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© 2012 by Proceq SA
If the results obtained are doubtful, then it is often the case that there is a contact problem, e.g.
connection to the reinforcement or the connection between the probe and the Canin
+
-instrument,
respectively inadequate preparation of the probe (copper sulphate solution). Furthermore it is pos-
sible that a film of water on the probe or telescopic extension can create an electrical connection to
the person carrying out
the measurement. This can also affect the results. These error sources are
easily corrected and the check should be repeated.
Check the instrument configuration (See 5.4).
4.6
Preparation of the test surface
It is recommended to mark out a grid on the surface corresponding to the grid you wish to use. For
small areas where point measurements will be made with the Rod Electrode this can be done by
using a tape or by drawing the grid on the element. For large areas such as parking and bridge decks
the wheel electrode is preferable. The integrated path measurement ensures the correct grid in the
direction of measurement. To ensure the correct grid between parallel measurement paths marks
can be drawn on the surface. Please note the 4-Wheel Electrode ensures a stable parallel grid and
requires less marks to be drawn on the surface.
4.7
Check to see if coatings need to be removed
It is not possible to make a measurement through an electrically isolating coating (e.g. an epoxy resin
coating, sealing sheets or asphalt layers.)
It is possible to make a measurement through thin dispersion coatings, that are often used, for
example on the walls and ceiling of underground car parks, however this can cause a small shift of
the potentials.
It is always necessary to check whether or not a measurement can be made through a coating.
To do this, potentials should be measured at a few locations
•
in the first place through the coating and
•
with the coating removed
If possible areas with largely varying potentials should be chosen. If there is no alteration of the
potential, or if a shift of the potential can be compensated by a correction (e.g.
Δ
E = ± 50 mV), then
a measurement can be made directly on the coating. If not, then the coating must be removed before
making the measurement.
4.8
Pre-moistening the concrete surface
The contact between the pore solution of the concrete and the probe can be impaired by a dried out
concrete skin. This can greatly increases the electrical resisitivity of the concrete.
It is therefore recommended to moisten the surface approximately 10 to 20 minutes before carrying
out the measurement.
If this is not possible, it must be ensured that the sponge on the Rod Electrode or the felt hoops
on the wheel electrode are sufficiently moistened. In this case, when making a measurement, the
probe must be held against the surface until a stable end value is reached. (If the surface is dry at
the beginning of the measurement, it has to be moistened by the sponge on the probe so a stable
value will not be
present initially.)
This is only possible with the Rod Electrode.
In the case of the wheel electrode with its continual automatic measurement, it is not possible to
monitor whether or not the measured value is stable. Therefore it is recommended to pre-moisten
the surface section wise and to measure in intervals of a few minutes.
