A Study on Effect of Addition of Recycled Bituminous Material to Stone Matrix Asphalt Using Polymer Modified Bitumen (PMB-40)

Stone Matrix Asphalt (SMA) is a gap-graded mix with a high proportion of coarse aggregate, binder, and fiber additives for stability. A high concentration of coarse aggregate enhances stone-on-stone contact and interlocking, resulting in strength and durability. Stabilizing additives prevent bitumen draindown material. This study assesses the influence of incorporating Recycled Asphalt Pavement (RAP) into Stone Matrix Asphalt (SMA) along with Polymer Modified Bitumen (PMB-40) in road construction to increase performance and sustainability. The study aims to determine the optimal binder content and evaluate the mechanical properties of SMA mixtures using varied RAP percentages (0%, 15%, 20%, and 25%) and cellulose fibers. The study also looks at important performance indicators such as Marshall Stability, Draindown characteristics, Indirect Tensile Strength (ITS), and Tensile Strength Ratio (TSR). The results indicate that the optimum binder content for RAP-modified SMA falls between 6.2% and 6.4%. The addition of RAP improved the mechanical performance, with RAP-modified mixes demonstrating a 5–7% increase in Marshall Stability and a 15–20% improvement in ITS as compared to control samples. Superior resistance to moisture-induced damage and cracking can be seen by TSR values that continuously exceed the mandatory minimum of 0.90. The combination of 15-25% RAP and 0.3% cellulose fibers significantly reduced draindown, ensuring proper binder retention during mixing and placement. These results show that by adding RAP to SMA mixes not only helps to preserve natural-environmental resources but also improves durability and resistance to environmental pressures. The study supports continued efforts to create environmentally friendly infrastructure by confirming that recycled bituminous materials can be used without sacrificing structural integrity