In this paper was analyzed the effect of additives for improving the milling cement of the trade name HEA 213 Grace or the HEA2® manufacturer of the GCP Applied Technologies Inc. on the hydration processes of cement prepared in the semi-industrial ball mill at the laboratory of the CEMEX Hrvatska d.d.. In the stage of cement preparation in a mixture of clinker and gypsum, additive HEA 213 Grace was added in an amount of 0.032% by weight on the cement mass. The influence of additives for improving the grinding on the hydration processes was performed by measuring the influence of the additive at the beginning and end of the bonding. For measuring the speed of bonding of cement paste the prepared pastes had a normal consistency and the water factor (V/C) ranged from 0.26 to 0.27. Since cement is often used for the purpose of preparing mixed cement, the impact of the substitution of the furnace slag on the hydration process is investigated. For this purpose, the furnace slag is added in the amount of 0, 5, 10, 15, 20, 25 and 30 mas. % on the cement mass. In this system hydration was monitored by conductometric measurements of electrical conductivity in prepared aqueous suspensions (water/cement = 4 (V/C)) at a constant temperature of 20°C. Hydration of free Ca 2+ ions was also performed on the same systems at different time intervals for up to 12 hours of hydration.