Determination of the ion diffusion coefficient of cracked porous media

摘要

The resistance of building materials against chemical attack is highly determined by their transport properties. Due to a complex interplay of hygrothermal, chemical and mechanical loading a connected network of cracks, microcracks and pores is formed. These are important pathways for infiltrating water and dissolved ions. Transport into a cracked medium consists of a combination of convection, diffusion and chemical reactions. In order to understand and describe these processes an accurate determination and prediction of ion diffusivity and water permeability is necessary. This paper deals with the diffusivity of cracked and uncracked saturated brick samples. In a first step the 3-D cracked geometry (of the samples) is quantitatively measured by means of μCT. Secondly, the experimental data of the diffusion cell test at different ion concentrations is analysed. The validity of the use of a concentration independent diffusion coefficient is examined.