Granulated air-cooled silicomanganese slag from ferro-alloy manufacturing plants is mainly disposed as a landfill waste. On the other hand, it is highly advisable and beneficial to partially replace Portland cement with suitable industrial wastes. The present work investigates the viability of using air-cooled silicomanganese slag as a supplementary cementing material. The silicomanganese slag possesses an acid composition with SiO2, CaO, and Al2O3, as main oxides and a MnO-content of nearly 10% by weight. The lime combinability test by thermo-gravimetry and the results obtained by FT-IR confirm weak to moderate pozzolanic properties compared to silica fume and natural pozzolans. Experimental results prove the effectiveness of mechanical activation for replacement levels up to 35% with no significant variation in setting times. The blended cements fulfill all the chemical requirements of the standard specification and do not exhibit any volume instability. The compressive strength reduction for replacement levels up to 15% and for 3, 7 and 28 days of curing is limited to only about 10%. (C) 2013 Elsevier B.V. All rights reserved.