Reinforced Concrete Pipes And Pillars; Unknown Bar Sizes (Diameter Determination) - Elcometer Protovale CoverMaster CM52 Operating Instructions Manual

5.8 Reinforced concrete pipes and pillars

Reinforced concrete pipes and pillars contain a cage of reinforcement, made from
typically six lengthwise bars and a continuous spiral, all welded together. Larger pipes or
round pillars may contain two or more concentric cages.
Cover measurements on the ends of pipes can be regarded as essentially accurate. In
measurement on inside and outside faces, the welded-mesh effect may significantly
decrease the apparent depth of cover. When measuring the depth of cover on the spiral
reinforcement, the curvature of the concrete will also space the search head away from
the surface.
If these effects are troublesome, it will be necessary to break out a section of concrete
and compare the instrument reading with the true depths of cover. Corrections can be
made either by drawing up charts relating indicated readings to the correct depths of
cover, or sometimes by offsetting the DIAM control to compensate for the inaccuracies.
The midget search head available will simplify measurements on reinforced pipes– see
section 5.12, or contact Protovale for further details.
5.9 Unknown bar sizes
It is not always possible to know in advance the correct setting for the bar DIAM control –
yet accurate depth measurements rely on this being set correctly.
The solution is to set the DIAM control to give the correct relationship between depth
measurements made from the normal black face of the search head, and measurements
made using a 30mm spacer – for example, using the white face. Cover measurements
will them be correct (note: NOT applicable to midget head).
There are two methods for doing this:
Method A (preferred)
This method has been developed by Protovale for use specifically with the CM52
CoverMaster, and is an improvement on the method described in BS1881:204:1988
(method B).
In the following steps, references to a 'spaced' reading mean that the head should be
spaced 30mm away from the concrete surface. For simplicity, the head may be turned
over and the white face used; but for best accuracy, it is better to use a spacer of
exactly 30mm thickness placed between the black face and the concrete surface.
'Direct' readings are taken with the black face of the head in contact with the concrete
surface, in the usual way.
1. Set the MODE switch to CALibrate and zero the instrument carefully.
2. If the expected depth is greater than about 35mm, set the DIAM switch to a
number smaller than the expected diameter, If the expected depth is less than
about 35mm, set the DIAM switch to a number greater than the expected
diameter.
3. Leaving the MODE switch still on CALibrate, apply the 30mm-spaced face of the
search head to the surface and very carefully adjust the orientation over a bar
until the maximum possible reading is obtained on the digital display; make a
note of the reading. This should be at least .030
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