A Combined Electrical and Electromechanical Impedance Study of Early-Age Strength Gain in Cement Mortars

From simple strain gauges to more sophisticated techniques such as acoustic emission and digital image correlation methods, a variety of non-destructive methods are proposed in the literature for inspecting civil structures. However, in addition to accuracy and simplicity, automation and timely data collection are the main requirements for an efficient in situ non-destructive testing technique. Electrical impedance and the electromechanical impedance tests of cementitious members, are perceived to be suitable candidates for fulfilling the simplicity, automation and accuracy requirements, hence providing an efficient yet relatively non-expensive remote monitoring system. Throughout the first 28 days of a cementitious composites age, significant gain of strength is typically developed. It is crucial during this period to characterize the in situ strength gain profile for both planning and quality control purposes. This study investigates the viability of both the electromechanical impedance technique and the electrical impedance spectroscopy technique as non-destructive strength testing methods. These were assessed against their ability to detect strength changes due to the ongoing hydration reaction in cementitious mortars conforming with BS EN 196-1:2016. Results from both techniques were compared with the compressive and flexural strengths. The electromechanical impedance was assessed in terms of the change in the electrical impedance signature response through time, which was obtained through surface attached PZT sensors. Concurrently the electrical impedance response was collected through embedded stainless-steel electrodes across the frequency range of 1–10 MHz. This study will act as a guide for selection of a suitable technique for in situ strength gain monitoring using electrical methods.