Recycled Aggregates can be sourced from a variety of material: arising from construction and demolition (concrete, bricks, tiles), highway maintenance (asphalt planings), excavation and utility operations. They can be purchased from demolition sites or from suitably equipped processing centres. The quality of the recycled aggregate is dependent on the quality of the materials that are processed, the selection and separation processing used, and the degree of final processing that these materials undergo. There are two methods of producing recycled aggregates: in situ at the site of the arisings, or ex situ in a central plant. Major cost savings can be achieved by in situ production of recycled aggregate, including transport costs and the accrual of the environmental benefits of reducing lorry movements.

Secondary Aggregates are derived from a very wide range of materials that may be used as aggregates. Many arisings of secondary materials have a strong regional character. For example, china clay sand in SW England, slate waste in North Wales, and metallurgical slag in South Wales, Yorkshire and Humberside.

 The recently introduced European Standards for Aggregates do not discriminate between different sources, and are for “aggregates from natural, recycled and manufactured materials”. The focus is on fitness for purpose rather than origin of the resource.