Determination of the electrical resistivity of concrete structures using electrical impedance tomography

The electrical resistivity of concrete is an important material parameter for evaluating the current condition of a concrete structure. It can be correlated with different durability related parameters, e.g. the water content, the corrosion rate of the reinforcement and the chloride diffusion coefficient. Usually the determination of the concrete resistivity in existing structures is made by drilling out cores and measuring the resistivity in the laboratory, which goes along with a local destruction of the concrete. Another option is to determine the concrete resistivity non-destructively using a Wenner probe by making the assumption of a homogeneous half-space with a homogeneous resistivity. In practice, however, there are distinctive heterogeneities (e.g. reinforcement or moisture distributions), which can lead to significant misinterpretations. To counteract this problem (see also Asgharzadeh et al, 2014 and Reichling, 2015), the application of Electrical Resistance Tomography (ERT) has been studied. This method is based on the measurement of several apparent resistivity values resulting from different electrode spacings and positions. The actual resistivity distribution in the concrete is calculated by inverse calculations based on iterative numerical methods. This allows the effect of heterogeneities to be considered and to reconstruct the distribution of the actual concrete resistivity. This paper focuses on the applicability of ERT on reinforced concrete structures.