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Recycled aggregates for concrete

The concrete industry makes up approximately 30% of the total market for aggregates and it is estimated that 165 million tonnes are used annually in concrete. There is, therefore, considerable incentive to develop alternative aggregate sources based on waste materials.

The aggregate products currently coming from most aggregate recycling plants are unbound fills, capping, sub-base and pipe bedding but when used in concrete as a recycled aggregate (RA) it is blended with other materials. A crushed concrete aggregate (CCA) is not widely used due to the limited availability for ready-mixed concrete, but not precluded and should be subject to site trials before use.

Trench arisings, containing stone, concrete, brick, asphalt and clay, are produced by utilities companies, which can then be incorporated into a low strength concrete producing a cost effective trench fill material. Foamed concrete using the <4mm fines from RA is also used in trench reinstatement and there is potential to use incinerator bottom ash aggregate in foamed concrete as well.

The concrete standard BS 8500 has improved the potential for use of recycled aggregates in concrete as has BS EN 12620, Aggregates for concrete. Further reading can be found in Concrete Engineering International, Autumn 2006, where there are several articles on recycled aggregates for concrete.

For more information see the MPA publication Specifying Sustainable Concrete