科研之友
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摘要
Profiles of samples infiltrated by chloride ions are analyzed in this study. The samples were made of simple concrete, cylindrical shape with water/cement (w/c) ratios of 0.6 and 0.46, without chloride, and the 3.5% of its weight of chloride in the mixing water for both w/c ratios. Systematic monitoring of electrochemical parameters on samples with steel rod in the center at the same proportions was done in parallel. The concrete samples were exposed under three media: natural atmosphere, total immersion and to alternating wetting-drying cycles in natural sea water. Profiles of chloride concentration after an exposure of 90 to 365 days were obtained and processed assuming a diffusion mechanism in a finite porous medium, according to the equation of Fick%26apos;s second law. The time considered to reach the critical chloride threshold (0.4% by weight of cement) in rebar-concrete interface was calculated by using a lineal approximation for the diffusion coefficient. Chloride concentrations were also calculated at the time that electrochemical measurements reported the onset of corrosion. On the other hand, the electrochemical impedance spectroscopy diagrams show the depassivation of rebar at exposure times that do not correspond to a critical threshold of 0.4% by weight of cement. Electrochemical techniques suggests that depassivation of embedded steel rebar in concrete occurs at different thresholds to 0.4% by weight of cement; therefore, the critical time is also modified. It is clear that the elaboration and exposure conditions are determining in the onset of the corrosion process of steel rebar.
- 出版日期2012-1
