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The precipitation of magnesium hydroxy-carbonate hydrates has been suggested as a route to sequester CO2 into solids. We report the development of self-cementing compositions based on nesquehonite, MgCO3⋅3H2O, that are made from CO2-containing gas streams, the CO2 being separated from other gases by its high solubility in alkaline water, while magnesium is typically provided by waste desalination brines. Precipitation conditions are adjusted to optimize the formation of nesquehonite and the crystalline solid can readily be washed free of chloride. Products can be prepared to achieve self-cementation following two routes: (i) thermal activation of the nesquehonite then rehydration of the precursor or (ii) direct curing of a slurry of nesquehonite. The products thus obtained contain ~30 wt% CO2 and could form the basis for a new generation of lightweight, thermally insulating boards, blocks, and panels, with sufficient strength for general construction.

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Dolomite (CaMg(CO3)2) is widespread in nature and can be thermally activated to form a product composed of an intimate mixture of periclase (MgO) and calcite (CaCO3). This mixture, referred to as ‘half-burnt dolomite’, can be obtained under specific experimental conditions of temperature and atmosphere composition. The decomposition product consists of nanometric platelets of periclase enclosed within a porous calcite matrix. The reactivity of half-burnt dolomite as a supplementary cementitious material depends on the size and accessibility to water of the periclase crystallites; both parameters are influenced by the conditions prevailing during partial decomposition, especially the extent of sintering, and by the initial properties of the dolomite. Under the experimental conditions used, the substitution of up to 20–25 mass% of cement by half-burnt dolomite was found to preserve the 28 d compressive strength of cement pastes, with maximum values being obtained for a substitution level around 10–15 mass% half-burnt dolomite.