Incinerator ashes are ashes from energy-from-waste recovery. They are available in two forms:

• Incinerator bottom ash aggregate (IBAA) is a granular material that can be used as a partial replacement of natural aggregate (normally up to a maximum of 25% by mass) in new low-strength concrete.
•Incinerator fly ash (IFA) is a powder-like material that can be used to promote the reaction between fly ash and Portland cement.

600,000 tonnes of IBAA and 70,000 tonnes of IFA created from incineration of municipalsolid waste are produced in the UK each year. The vast majority of this is currently sentto landfill. Whilst their use in concrete will have only a small impact on the 165 milliontonnes of natural aggregate and 15 million tonnes of Portland cement used each year,they can be used to prevent higher-value materials being used inappropriately in lowvalueapplications.

Use of incinerator ashes in concrete will contribute towards sustainable development by:

•using a material that would otherwise be sent to landfill
•reducing overall greenhouse emissions
•reducing natural aggregate usage
•potential reduction in transport impacts.