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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 as the recycled concrete aggregate (RCA) is blended with other materials and is thus unsuitable for ready-mixed concrete. There have been some site trials with RCA supplied in ready-mixed concrete, but these were not mainstream options.
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 RCA 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. It is expected that there will be an increase in the use of recycled aggregates for concrete in the next few years, but currently it is not widely available.
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