Relating rapid chloride transport parameters of concretes to microstructural features extracted from electrical impedance

The rapid chloride transport parameters such as the rapid chloride permeability (RCP) and non-steady state migration coefficient are related to the material microstructural parameters in this paper. Electrical impedance spectroscopy and associated equivalent circuit modeling are used to extract the microstructural features of the plain concrete as well as concretes modified with varying amounts of Class F fly ash or silica fume. A methodology is developed in this paper that utilizes the ratios of RCP values and the ratios of effective conductivities to pore solution conductivities of plain and modified concretes, to quantify the relative influence of pore solution conductivity and pore structure on the RCP values. The resistance attributable to the connected pores is extracted from an equivalent circuit model for the impedance spectra of concretes, which is found to relate well to the rapid chloride transport parameters as well as the microstructural parameters. Based on the experimental results and electrical circuit models, it is shown that a reduction in pore connectivity has a higher impact on the rapid chloride transport parameters than a reduction in the porosity, and reduction in pore sizes is more consequential than porosity reduction in reducing pore connectivity.