Aging evaluation of base and SBS modified bitumens under the coupling effect of multiple aging factors

The thermal-oxidative aging of bitumen is extensively studied under the guidance of current norms in laboratory investigations, while the photo-oxidative aging is not standardized and the moisture is seldom considered. To evaluate the aging behaviors of bitumen under the coupling effect of multiple aging factors, two binders, a base bitumen and an SBS modified bitumen (SBSMB), were treated by different aging inducements, such as heat, oxygen, ultraviolet (UV) radiation and moisture, then their physical and rheological properties, morphology and chemical structures were investigated. Results indicate that two binders exhibit similar aging behaviors, the elevated aging temperature, prolonged aging time and coupled aging inducements will accelerate the aging process, and the aging susceptibility of two binders is higher at temperature above 65 °C or aging time within 10 days. The more aging inducements would cause more serious aging, the heat-oxygen-UV-moisture coupling aging causes the highest aging degree, indicating an obvious coupling effect in aggravating the deterioration of binders. Compared with thermal-oxidative aging, the UV or UV-moisture results in an entirely different surface morphology of bitumen, leaving a very rough, dry and pale surface. The transformations of chemical structures for two binders caused by various aging show a similar trend, but the variation extents of evaluated parameters of SBSMB is less than that of base bitumen under the same aging condition, indicating the modification of SBS could inhibit the aging of bitumen to some extent. Therefore, UV radiation and moisture should not be neglected in laboratory aging simulations.