Thermally activated dolomite as pozzolanic addition to Portland cement

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.