Effect of Silica on Hydrated Magnesium Carbonate Cements Containing Different Amounts of Nesquehonite

Abstract

Cements based on hydrated magnesium carbonates are an alternative binder system with high CO2 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 hydrous carbonate-containing brucite (HCB) phase and 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 stablised until the complete reaction of silica. Low quantities of nesquehonite, ≤10 wt%, accelerated M-S-H formation, while ≥16 wt% hindered it. CO2 quantification showed that up to 12 g of CO2 per 100 g of 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.

Keywords: MgO-based cement, Nesquehonite, magnesium silicate hydrates (M-S-H), CO2 sequestration, hydrous carbonate-containing brucite (HCB)