Assessing Asphalt Binder Aging with 1H Spin-lattice NMR Relaxometry: A Comparative Study of Temperature and UV Radiation Effects

Objective: Asphalt binder, a byproduct of the crude-oil refining process, is commonly used in road construction due to its favorable response to physical stresses. However, it is also susceptible to environmental aging, including temperature variations and ultraviolet (UV) radiation. Standard laboratory methods for studying asphalt binder aging primarily focus on factors like temperature, pressure, and oxygen, often neglecting the impact of UV radiation. This study employs 1H spin-lattice nuclear magnetic resonance (NMR) relaxometry to investigate the effects of UV radiation on asphalt binder aging compared to temperature-induced aging. Methods: Primary relaxation times and ratios were derived from a bi-exponential fit of the experimental relaxation decay induced by a 200-MHz NMR magnet. NMR relaxometry analysis revealed that 90% (0.9 primary ratio) of the protons in unaged asphalt binders exhibited a characteristic primary spin-lattice relaxation time (T1) of approximately 470ms. Results: Cold exposure did not significantly alter these parameters. Mimicked heat aging, which considered only temperature and duration, resulted in slight increases in both the primary relaxation time and ratio. In contrast, after 72h of UV exposure, binders showed variable T1 values at a significantly decreased primary ratio. This variability was summarized with the new performance parameter, the Herbaw. Further testing showed that standardized heat aging, which considered sample size and pressure, reduced both the primary relaxation time and ratio when compared to the mimicked aging. Conclusion: These results demonstrate that UV radiation induces significant structural changes in asphalt binder, which can be effectively detected using spin-lattice NMR relaxometry. The Herbaw performance parameter was successful in describing the variability of the UV aging which greatly impacted the primary ratio, indicating oxidative stress. The Herbaw Parameter was not as successful in describing heat aging since only slight changes in the primary relaxation time were detected. While the hydrogen environments were not significantly impacted, temperature-based aging may depend on multiple mechanisms.