Blast-furnace slag is the nonmetallic product consisting essentially of silicates and aluminosilicates of calcium and other bases that develop in a molten condition simultaneously with iron in a blast furnace. Granulated slag is the glassy, granular material formed when molten slag is rapidly chilled. Slag cement or GGBFS is granulated blast-furnace slag that has been finely ground and that is hydraulic cement. When slag cement is mixed with water, however, the initial hydration is much slower than portland cement mixed with water; therefore, portland cement or salts of alkali metals, principally sodium and potassium or lime, are used to increase the reaction rate of slag cement (ACI 233R).
