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.
Physical characteristics
Although ridges on the rebar bind it mechanically to the
concrete with friction, it can still be pulled out of the concrete
under high stresses. To prevent this, rebar is either deeply
embedded into adjacent structural members, or bent and hooked at
the ends to lock it around the concrete and other rebar.
Rebar is commonly made of unfinished steel, though
epoxy-coated rebar or stainless steel rebar may be employed in
situations where environmental conditions dictate. Fibre reinforced
polymer rebar is now also being used in high-corrosion
environments.
Metric bar designations represent the nominal bar diameter in
millimetres. Bars in Europe will be specified to comply with the
standard EN 10080 (awaiting introduction as of early 2007),
although various national standards still remain in force (e.g. BS
4449 in the United Kingdom).
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.