Pomegranate Molasses as a Novel Bio-Modifier for Asphalt Binder: An Experimental Investigation

Biobinders are increasingly gaining attention in the pavement community as sustainable alternatives to conventional petroleum-derived asphalt binders. While complete replacement of asphalt binder remains challenging, growing environmental concerns and energy crises demand at least partial substitution with renewable and ecofriendly materials. In this context, this study explores the use of pomegranate molasses (PM), a natural biobased product, as a novel asphalt binder modifier. A comprehensive experimental program was conducted to evaluate the chemical, thermal, rheological, and mechanical effects of PM incorporation at three dosages (10%, 20%, and 30% by weight of asphalt binder) compared with a reference binder. Fourier transform infrared spectroscopy confirmed the presence of oxygenated functional groups (O─H, C═O, S═O) introduced by PM, while thermogravimetric analysis showed that the modifier is thermally stable under asphalt mixing and compaction temperatures. Binder-level testing revealed improved viscosity and high-temperature performance with PM addition, along with enhanced fatigue life at moderate dosages. At the mixture level, Marshall stability increased by about 11%, wheel-tracking results showed up to a 45% reduction in rut depth, and cracking resistance evaluated through the asphalt flexibility ratio improved at PM10% and PM20% before declining at PM30%. The tensile strength ratio (TSR) remained above the 80% threshold for all mixes, while the resilient modulus increased with PM content. One-way ANOVA confirmed that PM had a statistically significant effect on rutting resistance ( p - value = 0.011 ) but no significant effect on fatigue, TSR, or stiffness. Overall, PM demonstrated strong potential as a sustainable biomodifier, with 20% PM (by weight of the asphalt binder) identified as the optimum dosage, offering the best balance of resistance to rutting, fatigue, cracking, and moisture damage. Further field validation is required to translate these laboratory findings into practical applications.