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Surface Characteristics of Ageing Asphalt Binder Coupling Thermal Oxidation and Ultraviolet Radiation

In this study, styrene-butadiene-styrene (SBS) modified asphalt binder was aged by thermal oxidation coupled with ultraviolet (UV) radiation. Fluorescence microscopy (FM), scanning electron microscopy (SEM) with energy dispersive x-ray (EDX) detector, surface free energy, optical technology, Fourier transform infrared spectroscopy, and dynamic shear rheometer were used to explore the surface characteristics and trace the chemo-rheological evolution of the asphalt binder at various durations of aging. Both FM and SEM could observe two phases of degradation of the polymer under thermo-oxidation. The surface of UV-aged asphalt binder produced more cracks, observed by FM and SEM, and bulged along these cracks and some fragmented blocks appeared. EDX results indicated that the oxygen content of the surface of the asphalt binder increased with increasing aging duration, leading to more oxygen-containing compounds, more carbonyl and sulfoxide groups, increasing polarity, and decreasing contact angle of water droplets on the surface of the asphalt binder. Coupled aging increased the reflectance in all regions from 200 nm to 2,500 nm, while thermo-oxidative aging alone increased the reflectance from 200 to 400 nm and produced the opposite result in the other region. With increased aging duration, UV-aged asphalt binder becomes brighter and thermo-oxidative aged asphalt binder becomes darker. The asphalt binder samples did not discolor much with varying aging duration, and the color difference was more similar than opposite. The results of testing chemo-rheological properties indicated that the addition of UV radiation significantly increased the stiffness and elasticity and produced more obvious effects on the surface characteristics of variously aged binders.