The use of galvanized bars is one of the solutions recommended to avoid corrosion of reinforced concrete structures. The reaction between the galvanized coating and the wet concrete produces zinc hydroxide, and subsequently calcium hydroxyzincate, accompanied often by the evolution of hydrogen. The tests carried in this study show, 19 h after casting, a modification of the pore size distribution and an increase in porosity of the interfacial transition zone (ITZ) between the cement paste and the galvanized steel, in comparison with the ITZ of cement paste–steel contact surface. However, the characteristics of the ITZ change over time: at the test period of 28 days, the porous structure of the ITZ around galvanized and ordinary steel is not significantly different. This difference decrease is due to the formation of calcium hydroxyzincate. Calcium hydroxyzincate favors the hydration at the ITZ. This compound, as well as cement hydration products can fill the porous structure in this zone.