| Resistivity meter to assess corrosion currents in concrete.
Technical
The electrical conductivity of concrete is an electrolytic process
that takes place by the movement of ions in the cement matrix. This
ionic movement will occur when contaminants such as chloride ions
or carbon dioxide are introduced into the cement mortar matrix.
A highly permeable concrete will have a high conductivity and
low electrical resistance. Because resistivity is proportional to
current flow, the measurement of the electrical resistance of concrete
provides a measure of the possible rate of corrosion. Since carbonation
seriously affects surface resistance, measurement on the concrete
surface should be avoided.
The James resistivity meter, OhmCorr™, has two probes spaced 5cm (1.97 inches) apart which are placed in two holes drilled to a depth of 8mm (3/8 inch) and filled with conductive gel. The concrete resistivity is displayed on an LCD when the control switch is activated.
The following table correlates a range of values vs. the possible rate of corrosion of the reinforcement bars.
RESISTIVITY
LEVEL
(K OHMS CM) |
POSSIBLE CORROSION
RATE OF
REINFORCEMENT REBARS |
<5
5 to 10
10 to 20
>20 |
Very High
High
Moderate to Low
Insignificant |
The James OhmCorr™, when used in conjunction with the James CorMap™ System provides an economic and sound means of diagnoses of corrosion in reinforced concrete. |
