Monitoring early-age hydration and setting of portland cement paste by piezoelectric transducers via electromechanical impedance method

Monitoring the early-age hydration and setting process of cement paste is of great significance to help engineers determine the cement solidification status and evaluate the development of the strength and stiffness of cements. As a promising non-destructive testing (NDT) method, the electromechanical impedance (EMI) method has been extensively applied in many fields of structure health monitoring (SHM) using piezoelectric transducers. In this research, the feasibility of this method in monitoring the early-age hydration and setting process of Portland cement paste was explored. Experiments and observations on the conductance signatures obtained from the embedded piezoelectric transducers inside the cement pastes with two different water-to-cement (w/c) ratios have been conducted within 72 h of hydration. Moreover, the trends of EMI spectra in response to two different excitation frequency ranges, 100 Hz-1000 kHz and 100 Hz-3000 kHz, were captured. It is revealed that the variation of the conductance signatures in the higher frequency range well corresponds to each stage of the cement setting process determined by the Vicat needle testing. Both the resonance peak shift and the statistic index-based approaches perform effectively in monitoring the transformation of cement pastes from liquid to solid state controlled by the cement hydration. In addition, the hydration mechanism has also been interpreted through the hydration exothermic test, XRD and SEM measurements on cement specimens at different ages. (C) 2020 Elsevier Ltd. All rights reserved.