Electrochemical study on inhibitors of rebar corrosion in carbonated concrete

Electrochemical Impedance Spectroscopy (EIS) was used to evaluate the inhibitive action of some organic compounds towards the corrosion of a carbon steel, both in a solution simulating the pore chemistry of carbonated concrete and in carbonated concrete. The synthetic solution (SS) has been made by bubbling pure CO2 in a saturated Ca(OH)2 solution till obtaining pH 7 and then filtering it. Concrete carbonation has been obtained by maintaining the concrete specimens in CO2 atmosphere for 80 days, at 68% RH and room temperature. In SS, benzoate, its amino-derivatives and dicarboxylates were able to form a long-lasting passive layer on the steel surface. Their efficiency improved with time. In carbonated concrete the additives inducing a decrease in the concrete compressive strength were discarded. Some compounds were monitored for up to 400 days, but only two (the sodium salts of benzoic acid and, particularly, 2-amino benzoic acid) exhibited some inhibitive effect towards the rebar corrosion process.