# Surface Resistivity

## Definition - What does Surface Resistivity mean?

Surface resistivity refers to the resistance experienced by the leakage of current along the surface of coat/insulating material. It also can be defined as the electrical resistance that exists between two parallel electrodes in contact through the surface. The electrodes must be separated by a distance equal to the contact length of said electrodes. The four ends of the electrodes form a square; thus, the resistivity is reported in ohms and sometimes ohms per square.

Surface resistivity is calculated as the quotient of the potential gradient with units V/m, and current per unit of electrode length, A/m. This is summarized as the ratio of the DC voltage drop per unit length of the electrode to current per unit width.

## Corrosionpedia explains Surface Resistivity

Surface resistivity dictates the conduction of any given material. The higher the surface resistivity, the lower the conduction of the material because there will be low leakage current. To illustrate this for clear understanding, find below an example of a surface resistivity test. This test is used to estimate hardened concrete permeability.

Procedure:

1. Find any practical specimen of any form, although a 4-inch specimen is recommended.
2. Place the test specimen between the two electrodes and apply voltage to the electrodes for 60 seconds.
3. Measure the resistance.
4. Calculate the surface resistivity and give the apparent value.

When calculating the data, you have to calculate the surface resistivity and express its units appropriately. It is also necessary to note that the above description gives you only the basics of the surface resistivity test. Experts have recommended the test to approve any concrete mixture design when it’s to be used in environments that are prone to steel corrosion. This is when embedded steel is used for reinforcement purposes.

Using the above test, labor and time can be reduced, since some other methods take time to approve the mixture designs. The test only takes 10 minutes, which makes it effective and efficient. When compared to other specimen testing methods, this test can be performed in cylindrical specimens before being used for compression testing.