Slag and Concrete

Ground Granulated Blast furnace Slag (GGBS) is a by product from the blast furnaces used to make iron. These operate at a temperature of about 1500 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 from 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 GGBS it has to be rapidly quenched in large volumes of water. The quenching optimises the cementitious properties and produces granules similar to coarse sand. This "granulated‟ slag is then dried and ground to a fine powder.

Although normally designated as “GGBS” in the UK, it can also be referred to as “GGBS” or “Slag cement”

Other than improving workability, the addition of Ground Granulated Blastfurnace Slag (GGBS) increases the workability of concrete. It also increases the compressive, split tensile and flexural strength with maximum increase observed when the addition is at 40% replacement of cement.

Durability is also enhanced through the use of GGBS. The compressive strength of acid affected concrete decreases compared with normal concrete. However the effect of acid on concrete decreases with the increase of percentage of GGBS.

The major use of GGBS is in ready mixed concrete, and it is utilised in a third of all UK ready-mix concrete deliveries. Specifiers are well aware of the technical benefits, which GGBS imparts to concrete, including:

• Better 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

• Considerable sustainability benefits.

#GGBS #strength