CALCULATION OF CHLORIDE DIFFUSIVITY IN CONCRETE FROM MIGRATION EXPERIMENTS, IN NON-STEADY-STATE CONDITIONS

Shortening of the testing time to characterize concrete resistance to chloride penetration was the main practical improvement of the so called ''Rapid Chloride Permeability Test'' developed by Whiting. Recently, numerous papers were published presenting results using this method already standarized by AASHTO, although the claims on its real meaning are also numerous. In a previous paper, a solution for calculating ionic diffusivity from a migration test performed under steady-state conditions was presented based in the known Nernst-Planck equation which models mass transport in electrolytes. Some simplifying assumptions were made in order to solve the particular case of concrete. In the present paper, a solution is presented for non-stationary conditions also assuming the same simplifying conditions. The solution refers to a mathematical expression similar to that of simple diffusion, but considering ZFDELTAE/RT as the multiplying factor. Results from preliminary tests are presented which confirm the promising procedure of accelerated diffusion tests. Finally, calculation of the diffusion coefficient from concrete electrical resistance values is justified.