IMPEDANCE SPECTROSCOPY OF HYDRATING CEMENT-EASED MATERIALS - MEASUREMENT, INTERPRETATION, AND APPLICATION

This work concerns the state of the art for use of impedance spectrosc opy for studying the evolving microstructure of cement-based materials during hydration. Features of the spectra are discussed and related t o components of the microstructure with the assistance of pixel-based computer modeling techniques. It is proposed that the enormously high relative dielectric constants (similar to 10(5)) observed just after s et are the result of dielectric amplification and are related to the d istribution of pore sizes and the thickness of product C-S-H layers se parating the pores. The conductivity is related to the volume fraction of porosity, the conductivity of the pore solution, and the interconn ectivity of the porosity. The conductivity, when normalized by that of the pore solution, i.e., inverse formation factor, is a measure of th is interconnectivity and can be used to predict such engineering prope rties as ionic diffusivity and water permeability. Composite mixing la ws are employed to aid in explaining the behavior of the conductivity and to obtain a qualitative measure of the pore shape with hydration. Procedures for predicting the conductivity of the pore solution and fo r subtracting out electrode lead effects at high frequency are discuss ed.