The moisture content in concrete structures has an important influence in their behavior and performance. Several vali-dated numerical approaches adopt the governing equation for relative humidity fields proposed in Model Code 1990/2010. Nevertheless there is no integrative study which addresses the choice of parameters for the simulation of the humidity diffusion phenomenon, particularly in concern to the range of parameters forwarded by Model Code 1990/2010. A software based on a Finite Difference Method Algorithm (1D and axisymmetric cases) is used to perform sensitivity analyses on the main parameters in a normal strength concrete. Then, based on the conclusions of the sensi-tivity analyses, experimental results from nine different concrete compositions are analyzed. The software is used to identify the main material parameters that better fit the experimental data. In general, the model was able to satisfactory fit the experimental results and new correlations were proposed, particularly focusing on the boundary transfer coeffi-cient.

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An experimental investigation was carried out on chloride induced corrosion of steel bars in concrete under marine en-vironment with the variation of micro-structure of steel-concrete interface. To create the variation of micro-structure of steel-concrete interface, steel bars coated with cement paste of different W/Cs and cement types were used. For investi-gation, cylindrical concrete specimens were made with steel bars (with and without cement paste coating). W/C ratios of cement paste coat were 0.3, 0.5, 0.7 and 1.0. The specimens were exposed to an accelerated seawater exposure con-trolled with automatic wetting and drying. The specimens were tested till 45 cycles in the exposure. Test items include compressive strength of concrete, chloride ingress into concrete, electrochemical evaluation of corrosion, microscopic investigations of steel-concrete interface by optical microscope, scanning electron microscope (SEM), and linear trav-erse. It is revealed that the initiation of corrosion is significantly influenced by the nature of micro-structure of the steel-concrete interface, such as size of voids at the steel-concrete interface.

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