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Hardened concrete - environmental aspects

Concrete (and other building materials) can be crushed, graded and recycled as coarse aggregate in new concrete if deleterious materials (such as steel reinforcement, timber etc) can be separated and removed. Rejected hardened products from precast concrete factories, crushed to form aggregate, are particularly suitable. As the source and quality of such recycled concrete aggregate is known, it can be safely used.

This may not be so for concrete recycled from unknown sources, but these are increasingly being used in low-grade concrete applications. The environmental advantages of recycled concrete as aggregate and recycled aggregate must be considered carefully, as the energy needed for processing and transport may negate the perceived environmental benefits and may limit the range of potential applications.

However, the rapidly rising cost of landfill disposal makes recycling more economically attractive. At present the limited availability of hardened concrete for recycling means that it is unlikely to constitute more than 10% of the national aggregate requirement.

The use of coarse recycled aggregates has an insignificant effect on the performance of concrete when used to replace up to 30% of the coarse aggregate. When used at higher proportions, some adjustment to the concrete mix may be required. Guidance on the use of recycled coarse aggregates in concrete is given in BS 8500-2, with some limitations on their application. BS 8500-2 does not cover the use of fine recycled aggregates, because of concern that they would contain high proportions of gypsum plaster and other contaminants.

Further information on recycled and secondary aggregates may be obtained from WRAP (the Waste and Resources Action Plan).

For further information see:

Concrete and the Environment, published in CONCRETE in September 2001, pp 3946

Recycled aggregates for use in concrete, published in CONCRETE in March 2005, p 43

Research Information Digest 1, Recycled concrete aggregate, published in CONCRETE in May 2005, pp 2729.

Copies are available as a free download from the Members Area of the Concrete Society web site.

Acknowledgement: The Concrete Society