Therefore, be sure that the electrical resistivity of the concrete is
affected
by
the
ambient
temperature
and
the
moisture
content
change. Also an electrical current is affected by the reinforcement bar in the
concrete. Therefore, if the measurement is to be conducted on the area of
concrete with reinforcement bar, use the Covermeter-3000 (Q-see man int'l) or
other concrete cover meters to locate precisely the position of the reinforcing
bars. Thereafter, keep the Wenner sensor as far as possible from reinforcement
bars.
When the surface of the concrete is more narrower than the widthof the
Wenner sensor (150 mm) or when all of the four electrodes could not contact
with the surface of the concrete that is too rough, the measurements are
impossible. The Resitest-400M consists of a row of electrodes arranged at 50
mm spacing in a straight line. If the spacing is too small, the presence or
absence of the individual aggregate particles, usually having a very high
resistivity, will lead to high degree of scatter in the measurements. Using
larger spacing may lead to inaccuracies due to the current field being
constricted by the spacing will also increase the error in the measurement of
the concrete resistivity due to the increased influence of the conductive
reinforcing steel embedded below the surface of the concrete. Therefore, in
case that the surface of the concrete is more smaller the 150 mm, the
measurements could be impossible. In case that the surface of the
concrete is crooked or hollow, the measurement could be impossible as
well. Because the Wenner sensor is paralleled, all of the four electrodes
should be contacted on the surface of the concrete.
The results may be affected by the contact condition between the
electrodes and the concrete surface of the concrete.
In case Resitest-400M, it is easy to get the most accurate results using
special ring, should always pay attention to the contact condition.
Resitest 400M-June-2011-mkc-7/28
