The Effect of Pistachio Skin Ash as An Additive on the Performance of Bitumen and Asphalt Mixtures

In light of the burgeoning global production of pistachios, the consequent generation of waste from this agricultural staple has also escalated, necessitating effective management and recycling strategies to mitigate environmental impacts. This study investigates the potential reuse of Pistachio Hard-Skin Ash (PHSA) as a modifier in bitumen to enhance the performance characteristics of Hot Mix Asphalt (HMA). Specifically, four asphalt mixture variants were prepared with PHSA incorporated at varying proportions (5%, 10%, 15%, and 20% by weight of bitumen). Comprehensive experimental analyses were conducted, including Marshall stability tests, moisture susceptibility assessments, and evaluations of resilient modulus and indirect tensile strength. The investigation into the properties of the modified bitumen revealed a notable trend: as the percentage of PHSA increased, both the density and softening point of the mixtures improved, while ductility, penetration value, and dynamic shear modulus exhibited a decline. Significantly, the results indicated that increased PHSA levels correlated with enhanced Marshall stability, reaching a 15% improvement in moisture susceptibility at the optimal 15% additive concentration. Furthermore, the resilient modulus demonstrated superior performance under triangular loading compared to haversine loading, while an elevation in load from 1500 to 3000 N correspondingly led to a reduction in stiffness modulus. Notably, indirect tensile strength increased by 19% at the 15% PHSA concentration relative to the control mixture, affirming the viability of PHSA as an environmentally friendly additive in asphalt applications.