreases with an increase in the RA and diatomite dosage. In detail, the phase angle \(\delta\) for the control, 13% RA+7% diatomite-, and 16% RA+9% diatomite-modified bitumens are 84.9\({}^{\circ}\), 74.6\({}^{\circ}\), and 68.3\({}^{\circ}\), respectively at 10 Hz. However, the phase angle \(\delta\) of 13% RA+7% diatomite-modified asphalt shows different characteristics. The phase angle \(\delta\) rises sharply when the frequency is less than 6 Hz, and it decreases gradually after 6 Hz. This indicates that the phase angle \(\delta\) of RA and diatomite-modified asphalt shows a completely different behavior at low frequency and high frequency with a low dosage of RA and diatomite. Therefore, it is suggested that a higher dosage of compound RA and diatomite be used. By comparison, the phase angle \(\delta\) of the petroleum bitumen  
Figure 4: The frequency sweep results: (**a**) dynamic shear modulus; (**b**) rutting index; (**c**) phase angle; (**d**) loss tangent; and (**e**) fatigue index.  
is close to 90\({}^{\circ}\), indicating that the petroleum bitumen is going to lose its elasticity and enter into viscous flow. The phase angle \(\delta\) of two modified bitumens are no more than 75\({}^{\circ}\), indicating that RA and diatomic constrain the free movement of bitumen molecules, ensuring the bitumen maintains a good overall structure, and performing a resistance to permanent deformation. As shown in Figure 4d, the change rule of the loss tangent tan\(\delta\) is the same as that of the phase angle \(\delta\).  
The fatigue index \(\mid\)G*\(\mid\)sin\(\delta\) of each bitumen increases with an increase in frequency, as shown in Figure 4e. The fatigue index \(\mid\)G*\(\mid\)sin\(\delta\) increases sharply when the frequency is less than 5 Hz. Correspondingly, the fatigue factor \(\mid\)G*\(\mid\)sin\(\delta\) increases gradually when the frequency exceeds 5 Hz. In detail, the fatigue index \(\mid\)G*\(\mid\)sin\(\delta\) of two modified bitumens is larger than that of control bitumen at the same frequency. According to this, the modified bitumen mortar with RA and diatomic contains a certain amount of minerals and reduces its fatigue performance.