Blast Furnace Slags

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When iron ore is reduced at 1500°C in a blast furnace it yields molten iron while the other components (from the ore, fluxes and coke ash) form a slag. These two liquids flow to the bottom of the furnace, where the less dense slag forms a layer above the molten iron. When the slag is tapped from the furnace it can be treated in a number of ways, but most commonly, is air-cooled, granulated or pelletised.

Air-cooling produces a crystalline structured mass which, after crushing and screening, provides an eminently suitable material for use as a construction aggregate in bound or unbound form, like any natural rock.

Granulated and pelletised slags are rapidly cooled by the addition of water. Granulation gives a glass with all the components in non-crystalline solution and which is inherently hydraulic, whilst pelletising provides an expanded material. Both can be used as construction materials and, if ground to a fine powder, become an excellent constituent of cement material for concretes, mortars and grouts.