Civil Engineering Reference
In-Depth Information
Apart from establishing that the concrete is of the right quality and that
it has been correctly placed, cover to the reinforcement is the next most
important parameter.
Figure 1.3
illustrates a modern covermeter. Engineers,
in the author's experience, rarely know how to use covermeters and have
no idea of the importance of bar size on the results and how misleading
cover data can be obtained if the bar size is set incorrectly, or if lapped bars
are encountered. These details are covered in the section on covermeters
that follows. At the time of construction, it is entirely possible to check
that the steel has the appropriate cover both before and after placing the
concrete. This can be done through timber formwork (though not with steel
formwork), simply deducting the timber thickness from the results. The
covermeter only 'sees' the steel reinforcement and timber or concrete have
no influence (though some aggregates, such as Lytag, can rarely interfere
due to a property called 'magnetic viscosity' (Elcometer, 2010). Thus it is
possible to ensure that the cover is correct at the point of construction, while
the concrete has not yet hardened and while there is still time to intervene if
a mistake has been made.
1.3.2 Understanding the problem
It is critically important to understand what has caused the deterioration in
the structure and to fully understand the extent and reasons for it, prior to
deciding on a repair strategy. Failure to do so can mean an inappropriate repair
is chosen, which will inevitably fail more quickly than a correctly selected
repair. For example, failure to understand that chloride contamination in the
concrete has caused reinforcement corrosion, and simply attempting to patch
repair it, causes early failure because new corrosion cells immediately form
around the patch repair (Broomfield, 2007), resulting in further spalling
