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• Wood biochar was used as a replacement of fine aggregates at 10, 20 and 30% replacement levels. • Effect of CO 2 curing of biochar blended concrete was also investigated. • All three replacement levels provide compressive strength higher than the control mix. • CO 2 curing shows a positive influence on the compressive strength of the biochar concrete. The production of concrete is heavily reliant on the continuous mining of natural resources, with the majority component being the natural aggregates which make up about 70–75% of the concrete volume. As the emphasis shifts towards promoting sustainability through recycling all types of waste to create a closed-loop circular economy, it's vital to explore alternative waste materials that can replace traditional raw materials in concrete production. Biochar derived from different organic waste materials has shown to improve the strength properties of concrete. However, the majority of the research has focussed on using biochar as a cement replacement material with very low cement replacement levels. Therefore, this research focuses on significantly increasing the uptake of the pyrolysed form of organic waste (wood biochar) by using it as a replacement of fine aggregates at replacement levels of 10, 20 and 30 vol%. The biochar blended concrete showed an improvement of 63.9, and 45.6% and a reduction of 9.6% in the 7-day compressive strength results at 10, 20 and 30% replacement levels, respectively. At 28 days, the biochar blended concrete samples showed an improvement of 20.1, 22.6, and 16% in the compressive strength results at 10, 20 and 30% replacement levels, respectively. Separately, the 10% WBC blended concrete was also cured in a CO 2 environment for 7 and 28 days. The results showed an improvement of 24.7 and 37.3 in the 28-day compressive strength results with the respective CO 2 curing of 7 and 28 days, compared to the control mix. [ABSTRACT FROM AUTHOR]