# Evaluation of Aging Resistance of Graphene Oxide Modified Asphalt
## 3 Results and Discussion
### UV Aging Resistance Performance
#### 3.2.2 Physical Performance  
Three indicators, such as residual penetration ratio (PRR), softening point incremental (SPI), and residual ductility ratio (DRR) can characterize the physical properties attenuation amplitude during the UV aging process. Therefore, these three indicators were used in evaluating the UV aging degree of the asphalts used in this research project. The PRR, the SPI, and the DRR were calculated according to the Equations (3)-(5), respectively:  
\[\mathrm{PRR}=\frac{\mathrm{P_{UV}}}{\mathrm{P_{TOT}}}\times 100\% \tag{3}\]  
\[\mathrm{SPI}=\mathrm{SP_{UV}}-\mathrm{SP_{TOT}} \tag{4}\]  
\[\mathrm{DRR}=\frac{\mathrm{D_{UV}}}{\mathrm{D_{TOT}}}\times 100\% \tag{5}\]  
where, \(\mathrm{P_{TOT}}\), \(\mathrm{D_{TOT}}\), and \(\mathrm{SP_{TOT}}\) are the penetration (0.1 mm), the ductility (cm), and the softening (\({}^{\circ}\)C) after TFOT, respectively; \(\mathrm{P_{UV}}\), \(\mathrm{D_{UV}}\), and \(\mathrm{SP_{UV}}\) are the penetration (0.1 mm), the ductility (cm), and the softening (\({}^{\circ}\)C) after UV aging, respectively. In general, it is expected that the asphalt with a good UV aging resistance should have higher PRR, lower SPI, and higher DRR values indicating that the physical performance of the asphalt will not change significantly after UV aging. Figure 4 shows the PRR results after UV aging. It can be seen that the PRR value of all asphalts decrease gradually with the extension of UV aging time, when the UV ageing time increases from three days to nine days, the PRR value of 90 A decreases from 59.2% to 36.4%, and the PRR value of SBS MA decreases from 67.3% to 38.6%. The higher PRR value means a lower aging degree, and vice versa. After adding the GO, the PRR value of 90 A and SBS MA after UV aging increased, when the GO content was 3%, the PRR of 90 A after nine days of UV aging increased from 36.4% to 57.3%. In addition, the PRR value of SBS MA after nine days UV aging increased from 38.6% to 64.3%, which shows that the GO can alleviate asphalt penetration attenuation in the process of UV aging. Figure 5 shows the SPI results after UV aging. The higher the SPI, the higher is the aging degree and vice versa. The SPI values of 90 A, SBS MA and the GO modified asphalts increased gradually with the extension of UV aging time. Compared to the asphalt without modifiers, after adding the GO, the SPI values of all asphalts decreased at the same UV aging condition, and the SPI value was lower when the GO content was 3% compared to 1%. This shows that the GO can retard the softening point increase in the UV irradiation process, and the retarding effect is more pronounced when the GO content is increased. Figure 4: The PRR of asphalt after UV aging. The DRR results after UV aging are shown in Figure 6. The lower value of DRR indicates an increase in the aging degree of the binder. With the extension of the UV times, the DRR values decrease obviously. At the same UV aging condition, the ductility attenuation rate decreases with the GO, and the decrease effect is more obvious when the GO content is increased from 1% to 3%. For instance, the DRR values of the GO modified 90 A will increase from 21.2% (without GO) to 38.1% (with 3% GO), and the DRR values of the GO modified SBS MA will increase from 25.0% (without GO) to 45.4% (with 3% GO). The asphalt viscosity after TFOT and UV aging was tested at different temperatures, namely 30 \({}^{\circ}\)C, 45 \({}^{\circ}\)C, 60 \({}^{\circ}\)C, 75 \({}^{\circ}\)C, 90 \({}^{\circ}\)C and 105 \({}^{\circ}\)C. The viscosity aging indices (VAI) of all temperatures were calculated based on the Equation (6):  
\[\text{VAI}=\frac{\text{V}_{\text{UV}}-\text{V}_{\text{TFOT}}}{\text{V}_{\text{ TFOT}}}\times 100\% \tag{6}\]  
where, VUV is the viscosity after UV aging in Pa-s; and \(V_{\text{TFOT}}\) is the viscosity after TFOT in Pa-s. In general, a higher VAI value is an indication of a higher UV-aging degree. The VAI results of 90 A  
Figure 5: The SPI of asphalt after UV aging. Figure 6: DRR of asphalt after UV aging.