Porous biochar for improving the CO2 uptake capacities and kinetics of concrete

Abstract

Carbonation is a natural process in concrete where atmospheric CO₂ diffuses into the pores of the material and reacts with cement hydrates to form calcium carbonate. Although this process can help to sequester atmospheric CO₂ and mitigate rising levels in urban areas, it slows down over time, resulting in low CO₂ uptake over the service life of concrete. This study proposes a sustainable method to improve carbonation kinetics and CO₂ capture in cement materials by incorporating highly porous biochar. The biochar, derived from seaweed pyrolysis, has a highly developed surface area, including micropores optimised for CO₂ adsorption, mesopores and macropores, as well as oxygen-rich surface groups. These properties allow the biochar to efficiently adsorb CO₂ and retain water. The biochar particles embedded in the cement matrix act as reservoirs for water and CO₂, influencing hydration and carbonation. The addition of biochar increases water retention in the composite, which promotes the formation of capillary pores and enhances the carbonation process. Experimental data and numerical simulations show that the adsorption of CO₂ in the micropores of biochar facilitates the flow of CO₂ through the composite, allowing deeper carbonation. The interaction between biochar and cement matrix enhances CO₂ diffusion and promotes calcium carbonate formation both within the biochar and at the biochar-cement interface, further improving CO₂ uptake. The study demonstrates that the incorporation of porous biochar into cement materials significantly increases their potential for CO₂ capture, offering a promising approach to sustainable construction and carbon sequestration.