Behaviors of asphalt under certain aging levels and effects of rejuvenation

Aging has an undesirable effect on asphalt properties, which can be restored by rejuvenation. In this study, neat asphalt was aged by the standard rolling thin-film oven (RTFO) test with varying times to obtain asphalts at different levels of aging; these asphalts were then rejuvenated to their original penetration grade. Analysis of the asphalt fractions, Fourier-transform infrared spectroscopy (FTIR), and atomic force microscopy (AFM) were employed to investigate the evolution of the distributions of SARA fractions, the functional groups, and the microstructures during aging and rejuvenation. Physical and rheological properties were tested to evaluate the pavement performance of the asphalts. The results showed that aging can convert the aromatics to resins and further to asphaltenes, and increase the carbonyl and sulfoxide contents due to oxidation. Consequently, the micelle number and proportion in the colloidal structure increased at the micro-scale, and the penetration and ductility decreased while the softening point increased at the macro-scale. These trends were more evident at increased aging levels. A rejuvenator with a high content of aromatics can adjust the fractions and dilute the aggregated micelles in aged asphalt, thus achieving the thermodynamically reversible process of the asphaltenes and resins being converted to saturates and aromatics; this balances the fraction distribution and restabilizes the colloidal structure. The performance-related properties were basically restored to their unaged levels. Comparing the results of the aged asphalts from the laboratory and field, the ductility and asphaltene content of the latter cannot be restored to their original level, though other properties can be, which indicates the complex service conditions of asphalt in the field.