Aggregates – general information

The use of slag aggregates from iron and steel production in construction dates back to the Romans who used crushed slag from the crude iron production of that time to build their roads. Nowadays, slag is still used to build roads.

However, slag use is not limited to roads anymore, but slag aggregates are widely used in all kinds of civil works. An aggregate is a granular material used in construction. Properly applied aggregates contribute to the strength and mechanical stability of the construction.

The grains can be regarded as the skeleton of the structure, because they divide and conduct mechanical forces. Slag is particularly useful as an aggregate, due to the high mechanical resistance of the slag grains which exceeds many natural aggregates. For the production of aggregates, processing crude slag mainly consists of crushing and/or screening. This gives a grading and other related properties in accordance with European product standards or specifications agreed upon with the customer.

The aggregate standards contain additional requirements for blast furnace slag and steel slag with respect to volume stability. In general the properties of iron and steel slag aggregate are comparable with the properties of natural aggregate.For some specific uses slag is even superior to natural aggregate.

Slag aggregate can be used as a construction material in unbound applications (where the aggregate is not bound) as well as in bound applications (mixtures which contain binding agents like cements, bitumen or a substance that has binding properties in contact with water). Besides construction, slag aggregates have some specific uses like waste water treatment due to their absorbing properties for pollutants.

Applications of slag aggregates:

Aggregate use	BLAST FURNACE SLAG		STEEL SLAG
	Granulated (GBS)	Air-cooled (ABS)	(BOS, EAF C and EAF S)
Unbound and hydraulically bound mixtures	x	x	x
Bituminous mixtures	x	x	x
Concrete	x	x	x
Mortar	x	x	x
Armourstone			x
Gabions		x	x
Railway ballast		x	x
Roofing		x	x
Embankments and fill	x	x	x
Sealants	x		x
Sand blasting	x
Waste water treatment		x	x
Air quality control			x