Theoretical assessment of the steady state diffusion cell test

The steady state diffusion cell test is often used to determine the chlorid e ion diffusion coefficient in cementitious materials. It involves the meas urement of the flux of chloride ions through a specimen under near steady s tate conditions. It has been noted that such a test may also provide data w hich characterises the chloride binding capacity of the specimen. In this w ork a numerical model of chloride diffusion subject to the effects of chlor ide binding is used to assess the effect of deviations from the steady stat e on the data obtained from a diffusion cell test. It is noted that there w ill be a tendency to underestimate the diffusion coefficient, although good practice should limit this error. The predicted error in the chloride bind ing isotherm is smaller than that in the diffusion coefficient. Furthermore , the influence of errors in the effective porosity on model predictions is limited as the resulting effect on the values of the calculated parameters describing chloride diffusion and binding counteract each other. (C) 1998 Kluwer Academic Publishers.