Proceq PM8500 User Manual page 11

Moisture
See the chart above for moist, carbonated concrete and dry, carbonated concrete. Moisture
has a large effect on the measured potential leading to more negative values.
Concrete cover thickness (Measure with PM8000 and PM8000 Pro)
The potential that can be measured at the surface becomes more positive with increasing
concrete cover. Variations in the concrete cover can cause deviations in the measurements.
Very low concrete cover can lead to more negative potentials which would seem to indicate
high levels of corrosion. Therefore, it is advisable to make concrete cover measurements along
with the half-cell measurements.
Electrical resistivity of the concrete (Measure with Resipod)
Low electrical resistivity leads to more negative potentials that can be measured on the surface
and the potential gradients become flatter. In this case the measurement grid for potential
measurements may be coarser, as the risk of undetected anodic areas with flatter gradients
becomes lower. However, as the resolution between corroding and passive areas is reduced,
this may lead to an overestimation of the actively corroding surface area.
High electrical resistivity leads to more positive potentials that may be measured on the surface
and potential gradients become steeper. In this case the measuring grid must be made finer,
to be able to locate an anode with a very steep gradient. However, the mere potentials may be
misinterpreted as passive areas when only considering the absolute value of the potential.
Temperature
The main effect of temperature on potential measurements is given by its influence on the
electrical resistivity. High temperature will cause concrete resistivity to be lower and low
temperature will cause concrete resistivity to be higher; the resulting effect on potential value
is as described in the previous paragraph "Electrical resistivity of the concrete".
In order to measure the potential, there must be a contact between the probe and the
electrolytes in the pore system of the concrete. Therefore, a measurement below the freezing
point is not recommended and can lead to incorrect readings.
Oxygen content at the reinforcement
With decreasing oxygen concentration and increasing pH-value at a steel surface its potential
becomes more negative. In certain cases of concrete components with a high degree of water
saturation, low porosity and/or very high concrete cover and thus low oxygen supply, the
potential at the steel surface may be highly negative even though no active corrosion is taking
place. Without checking the actual corrosion state this may lead to misinterpretation of the
potential data.
The air permeability of the concrete may be tested with Proceq's Torrent instrument.
25. September 2023 © Copyright 2023, PROCEQ SA 11