Coarse blast furnace slag as a cementitious material, comparative study as a partial replacement of Portland cement and as an alkali activated cement

The cementitious performance of a coarse granulated blast furnace slag, 2900 cm2/g, was investigated in concretes of 230, 280 and 330 kg binder/m3. First, the slag partially replaced 30%, 50% and 70% of Portland cement, the strength reduced as the amount of slag increased; however, for high binder contents, similar strengths were attained for lower Portland cement contents. Second, the slag was alkali activated with sodium silicate (moduli 1.7 and 2) at 4%, 6% and 8% %Na2O, the strength increased with the amount of slag in the concrete and developed faster as %Na2O increased. The microstructures of both type of concretes were dense; however, the strengths of activated slag were superior at similar binder loads, indicating that the hydration products of activated slag are of higher intrinsic strength.