Influence of the area and distance between electrodes on resistivity measurements of concrete

Differences between the cell cross section and the electrodes’ area produce a heterogeneous distribution of the electric field that causes a non-linear relationship between electric resistance and distance for low values of electrode separation. Therefore, in actual structures, it is usually not correct to measure the resistivity of concrete by using the direct method because the electrodes’ area is smaller than the cross section of the concrete piece. In this experimental research the influence of the area and the distance between electrodes on the resistivity measurement is analyzed and a semi-empirical model is explained, in which the values of the electrical resistance with respect to distance are adjusted. Based on this model, two new non-destructive methods are proposed in order to measure the electrical resistivity of concrete when using electrodes with a smaller area than the cross section of the piece: one includes varying the distance between electrodes and the other uses electrodes with a different area, but maintains a fixed distance between them.