Engineering Sustainable Asphalt with Biomass-Derived Surface-Functionalized Biochar through Molecular Conservation and Emission Mitigation

Sustainable asphalt technologies are increasingly vital for conserving resources, reducing environmental emissions, and enabling the beneficial reuse of carbon-rich waste materials. Surface-functionalized biochar (SFB) offers a promising strategy to enhance asphalt performance, while providing a sustainable platform for mitigating volatile organic compound (VOC) emissions; however, the roles of environmental humidity and asphalt binder composition in governing SFB’s VOC-mitigation efficacy remain poorly understood. Here, we evaluate SFB-modified asphalt at relative humidity (RH) ≈ 50% and 50 °C using environmental chamber measurements, volatility- and polarity-resolved emission analysis, molecular dynamics simulations, and density functional theory calculations. Across three asphalt binders, SFB reduced total organic emission factors by 94.5%, 84.5%, and 46.7%. Intermediate-volatility organic compounds (IVOCs) and semi-volatile organic compounds (SVOCs) were consistently suppressed by more than 70%, but light-polar VOC emissions showed an increase specifically in one out of the three binders. This in turn demonstrates that mitigation under humid conditions is strongly binder-dependent. Simulations indicate that interfacial water redistributes polar VOCs and competes with them for adsorption sites, weakening SFB–VOC interactions, particularly for small polar compounds. Unlike earlier studies focused mainly on dry-condition mitigation, the present work links binder-dependent humid-condition measurements with molecular-level competitive adsorption mechanisms. Study outcomes highlight the need to design emission-mitigation strategies tailored to specific climatic regions, where material chemistry and humidity conditions can govern suppressant effectiveness in real-world environments.