The use of high volumes of supplementary cementing materials in cement systems is considered strategic with respect to sustainable development issues. The decreased rate of hydration at early ages, however, continues to be a disadvantage. The accelerating effect of nano-sized CaCO3 addition to ordinary Portland cement paste (OPC) containing high volumes of ground granulated blast-furnace slag (GGBFS) in lieu of micro-sized CaCO3 addition was investigated by conduction calorimetry and determinations of microhardness and modulus of elasticity. The results indicate that the hydration of OPC containing high volumes of GGBFS is significantly accelerated by the nano-sized CaCO3 addition. The times of occurrence of the main calorimetry peaks are remarkably decreased and the rate of heat development increases depending on the amount of the nano-sized CaCO3 addition. It is apparent from the calorimetry results and the engineering properties of the systems studied that the nano-sized CaCO3 addition to cement systems containing high volumes of GGBFS fully compensates for the delayed hydration process.
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