Effect of Multifactor Coupling Aging on Rheological Properties of Asphalt Binders and Correlations between Various Rheological Indexes

The asphalt binder is exposed to unfavorable coupling aging of UV radiation, high temperature, and moisture, which accelerates the deterioration of the binder’s rheological properties. To investigate the effect of this coupled aging on the rheological properties of asphalt binder, an accelerated environmental aging oven considering ultraviolet (UV) radiation, temperature, and moisture was used in this paper to carry out multifactor coupling aging tests for the binder. The coupling aging test parameters are determined by the central composite design-response surface methodology (CCD-RSM). The rheological properties of asphalt binder before and after aging were examined by dynamic shear rheometer, and the effects of the coupling aging on the viscoelastic, high-temperature, fatigue, and low-temperature properties of the binders were evaluated by employing the complex shear modulus ($G^{*}$); the aging index (GI), which was established with $G^{*}$; the rutting factor ($G^{*}/\sin \delta$); the Glover–Rowe (G-R) parameter; and the ratio of asphalt binder creep rate to stiffness modulus ($m/S$), respectively. Further, the effect of the coupling aging on the chemical properties of the asphalt binder was evaluated with carbonyl index obtained from the Fourier transform infrared spectrometer. The results showed that the optimal values (temperature: 68.3°C; irradiation intensity: $\mathrm{2,221}\mathrm{W}/{\mathrm{m}}^2$; spraying interval: 250 min) of the coupled aging parameters were determined by the CCD-RSM, and the relationship between the coupled aging time and the carbonyl index was established by the Verhulst model with an $R^2$ value larger than 0.98. As the coupling aging degree increases, the $G^{*}$, $GI$, and $G^{*}/\sin \delta$ show an increasing trend, whereas the G-R parameter, $m/S$, shows a decreasing trend, indicating that the aging increases the stiffness and high-temperature resistance of the binder and decreases its fatigue properties and low-temperature properties. Based on the correlation analysis, the G-R parameter showed good correlation with the $GI$, $G^{*}/\sin \delta$ (45°C, 55°C, and 65°C), $m/S$ ($-6°\mathrm{C}$, $-12°\mathrm{C}$, and $-18°\mathrm{C}$), respectively, and the average $R^2$ value is larger than 0.98. Therefore, the G-R parameter can be used as a comprehensive index for evaluating the rheological properties of binders.