Microstructure of virgin and aged asphalts by small-angle X-ray scattering

Abstract

This study employed small-angle X-ray scattering (SAXS) to characterize the microstructure of asphalt and investigated the evolving patterns of microstructure during the aging process of asphalt. Furthermore, by utilizing Fourier transform infrared (FTIR) spectroscopy, a detailed explanation of the intrinsic mechanisms governing microstructural changes in asphalt during aging was provided. The study demonstrated that the unified power-law exponential equation is more suitable for analyzing the SAXS curve of asphalt compared to model-dependent analyses. This equation not only exhibits a strong fit to the SAXS curve of asphalt but also yields crucial parameters about asphalt's microstructure, including the scattering coefficient (P) of asphaltene clusters, the scattering coefficient (Ps) of micelles, and the radius of gyration (Rs) of micelles. The SAXS experiments indicate the presence of asphaltene clusters with a surface fractal structure in asphalt, by a size exceeding 100 nm. The asphaltene clusters exhibit a propensity for "phase separation" with the aging of asphalt. Furthermore, asphalt aging leads to an increase in the Rs of the micelles and alters the Ps of the micelles. These changes are attributed to both the aggregation of the micelles and alterations in the manner in which micelles aggregate, which are primarily caused by the excessive aging of the maltene fraction. To analyse the effect of microstructural changes on macroscopic properties during asphalt aging, the changes in high and low temperature properties of asphalt during aging were tested in this study using the multiple stress creep and recovery (MSCR) test and the bending beam rheometer (BBR) test, respectively. It was found that the changes in macro properties of asphalt during aging are not entirely due to the changes in microstructure. This study expands the application of SAXS for microstructural analysis of asphalt and contributes to a profound comprehension of the aging mechanism of asphalt from a microstructural perspective.