Initiation and inhibition of pitting corrosion on reinforcing steel under natural corrosion conditions

Initiation and inhibition of pitting corrosion on reinforcing steel in saturated, naturally aerated Ca(OH)₂ solutions, under natural corrosion conditions, are followed through measurements of corrosion current, electrochemical impedance spectroscopy and SEM investigation. Induction period for pit initiation and limiting corrosion current for pit propagation are found to depend on aggressive salt anion and cation-types, as well as, concentration. Ammonium chlorides and sulfates are more corrosive than the corresponding sodium salts. Benzotriazole and two of its derivatives are found to be good inhibitors for pitting corrosion of reinforcing steel. Adsorption of these compounds follows a Langmuir adsorption isotherm. The thermodynamic functions ΔE^∗, ΔH^∗ and ΔS^∗ for pitting corrosion processes in the absence and presence of inhibitor are calculated and discussed. - Highlights: • Cl⁻ and SO₄ ^2- induce pitting corrosion on passive reinforcing steel. • Initiation and propagation of pitting depend on cation and anion types. • Inhibition is based on adsorption according to Langmuir isotherm.