Modification of four point method to measure the concrete electrical resistivity in presence of reinforcing bars

Concrete resistivity is a material characteristic that can be related to its durability, as it indicates the amount and tortuosity of the pore network and also informs on the degree of water saturation. Its measurement is usually made in situ by the use of the four-point or Wenner method, but the accuracy of such measurements is affected by the presence of metallic reinforcement. In those cases, measurements should not be made on the surface immediately above the reinforcing bar. This paper examines the effects of rebar presence/absence on the resistivity measurements and the significance of a rebar presence factor, which is determined by means of numerical simulations using the COMSOL Multiphysics software package. The results indicate that the rebar presence apparently lowers the resistivity values in a proportion which is a function of the specimen geometry and the electrode spacing. Equations for its quantification are presented.