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Recycled glass aggregate

The concrete industry places a heavy demand on primary aggregate sources; it is estimated that 165 million tonnes are used annually. There is therefore considerable incentive to develop alternative aggregate sources based on waste materials.

Crushed recycled glass can be used as a complete fine aggregate replacement in concrete, while finely ground glass (powder) has pozzolanic properties and can be used as a Type II (pozzolanic) addition. Recycled glass aggregate fits within the definition of manufactured aggregate given in BS EN 12620. The guidance to the use of this Standard is provided in BS 6682-1. This gives limits for recycled glass and is reflected in BS 8500-2.

There is a risk of damaging alkali-silica reaction (ASR) when recycled glass is used in concrete and this must be minimised to an acceptable level. Research has shown that when glass powder is used at percentages greater than 20% of mass of cement, the pozzolanic reactions suppress ASR. When recycled glass is used as an aggregate, the risk can be minimised through the use of ground-granulated blast furnace slag (ggbs) and/or metakaolin as Type II additions.

For further information see Research Information Digest 2, Recycled glass, published in CONCRETE in June 2005, pp 44–46. Copies are available as a free download from the Members´ Area of the Concrete Society web site.

Acknowledgement: The Concrete Society