Thermal Activation of Dolomite

Decreasing amounts of available ideal materials, as well as environmental and economic considerations, lead the cement industry to investigate new products to be used as supplementary cement materials. Dolomite, ideally CaMg(CO3)2, is a carbonate that is already used by the concrete industry as an aggregate but which can be thermally activated to form a mixture of MgO and CaCO3 that is often referred to as "half-burnt dolomite". The production of this thermally activated dolomite and its use as an addition to Portland cement were investigated in this study. Half-burnt dolomite was successfully obtained under experimental conditions (i.e. temperature and atmosphere composition) which appear compatible with industrial production. The decomposition product consists of nanometric platelets of MgO within a porous calcite matrix. The reactivity of half-burnt dolomite, in aqueous solutions and cement paste, depends on the size of the MgO crystallites and on their accessibility to water (e.g. the surface area of the half-burnt dolomite), both parameters being influenced by the decomposition conditions and the properties of the dolomite. Sintering during partial decomposition seems to control, at least partially, the reactivity of half-burnt dolomite. The reactivity during early hydration stages (i.e. typically