An Investigation on the Effect of Aging on Chemical and Mechanical Properties of Asphalt Binders

The asphalt binder is exposed to aging conditions during production, placement, and service. This results in physical hardening, oxidation, and volatilization of the asphalt binder. The aging phenomenon affects the performance and, in turn, affects the pavement's service life. Understanding the aging behavior of asphalt binders in terms of physical and chemical properties will help to extend the pavement's service life. In the present study, the aging effect of the asphalt binder was investigated using chemomechanical evaluation. Five asphalt binders, namely viscosity grade 30 (VG30), viscosity grade 40 (VG40), polymer-modified binder (PMB), crumb rubber–modified binder (CRMB), and Sasobit-modified binder (SMB) at three aging levels (unaged, short, and long term) were selected for the investigation. The rolling thin-film oven (RTFO) and pressure aging vessel (PAV) were used to simulate short- and long-term aging conditions. Dynamic shear rheometer (DSR), Fourier-transform infrared (FTIR) spectroscopy, surface free energy (SFE), and thin-layer chromatography–flame ionization detector (TLC-FID) tests were performed to analyze the aging behavior of asphalt binders. Further, multiple stress creep and recovery (MSCR) and linear amplitude sweep (LAS) tests were performed to understand the effect of aging on rutting and fatigue damage of binders. From the FTIR test, the aging of binders showed a substantial increase in the formation of ketones and sulfoxide functional groups. The asphaltenes and resins contents increased, whereas aromatics and saturate contents reduced after aging. The higher asphaltenes content increases the stiffness of aged binders and improves rutting resistance. At the same time, aging is detrimental to the fatigue resistance of asphalt binders. Again, it is observed from the results that aging decreases the dispersive component of SFE and increases in the polar component. The effect of aging is less pronounced in PMB and CRMB than in unmodified binders (VG30 and VG40). This study will help in understanding the interrelation among chemomechanical behavior of a binder at different aging levels and will be useful for the selection of a better performing binder for field applications.