Blast Furnace Slag

Formed during the manufacture of iron, molten blast furnace slag is cooled and processed in three ways to form slag aggregates for different applications.


Cooled slowly by ambient air the slag is processed into different sizes for use primarily as a construction aggregate in ready-mixed and precast concrete, asphalt, as a fill material and also as a filter media in water and sewage treatment.

The largest air-cooled slag aggregate product, called riprap, is used to stabilise shorelines and stream banks and prevent erosion along slopes and embankments either loose or in gabion baskets. Air-cooled slag is also used in the manufacture of insulating mineral wool.


By casting the molten slag into a cold water vapour via a rotating drum, the slag is cooled rapidly forming lightweight aggregate pellets with high fire rating properties that are perfectly suited for use in ready-mixed concrete, precast concrete and masonry. Pelletised slag can also be used for lightweight fill applications over marginal soils.


The rapid cooling of molten slag by large quantities of water produces sand-like granule aggregate. Primarily ground into a cement replacement known as ground granulated blast furnace slag (GGBS) this is used in ready-mixed and precast concrete and masonry, floor levelling compounds and high temperature resistant building products.

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