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Ground Granulated Blastfurnace Slag (GGBFS) is a by-product from the blast-furnaces used to make iron. These operate at a temperature of about 1,500 degrees centigrade and are fed with a carefully controlled mixture of iron-ore, coke and limestone. The iron ore is reduced to iron and the remaining materials form a slag that floats on top of the iron. This slag is periodically tapped off as a molten liquid and if it is to be used for the manufacture of GGBFS, it has to be rapidly quenched in large volumes of water.

PROPERTIES :

The quenching optimizes the cementitious properties and produces granules similar to coarse sand. This ‘granulated’ slag is then dried and ground to a fine powder.

APPLICATIONS

The major use of GGBFS is in ready-mixed concrete.

Specifies are well aware of the technical benefits which GGBFS imparts to concrete, including:

• Workability-making placing and compaction easier.
• Lower early-age temperature rise, reducing the risk of thermal cracking in large pours.
• Elimination of the risk of damaging internal reactions such as ASR.
• High resistance to chloride ingress, reducing the risk of reinforcement corrosion.
• High resistance to attack by sulphate and other chemicals.

In the production of ready-mixed concrete, ggbs replaces a substantial portion of the normal Portland cement content, generally about 50%, but sometimes up to 70% or more. The higher the proportion, the better the durability. The disadvantage of the higher replacement level is that early-age strength development is somewhat slower.

GGBFS is also used in other forms of concrete, including site-batched and precast. Unfortunately, it is not available for smaller-scale concrete production because it can only be economically supplied in bulk. GGBFS is not only used in concrete: other applications include the in-situ stabilization of soil.