Impact of nesquehonite on hydration and strength of MgO-based cements

Hydrated magnesium carbonate cements prepared from MgO and carbonates such as hydromagnesite (Mg₅(CO₃)₄(OH)₂·4H₂O) or nesquehonite (MgCO₃ˑ3H₂O) have potential for carbon sequestration during hardening. This study investigates the hydration of MgO/nesquehonite blends with up to 50 wt% of nesquehonite. Nesquehonite is highly reactive in the presence of MgO and water. The replacement of 50 wt% MgO by nesquehonite causes a significant increase of compressive strength at higher nesquehonite contents with up to 43–44 MPa after 28 days. However nesquehonite delays early hydration and strength development. Progressive changes in XRD peak position and peak broadening with increasing amount of carbonate indicate the formation of hydrous carbonate-containing brucite, HCB, with variable content of gel-like water and CO₂ as confirmed by FTIR and TGA. This research indicate a high potential of nesquehonite to permanently store CO₂ in MgO-based cements, as up to 15 wt% of CO₂ can be taken up in the hydrated solid phase.