Effective medium method for predicting the chloride diffusivity in concrete with ITZ percolation effect

In predicting the chloride diffusivity in concrete as a three-phase material, composed of aggregates, interfacial transition zone (ITZ), and bulk cement paste, not only the volume fractions, physical properties, and interactions of the three phase constituents but also the ITZ percolation effect should be taken into account. This paper attempts to develop an effective medium method to achieve this. Based on the stereological analysis of the aggregate size distribution and the statistical geometry of composites, the ITZ volume fraction is formulated analytically for the general aggregate gradation. By taking the ITZ-coated aggregate as an "equivalent aggregate", the three-phase concrete is reduced to a two-phase composite material. An analytical solution is then derived for the chloride diffusivity in concrete applying the general effective medium theory. The primary advantage of the derived analytical solution is that the ITZ percolation effect and the Hashin-Shtrikman bounds are taken into account. Finally, the validity of the derived analytical solution is verified with two sets of experimental data and the effects of the ITZ thickness of and the chloride diffusivity in ITZ on the chloride diffusivity in concrete are evaluated through sensitivity analysis. The paper concludes that the presented analytical solution can predict the chloride diffusivity in concrete with an average relative error of 6%. (C) 2013 Elsevier Ltd. All rights reserved.