Two-point concrete resistivity measurements: interfacial phenomena at the electrode–concrete contact zone

TLDR

The study employs impedance spectroscopy to critically evaluate the two‑point resistivity testing technique for concrete, focusing on electrode–specimen interfacial effects and presenting a protocol to minimize these effects and ensure accurate bulk resistivity measurements. The authors compared two‑point and four‑point electrode configurations, modeled impedance to quantify contact‑region contributions, presented Bode and Nyquist data for BSEN206‑1 and BS8500‑1 concrete mixes with fly ash and slag, and proposed a measurement protocol specifying test frequency and contacting medium.

Abstract

Ac impedance spectroscopy measurements are used to critically examine the end-to-end (two-point) testing technique employed in evaluating the bulk electrical resistivity of concrete. In particular, this paper focusses on the interfacial contact region between the electrode and specimen and the influence of contacting medium and measurement frequency on the impedance response. Two-point and four-point electrode configurations were compared and modelling of the impedance response was undertaken to identify and quantify the contribution of the electrode–specimen contact region on the measured impedance. Measurements are presented in both Bode and Nyquist formats to aid interpretation. Concretes mixes conforming to BSEN206-1 and BS8500-1 were investigated which included concretes containing the supplementary cementitious materials fly ash and ground granulated blast-furnace slag. A measurement protocol is presented for the end-to-end technique in terms of test frequency and electrode–specimen contacting medium in order to minimize electrode–specimen interfacial effect and ensure correct measurement of bulk resistivity.