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Increasing the
strength of concrete, say from 40 MPa to 80 MPa, definitely helps in
improving the structural performance of the structure by
producing a denser, more durable and higher load capacity
concrete. The size of concrete members can be
significantly reduced resulting in substantial cost savings.
However, an
increase of concrete strength is also accompanied by the occurrence of
thermal
cracking. With an increase in concrete
strength, the cement
content is increased
and this leads
to higher thermal
strains.
Consequently, additional
reinforcement has to be introduced to
control these additional cracks caused by the increase in concrete
strength.
Moreover, the
ductility of concrete decreases with an increase in concrete
strength. Attention should be paid during the design of high
strength concrete
to increase the ductility of concrete. In
addition, fire resistance of high
strength concrete is found to be less than normal strength concrete as
suggested by
Odd E. Gjorv (1994).
Though the tensile strength of high
strength concrete is higher
than that of normal concrete, the rate of
increase of tensile strength is not proportional to the increase of
compressive
strength. For normal concrete, tensile strength is about
one-tenth of
compressive strength. However, for high strength concrete, it may only
drop to
5% of compressive strength.
Moreover, owing to a low aggregate content
of high strength
concrete, creep and shrinkage increases.
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