Evolution of Phase Structure in Rejuvenated Asphalts during the Aging Process: Insights from Morphology and Bulk Characteristics

Understanding the aging characteristics of rejuvenated asphalt binders is vital for the effective selection and optimization of rejuvenators prior to their application in aged asphalt. Traditional chemical approaches often disrupt the molecular structure of asphalt, potentially obscuring the full evolution of phase structures during thermal oxidative aging. This study employs nondestructive approaches in terms of environmental scanning electron microscopy (ESEM) and stress relaxation spectra to characterize the morphological and bulk phase structures of both rejuvenated and base asphalt throughout the aging process. Results showed that aging induces substantial morphological changes, increasing asphaltene content and aggregation, which transforms asphalt from a homogeneous to a more complex biphasic or multiphasic structure. Rejuvenated asphalt exhibits a faster aging rate than base asphalt, with larger asphaltene aggregates and more intricate phase structure evolution. As aging progresses, rejuvenated asphalts experience greater phase separation compared with base asphalt. These results highlight the complex phase evolution during aging and the challenges in maintaining the long-term benefits of rejuvenation in asphalt binders.