How GGBS is used and its typical substitution rates

How is GGBS used?

GGBS (Ground Granulated Blastfurnace Slag) is used all over the world as a direct replacement for Portland cement. It is added to the concrete mixer along with ordinary cement, aggregates and water.

The normal ratios and proportions of aggregates and water to cementitious material in the mix remain unchanged. Mixing times are the same as for ordinary cement. Both wet mixing and dry mixing processes can be used for making concrete with GGBS.

What is the substitution rates of GGBS in concrete?

Usually, replacement rates for GGBS vary from 30% to up to 85%, depending on the application and technical requirements. Typically 50% is used in most instances. Higher replacement rates up to 85% are used in specialist applications such as in aggressive environments and to reduce heat of hydration.

According to the EU code “EN-197-1-2000 Cement. Composition, specifications and conformity criteria for common cements“, slag in Blastfurnace cement CEM III/C can be used at a substitution rate as high as 95%.

Below are some typical Substitution Rates

Ready-mix Concrete:
50% GGBS is used for most mixes.

Precast Concrete:
30% to 50% GGBS primarily depending on concrete curing conditions.

Special Concrete:
Mass concrete typically has at least 70% GGBS for temperature control. Concrete in aggressive environments usually contains from 50% to 70% GGBS for enhanced durability performance.

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