The copper corrosion was studied for 30 days in two alkaline electrolytes: saturated Ca(OH)₂ and cement extract, employed to simulate concrete-pore environments. Electrochemical Impedance Spectroscopy (EIS) and Cyclic Voltammetry were carried out at the open circuit potential (OCP), and potentiodynamic polarization (PDP) curves were performed for comparative purposes. Electrochemical current fluctuations, considered as electrochemical noise (EN), were employed as non-destructive methods. The tests revealed that sat. Ca(OH)₂ is the less aggressive to the Cu surface, mainly because of the lower in one order pH. In consequence, the OCP values of Cu were more positive, the polarization resistance values were higher by one order of magnitude, and the anodic currents of Cu were lower than those in the cement extract. The analyzed EN indicated that the initial corrosion attacks on the Cu surface are quasi-uniform, resulting from the stationary persistent corrosion process occurring in both model solutions. XPS analysis and X-ray diffraction (XRD) patterns revealed that in sat. Ca(OH)₂, a Cu₂O/CuO corrosion layer was formed, which effectively protects the metallic Cu-surface. We present evidence for the sequential oxidation of Cu to the (+1) and (+2) species, its impact on the corrosion layer, and also its protective properties.

This study compares corrosion activities of carbon steel B450C and SS 430 (Mn in low content) exposed for 30 days in cement extract solution. Iron oxide and hydroxide were formed as corrosion products, in addition to CaCO₃, in the presence of Cr₂O₃ on SS 430. Because of the decrease in pH, B450C lost the passive state when OCP shifted to negative values, while SS 430 showed positive OCP values, maintaining its passive state. The SEM images confirmed that the corrosion attack on the surface was less aggressive for SS 430. The Nyquist plots of EIS initially showed capacitive behavior and later changed to semi-linear diffusion impedance, which SS 430 maintained firmly. The phase angle Bode diagrams confirmed these changes. Two equivalent circuits were applied. The calculated values of R_p for SS 430 increased over time (protective passive layer mainly of Cr₂O₃ oxide), while for carbon steel, R_p reached maximum value after 168 h and then decreased, maintaining minimum values approximately five orders lower than those of the stainless steel.

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 (R_p), 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.

In this study, waste materials such as recycled glass employed to synthesize mesoporous silica nanoparticles (NPs) and/or sugarcane bagasse fiber (SBF) were used to reinforce concrete samples, and their properties were evaluated. The cement additions used in this study were 0.8% NPs (0.8N), 1% SBF (1F), or a combination of the two (0.8N-1F). The addition of 0.8N-1F slightly improved the mechanical performance of concrete and offered the greatest decrease in carbonation, likely because these materials had the fewest permeable voids. The thermodynamic properties at the concrete‒steel interface tended to be reduced when the components were added, and there were marked differences in the corrosion potential and corrosion kinetics in concrete with the addition of SBF and NPs. Each material enhanced the performance properties of concrete, but the combination of both materials had a positive synergistic effect on all the studied properties.