The study of the electrochemical behavior of the cement-based materials pore solution interface is an important topic in order to understand the transport of ionic species. It is also relevant for the purpose of interpreting the experimental results obtained in ionic transport tests (natural diffusion, or migration). The inherent issue in the interpretation of experimental results from ionic transport tests is the link between transport phenomena occurring at pore scale and the access to only macroscopic data and results. Indeed, the ionic concentrations of the pore solution are necessary data for the application of the Nernst-Planck equation. We demonstrate here that the pore size has impact on the results on the ionic concentrations distribution at macroscopic scale. Consequently the electrical conductivity is also modified. This works helps to understand why the results of migration tests may lead to wrong interpretations in terms of material conductivity and ionic diffusivity. (C) 2017 Elsevier Ltd. All rights reserved.