Life Cycle Assessment of Both Cement and Sand-replaced Biochar Concrete

Abstract

Biochar holds significant potential for reducing carbon emissions in the concrete industry. However, despite increasing interest in biochar-concrete, there is a lack of life cycle assessment (LCA) studies to elucidate the mechanisms by which biochar reduces carbon emissions of concrete across stages such as raw material acquisition, transportation, manufacturing, etc. This study compares the environmental impacts of using biochar derived from wood and fruit waste as partial replacements for cement and sand in concrete. The research applies LCA methodology, in line with ISO 14040 and 14044, to evaluate the environmental impacts and resource use of biochar-concrete across its cradle-to-gate life cycle. Cement exhibits high carbon emissions of 0.63 kg CO₂-eq per kg, of which 80% originates from the calcination whereas crushed sand demonstrates very low carbon emissions. On the other hand, both wood and fruit biochar exhibit negative carbon emissions due to the combined effects of co-product energy recovery and carbon sequestration. Using wood biochar to replace 20 vol.% of cement reduces carbon emissions of concrete by 42%. Replacing 60 vol.% of sand with fruit biochar reduces concrete carbon emissions by 167%, indicating a net-negative carbon footprint. Moreover, the fruit biochar shows a greater potential for reducing the carbon footprint of concrete and exhibits higher sensitivity to intensity analysis due to the larger volume replacement it offers for sand. The findings indicate that key parameters, such as biomass moisture content and biochar yield rate significantly influence the decarbonization potential, whereas applied average transportation distance contributes minimally to overall emissions.