Assessing the performance and transport properties of concrete using electrical property measurements

The electrical properties of porous systems are intimately linked to mass transport and flow processes such as diffusion and permeability and offer a simple testing methodology for assessing those properties which are responsible for the durability and long-term performance of construction materials. In the current study, electrical impedance spectra for concretes containing both plain and blended Portland cement binders were obtained over a period of 360 days. In-situ impedance measurements were used to accurately identify the bulk resistance (hence evaluation of resistivity) of the concretes and the optimum frequency range for bulk resistance measurements. The bulk resistivity was normalised by that of the pore-fluid resistivity obtained from computer simulations and the results indicated that the pore-fluid resistivity decreased only marginally with time once the hydration process had advanced beyond 28 days. It is shown that the normalised resistivity – termed the Formation Factor – displayed a continual increase with time, highlighting on-going hydration/pozzolanic reaction and pore structure refinement over the entire test period. This was particularly evident for the slag concretes. Using the normalisation process, a simple approach is presented to evaluate the effective diffusion coefficient of the concretes and a durability/performance classification system, based on the Formation Factor, is presented.