How do you measure resistivity?
The resistance of a given material is proportional to the length, but inversely proportional to the cross-sectional area. Thus resistivity can be expressed using the SI unit ohm metre (Ω⋅m) — i.e. ohms divided by metres (for the length) and then multiplied by square metres (for the cross-sectional area).
Why is resistivity of concrete important?
Resistivity is also one of the key controlling factors once corrosion begins (i.e. the propagation phase). Corrosion requires a flow of ions between anodic and cathodic sites on the reinforcement of concrete; the resistivity controls the rate of this flow of ions and therefore directly controls the rate of corrosion.
How do you calculate surface resistivity?
Two parallel electrodes within a distance of each other equal to their contact length come in contact with the material’s surface to measure surface resistivity. Therefore, the potential gradient’s quotient (V/m) and current per unit of electrode length (A/m) represent the resistivity.
How do you measure bulk resistivity?
The equations for calculating bulk resistivity are different from those used to calculate sheet resistance, however, if one already knows the sheet resistance, bulk resistivity can be calculated by multiplying the sheet resistance in Ohms-per-square by the thickness of the material in centimeters.
How is the electrical resistivity of concrete measured?
There are different ways to measure the electrical resistivity of concrete, the most common are; bulk resistivity, surface resistivity, and embedded electrodes for fresh concrete. Giatec has built devices to measure the electrical resistivity of concrete based on these techniques.
How is resistivity measured in a transformer circuit?
In this method a transformer is used to measure resistivity without any direct contact with the specimen. The transformer consists of a primary coil which energises the circuit with an AC voltage and a secondary which is formed by a toroid of the concrete sample.
How is the resistivity of a surface determined?
The resistivity is given by: D is the diameter of the surface probe. Corrosion is an electro-chemical process. The rate of flow of the ions between the anode and cathode areas, and therefore the rate at which corrosion can occur, is affected by the resistivity of the concrete.
How does the porosity of concrete affect electrical resistivity?
The porosity of concrete can significantly affect electrical resistivity measurements. The more porous the concrete is, the more space for ionic movement. In the big picture, these pores can make way for chemical agents to penetrate into concrete.
