Theoretical Model and Experimental Tests on Chloride Diffusion and Migration Processes in Concrete

Abstract

This paper focuses on the effect of the electric field on the thermodynamic model of ion flows in the concrete pore solution. The equation for ion migrations was derived from the mass balance in the multi-component system and material constants. Then, using only one component -chloride ion, a reliable diffusion coefficient was determined from the formulated converse task of the migration equation. Taking into account experimentally obtained distribution of chloride concentrations under the electric field, the diffusion coefficient was determined. The distribution of the chloride concentrations was calculated on the basis of that coefficient. And then, it was compared with the measurement results for concentrations of chlorides penetrating into concrete via diffusion. The lowest mean square error between the experimental and calculated distributions of mass densities indicated the reliable value of the chloride diffusion coefficient.

The kinetic competition between transport and oxidation of ferrous ions governs precipitation of corrosion products in carbonated concrete

“…1•10 -5 cm 2 /s, while in concrete the Cleffective diffusion coefficient (D eff ) has been measured to be between ca. 1•10 -8 cm 2 /s and 2•10 -7 [38][39][40][41]. The same proportionality has been assumed to hold for Fe 2+ .…”

New method development for evaluation concrete chloride ion permeability

“…This is due to the fact that conductivity and diffusivity are easily measurable in steady state conditions. Nonetheless, in methods which are merely associated with measuring diffusivity and for concrete samples with suitable thickness, a period of one year or longer is required to reach a steady state condition [27]. The driving force for diffusion is the difference in ionic concentration so that a higher gradient leads to increase in flux of ions [28].…”

Modeling of Chloride Distribution in Cement‐Based Materials with Neumann Boundary Condition

“…It is reasonable to consider that the determination of the transport of chloride is the basic and most important research to promote theories from the experimental results [3,12] and develop life prediction models of concrete structures [13][14][15][16]. e diffusion caused by the chemical potential gradient [2] and the convection caused by the collective movement of groups or aggregates of molecules within fluids [17] are two main mechanisms of chloride transport in general conditions.…”

“…Note that the actual transport of chloride needs to take into account several different mechanisms and the coupling between them; it is unsuitable to describe its transport character as the diffusion coefficient. e actual transport of chloride is normally defined as zC/zt � D app ∇ 2 C, where D app is the apparent diffusion coefficient generally obtained by the curve fitting of free chloride concentration with Fick's second law [12,[33][34][35]. Also, a series of models based on this basic law have been developed to take into account the multi-ionic effect [36], temperature [37,38], stress [39][40][41], electrical field [42], curing age [14,43,44], etc.…”