Effect of Waste Plastic and Fiber Modification on Asphalt Mixture Properties

Stone Matrix Asphalt (SMA) and Asphalt Concrete (AC) are widely used in road construction due to their excellent mechanical properties and long-term durability. This study investigates the effect of sisal fiber and waste plastic as modifiers to enhance the performance of SMA and AC mixtures. The Marshall mix design method was employed to determine the optimum bitumen content (OBC) and optimum fiber content (OFC), evaluating parameters such as Marshall stability, flow value, air voids, voids in mineral aggregate (VMA), and voids filled with bitumen (VFB). VG 30 grade bitumen was used as a bitumen, and fly ash was utilized as a filler. Sisal fiber was incorporated to reduce bitumen drain down and improve crack resistance, with the optimal fiber content identified as 0.4% by total mix weight. Simultaneously, waste plastic was added to improve workability and mechanical performance, with 2.5% content enhancing handling characteristics and 3% improving drain-down resistance and tensile strength. Results from drain down and moisture susceptibility tests indicated that the combined use of sisal fiber and waste plastic significantly improved the durability and overall performance of the asphalt mixes.