Aggregates are inert granular materials such as sand, gravel
or crushed stone that are an end product in their own right. They
are also the raw materials that are an essential ingredient in
concrete. For a good concrete mix, aggregates need to be clean,
hard, strong particles free of absorbed chemicals or coatings of
clay and other fine materials that could cause the deterioration of
In the UK we are self-sufficient in aggregates and produce
99.98% of all that we consume.
Aggregates, which account for 60 to 75 percent of the total
volume of concrete, are divided into several distinct categories,
and are either coarse or fine:
Coarse aggregates are particles greater than 4.75mm, but
generally range between 9.5mm to 37.5mm in diameter. They can
either be from Primary, Secondary or Recycled sources. Primary, or
'virgin', aggregates are either Land- or Marine-Won. Gravel is a
coarse marine-won aggregate; land-won coarse aggregates include
gravel and crushed rock. Gravels constitute the majority of coarse
aggregate used in concrete with crushed stone making up most of the
Secondary aggregates are materials which are the by-products
of extractive operations and are derived from a very wide range of
Recycled concrete is a viable source of aggregate and has been
satisfactorily used in granular subbases, soil-cement, and in new
concrete. Recycled aggregates are classified in one of two ways,
- Recycled Aggregate (RA), or as
- Recycled Concrete Aggregate (RCA).
Fine aggregate are basically sands won from the land or the
marine environment. Fine aggregates generally consist of natural
sand or crushed stone with most particles passing through a 9.5mm
sieve. As with coarse aggregates these can be from Primary,
Secondary or Recycled sources.
Lightweight aggregates are manufactured from natural materials
or from the manufacture or processing of industrial by-products.
The required properties of the lightweight concrete will have a
bearing on the best type of lightweight aggregate to use.
||On site CO2 emissions from aggregates supply are 4 -
6 kg per tonne. 15 per cent of UK aggregates are transported by
rail and ship/barge. The average road delivery distances is 38
||With a growing commitment to recycling construction waste
materials, there is now little evidence that any hard demolition
and construction waste is sent to landfill (ii). Recycled and
secondary aggregates account for 20 per cent of the total market:
this is the highest for all countries in Europe.
||Seven hundred sites of special scientific interest (SSSIs) in
the UK are current and previous sites of mineral extraction. The
aggregates sector is actively involved in site stewardship and
biodiversity initiatives, including encouraging exemplar
||Aggregates are abundant the world over. The UK has enough
aggregate reserves to last for hundreds of thousands of years at
current rates of usage (i).
|Health and safety
||With improving working practices, year on year aggregate
extraction is becoming an increasingly safe industry. MPA is
seeking to achieve a 2014 target of a 50 per cent reduction in lost
time incidents (LTI) for direct employers and contractors, with an
overarching aim of 'Zero Harm'.
Source: Concrete Credentials: Sustainability, MPA - The
Concrete Centre, 2010