Accelerated carbonation curing of biochar-cement mortar: Effects of biochar pyrolysis temperatures on carbon sequestration, mechanical properties and microstructure

The integration of biochar with accelerated carbonation curing (ACC) has the potential to reduce the carbon footprint of cementitious materials. However, the effects of biochar pyrolysis temperatures on the performance of accelerated carbonation-cured cementitious materials remain unclear. In this study, corn straw was used as the raw material to prepare biochar at 300℃, 500°C, and 700°C for incorporation into cement mortar. The effects of biochar pyrolysis temperatures on carbon sequestration, mechanical properties and microstructure of cement mortar were investigated at 3 days and 28 days of ACC. The results showed that incorporating the biochar at 500℃ into cement mortar exhibited the highest carbon sequestration with up to 31.6 % increase compared to 300℃ and 700℃. The porosity of biochar dominated the inward CO2 transport rather than the chemisorption effect of oxygen-containing functional groups under ACC. The biochar at 500℃ showed the most improvement in compressive strength. The biochar at 700℃ enhanced the early-stage compressive strength due to its significant hydrophobicity at high dosages (7 % by mass), while excessive amounts adversely affected the overall compressive strength. The incorporation of biochar effectively reduced the porosity of cement matrix and narrowed the differences in carbonation degree among layers, with the biochar at 500 °C showing the best results due to its larger specific surface area and pore volume. This study provides insights to further advance the efficient application of biochar in low-carbon building materials. •The porosity of biochar dominates the inward CO2 transport under ACC.•Superior porosity of biochar at 500°C compared to 300°C and 700°C.•Highest carbon sequestration and compressive strength of biochar at 500°C in mortar.•Differences in carbonation degree among layers of matrix were narrowed by biochar.