Effect of embedded steel on electrical resistivity measurements on concrete structures

For corrosion of embedded steel in concrete structures, the electrical resistivity of the concrete is a very important controlling factor for the rate of corrosion. Therefore, measurements of electrical resistivity of the concrete are normally an important and integrated part of the measurements carried out during condition surveying of concrete structures. Because the embedded steel may significantly affect the observed resistivity, however, it may not be easy to interpret the results of such resistivity measurements. To provide more information about the effect of embedded steel on electrical resistivity measurements on concrete structures, an experimental investigation was carried out, the results of which are presented in the present paper. The test program was based mainly on the fourelectrode (Wenner) testing of the electrical resistivity and included different probe spacing and test specimens with embedded steel. The tests were carried out in two different directions relative to the embedded steel. Effects of cover thickness and curing conditions on the resistivity were also investigated. The results show that electrode spacing can substantially affect the observed resistivity of concrete. For field measurements of electrical resistivity on concrete structures, the investigation confirmed that all measurements should be carried out as far away as possible from all embedded steel. If this is not possible due to very dense reinforcement, the electrode spacing of the Wenner device should be kept small relative to the cover depth.