Experimental investigation into the self-carbonation mechanism of magnesium oxide carbon sequestration foamed concrete

A novel technique involves the preparation of foamed concrete utilizing MgO as a substitute for Portland cement (PC) and CO2 foam in place of air foam. This technique is referred to as "magnesium oxide (MgO) carbon sequestration foamed concrete (MCFC)" that enables self-carbonation of Reactive MgO cement-based concrete under ambient conditions without any accelerated carbonation curing conditions. The developed technology enhances the carbonation efficiency of MgO-based materials by combining a foaming agent with CO2 curing. The even mixing of CO2 foam with MgO, referred to the uniform distribution and incorporation of CO2 throughout the sample, facilitated by the foaming agent, leads to the production of ions within the cement, promoting the carbonation of dissolved Mg2+ ions and the formation of hydrated magnesium hydroxyl carbonates (HMHCs). Eight sample groups were prepared to explore the potential of MCFC in CO2 sequestration. XRD, TG-DTA, and SEM techniques were employed to investigate the mineral phase and carbonation products in MCFC. The pore structure, pore-size distribution, and porosity of MCFC under different curing conditions were investigated using X-ray and NMR. The self-carbonation enabled by CO2 foams improved the microstructure and mechanical performance of MgO-based samples. Notably, the morphology, microstructure, and carbonate content improvements resulted in a significant 100% increase in the 28-day compressive strengths (2 MPa) compared to the control sample cured under ambient conditions.