Sustainable Pavement Materials: Evaluating the Effects of Biochar on Stone Matrix Asphalt and Bituminous Concrete Mix Designs

This study looks into the mix design process for Stone Matrix Asphalt (SMA) and Bituminous Concrete (BC) in compliance with IRC: SP: 79-2008 and MoRT&H-2013 requirements. In comparison to standard dense and open-graded asphalt mixes, SMA has a better structure characterized by gap-graded aggregate, mastic, and fiber. The study uses coconut shell biochar as a filler in both SMA and BC, acting as a carbon-neutral and sequestration material. Using gap-graded aggregates, the study applies STAB (Simple Tool for Aggregate Blending) software for aggregate blending to establish ideal amounts. Following confirmation of the blends using Bailey's gradation technique, the Optimum Bitumen Content (OBC) is calculated using the Marshall method. The initial bitumen concentration is 4% for BC and 6% for SMA, with 0.5% increases up to 7%. Theoretical specific gravity is determined at 6% for the loose mix using ASTM D 2041. Gse is then computed, with OBC set at 6% for SMA and 4.2% for BC, meeting a 4% average air voids criteria among other volumetric parameters. At the appropriate bitumen percentage, all blends are subjected to a variety of tests, including indirect tensile strength, rutting, and resilient modulus. The study replicates moisture resistance deterioration by freezing, thawing, and humidifying materials. The number of blows used to compute refusal density ranges from 25 to 150. ITS determined retained tensile strength to be 93.88% and 98.8% for freezing and thawing BC samples and 93.88% and 98.8% for humidity-conditioned BC samples, respectively. The equivalent figures for SMA are 84% and 89%. Proportional rut depth and wheel tracking speed measurements are given for freezing, humidity, and unconditional samples, and robust modulus values are also supplied. Refusal density air voids that do not decrease below 4% up to 100 blows for BC are within the specified range of 3-5%. This extensive laboratory investigation demonstrates the feasibility of using biochar as a filler in bituminous concrete and stone matrix asphalt. This sustainable method helps eco-friendly and long-lasting road construction practices in addition to improving the durability and performance of highways.