Calculation of Ionic Diffusion Coefficients on the Basis of Migration Test Results.
Calculation of Ionic Diffusion Coefficients on the Basis
of Migration Test Results.
Samson, E.; Marchand, J.; Snyder, K. A.
Materials and Structures, Vol. 36, No. 257, 156-165,
concretes; diffusion; duffision potential; migration;
Migration tests are now commonly used to estimate the
diffusion coefficients of cement-based materials. Over
the past decade, various approaches have been proposed
to analyze migration test results. In many cases, the
interpretation of test data is based on a series of
simplifying assumptions. However, a thorough analysis of
the various transport mechanisms that take place during
a migration experiment suggests that some of them are
probably not valid. Consequently, a more rigorous
approach to analyze migration test results is presented.
The test procedure is relatively simple and consists in
measuring the evolution of the electrical current
passing through the sample. Experimental results are
then analyzed using the extended Nernst-Planck-Poisson
set of equations. A simple algorithm is used to
determine for each experiment the tortuosity factor that
allows to best reproduce the current curve measured
experimentally. The main advantage of this approach
resides in the fact that the diffusion coefficients of
all ionic species present in the system can be
calculated using a single series of data. Typical
examples of the application of this method are given.
Results indicate that the diffusion coefficients
calculated using this approach are independent of the
applied voltage and depends only slightly on the
concentration level and the chemical make-up of the
upstream cell solution.