Effect of nesquehonite and silica on magnesia-silicate‑carbonate cements

Cements based on hydrated magnesium carbonates are an alternative binder system with high CO 2 sequestration ability. The present study examines the effect of silica, a by-product of MgO production from magnesium-silicate rocks, in MgO/nesquehonite binders. A high Mg/Si ratio of 3 was used to allow the formation of both the hydrous carbonate-containing brucite (HCB) phase and the magnesium silicate hydrate (M-S-H) phase. HCB formed within the first day. Its quantity was reduced during the formation of M-S-H and stabilized until the complete reaction of silica. Low quantities of nesquehonite, ≤10 wt%, accelerated M-S-H formation, while ≥16 wt% hindered it. CO 2 quantification showed that up to 12 g of CO 2 per 100 g dry cement could be sequestered. MgO/silica/nesquehonite mortars with 10 wt% of nesquehonite and a water/cement ratio of 0.65 exhibited overall good mechanical strength, achieving 23 MPa at 2 days and 36 MPa at 182 days.