Hydration, carbonation and strength development of reactive MgO cement blended with lime (CaO) under different curing conditions

Abstract

This paper investigated the effect of lime added as substitution (by up to 30 wt%) of magnesia on the performance, phase composition and CO2 sequestration capacity of blended reactive MgO cement (RMC) under two different curing conditions. A relationship between the strength development and formation of hydration and carbonation phases was also established. The results showed that the incorporation of lime promote the setting and initial heat generation of RMC. More lime replacement led to higher CO2 absorption capability under both ambient and accelerated carbonation conditions, mainly due to the improved calcite. The presence of uncarbonated portlandite was found to have negative impact on strength development of blended RMC before and after water exposure. Carbonation curing enhanced the conversion of portlandite and brucite into calcite and nesquehonite, respectively, which effectively reduced the porosity and improved the denseness of blended RMC. The improvements in carbonates content, morphologies and microstructure in samples containing 20% lime resulted in ∼30% higher 28-day compressive strength than the plain samples.