Microstructure of Virgin, aged and recycled asphalt based on small-angle X-ray scattering

The microstructure of asphalt plays a crucial role in determining its overall performance. However, the lack of comprehensive research on parameterizing the microstructure of asphalt has hindered the establishment of a clear relationship between microstructure and macroscopic performance. To address this gap, this paper conducted a study involving small-angle X-ray scattering (SAXS) experiments to investigate the changes in the microstructure of asphalt during aging and regeneration processes. The SAXS experimental results were then subjected to fitting using the Unified function, enabling us to derive key microstructural parameters. The SAXS data profiles obtained from virgin, aged, and recycled asphalt samples exhibit a remarkable degree of similarity, suggesting that their microstructural features are highly comparable. Additionally, the scattering characteristics observed in the SAXS data point to the presence of secondary structure scatterers within the asphalt samples. The presence of secondary structure scatterers suggests that the asphalt samples consist of microstructural entities, such as micelles or aggregates, which form the basis for the scattering patterns observed. During the aging of asphalt, the size of micelles and the heterogeneity of their sizes undergo a progressive increase. Simultaneously, the surface activity of these micelles gradually diminishes. However, a notable reduction in micelle size and size heterogeneity is achieved when regenerating aged asphalt using virgin asphalt. Furthermore, the surface activity of micelles is improved through the regeneration process. On the contrary, the rejuvenator used in this study did not exhibit a significant restorative effect on the microstructure of aged asphalt. Rheological analysis indicates that the observed viscoelastic changes in asphalt during aging and regeneration align with microstructural variations, but the effect of the rejuvenators on viscoelasticity do not correlate directly with their impact on microstructure. The differences between rejuvenators in improving the properties of aged asphalt cannot be solely inferred from their effect on microstructure. The findings in this paper contribute significantly to our understanding of asphalt microstructure and its evolution during aging and regeneration processes.