Compressive strength of cement mortars were tested. Samples were made with usage of portland cement and portland slag cement. Several hardening accelerating admixtures, based on calcium formate, CSH crystal seeds and calcium nitrate were used. Mortars had water-cement ratio equal to 0,5 and 0,35. In order to lowering of water content and saving consistency the modified polycarboxylate superplasticizer were used. Research had shown that accelerating admixtures effectiveness depends on presence of ground granulated blast furnace slag (GGBFS) and water-binder ratio. Lowering of water content, by superplasticizer addition, inmortars did not improve compressive strength. Instead the retardation, probably caused by secondary components of superplasticizer,may be observed. Cooperation of lowered waterbinder ratio and accelerating admixtures usage gives great effect of compressive strength level.

Keywords: accelerating admixtures; portland cement; portland slag cement; compressive strength.