Accelerated carbonation of reactive magnesium oxide cement (RMC)-based composite with supercritical carbon dioxide (scCO2)

Abstract

Reactive magnesium oxide cement (RMC) has the potential to become a sustainable alternative to ordinary Portland cement (OPC). In this study, an approach utilizing supercritical CO2 (scCO2) was investigated to accelerate carbonation of an RMC-based composite and to overcome its long carbonation process under the natural environment. It was found that scCO2 led to an extremely rapid strength gain of the composite, with a mature strength level achievable within a period of hours. CO2 sequestration factors were also increased by three folds as compared to samples cured under a 20% CO2 concentration environment for 28 days. It was also revealed that the carbonation phases under scCO2 were dominated by nesquehonite followed by hydromagnesite and some other intermediate hydrated magnesium carbonates (HMCs). More uniform carbonation within the matrix was also attained under the scCO2 condition. Despite the promising outcomes, technical and cost challenges would need to be resolved before a possible scale-up.