Laboratory Tests for Evaluation of Corrosion Inhibitor Efficiency

Corrosion of steel reinforcements in concrete structures is the most important cause of premature failure. To improve service life of concrete structures, corrosion inhibitors are often proposed and used to prevent chloride induced corrosion and carbonation corrosion. This paper deals with a laboratory investigation both in concrete and in a synthetic pore solution on the effectiveness of mixed-in commercial corrosion inhibitors to hinder corrosion initiation and propagation of reinforcements in concrete structures. The results of a laboratory research aimed at studying the effect of inhibitors added to the concrete mixture are discussed. Three organic commercial corrosion inhibitors and, by comparison, nitrite based inhibitors were added to fresh concrete in concentration suggested by the manufacturers. Experimental tests were carried out on reinforced concrete specimens with carbon steel reinforcement in chloride contaminated concrete (both adding chlorides directly in the mixture and penetrating the hardened concrete by means of ponding cycles). In order to study the inhibitors effect, the results, in terms of two electrochemical parameters, i.e. free corrosion potential and polarisation resistance, are compared with those obtained considering concrete specimens without inhibitors. For comparison purposes, results on some pure organic substances are reported, confirming data obtained on the commercial products. Some positive effects are achieved when both commercial products and pure substances were used at dosage rates higher than that recommended.