Work

The synergistic effects of straw biochar and MgO carbonation on improving the physico-mechanical properties of silty clay

Year: 2025

Type: article

Abstract: To overcome the CO₂ diffusion, uneven carbonation, and slow strength development when using reactive MgO carbonation in high-water-content soil, the straw biochar was introduced as a multi-functional synergistic medium to establish a novel green stabilization approach integrating "waste recycling-CO2 sequestration-soil enhancement". An orthogonal programme varying biochar, MgO, and initial water contents was designed. Unconfined compressive strength, mass/volume and pH were measured; SEM and XRD analyses were incorporated into a diffusion–reaction–mechanics model accounting for the discrete effect of biochar. The strengthening mechanism of biochar-synergized MgO carbonation was revealed by comparing it with traditional cement-stabilized soil. The results indicate that biochar significantly enhances the CO₂ carbonation degree. When the biochar content was 6%, MgO content was 15%, and initial water content was 30%, the specimen achieved a strength of 4.51 MPa, which is 3.1 times that of the control group without biochar and 131% higher than cement-stabilized soil with the same condition. The microscopic mechanisms demonstrate that: the porous biochar created preferential CO2 pathways; surface oxygen-bearing functional groups supplied abundant nucleation sites, promoting the oriented growth of nesquehonite and dypingite; and carbonation products cement together with biochar-soil particles, forming a physical-chemical composite reinforced structure. Through the synergistic effects of channeling-adsorption-nucleation, straw biochar improves the uniformity of MgO carbonation and cementation efficiency of products, achieving low-carbon and efficient soil stabilization. The findings provide a green improvement method characterized by carbon sequestration and toughness enhancement for rapid stabilization of soft soil, offering technical support for the utilization of agricultural waste and low-carbon geotechnical stabilization.

Source: Results in Engineering

DOI: 10.1016/j.rineng.2025.108575