On the applicability of the Wenner method for resistivity measurements of concrete

Concrete resistivity measurements are favored for durability assessments due to the relatively simple measurement procedure and the documented correlations between concrete resistivity and transport properties, as well as reinforcement steel corrosion rates. For the measurement, it is common to use a four-point probe with four equally spaced electrodes (spacing distance a) and convert the measured resistance R into apparent resistivity with the so-called Wenner expression, rho(app) = 2 pi aR. By means of experimental measurements and model simulations, the present study confirmed that the application of this formula is adequate, even if most of the assumptions underlying its derivation are violated. The reasons for this are systematically discussed. The experimental results also indicate that measurements with common four-point setups overestimate the resistivity with respect to bulk resistivity measurements. This is likely due to the presence of coarse aggregates that distort the current field at the sense electrodes.