Environmental life cycle assessment of forestry biochar for low-carbon concrete: influence of biogenic carbon accounting

Abstract As global interest grows in innovative and sustainable uses of biomass, understanding the environmental implications of integrating timber-derived biochar into concrete is increasingly important. This study presents a cradle-to-gate life cycle assessment (LCA) of biochar production and its application as a 15% sand replacement in 32 MPa concrete, evaluating four portable biochar production systems, the 6050 Carbonator, Air Curtain Burner, Oregon Kiln, and Biochar Systems Incorporated, using feedstocks sourced from forest residues and plantation-derived timber. Two biogenic carbon accounting approaches were applied: the carbon–neutral approach and the recommendation approach. The results show that carbon accounting choices strongly influence Global Warming Potential (GWP) outcomes. Under the Carbon–Neutral approach, the 6050 Carbonator exhibited the lowest net GWP (–1.90 kg CO 2 -eq kg⁻ 1 biochar), while the corresponding biochar-modified concrete achieved an approximately 40% lower net GWP than conventional concrete when carbon sequestration was included. Under the Recommendation approach, which explicitly includes biogenic CO 2 flows, the plantation-derived biochar concrete scenario achieved a net-negative GWP of –17.49 kg CO 2 -eq m⁻ 3 due to biogenic carbon uptake during forest growth. However, several non-GWP impact categories, including acidification, ozone depletion, and eutrophication, increased due to forestry operations and long-distance transportation, with transport contributing up to 78% of impacts in some categories. Overall, the study demonstrates the strong influence of biomass sourcing assumptions and biogenic carbon accounting methodology on LCA outcomes for biochar-based concrete systems. The findings highlight the potential of forestry biochar to support lower-carbon construction while emphasizing the importance of transparent system boundaries, transport logistics, and carbon accounting approaches in sustainability assessments.