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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