Surface-Functionalized Biochar for Low-Carbon and Low-Emission Asphalt

The chemistry-informed development of low-carbon, low-emission asphalt binders is essential for promoting sustainable infrastructure and reducing environmental and health risks. Asphalt binders are major sources of volatile organic compounds (VOCs), which contribute to secondary organic aerosol (SOA) formation, ground-level ozone, and global warming. This study presents a chemistry-driven approach to mitigating asphalt emissions using surface-functionalized biochar (SFB). Laboratory tests and computational analysis were used to evaluate the effectiveness of SFB in producing low-emission asphalt binders (LEABs). SFB is a carbon-negative material with a net carbon sequestration capacity exceeding 415 kg CO₂per ton and exhibits strong affinity for polar VOCs. Incorporating SFB into asphalt reduces the carbon footprint and suppresses VOC emissions by up to 40%, with the greatest efficacy for highly polar binders. This selectivity is attributed to SFB’s polyaromatic structures and functional groups, enabling hydrogen bonding and π–π stacking with polar VOCs, with binding energies up to 26.48 kcal/mol. These interactions limit VOC diffusion, reducing ozone formation potential by up to 57% and reducing SOA formation potential by up to 54%. These findings highlight SFB’s dual role as a carbon-sequestering additive and as an VOC emission suppressant, emphasizing the value of chemistry-informed material design for sustainable pavements.