Influence of two specific inhibitors on steel corrosion in a synthetic solution simulating a carbonated concrete with chlorides

The present research aims at studying two corrosion inhibitors, that is sodium 2-amino-benzoate (2AMB) and sodium glycero-phosphate (GPH), in a synthetic solution simulating the composition of the pore solution in a carbonated concrete, containing chlorides. Tests have been performed to verify if the simultaneous use of the two substances is compatible and if their addition can efficiently hinder the corrosion attack in the presence of both chlorides and carbonation. The synthetic solution has been prepared by bubbling carbon dioxide through a saturated (and filtered) solution of Ca(OH)2, containing 0.1M NaCl, in order to reach pH 7. Polarization curve recording and EIS technique have shown that, after an induction period of about 24h, the highest inhibiting efficiencies are obtained by mixtures of the two additives at the concentration of 0.05 M, which still produce high inhibiting efficiencies (87%) at the end of 120h immersions. At the end of this exposure period, also more diluted symmetric mixtures (0.025 M and 0.01 M) exhibit comparable efficiencies. The analysis of EIS spectra gives interesting information concerning the inhibiting mechanism of the studied mixture.