Influence of cation type on diffusion behavior of chloride ions in concrete

In the previous paper, a model considering multi-phase reactions and ionic interactions was created to describe the diffusion behavior of chloride ions in concrete immersed in NaCl and CaCl2 solutions. In this paper, more experimental tests and numerical simulations are conducted to improve the model and to study the influence of cation type on chloride diffusion behavior in concrete. In the experimental part, the total and the water-soluble chloride concentrations are determined after 180 days of immersion in the NaCl, KCl, MgCl2 and CaCl2 solutions. The test results show that the chloride binding capacities associated with the four cation types decrease in the order Ca2+ > Mg2+ > Na+ ≈ K+ while the apparent diffusion coefficients of them decrease in the order K+ ≈ Na+ > Ca2+ > Mg2+. In the numerical part, the equations of magnesian ions are newly considered so that the improved model can be applicable for more cation types. Based on the improved model, the chloride binding capacity of concrete in natural diffusion process is a complicated function concerning with many factors, among which the cation type and the contact duration are significantly important.