Technical Questions

ACI Committees, Membership, and Staff have answered common questions on a variety of concrete related topics.



What is slag cement or ground granulated blast-furnace slag (GGBFS)

Q. What is slag cement or ground granulated blast-furnace slag (GGBFS)?

 

A. 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). The ASTM C989 slag-activity index is often used as a basic criterion for evaluating the relative cementitious potential of slag cements. Slags are classified into three grades (80, 100, and 120) based on their respective mortar strengths when blended with an equal mass of portland cement (ASTM C989).

 

References: SP-1(02); ACI 233R-03; E3-13 ; SP-221; ACI 225R-19; ACI CT-18; ASTM C989

Topics in Concrete: Slag; Cementitious Material; Materials; Concrete Fundamentals

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