Aggregates
European Standard (EN12620: 2002) defines aggregates as
'granular material used in construction' which may be natural,
manufactured or recycled. Aggregates are used in applications
such as roadstone, railway ballast, drainage and bulkfill.
They are also used with the addition of cement, lime or a
bituminous binder in applications such as concrete and mortar.
Aggregates account for 60% to 70% of a concrete mix by mass
and need to be hard, strong particles free of
contaminating chemicals or very fine materials that could reduce
performance.
Great Britain uses around 205 million
tonnes of aggregates or four tonnes per year for every man woman
and child in the country. Almost 90% of total aggregate
minerals are used by the construction industry. Great Britain is
virtually self-sufficient in aggregates with over 97% sourced
domestically, and most are extracted locally to the construction
site.
Recycled aggregates reduce the demands on
aggregate extraction and dredging. Around 25% of aggregate
demand in Great Britain is met from recycled sources, a figure
higher than in most other European countries. The supply of
recycled and secondary aggregates has doubled over the past twenty
years and the great majority of available materials are now used in
aggregate markets. Their use, however, needs to be carefully
considered if local availability of recycled material is
restricted. Transporting recycled aggregates significant
distances can represent a less sustainable option than locally
sourced primary aggregates.
The particle size of aggregates will have a significant impact
on the performance of concrete. Coarse aggregates used in
concrete are larger than 4mm but generally in the range
between 9.5mm to 37.5mm in diameter. Fine aggregates or sand are
smaller than 4mm in diameter and are retained on a 0.063mm sieve.
With a smaller aggregate size there is a higher surface area
which increases the potential demand for
water.
They can either be from Primary, Recycled or Secondary
sources. Primary, or 'virgin', aggregates comprise crushed rock and
sand and gravel from quarries, and sand and gravel from marine
dredging licenses. Gravels constitute the majority of coarse
aggregate used in concrete and together with crushed stone make the
majority of primary course aggregates.
Secondary aggregates are by-products
of non aggregates extractive operations and industrial processes
such as iron and steel manufacture and are usually considered as a
recycled aggregate.
Recycled aggregates also cover
material such as the re-use of construction and demolition waste
and provide an opportunity to reduce primary raw material use and
diverting material from the waste stream.
