Carbon steel B450C and low-chromium stainless steel SS430 were exposed for 30 days to supersulfated “SS1” cement extract solution, considered as a “green” alternative for partial replacement of the Portland cement clinker. The initial pH of 12.38 dropped since the first day to 7.84, accompanied by a displacement to more negative values of the free corrosion potential (OCP) of the carbon steel up to ≈−480.74 mV, giving the formation of γ-FeOOH, α-FeOOH and Fe₂O₃, as suggested by XRD and XPS analysis. In the meantime, the OCP of the SS430 tended towards more positive values (+182.50 mV), although at lower pH, and XPS analysis revealed the presence of Cr(OH)₃ and FeO as corrosion products, as well the crystals of CaCO₃, NaCl and KCl. On both surfaces, a localized corrosion attack was observed in the vicinity of local cathodes (Cu, Mn-carbides, Cr-nitrides, among others), influenced by the presence of Cl⁻ ions in the “SS1” extract solution, originating from the pumice. Two equivalent circuits were proposed for the quantitative analysis of EIS Nyquist and Bode diagrams, whose data were correlated with the OCP values and pH change in time of the “SS1” extract solution. The thickness of the corrosion layer formed on the SS430 surface was ≈0.8 nm, while that on the B450C layer was ≈0.3 nm.

Stainless steel SS430 and carbon steel B450C were exposed for 30 days to the aqueous extract of sodium silicate-modified limestone-Portland cement as an alternative for the partial replacement of the Portland cement clinker. The initial pH of 12.60 was lowered and maintained at an average of 9.60, associated with air CO₂ dissolution and acidification. As a result, the carbon steel lost its passive state, and the corrosion potential (OCP) reached a negative value of up to 296 mV, forming the corrosion layer of FeO, and FeOOH. In the meaning time, on the stainless steel SS430 surface, a passive layer of Cr₂O₃ grew in the presence of FeO, Fe₂O₃ and Cr(OH)₃ corrosion products; thus, the OCP shifted to more positive values of +150 mV. It is suggested that a self-repassivation process took place on the SS430 surface due to the accumulation of alkaline sulfates on the interface. Because of the chloride attack, SS430 presented isolated pits, while on B450C, their area was extended. The quantitative analysis of EIS Nyquist and Bode diagrams revealed that the Rp of the corrosion process for SS430 was 2500 kΩcm², ≈32 times lower in magnitude than on B450C, for which the passive layer tended to disappear, while that on SS430 was ≈0.82 nm.

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.

The change in the corrosion activities of SS304 and the carbon steel A36 were studied during their exposure for 30 days to hybrid pumice-Portland cement extract (CE), to simulate the concrete–pore environment. The ionic composition and the initial pH (12.99) of the CE were influenced by the reduction of Portland cement (PC) content, volcanic pumice oxides and alkaline activators. Because of the air ${\mathrm{CO}}_{2 }$ dissolution, the pH decreased and maintained a constant value ≈ 9.10 (established dynamic ionic equilibrium). The CE promoted the passivation of both steels and their free corrosion potential (OCP) reached positive values. On the surfaces, Fe and Cr oxides were formed, according to the nature of the steel. Over the time of exposure, the presence of chloride ions in the pumice caused a localized pitting attack, and for carbon steel, this fact may indicate an intermediate risk of corrosion. The chloride effect was retarded by the accumulation of ${{\mathrm{SO}}_4}^{2-}$ ions at the steel surfaces. Based on electrochemical impedance (EIS), the polarization resistance (Rp) and the thickness of the passive layers were calculated. Their values were compared with those previously reported for the steels exposed to CEs of Portland and supersulfated cements, and the hybrid cement was considered as a PC “green” alternative.

The effect of chlorides on the corrosion activities of SS304 and carbon steel A36 was investigated during immersion in a hybrid pumice–Portland cement extract solution, containing high concentration of chlorides (5 g ${\mathrm{L}}^{-1}$ NaCl), in order to simulate the concrete–pore marine environment. The hybrid pumice–Portland cement (HB1) has been considered an alternative “green” cement system. The initial pH of the extract (12.99) decreased to 9.5 after 14 days, inducing a severe corrosion risk for A36, as suggested by the very negative corrosion potential (OCP ≈ −363 mV). Meanwhile, the SS304 tended to passivate and its OCP shifted to positive values (≈+72 mV). Consequently, the surface of the A36 presented a corrosion layer mainly of $\mathrm{FeOOH}$, while that of the SS304 was composed of ${\mathrm{Cr}}_2{\mathrm{O}}_3$, ${\mathrm{Fe}}_3{\mathrm{O}}_4$ and $\mathrm{NiO}$, according to the SEM-EDS and XPS analysis. An extended area of an almost uniform corrosion attack was observed on the A36 surface, due to the less protective Fe-corrosion products, while the SS304 surface presented some small pits of ≈1 µm. Based on electrochemical impedance measurements, the polarization resistance (Rp) and thickness of the passive layer were calculated. The Rp of the SS304 surface increased by two orders of magnitude up to ≈11,080 $\mathrm{k}\mathsf{\Omega } {\mathrm{cm}}^2$, and the thickness of the layer reached ≈1.5 nm after 30 days of immersion. The Rp of carbon steel was ≈2.5 $\mathrm{k}\mathsf{\Omega } {\mathrm{cm}}^2$ due to the less protective properties of its corrosion products.