Preparation of negative carbon cement soil by corn straw biochar collaborative carbonization technology: Mechanical...

Resourceful utilization of waste is a global research hotspot. Biochar has attracted great interest in building industry due to its good carbon sequestration properties, but it is not clear whether it is feasible to use corn straw biochar (CS-Biochar) synergistic carbonation technology to prepare negative cement soil. In this study, the effects of CS-Biochar and carbonization technology on the mechanical properties of modified cement soil (CSBS) were investigated by unconfined compressive strength (UCS) and triaxial tests. In addition, the microstructure, mineral composition, carbonization depth and carbon sequestration of CSBCS were studied based on microstructure characterization methods. The results indicated that both CS-Biochar and carbonation conservation techniques resulted in a significant increase in the compressive and shear strength of CSBCS. With the increase of CS-Biochar content, the carbonization depth and relative carbon sequestration of CSBCS specimens increased first and then decreased. In addition, after carbonization for 15 h, the CO₂ emissions of 1 ton of CSBCS-3 and CSBCS-5 were -2.4 kg and -8.2 kg, respectively, which proved the feasibility of using biochar synergistic carbonization technology to prepare negative carbon cement soil. Biochar not only had filling effect but also promoted cement hydration to generate a large amount of hydration products. Meanwhile, part of the hydration products participated in carbonization reaction, which further improved the interfacial bonding strength, density and carbon sequestration capacity of soil particles, reflecting the synergistic effect of biochar and carbonization technology. These findings could open up new avenues of research on biochar and carbonization techniques in cement soil.