New insights into hydration of MgO in the presence of polycarboxylate ether superplasticizers

Abstract

MgO-based cement offers a promising solution to lower the carbon footprint compared to that of Portland cement, where MgO is sourced from fossil-free minerals. The hydration of MgO plays a key role in these cements. However, MgO required higher water demand to achieve a workable mix, which poses drawbacks in microstructure and strength development. In this work, we investigated the effects of 7 polycarboxylate-based superplasticizers at different dosages on the fresh and hardened properties of MgO hydration. We found that some superplasticizers not only enhanced mix workability but also significantly increased compressive strength. The hydration, phase assemblage and evolution of MgO pastes using these superplasticizers were identical to those of the neat system, in which brucite formed as the primary hydration product. However, rheological evaluations demonstrated a marked reduction in yield stress and viscosity owing to the effects of superplasticizers. Furthermore, the addition of superplasticizer was found to improve the viscoelastic properties of the composites, as evidenced by an increase in critical shear strain and storage modulus. The insights gained from this research highlight the benefits of water-reducing additives in enhancing MgO reactivity and tailoring the formation of various MgO-bearing phases, such as magnesium carbonates or magnesium silicate hydrate, thereby facilitating more sustainable cement production.