Monitoring hydration of Sr-doped calcium zirconium aluminate (Ca,Sr)7ZrAl6O18 cement via electrochemical impedance spectroscopy (EIS) and supported techniques

The approach to equivalent circuit modelling of reference Ca7ZrAl6O18 and (Ca,Sr)(7)ZrAl6O18 cement pastes has been to interpret spectra obtained from impedance measurements, assigning electrical responses to the hydration features such as hydration products and microstructure. The early and long-term hydration behaviour of new cements was also traced by means of X-ray diffraction (XRD), simultaneous thermal analysis (DSC-TG-EGA-MS), scanning electron microscopy (SEM-EDS) and Raman microspectroscopy chemical mapping as supported techniques. In the structurally modified cement, (Ca,Sr)(7)ZrAl6O18 does not react as violently and immediately with water as Ca7ZrAl6O18 in a pure form. The overall bulk resistance of the Ca7ZrAl6O18-based cement paste significantly outweighs the value of (Ca,Sr)(7)ZrAl6O18-based cement paste. As well, the poor crystallization degree of hydration products at the early-age provides the particular EIS responses in Nyquist format for hydrating cements. The electrochemical behavior of hydrating cement pastes varied both with time and after strontium doping leading us to various equivalent circuit models used for fitting the EIS results. (C) 2019 Elsevier Ltd. All rights reserved.