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6/2 Diagnosis, inspection, testing and repair of reinforced concrete structures

mixture of materials each component of which may, in itself, vary or be affected by
environmental factors.

From experience it is true to say that 90 per cent of the problems that will be experienced
in concrete repair will involve steel reinforcement corrosion as a primary problem. For
the most part this will have been caused entirely by simple carbonation/low cover and/or
the presence of chloride salts either from calcium chloride used as an accelerator, or from
de-icing salt.

However, in some cases, some other more subtle defect may be present, such as a
shrinkable aggregate, alkali–silica reaction, freeze–thaw damage, sulfate attack, structural
cracks or a whole variety of other possibilities. It must be borne in mind that many of
these phenomena may reveal themselves first of all in areas of low cover and carbonated
concrete, perhaps because microcracking from one or other of these causes has permitted
carbonation to advance more rapidly than might otherwise have been the case. In such
cases, it is all too easy to look at the effects of the problem, i.e. steel corrosion, and
attribute this as the cause. Attempting to repair concrete affected by such problems may
simply mean that the problem recurs in a relatively short space of time.

6.2 What is concrete?

Before considering some of the defects that can appear in reinforced concrete it is worth
pausing briefly to examine the components of the concrete and some of the potential
problems that can occur as a result of the materials themselves.

6.2.1 Cement

Cement
The significance of the alkali content in relation to possible alkali–silica reaction needs
to be considered. Have appropriate precautions been taken to avoid thermal cracking in
high cement content deep-section members? Has the concrete been adequately cured and
appropriate attention been given to the avoidance (as far as possible) of shrinkage cracking?

Sulfate-resisting cement
Where chloride salts are present, sulfate-resisting cement may show an increased
susceptibility to reinforcement corrosion.

High alumina cement
The converted form of HAC may show a reduction in strength and become more susceptible
to certain forms of chemical attack. More recently there has been increased concern over
the occurrence of carbonation in HAC which has been responsible for problems with
reinforcement corrosion on top of the problems due to loss of strength from to conversion.

6.2.2 Water

A good general rule is that if the water is drinkable it should be suitable for concreting
purposes and the vast majority of water employed for concrete will have been drawn from

the mains. However, circumstances may dictate the use of other sources and (very
occasionally) problems may be encountered.

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