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GGBS and finely ground palletized slags are marketed separately to the concrete producer and used as a partial replacement for Portland cement. Replacement dosages between 5% and 70% by mass of cement material are common. Fineness, glass content and mineral constituents are generally considered to be important factors regarding the cement activity of slag. Effects of Slag on properties of fresh and hardened concrete. Concrete with Type IS cement or with higher dosages of GGBS added at the mixer usually will have lower heat of hydration. Concrete containing slag may show longer time of setting than straight Portland cement mixtures particularly for moderate and higher dosages and at lower ambient temperatures. Increasing slag dosage is associated with lower permeability in concrete. Concrete containing GGBS dosages greater than 35% will give an improvement in the resistance to sulfate as well as suppression of alkali aggregate expansion.

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Chemical Properties of Portland Cement and Blast Furnace Slag

Constituents

OPC

GGBS

Lime (CaO)

60% - 66%

32% - 45%

Silica (SiO2)

19% - 24%

32% - 42%

Alumina (AIO3)

3% - 8%

7% - 16%

Iron (Fe2o3)

1% - 0.1% - 1.5 %

0.1% - 1.5%

Magnesia (MgO)

0% - 5%

5% - 15%