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Ground granulated blastfurnace slag

Ground granulated blastfurnace slag (GGBS) is the slag from iron producing blastfurnaces that is rapidly quenched in water and then ground into a powder. Chemically it is similar to, but less reactive than, Portland cement (PC).

When mixed with water it will hydrate in a similar way to Portland cement although very slowly unless activated with an alkali. Until recently GGBS was just used in combination with Portland cement (source of alkali), typically in the range 35% to 70% GGBS, depending on the application. The blends can be supplied as pre-blended factory produced cements, or can be formed in the mixer by adding Portland cement and GGBS each from its own silo. However, the drive for low-carbon cements has seen the commercial development of alkali activated cement (AAC) where the ggbs is activated by the addition of alkalis rather than Portland cement. 

Concretes containing GGBS/PC blends are slower reacting than pure PC concretes, but may have improved durability.

Acknowledgement: The Concrete Society

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