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The current literature on ionic diffusion through porous media teaches that the diffusion coefficient is a complicated function depending on concentration, concentration gradient, and electrical potential gradient. This paper documents how natural diffusion tests and migration tests (electrically enhanced transport) lead to the measurement of a unique diffusion coefficient for a given ionic species and a given material. Natural diffusion tests for chloride and a ceramic of TiO2 were implemented at two different concentration levels. The experiments were designed to emphasize the impact of the membrane potential in the pore solution on the chloride flux. By accounting for the membrane potential it is shown that the chloride diffusion coefficient is unique for a given material. An iterative method based on a numerical model solving the continuity equations and the current law is proposed to determine the diffusion coefficient. The approach is applied with success to published results on a cement-based material. Migration tests were also performed with chloride in a cementitious material, where the chloride transport is enhanced by an external electrical field. The experimental results reveal the competition between diffusion and electrical effects in the case of noncontaminated porous materials. By varying the electrical potential difference it is shown that the flux of chloride varies linearly with the electrical field, meaning that the chloride diffusion coefficient does not depend on the electrical field. The main conclusion is that there is only one chloride diffusion coefficient for a given porous material.

The paper presents results regarding the mechanical properties of concretes prepared with various amounts of recycled concrete aggregate (RCA). RCA was obtained by the crushing of concrete rubble resulted during the demolition of a block of flats. The concretes with RCA were prepared using three different mixing approaches: one stage mixing (1SM), two stages mixing (2SM) and two stages mixing with polyvinyl acetate addition (2SM PA). Two stages mixing method in the presence of polyvinyl acetate addition, leads to an improvement of the mechanical strengths (compressive and splitting tensile strength due to a better bonding between the binding matrix formed in the new concrete and the old mortar adhered at the surface of RCA grains.

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