Evaluation of pomegranate peel extract as a natural antioxidant additive for mitigating oxidative aging of bitumen

Abstract Bitumen, as the primary binder in asphalt pavements, is subjected to thermal and oxidative aging, leading to increased stiffness, reduced flexibility, and deterioration of rheological performance. This study investigated pomegranate peel extract (PPE), a natural polyphenol-rich additive, as an antioxidant for mitigating oxidative aging of PG 64-16 bitumen. Bitumen samples containing 0.5, 1, 1.5, and 2 wt.% PPE were evaluated before and after short- and long-term aging using physical, rheological, and chemical analyses. The results showed that PPE reduced penetration by up to 18% and increased the softening point, indicating improved high-temperature resistance. At 1.5% PPE, rotational viscosity at 110 °C increased by approximately 77%, while thermal sensitivity decreased. The performance grade increased from 64 to 70, indicating improved high-temperature rutting resistance. Saturates, Aromatics, Resins, and Asphaltenes (SARA) analysis showed that PPE reduced the aging-induced increase in the asphaltene fraction compared with the base bitumen, particularly after long-term PAV aging. Fourier-transform infrared spectroscopy (FTIR) analysis also showed lower increases in the Carbonyl and Sulfoxide Indices after aging for the 1.5 wt.% PPE-modified bitumen compared with the base bitumen, indicating reduced formation of oxidation-related functional groups. Overall, 1.5 wt.% PPE provided the most balanced improvement in stiffness, high-temperature performance, and workability, while maintaining acceptable low-temperature performance. More importantly, the combined physical, rheological, SARA, and FTIR results demonstrate the potential of a targeted polyphenol-rich extract derived from pomegranate peel as a bio-based approach for controlling chemical aging while maintaining the functional performance of bitumen. This provides a value-added route for utilizing pomegranate processing waste as a sustainable antioxidant additive for bitumens.