Chemical, microstructural and strength development of calcium and magnesium carbonate binders

The influence of magnesium on the chemistry of calcium carbonate formation has been studied. It was found that the type of carbonate formed by subjecting compacts of Ca(OH)2 and Mg(OH)2 to carbon dioxide (up to 20 atm CO2 pressure) for variable periods of time is largely controlled by the molar proportion of calcium to magnesium in the initial mixture. Increasing magnesium content in the initial mixture favours the formation of nesquehonite and other carbonates containing both calcium and magnesium. The compressive strength of the carbonate is improved with the presence of nesquehonite and/or other magnesium-containing phases. Curing time and CO2 exposure influence the strength differently, depending on the initial Ca/Mg ratio of the initial mixture. The formation of magnesium-containing carbonate phases is particularly favoured at higher CO2 pressures combined with prolonged exposure times.