Specialist aggregates

Specialist aggregates are required for use in certain demanding applications; notably where lightweight solutions are required in constructions or where heavy, high density materials are required.

Light weight aggregate
Light weight aggregates (LWA) are needed for situations where concrete is required that imposes low loads on structural elements of constructions. The aggregates therefore must have low density and weight, achieved by using porous materials with adequate strength.

A variety of materials can be pelletised and heated causing them to harden and expand. These include clay, shale and slate, sludge from sewerage works, fine grained sediments dredged from the sea or rivers, and pulverised fuel ash from industrial by-products.

Other materials that can be used are natural volcanic materials that are full of gas cavities including pumice and scoriae. The volcanic materials do not occur in the United Kingdom but can be imported, particularly from Italy.

High density aggregate
High density aggregates are required for manufacture of concrete that is capable of, for instance, attenuating radiation and thus be suitable for shielding nuclear installations and medical facilities such as radio-therapy treatment rooms.

Aggregates are most critical and important component of high density concrete and are principally crushed minerals containing relatively heavy elements, in combination with various additives but can also include scrap steel or certain ceramics. The relevant minerals include crushed hematite and magnetite (both iron oxides), limonite (iron hydroxide) ilmenite (iron titanium oxide) and barite (barytes – barium sulphate). Other additives can include serpentinite (hydrous calcium magnesium silicate) and borax (sodium borate).