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.

The self-healing performance of an engineered cementitious composite (ECC) exposed to the natural environment is presented. Fifteen dog-bone shaped ECC samples were preloaded after 14 d of curing and then placed outside in an open area at Heriot-Watt University (Edinburgh campus). Ultrasonic pulse velocity measurements were used to determine the rate and extent of the self-healing capabilities of the ECC in the natural environment. The results showed that, while the more highly damaged samples displayed the greatest decrease in ultrasonic velocity, they also displayed initial accelerated healing, which implies an increased quantity of individual cracks in the more damaged samples rather than an increase in individual crack widths. It was also found that the self-healing of microcracks in the ECC was robust. Narrow hairline cracks (< 10 μm width) healed in less than 6 d, while 20–30 μm wide cracks either partially or fully healed after 6 d of intermittent rainfall. Wider microcracks (40–75 μm) partially healed after 3 weeks of outdoor exposure.