Ground granulated blast-furnace slag

Ground granulated blast-furnace slag (GGBS or GGBFS) is obtained by quenching molten iron slag (a by-product of iron and steel-making) from a blast furnace in water or steam, to produce a glassy, granular product that is then dried and ground into a fine powder.

Ground granulated blast furnace slag is a latent hydraulic binder forming calcium silicate hydrates (C-S-H) after contact with water.

Silicate and aluminate impurities from the ore and coke are combined in the blast furnace with a flux which lowers the viscosity of the slag.

Slow cooling of slag melts results in an unreactive crystalline material consisting of an assemblage of Ca-Al-Mg silicates.

Alternatively, in the pelletization process, the liquid slag is partially cooled with water and subsequently projected into the air by a rotating drum.

[1] GGBS is used to make durable concrete structures in combination with ordinary Portland cement and/or other pozzolanic materials.

GGBS has been widely used in Europe, and increasingly in the United States and in Asia (particularly in Japan and Singapore) for its superiority in concrete durability, extending the lifespan of buildings.

Use of GGBS significantly reduces the risk of damages caused by alkali–silica reaction (ASR), provides higher resistance to chloride ingress — reducing the risk of reinforcement corrosion — and provides higher resistance to attacks by sulfate and other chemicals.

Most projects in Dublin's docklands, including Spencer Dock, are using GGBS in subsurface concrete for sulfate resistance.

In most NRA projects in Ireland GGBS is now specified in structural concrete for bridge piers and abutments for protection against chloride attack.

The use of GGBS in such instances will increase the life of the structure by up to 50% had only Portland cement been used, and precludes the need for more expensive stainless steel reinforcing.

GGBS cement prevents the occurrence of efflorescence, the staining of concrete surfaces by calcium carbonate deposits.

[2] Since GGBS is a by-product of steel manufacturing process, its use in concrete is recognized by LEED, as well as Building Environmental Assessment Method (BEAM) Plus in Hong Kong, etc.