Corrosion inhibitors for application in carbonated mortars

Impedance measurements have been used to evaluate the inhibitive action of some organic sodium salts (i.e. sodium salts of benzoic acid derivatives or dicarboxylic acids) towards the corrosion of a carbon steel, either in a solution simulating the pore chemistry of carbonated mortar and concrete. The synthetic solution has been made by bubbling pure CO2 in a saturated Ca(OH)2 solution till obtaining pH 7 and then filtering it. Efficient additives were able to form and maintain on the steel surface a passive layer also at the low pH value of carbonated mortar. In synthetic solution, their efficiency improved with time, because the thickness of the protective layer augmented and its defectiveness decreased during the immersion (20 days). In carbonated concrete (tests lasting more than 20 months), additives decreasing the concrete compressive strength were discarded. Some additives maintained their inhibiting action for many months. The best results were obtained from BEN and AMB