Leaching of Conductive Species: Implications to Measurements of Electrical Resistivity
Robert Spragg, Scott Z. Jones, Yiwen Bu, Yang Lu, Dale P. Bentz, Kenneth A. Snyder, Jason Weiss
Electrical tests have been used to characterize the microstructure of porous materials, the measured electrical response being determined by the contribution of the microstructure (porosity and tortuosity) and the electrical properties of the solution (conductivity of the pore solution) inside the pores of the material. It has been suggested that differences in concentration between the pore solution (i.e., the solution in the pores) and the storage solution surrounding the test specimen may lead to significant transport (leaching) of the conductive ionic species between the pore solution and the storage solution. Leaching can influence the resistivity of the pore solution, thereby influencing electrical measurements on the bulk material from either a surface or uniaxial bulk resistance test. This paper has three main objectives: 1.) to demonstrate that leaching of conductive species does occur and that a diffusion based approach can be used to estimate the time scale associated with this change 2.) to show that leaching of ions in the pore solution can influence resistivity measurements and the relationship between two different resistivity test geometries and 3.) to provide an estimation of the magnitude of leaching for the standardized tests of cementitious materials.