Long-Term Property Evolution of SBS-Modified Asphalt Binders in Simulated Natural Aging

Pressure aging vessel (PAV) generally cannot well simulate field aging conditions and reveal the long-term property evolution of asphalt binder. In this study, an accelerated natural aging method was used to investigate the evolution of physicochemical and rheological properties of styrene-butadiene-styrene (SBS)–modified asphalt binders, with the consideration of the effects of polymer content and polymer structure. First, different types of modified binders were produced and short-term aged. Subsequently, thin binder films were prepared and naturally aged in a dark and ventilated environmental chamber at 60°C, and the maximum aging duration was 70 days. The aged binders were collected from the environmental chamber at various sampling intervals, followed by the characterization of the morphology, functional groups, complex shear modulus, phase angle and rutting performance of the binders. The results indicate that most physicochemical (carbonyl and sulfoxide index) and rheological (complex shear modulus and phase angle) indicators experience a fast development stage followed by a steady development stage during the natural aging process. Polymer content and polymer structure play a minor role in the evolution of physicochemical properties. For rheological properties, modified binder with 3% of SBS shows similar evolution trends to base binder. However, at 6% of SBS, some inconsistent trends can be observed due to the opposite effects of asphalt binder aging and polymer degradation, especially for the binder with radial SBS polymer. Overall, a combination of high polymer content and radial SBS polymer leads to the best durability of the modified binder in accelerated natural aging.