End of life recycling
The construction industry in the UK accounts
for the use of 295 million tonnes of virgin material per year,
displaces 22 million tonnes of industrial 'by-product' by
industrial ecology each year and produces approximately 150 million
tonnes of construction and demolition waste annually. Of
this, 46 million tonnes is recycled for use as building
products, in road construction, or land reclamation
thereby reducing the amount of material that is landfilled and
reducing the need for virgin materials in new
It is more than likely that a modern concrete
building will come to the end of its life because no further use
can be found for it, rather than the concrete having failed due to
Due to the flexibility and adaptability of
concrete, seemingly redundant structures can often be stripped back
to their core and then rebuilt to new, contemporary specifications.
If a building has to be demolished, then it provides a potentially
rich source of recycled aggregate (RA) for a range of applications.
RA was estimated to account for almost a fifth of the UK's
aggregate supply in 2001. That proportion is set to grow.
A specific subset of recycled aggregates is
recycled concrete aggregates (RCA) where the masonry content is
limited to not more than five per cent. The performance
characteristics of RCA are better than RA and consequently there
are fewer restrictions on the use of RCA in concrete. Provision for
the use of RCA in concrete is given in BS 8500-2.
About 75-80 per cent of secondary and recycled
aggregates are thought to end up as sub-base and fill, including
use in road building and airfield pavements. However, the concrete
industry actively utilises industrial ecology in the production of
modern concrete products due to concrete's inherent inert nature.
The constituents of concrete can be recycled materials, and
concrete itself can also be recycled; these materials are usually
available locally. Concrete pieces from demolished structures can
also be reused to protect shorelines, for example in gabion walls
or as rip rap.
Many formwork options are reusable at the end of their
life. About half of all concrete produced in Britain is
reinforced and unlike structural steel the reinforcing steel made
in the UK is made entirely from recycled steel, which itself can be
recovered for reuse at the end of the building or structure's life.
Although steel manufacture is an extremely energy-intensive
business, the energy needed to produce one tonne of reinforcing
steel is as low as half of that needed to make one tonne of
structural steel from iron ore.
Many cement plants burn waste-derived fuels
such as spent solvents, used oils and tyres. Every year the UK
produces 400,000 tonnes of waste tyres, posing a significant
environmental problem. Legislation prevents the dumping of tyres in
landfill and currently around 40 per cent of waste tyres are
recycled into retreads, all-weather surfaces and other uses, but
that still leaves 28 million tyres with seemingly nowhere to
Used tyres make an ideal kiln fuel for the
production of cement, without any adverse environmental effects.
Kiln temperatures are so high that tyres burn without fumes or
flame and what's more the residue from burning tyres can be
chemically treated and reused again as fuel. The obvious pay-off
from burning tyres is the fossil fuel and carbon emissions saved.
It is estimated that the UK cement industry currently consumes 5.6
million waste tyres. Trials are also underway with other
alternative fuels in cement making, such as recycled liquid fuel,
inert processed sewage pellets (PSP) and packaging waste. Used
tyres have even been recycled into concrete as they contain steel
fibre, according to recent research sponsored by the Department of
Trade and Industry (DTI). The research found that recycled steel
fibre (which is cheaper than conventional steel fibre) leads to an
increase in concrete's strength, ductility and toughness, making it
suitable for a range of specialised applications such as impact and
Recycled concrete can be used as aggregate in
new concrete, particularly the coarse portion. When using the
recycled concrete as aggregate, the following should be taken into
- Recycled concrete as aggregate will typically have higher
absorption and lower specific gravity than natural aggregate and
will produce concrete with slightly higher drying shrinkage and
creep. These differences become greater with increasing amounts of
recycled fine aggregates.
- The chloride content of recycled aggregates is of concern if
the material will be used in reinforced concrete. The alkali
content and type of aggregate in the system is probably unknown,
and therefore if mixed with unsuitable materials, a risk of
alkali-silica reaction is possible.