PURPOSE: To provide a cement compsn. which consists of ground cement clinker material, granulated blast furnace slag and comminuted steel slag and may be hydraulically hardened.

CONSTITUTION: The comminution of the steel slag is preferably carried out to a grain size of 0.2 to 0.09 mm. The comminuted steel slag has a Blaine value of 400 to 473 m2/kg and a weight per unit volume of 2,800 to 4,000 kg/m2. The steel slag is selected from air-cooled steel slag, foamed steel slag, granulated steel slag or a combination thereof. The cement clinker material and the granulated blast furnace slag are mixed with the comminuted steel slag at and under the temp. and pressure higher than ordinary temp. and atm. pressure and the mixture is cooled and ground, by which the hydraulic cement compsn. is obtd. A cement furnace is used when the compsn. is produced at the temp. higher than ordinary temp. The mixture composed of the blast furnace slag cement contg. up to 30% steel slag and the comminuted steel slag or the mixture composed of Portland cement contg. up to 50% steel slag and the comminuted steel slag is preferably formed.