Development of mathematical models for predicting the compressive strength and hydration process using the EIS impedance of cementitious materials

In this study, the early-age hydration process of cement paste is characterized using the rate of change in the impedance measured by electrochemical impedance spectroscopy (EIS). To effectively describe the microstructure variation during the hydration process, specific hydration models corresponding to four related primary hydration stages with variation in the impedance are explained. An impedance evaluation function for the degree of hydration and heat evolution has been proposed and the correlation has been deduced as alpha(t) = w(n)(t)/w(total) = Q(t)/Q(total) = D ln(k(1)rho(z)(t))/ln(k(2)rho(total)). The hydration degree and heat evolution of cementitious materials with different amounts of w/c ratio and fly-ash (FA) contents are both characterized using the rate of change in the impedance. Early-age impedance can be considered as an equivalent index for the total heat release and offers a promising method of evaluating the cement-hydration degree. Moreover, the impedance can be applied to predict the compressive strength of the FA-blended cement paste. In most cases, the hydration properties of cementitious materials are measured using damaged samples for further analysis. EIS provides additional technical foundations for theoretical and nondestructive testing to investigate the hydration progress and strength estimation, which further aids in achieving improved understanding of the change rate in the electrical impedance of cement-based materials at early ages. (C) 2019 Elsevier Ltd. All rights reserved.