Simultaneous Transport of Chloride and Calcium Ions in Hydrated Cement Systems

Abstract

This paper presents a new method for numerically calculating the concentration profiles of both solid calcium and total chloride ions (Cl -) in concrete in contact with 3% (0.5 mol/l) sodium chloride (NaCl) solution. Since the diffusion of ions present in the pore solution is a primary controlling factor, the application of mutual diffusion coefficients of corresponding ions that are influenced by the concentration of other coexisting ions is proposed. The method of calculation is based on the generalized form of Fick's First Law suggested by Onsager, which is composed of the Onsager phenomenological coefficient and the thermodynamic force between ions, which occurs according to the gradient of electrochemical potential in a multicomponent concentrated solution for the pore solution. In addition, the chemical equilibrium for Ca(OH) 2 dissolution and C-S-H decalcification are also modeled and coupled with diffusion. Increased porosity due to dissolved Ca 2+ and a chloride binding isotherm are taken into consideration. The concentration profiles of solid calcium and the presence of Friedel's salt in mortar specimens are experimentally identified by the X-ray diffraction method (XRD) and the thermal analysis (TG/DTA) as well as the total chloride profile using an acid extraction method after three years of exposure to 0.5 mol/l NaCl solution. This experimental result verifies the calculation result.

Determination of the transport properties of a blended concrete from its electrical properties measured during a migration test

“…In the references (Claisse and Beresford, 1997;Khitab et al, 2005;Krabbenhoft and Krabbenhoft, 2008;Lorente et al, 2007;Narsilio et al, 2007;Sugiyama et al, 2003;Truc et al, 2000) the Nernst-Planck equation has been used as the way to find the flux of ions and the transport properties of chlorides in concrete. Some researchers have used it coupled either to the conservation equation or accounting for the distribution and evolution of the electrical field.…”

Quantification of tortuosity in hardened cement pastes using synchrotron-based X-ray computed microtomography

“…The pore structure of cement-based materials is of primary importance for understanding and modeling the transport phenomena that influences the durability performance of these materials [1][2]. It is well understood that a typical characteristic of any material transport in such complex porous media is that the actual path followed by the transported material is very complicated or tortuous even in the microscopic scale.…”

Calculation of reinforced concrete corrosion initiation probabilities using the Rosenblueth method

“…The retardation of the chloride ion front with respect to the convection induced water movement is taken into account by including the retardation coefficient R Cl (Lunk et al, 1998). Hardening cement paste and the carbonation rate facilitates the binding of a certain amount of chloride ions (Lindvall, 2001;Ritthichauy et al, 2002;Sugiyama et al, 2003;Tang, 1996;Tang and Nilsson, 1996). Thus, chloride ions bound in the cement paste C B are distinguished from the free chloride ions moving through the concrete C F .…”