Nuclear Magnetic Resonance (NMR) Assessment of Bio and Crude Oil-Based Rejuvenation

Asphalt binders in pavements lose their stability through aging and eventually fail in the field. Using nuclear magnetic resonance (NMR) to monitor the primary longitudinal relaxation time of asphalt samples and the ratio of material that carries this primary relaxation time has been shown to indicate the impact of ultraviolet (UV) radiation on the aging of asphalt pavements. Longitudinal NMR relaxation was used to investigate two types of proposed asphalt rejuvenators, a bio-oil-based rejuvenator and a crude-oil-based rejuvenator. Two different binders with the performance grades (PG) 64-22 and 76-22 were considered for their interactions with the rejuvenators. After 72 h of exposure to intense UV radiation, specifically designed NMR relaxometry experiments were applied to compare the rejuvenation capabilities of the two rejuvenator samples. The crude oil-based rejuvenator was found to exhibit relaxation times similar to the binder samples while the bio-based material showed relaxation times that pointed to different nuclear hydrogen environments. Both rejuvenators reduced the primary relaxation time of the PG 76-22 binder, which indicates that their stiffness was reduced. Both types of rejuvenators also seemed to prevent the effects of UV aging. Two mechanisms of rejuvenation were identified by NMR relaxometry. The primary relaxation time can be used to indicate a change in stiffness while the primary ratio of the material is tied to oxidative aging. Oxidative aging creates distinct hydrogen environments due to asphaltene aggregation. The bio-based rejuvenator only reduced the binder’s stiffness, while the crude oil-based rejuvenator also reduced the aggregation of asphaltenes. Consequently, the bio-based rejuvenator could be classified as an asphalt softener, while the oil-based material acted like a true rejuvenator.