Effect of the non-linear membrane potential on the migration of ionic species in concrete

In a concrete migration test the ionic species are present either in the boundary layer or in the pore solution and they flow as is indicated by the Nernst–Planck equation. This equation supposes that the flux of each ion is independent of every other one. However, due to ion–ion interactions there are ionic fields that affect the final flux producing an additional voltage known as the membrane potential. In order to understand this phenomenon, this paper describes a theoretical and experimental investigation of the implications of the membrane potential on the migration of chlorides in concrete. A new electrochemical test has been carried out and its results were compared with a numerical simulation. From the results it has been proved that the voltage drop during a migration test is not linear and changes during the test. Thus the Nernst–Planck equation may be applied to the simulation of migration of any ionic species through a saturated porous medium by using the non-linear voltage to represent all the microscopic interactions in a macroscopic way. The results may be used to improve the reliability of the ASTM C1202 chloride migration test.