1 / 2023-03-27 21:22:02

Use of Biochar and Accelerated Carbonation for Production of Low-Carbon Cement-Based Composites

Engineered biochar,Biomass waste management,Carbon-negative materials,Supplementary cementitious materials,Sustainable construction

Biochar is a green material obtained from the thermochemical conversion of biomass under an oxygen-limited condition. This study demonstrated a novel and sustainable method for incorporating wood biochar in cement-based composites with carbon dioxide curing. The X-ray diffraction (XRD) and thermogravimetric analyses (TGA) illustrated that the incorporation of biochar in an ordinary Portland cement system promoted the generation of additional hydration products due to moisture regulation effects, but did not accelerate or delay the hydration process, as indicated by the isothermal calorimetry results. Specifically, the addition of 1 wt% biochar increased the compressive strength of the composites by 8.9%. However, the incorporation of 5 wt% biochar reduced the compressive strength due to the porous and brittle structure of biochar. CO₂ curing was employed to mitigate these adverse effects. After carbonation, the additional hydrates enhanced the bonding strength and the carbonates densified the microstructure, which substantially enhanced the mechanical strength and carbon sequestration. Moreover, biochar also could be recycled into magnesia cement (MC) and magnesia-Portland binary cement (MP)-based composites. The TGA and XRD showed that the incorporation of biochar, especially CO₂ gasification biochar, promoted the generation of hydration products. The use of CO₂ curing effectively accelerated the carbonation of composites. Hydrated magnesium carbonates were preferentially formed in CO₂-cured MC composites, whereas CaCO₃ was preferentially generated in CO₂-cured MP composites. Furthermore, the incorporation of porous biochar could further facilitate CO₂ diffusion and promote carbonation. As a result, the synchronous use of biochar and CO₂ curing significantly enhanced the mechanical strength of composites. Therefore, biochar-augmented and CO₂-enhanced composites could be novel and low-carbon construction materials for sustainable engineering applications.