Impedance study on calcium nitrite as a penetrating corrosion inhibitor for steel in concrete

Compressive strength and corrosion evaluation of concretes containing pozzolana and perlite immersed in aggressive environments

Corrosion is one of the major deterioration problems in the reinforced concrete industry. Approximately, more than 18 billion dollars per year is incurred on the repair and rehabilitation of corroded structures throughout the world. The occurrence of corrosion is because of chloride particles present in the atmosphere and carbonation process in concrete. Reinforcement corrosion is an electrochemical process that defines the concentrations between variations of dissolved ions in the concrete. This paper focuses on the corrosion inhibitors which are used as migration corrosion inhibitors (applied on the surface) of the concrete specimen and admixed into the concretes. An in-depth study on the mechanism of corrosion and the effect of migrated, cathodic and anodic on reinforced concrete has been performed. A critical review of the causes of the corrosion as well as preventions by using organic, inorganic and natural inhibitors is carried out.

Corrosion Inhibitors Behaviour on Reinforced Concrete—A Review

The effect of calcium nitrite (Ca(NO2)2) was assessed by electrochemical means such as open circuit potential (OCP), electrochemical impedance spectroscopy (EIS), and potentiodynamic studies in saturated Ca(OH)2 solution contaminated with 0.99 and 7.91 g/L NaCl. The preliminary results of OCP showed that the potential is shifted towards positive (noble) side as content of inhibitor increased. The EIS results indicate that Ca(NO2)2 works effectively in reduction and initiation of corrosion of steel rebar in NaCl contaminated Ca(OH)2 solution. Potentiodynamic studies revealed the pitting tendency of steel rebar exposed in 0.99 g/L NaCl at [Cl−/ ] = 1.2 attributed to low conductivity of passive film which causes interference for Cl− ions attack during anodic polarization. The 85.75% efficiency is found in 0.99 g/L at [Cl−/ ] = 1.2. The Ca(NO2)2 inhibitor transformed the unstable iron oxides/hydroxides into stable and protective oxides/hydroxides due to its strong oxidizing nature. Therefore, this inhibitor is sufficiently and significantly reducing the corrosion of steel rebar at even its low concentration with 0.99 and 7.91 g/L NaCl solution.

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An Electrochemical Study to Evaluate the Effect of Calcium Nitrite Inhibitor to Mitigate the Corrosion of Reinforcement in Sodium Chloride Contaminated Ca(OH)2 Solution

The occurrence of quick weakening of reinforced concrete due to chloride (Cl−) and sulfate (SO42-) ions is a serious concern now a day. The existence of SO42− ions and allied cation types in chloride solutions altered the chloride-generated corrosion behavior of reinforced concrete and it is still unclear what effect SO42- ions and allied cations types have on the chloride-generated corrosion behavior of reinforced concrete. For this purpose, the study has been conducted to assess the corrosion of surrounded rebar in concrete exposed to Cl− and combined Cl− and SO42- solutions allied with sodium (Na+) and magnesium (Mg2+) cation with low and higher concentrations of Cl− and SO42- ions till 27 months of exposure. The results reveal that the existence of SO42- ions in corrosive solutions retard the ingress of Cl− ions, and result in less rebar surface chloride (Crs) content and this effect is governing in the case of SO42- ions allied with Na + cation as compared to Mg2+ cation. The existence of SO42- ions allied with Na+ cation enhanced the corrosion activity. The ordinary Portland cement concrete (OPC–C), ordinary Portland cement with 20% fly ash concrete (O20FA-C) and Portland pozzolana cement concrete (PPC–C) exhibited an average of 1.86, 1.87, and 1.34 times respectively higher Icorr when exposed to composite solutions containing sulfate allied with Na + cation as compared to Mg2+ cation. The corrosion current density increased with an increase in the concentration of sodium sulfate in composite solutions however the opposite variation is observed for magnesium sulfate. The PPC-C showed excellent performance against corrosion of surrounded rebar as compared to O20FA-C followed by the OPC-C. The developed empirical model between Crs and Icorr from OPC-C and PPC-C predicted well Icorr values for O20FA-C. 

Long term effect of chloride and sulfates concentration, and cation allied with sulfates on corrosion performance of steel-reinforced in concrete

The influence of calcium nitrite corrosion inhibitor on the durability of Portland cement mortars against sulphate solutions was investigated experimentally in the present research. For this reason, mortar specimens were produced using CEM I 42.5N cement and were immersed in different sulphate and sulphate‐chloride contaminated solutions. Sulphate resistance was evaluated according to the procedure described in ASTM C1012. The properties measured were the specimens' expansion, development of compressive strength, changes in corrosion potential and corrosion current density measurements of steel‐containing specimens.

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P. Pantazopoulou

Papers

Influence of calcium nitrite inhibitor on the durability of mortars under contaminated chloride and sulphate environments