# Evaluation of Waste Express Bag as a Novel Bitumen Modifier
## Discussion
### High Temperature Performance  
High temperature performance was evaluated by both the Superpave rutting factor test and the MSCR test. The main test data of the Superpave rutting factor test include the rutting factor, storage modulus, loss modulus and phase angle, which are shown in Figure 3. It can be seen that the rutting factor of WEB-modified bitumen was increased with an increase in the modifier dosage at the same temperature level. Similar to the softening point, the improvement of the rutting factor was stable in the range of 0-6%, however, when the dosage of the WEB modifier reached 8%, the rutting factor had a significant increase. This phenomenon is very interesting, which indicates that the high temperature performance of WEB-modified bitumen will be greatly improved when the dosage of the WEB modifier reaches a certain degree. Figure 2: The three empirical characteristics: (**a**) softening point; (**b**) penetration; (**c**) ductility. In this research, the test temperatures of different dosages of WEB-modified bitumen were different. There were two reasons for this design. First, the measurement range of the DSR was limited, so the initial test temperature of high dosage WEB-modified bitumen would be higher. For example, Figure 3a shows that even at 88 \({}^{\circ}\)C, the rutting factor of 10% WEB-modified bitumen was extremely large. If the starting temperature of 10% WEB-modified bitumen was set too low, the experimental results may have exceeded the DSR detection range. Another reason was also related to the dosage of the WEBs. Different WEB-modified bitumen had different failure temperatures. After failure, the viscosity of low dosage WEB-modified bitumen was too low for the DSR to detect and the DSR would stop the test and unload the sample automatically. The rutting factor (G*/sin8) is composed of complex modules and the phase angle. Therefore, the reason for the huge enhancement of the rutting factor should be analyzed from these two perspectives. The modification effect of the PE from WEB has been already demonstrated in other studies [21; 22; 23; 24; 25]. Generally speaking, the PE was harder than virgin bitumen. When it was blended with the virgin bitumen, it made the modified bitumen harder as the complex modules of the WEB-modified bitumen were enhanced. When the dosage of WEB reached 8%, the modifier was enough to cross-link with each other within the virgin bitumen to form a spatial network structure. When this structure was formed, the WEB-modified bitumen became less deformable under traffic load. The results were similar to the findings of [PERSON]'s study [23]. Additionally, the phase angle data of high dosage modified bitumen (over 8%) showed different trends. One distinction with normal bitumen was that the phase angle of the high dose WEB-modified bitumen decreased with the increase of temperature. As bitumen is viscous-elastic material, the phase angle will grow with the increasing temperature, regardless of whether it is virgin bitumen or modified bitumen. The viscous-elastic material's phase angle had the same tendency with temperature. This abnormal phenomenon may be due to two reasons. The modification mechanism of WEB-modified bitumen is that the matrix bitumen is filled with small particles of PE. First, before the temperature  
Figure 3: Results of the Superpave rutting factor test: (**a**) rutting factors; (**b**) phase angle; (**c**) storage modulus; and (**d**) loss modulus. reached 88 \({}^{\circ}\)C, the WEB-modified bitumen was blended in a stable status. When the temperature rose, the phase angle decreased. However, when the temperature reached 88 \({}^{\circ}\)C, the virgin bitumen began to melt, indicating that it could no longer resist the force. The DSR detector basically conducted the test on the PE portion covered by bitumen. The phase angle of the PE powder was significantly higher than the WEB-modified bitumen.