Applications of electrical impedance methods in linking structure of micro- and macro-porous concretes to their transport properties

Electrical impedance based methods are frequently used to monitor the microstructural development in cement-based materials due to their non-invasive nature and the ability to make continuous measurements. This paper discusses two other applications of electrical impedance for two different classes of concretes - micro-porous conventional concretes and macro-porous pervious concretes. The effectiveness of a microstructural parameter derived from electrical impedance data to relate to the rapid chloride transport parameters of conventional concretes is described. The influence of the non-steady state migration test in changing the microstructure of concretes due to formation of new solid products through chloride binding of cement hydrates is also evaluated in detail through a combination of measured electrical impedance parameters and an equivalent electrical circuit model. The values of the components of the model determined before and after the migration test provide confirmation of the formation of binding products along the pore walls in concrete. Electrical impedance observations along with a modified Bergman equation are used to predict the porosity of pervious concretes. The experimentally determined and predicted porosities match adequately. The effective electrical conductivity can also be used in well known permeability prediction equations such as the Kozeny-Carman or Katz-Thompson equations for performance prediction of pervious concretes.