Due to increased traffic and environmental concerns, this study addresses challenges in conventional asphalt concrete. Our focus is on enhancing the water resistance of asphalt mixes through the optimization of both the asphalt binder and the biochar-based geopolymer composite. We employ experiments and response surface methodology to assess their impact on volume, Marshall parameters, and water resistance. Asphalt binders were evaluated within the range of 4�6, while biochar-based geopolymer composite levels varied from 0 to 4. According to the findings, the incorporation of the biochar-based geopolymer composite improves asphalt properties, stiffness, and temperature sensitivity. Response surface methodology (RSM) was utilized to construct robust mathematical models with high R 2 values (90) and low p-values. Multi-objective optimization indicated that optimal content levels were 4.56 for the binder and 2.71 for the biochar-based geopolymer composite. Model accuracy was confirmed with less than a 5 error in validation tests. The research also identified structural changes in the asphalt binder caused by the BGC Si�O phase. Additionally, the leaching value for both BGC and BGC-MAB asphalt concrete was found to be substantially below the regulatory limit, demonstrating the environmental safety of incorporating BGC into the asphalt sector. © 2023, The Author(s).