Concrete electrical resistance can be measured by applying a current using two electrodes attached to the ends of a uniform cross-section 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.
The probes are all applied to the same surface of the specimen and the method is consequently suitable for measuring the resistivity of bulk concrete in situ.
Resistivity strongly affects corrosion rates and electrochemical measurements require an electrical connection to the rebar.
These values have to be used cautiously as there is strong evidence that chloride diffusion and surface electrical resistivity is dependent on other factors such as mix composition and age.
When the electrical resistivity is high, e.g. in case of dry and carbonated concrete, the rate of corrosion decreases.