Evaluation of Mechanical Properties of Asphalt Concrete Incorporating Fly Ash and Crumb Rubber

The growing demand for environmentally sustainable pavement construction has led to the exploration of industrial byproducts and recycled waste materials as alternatives to conventional raw constituents. Bitumen, the most costly ingredient in flexible pavements, requires optimization to reduce usage without compromising performance. This study presents an experimental investigation on the incorporation of fly ash (FA) and crumb rubber (CR) as partial substitutes for mineral filler and fine aggregates in asphalt concrete. The control asphalt concrete (AC0) was produced using 5.0% bitumen, whereas modified mixes integrated fly ash and crumb rubber at replacement levels of 5–15% while reducing bitumen content progressively from 4.8% to 4.4%. Mechanical properties, including Marshall stability, flow values, bulk density, and indirect tensile strength (ITS), were evaluated, along with durability factors such as water absorption, stripping resistance, and aging resistance. The optimum performance was observed for AC2 (10% FA + 10% CR at 4.6% bitumen), which achieved the highest stability (13.8 kN), enhanced ITS (1.05 MPa), and excellent durability (TSR = 85.7%). These results indicate that FA and CR can effectively lower binder consumption while improving mix performance, thereby contributing to sustainable and cost-efficient pavement construction.