# Evaluation of Aging Resistance of Graphene Oxide Modified Asphalt
## 3 Results and Discussion
### UV Aging Resistance Performance
#### 3.2.3 Evaluating the Rheological Properties  
The complex modulus (G*) and the phase angle (\(\delta\)) of the 90 A and the GO-modified 90 A before aging and after TFOT aging are shown in Figure 9. In general, a nano-material powder always brings a hardening effect to the asphalt, and G* always increases. From Figure 9, before aging, the G* increment of 90 A with 1% GO content is minimal, and the G* value of the 3% GO-modified 90 A is slightly lower than 90 A. This is possible due to the softening effect of the CO\({}_{2}\) sealed in the asphalt [33; 34]. The \(\delta\) value of the GO-modified 90 A is lower than the \(\delta\) of 90 A, the difference is more notable from \(-10\)\({}^{\circ}\)C to \(0\)\({}^{\circ}\)C. After TFOT, the ranking order of the G* of 90 A is 1% GO-modified 90 A < 3% GO-modified 90 A < 90 A, and there is little difference of the \(\delta\) of 90 A and the GO-modified 90 A; the G* increment of the 3% GO-modified 90 A is almost the same as 90 A, but the \(\delta\) reduction of 3% GO-modified 90 A is less than 90 A. This indicates that 3% GO can improve the thermo-oxidative aging resistance performance of 90 A; when the GO content is 1%, the G* is much smaller than that of 90 A. In addition, the \(\delta\) reduction is also less than 90 A, so that 1% GO can obviously improve the thermo-oxidative aging resistance performance of 90 A. On the improvement in the thermo-oxidative aging resistance performance of 90 A, the 3% GO-modified effect is not as good as the 1% GO. This could be attributed to the residual CO\({}_{2}\) in the asphalt; the CO\({}_{2}\) will be released at the temperature of 163 \({}^{\circ}\)C during TFOT. The release process is equivalent to a stirring action and the asphalt film near the CO\({}_{2}\) bubble is very thin, which can, more or less, speed up the TFOT aging rate and weakens the improvement effect of the GO. In this paper, we simply name the process of releasing CO\({}_{2}\) as stirring and film action. When the GO content is 1%, this stirring and film action is less obvious than with the 3% GO content; hence, a better anti-aging performance. The G* and the \(\delta\) of 90 A and the GO-modified 90 A after TFOT and after nine days of UV aging are shown in Figure 10. After nine days of UV aging, the order of the G* of 90 A was found to be 3% GO-modified 90 A < 1% GO-modified 90 A < 90 A. The G* value is decreased by the utilization of the GO, especially the G* of the 3% GO-modified asphalt after nine days of UV aging is almost the same as the G* of 90 A. The G* of the 3% GO-modified 90 A is less than 90 A. This indicates that 3% GO-modified 90 A is less than 90 A. This indicates that 3% GO-modified 90 A is less than 90 A. This indicates that 3% GO-modified 90 A is less than 90 A. This indicates that 3% GO-modified 90 A is more than 90 A. This indicates that 3% GO-modified 90 A is more than 90 A.  
same as before aging, which shows the GO has an excellent UV aging resistance performance. The GO can significantly improve the anti-UV aging performance of 90 A, and the improvement effect of the 3% GO is much better than 1% GO. The UV test temperature (50 \({}^{\circ}\)C) is only slightly higher than its softening point; on the other hand, after 5 h of TFOT aging, CO\({}_{2}\) is released completely out of the GO-modified asphalt, so the stirring and film action will not affect the improvement effect of the GO. The fatigue cracking factor (G*sin\(\delta\)) is used to evaluate the anti-fatigue performance of an asphalt binder where the lower value of the G*sin\(\delta\) is an indication of better anti-fatigue performance. Superpave specifications specify that the G*sin\(\delta\) should not be higher than 5.0 MPa [35]. In this paper, in order to quantitatively evaluate the effects of the GO on the anti-fatigue performance of asphalt at different aging states, the corresponding temperature fatigue cracking factor of 5.0 MPa is also calculated; this temperature is simply referred to as FFT. Figure 11 shows the G*sin\(\delta\) results of 90 A and the GO-modified 90 A.