Analysis of the theoretical model of the rapid chloride migration test

Chloride ion diffusion coefficient in concrete is estimated very often by using electromigration tests, among which the Rapid Chloride Migration (RCM) test is becoming more and more popular. Nevertheless, this test receives much criticism due to lacks in its scientific background. In this paper the theoretical background of the RCM test is critically evaluated in order to show the weak points. Chloride concentration profiles measured after the migration tests give serious evidence of oversimplification of the chloride transport model adopted in the RCM test as they are substantially different from the theoretical ones. Besides this, foregoing research unveils that the chloride ion diffusion coefficients obtained from the traditional non-steady-state diffusion test and from the RCM test are correlated but not identical. As concluded in this paper, the chloride transport model currently adopted for the RCM test should be modified with the non-linear chloride binding isotherm and nonequilibrium between the concentrations of free and bound chlorides. With these phenomenon included, the diffusivity of chlorides obtained from the RCM test should have a new and correct meaning.