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.

Abstract. The presented model of carbonated concrete realkalization is compiled on the basis of the multi-component medium theory equations. The process equations have been obtained from an analysis of the partial equations of mass, electric charge, momentum, energy, and entropy inequality. The experimental testing reported is related to a theoretical model which determines changes of ion concentrations in the pore solution of the cover, as a result of the realkalization. On the basis of the test results, the process equations have been simplified and formally transformed into the form of an equation for the OH -ions flow, coupled with the Na + ions transport. By solving the converse problem of this equation, the determinant OH -ions electro-diffusion coefficient is calculated and then, after taking the experimental test results into account, its numerical values, the range of stable solutions and the influence of the process non-stationariness are determined.

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During the extraction of chlorides from concrete there occur processes involving transfer of mass and electric charge via pore solution components. On the basis of the relations which exist between the concentrations of these components, the electric field intensity, the temperature, and the mechanical stress, thermomechanics equations of a multicomponent medium have been used for analytical description. On the basis of equations for the balance of mass, electric charge, momentum, energy and entropy inequality, equations of ion flows have been determined, which are justified in the general effect of the electric field action on the concrete covering. The occurrence of processes which are recognised as dominant ones during the chloride extraction has allowed us to significantly simplify the equations and reduce them to formulas permitting a practical use. By approximating the electrochemical potentials of the leading ions via the linear function of concentration and electric field potential, a flow equation has been determined which has a shape similar to the classical diffusion equation. In order to define the electrodiffusion coefficient occurring in this equation an inverse problem has been formulated and then numerical values of this coefficient have been evaluated using the results of experimental tests.

One of the products of concrete sulphate corrosion, besides gypsum and ettringite, is thaumasite. The thaumasite is a very dangerous, non binding crystalline phase, which is forming at the expense of C-S-H phase. There was a conviction that the conditions required for the formation of thaumasite in concrete are: source of calcium silicate, sulfate ions, carbonate ions and a very wet, cold (below 15°C) environment. The corrosion of concrete caused by the external source of sulphate ions during which thaumasite is formed was called thaumasite sulphate attack (shortly TSA). While the TSA is recognized, the thaumasite non-sulphate attack (T n S A) must be highlighted, because is also possible. The purpose of this work is to show that thaumasite, or solid solutions of Ett-Th (ettringite with thaumasite) are able to form in hardened cement paste without external source of sulphate ions, at ambient temperature and pressure (25±2°C (298.15 K) and 102±1 kPa). The experiment appeared on thaumasite formation in corroded specimen made of CEM I (Portland cement) and of CEM III (slag cement) after 4 days of immersion in saturated water solution of NH 4 Cl.