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Abstract: This paper proposes to compare several experimental ways of obtaining the chloride diffusion coefficient through saturated porous materials. The first method is based on the application of the Nernst–Einstein equation for which the conductivity of the saturated sample is measured by impedance spectroscopy for two kinds of materials: inert samples of TiO2, and concretes based on type I and type V cements. The second method is a migration test in which the flux of chloride measured upstream allows calculating the diffusion coefficient by means of the Nernst–Planck equation. In the third case, the diffusion coefficient is calculated by current measurements in an equivalent configuration as the second method. It is shown that the formation factor does not vary neither with the ionic strength of the saturation solution, nor with the change in the pore solution constituents when the material is without mineral additions. The CEM-V concrete exhibits a specific behavior with a strong influence of the addition of chloride in its pore solution on the formation factor. The diffusion coefficients calculated with the three methods are in good agreement provided the metrology of the experiments is carefully controlled. [Copyright &y& Elsevier]

Abstract: The healing of cracks plays an important role with regard to the air- and water-tightness of concrete structures and the durability of cement based materials in general. This paper aims at further characterization and better comprehension of the healing phenomenon induced by the precipitation of calcite in localized cracks. The experimental program consisted in generating a localized crack in a cement paste or concrete specimen and healing the crack created by percolation tests with carbonated water or gas (CO2-air mixture). For tests with liquid, results show that the healing process depends on physical parameters like crack width, pressure gradient and carbonate content in the percolating fluid. For tests with gas, the supply of the crack with Ca2+ ions to form calcite depends on the moisture transport mode on the crack edges, conditioned by the relative humidity of the percolating gas mixture. A simplified model of the leakage rate evolution is proposed. It provides indications concerning the effect of each test parameter on the healing process and allows the experimental results to be reproduced. Application of the model to other tests from the literature shows its limits and gives guidance for future investigations. [Copyright &y& Elsevier]

The conditions that lead to Transient Thermal Deformation (TTD), also called Thermal Transient Creep (TTC), of concrete subjected to various temperatures and compressive loads in sealed conditions are analysed and a model based on a two-scale porosity is proposed. In this model, water expands in the smaller pores and diffuses progressively to the capillary pores at the upper scale. It is then shown that the water overpressure in smaller pores and the duration of the diffusion process between the two scales of porosity control the TTD. It is also shown that creep or shrinkage before the temperature transition mitigates TTD. The aim is to provide a model able to predict the conditions for TTD to appear and the amplitude of the TTD under various thermo-mechanical conditions. The TTD model is implemented in an existing basic creep model, fitted and compared with different experimental results. [ABSTRACT FROM AUTHOR]