Slag is the by-product from the production of iron and steel and is an increasingly important source of aggregates and cementitious material.

Production

Blastfurnace slag

Production of high quality iron in an efficient furnace is the basis for good blastfurnace slag. After being tapped from the furnace, the slag is cooled. The cooling rate of the molten material determines that its physical and chemical characteristics.

There are two main methods of cooling. One is leave the slag to air-cool on a stockpile over many days, producing a material that is ideal for processing as an aggregate.

Alternatively, instantaneous cooling by quenching with large volumes of cold water produces a material that has, subject to processing, good cementitious properties.

The granulated blastfurnace slag is then dried in a rotary drier and ground to produce a powder similar in texture to cement. (Ground Granulated Blastfurnace Slag GGBS).

Steel slag

Produced from the further processing of iron and the recycling of steel scrap in electric arc furnaces.

Uses

Slag in concrete (GGBS)

In the second half of the 19th century, it was discovered that GGBS had natural cementitious properties. It was however, many years later before they were put to commercial use.

Since then, it has played a key role in major projects such as the Humber Bridge, Brighton Marina, Hartlepool and Heysham Power Stations and the M180.

GGBS is widely used as a cementitious material and most ready-mixed concrete plants in the UK routinely produce GGBS concrete. It is used in tandem with Portland cement, whose alkalinity provides the catalyst to activate the cementitious properties of GGBS.

Partial replacement of cement with GGBS provides an economic alternative without compromising durability. By reducing the call on cement, it also reduces emissions and extends mineral reserves.

Slag in soil stabilisation (GGBS)

GGBS also has an important role to play in stabilising soils where increased strength, stability or durability is needed prior to development. The practice is widely used for cohesive soils where granular fill is not a practical or cost– effective means of stabilisation.

Slag as an aggregate

Air-cooled blastfurnace slag is widely used for roadstone, rail ballast and as a concreting aggregate.

Slag in surfacing

Used mainly in the road surfacing industry due to its excellent wear and skid resistance properties.

For more information contact Brian James

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