Reinforcement
Rebar (reinforcing bar) is an important component of
reinforced concrete. It is usually formed from ridged carbon steel;
the ridges give frictional adhesion to the concrete. Rebar is used
because although concrete is very strong in compression it is
virtually without strength in tension. To compensate for this,
rebar is cast into it to carry the tensile loads on a
structure.
Whilst any material with sufficient tensile strength could
conceivably be used to reinforce concrete, steel is used in
concrete as they have similar coefficients of thermal expansion.
This means that a concrete structural member reinforced with steel
will experience minimal stress as a result of differential
expansions of the two interconnected materials due to temperature
changes.
The steel used in UK reinforced concrete utilises 100 percent
recycled scrap steel as feedstock. At the end of its life, all
reinforcing steel can be recovered, recycled and used again. The
embodied energy values of reinforcing steel are based on the energy
used to melt and reform it. The energy input per tonne of
reinforced steel is less than half of that for structural
steel.
Non-steel reinforcement
Some construction cannot tolerate the use of steel. For
example, MRI (Magnetic Resonance Imaging) machines have huge
magnets, and need to be housed in nonmagnetic buildings. For these
purposes some structures have been constructed using
fibre-reinforced plastic rebar, grids or fibres. The 'plastic'
reinforcement can be as strong as steel.
Fibres are often also used in concrete to
produce fibre-reinforced concrete, which is a concrete mix that
contains short discrete fibres that are uniformly distributed and
randomly oriented. Types of fibres include steel, glass, synthetic
and natural fibres. Within these different fibres that character of
fibre reinforced concrete changes by varying the concrete's fibre
materials, geometries, distribution, orientation and
densities.
Sustainability credentials
| CO2 |
Manufacture of steel reinforcement bars for reinforced concrete
could be a course of significant energy consumption and a large
contributor to embodied CO2. However, the UK industry
uses the Electric Arc Furnace process, which generates up to six
times less CO2 than those emanating from the Basic
Oxygen Steel making system that is used for making other UK
steel. |
| Recycling |
UK produced reinfrocement for concrete is manufactureed from
100 per cent recycled UK scrap steel. Scrap steel reinforcement
from demolished buildings is recycled to manufacture raw steel
reinforcement. Two thirds of reinforcement used in the UK is
produced in the UK. The majority of imported reinforcement is also
produced from scrap steel by Electric Arc Furnace. |
| Resource depletion |
The use of Electric Arc Ffurnaces allows reinforcement steel to
be made from 100 per cent scrap metal, reducing the specific energy
(energy per unit weight) required to produced the steel, but also
relieving pressure on the Earth's natural ore resources. The UK is
a net exporter of scrap steel. |
Source: Concrete Credentials: Sustainability, MPA - The
Concrete Centre, 2010