Full list of Nuggets
Aggregates form the major part of concrete and are derived from many types of rock. Granite and limestone are extracted from quarries, crushed and graded. In many parts of the UK, land-based or marine sand and gravel are available: these require some processing, such as washing and grading, before use in concrete. Washing removes deleterious contaminants such as chlorides from marine-derived materials or excessive amounts of clay and silt from land-based sources. In some cases, silt particles can be recovered by flocculation so that they can be used as part of the fine aggregate. To minimise transport costs, aggregates are processed at their source or the landing point of marine materials. The major environmental concerns of aggregate production are outlined in the Table.
|Stage in aggregate processing
|Major environmental impacts
|Quarrying and processing raw material
|Scarring of landscape
|Dust and noise
|Some sources are in areas of outstanding natural beauty
|Proximity to major centres of population
|Loss of agricultural land (or removal from use for many years)
|Energy consumption; carbon dioxide emissions etc.
|Delivery of aggregate to concrete production plant
|Fuel, noise and traffic
Actions taken by the aggregate industry include: the increased use of recycled concrete as aggregate and artificial aggregates made from by-products of other industries; worked-out quarries used as landfill sites before landscaping; and gravel pits used for recreational water sports, natures reserves etc. Where feasible rail or water transport is used to reduce transport impacts.
Acknowledgement: The Concrete Society
Other references:Concrete and the Environment, published in CONCRETE in September 2001, pp39–46. Copies are available as a free download from the Members Area of the Concrete Society web site.