When to Use Concrete Resistivity Meter
Concrete electrical resistivity
is obtained by applying current into the concrete surface and measuring the
resulting response voltage. Different methods for measuring concrete
resistivity exist, ranging from laboratory two-electrode, four electrode and
transformer methods to onsite four probe and rebar methods.
The electrical properties of
concrete depend largely on its moisture content. Concrete may, therefore,
exhibit insulated or conductive characteristics depending on its moisture
levels. For instance, a concrete sample could exhibit high electrical
resistance when dry and at the same time have lower a resistance when it is
saturated. Concrete also has capacitive properties, meaning it can hold an electrical
charge, making it difficult to measure electrical resistance. Nevertheless,
several methods and approaches for measuring the
electrical resistivity of concrete are available, and of those, the four-probe
method is considered the most suitable for onsite investigation.
Modern concrete resistivity
meters are spring-loaded four-probe devices that are placed directly on the
concrete surface. Current is applied between the outer probes, and the potential
difference is measured between the inner probes. Analyzing electrical
resistivity of concrete is particularly useful in identifying areas of reinforced
concrete that is at risk of corrosion. However, concrete resistivity meter
measurements shouldn't be considered in isolation. Rather, they should be used
in conjunction with other methods and techniques like half-cell potential in
order to accurately determine the condition of underlying frameworks such as
reinforcing steel.
Corrosion of steel reinforcements,
just like other types of metal concrete support systems, is an electro chemical
process. A current must pass between the concrete's anodic and cathodic regions
for corrosion to occur. The electrical resistivity of concrete affects ion flow
as well as the rate at which corrosion can happen. Higher concrete resistivity
reduces the flow, resulting in an empirical relationship between electrical
resistivity of concrete and the corrosion rate of its underlying
reinforcements.
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