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.

Lead zirconium titanate (PZT) has recently emerged as a low-cost material for non-destructive monitoring for civil structures. Despite the numerous studies employing PZT transducers for structural health monitoring, no studies have assessed the effects of both damage and repair on the electromechanical impedance response in cementitious materials. To this end, this study was conducted to assess the effects of the damage and repair of mortar samples on the electromechanical response of a surface-mounted PZT transducer. When damage was introduced to the specimen in stages, the resonance frequencies of the admittance signature were shifted to lower frequencies as the damage increased, and an increase in the peak amplitude was detected, indicating an increase in the damping and a reduction in the material stiffness properties. Also, increasing the damage in the material has been shown to decrease the sensitivity of the PZT to further damage. During the repair process, a noticeable difference between the after-damage and the after-repair admittance signatures was noted. The root-mean-square deviation (RMSD) showed a decreasing trend during the repair process, when compared to the before repair RMSD response which indicated a partial recovery for the material properties by decreasing the damping property in the material.

The electrical properties of Portland cement, and cements containing supplementary cementitious materials (SCM), were obtained over the frequency range 1 kHz–10 MHz during the initial 24 h after gauging with water. The response was measured in terms of conductivity and permittivity with both parameters exhibiting significant temporal changes during this period. It was also evident that while the conductivity increased only marginally with increasing frequency of applied electrical field, the permittivity decreased by several orders of magnitude over this frequency range. Moreover, certain features of the permittivity response, which are related to bulk polarization processes, only revealed themselves in the higher frequency range (100 kHz–1 MHz), and went undetected at lower frequencies. The detailed frequency- and time-domain measurements allowed identification of several stages in the early hydration of cement-based materials and the response can be interpreted in terms of hydration kinetics, physico-chemical processes and microstructural development. It is shown that the methodology can be equally applied to cement pastes and concretes.

Satisfactory guidelines for ensuring adequate reinforced concrete durability can only be developed by monitoring concrete performance under a range of field exposure conditions over an extended period of time. Only then can there be a move from prescriptive durability specifications (minimum grade, maximum water-binder ratio, and minimum cement content) to performance-based methods. The situation is also made more complex by the range of cements now available – BS EN 197 defines a total of 27 products in the family of common cements. Implementation of both design for durability and performance-based standards and specifications are limited by the lack of rapid, simple, science-based test methods for characterizing the transport properties and deterioration resistance of concrete. This paper presents an overview of performance-based specification and developments in the application of electrical property measurements as a candidate testing methodology in evaluating the relative performance of concrete mixes. The technique lends itself to in situ monitoring, thereby allowing measurements to be obtained on the as-placed concrete.