Abstract
The carbon steel B450C and low chromium SS 430 ferritic samples were exposed for 30 days to chloride-containing (5 g L−1 NaCL) cement extract solution. The initial pH ≈ 13.88 decreased to pH ≈ 9.6, associated mainly with the consumption of OH− ions and the formation of γ-FeOOH, α-FeOOH, Fe3O4 and Cr(OH)3, as suggested by XRD and XPS analysis, in the presence of CaCO3 and NaCl crystals. The deep corrosion damages on B450C were observed around particles of Cu and S as local cathodes, while the first pitting events on the SS 430 surface appeared after 30 days of exposure. The change in the activity of each type of steel was provided by the potentiodynamic polarization curves (PDP). Two equivalent electrical circuits (EC) were proposed for quantitative analysis of EIS (Nyquist and Bode diagrams). The calculated polarization resistance (Rp), as an indicator of the stability of passive films, revealed that SS 430 presented relatively constant values, being two-three orders of magnitude higher than those of the carbon steel B450C. The calculated thickness (d) of the SS 430 passive layers was ≈0.5 nm and, in contrast, that of the B450C passive layers tends to disappear after 30 days.
Highlights
Carbon and stainless steel are being used to reinforce concrete and because of the steelconcrete union may improve the strength of concrete against a variety of mechanical forces
The deep corrosion damages on B450C were observed around particles of Cu and S as local cathodes, while the first pitting events on the SS 430 surface appeared after 30 days of exposure
The corrosion stability of these steels is acquired during the cement hydration process, when the Portland cement provides a high alkaline pH ≈ 13 (because of the formation of calcium hydroxide Ca(OH)2, portlandite) during the curing time, and the passive layer is formed on the steel surface [1,2,3]
Summary
Carbon and stainless steel are being used to reinforce concrete and because of the steelconcrete union may improve the strength of concrete against a variety of mechanical forces. The passive layers on AISI 316, grown during the exposure to saturated Ca(OH) and cement extract (CE) solutions, revealed that each model solution simulates the concrete-pore environment in a different way [29,30]; a more resistant layer, homogeneous in thickness and porosity, was formed in CE solution, which is due to its ionic, distinctive composition compared to that of saturated Ca(OH). The passive layers on AISI 316, grown during the exposure to saturated Ca(OH) and cement extract (CE) solutions, revealed that each model solution simulates the concrete-pore environment in a different way [29,30]; a more resistant layer, homogeneous in thickness and porosity, was formed in CE solution, which is due to its ionic, distinctive composition compared to that of saturated Ca(OH)2 This fact was confirmed by AFM (atomic force microscopy) and XPS, as well by cyclic voltammetry. No other research on this topic has been previously undertaken
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