The results presented in this paper concern the effectiveness of organic commercial migrating inhibitors on steel reinforcements corrosion. Four series of concrete specimens were cast to verify inhibitor ability to delay, reduce or stop corrosion, both on chlorides contaminated concrete (adding chlorides in the mixture, or penetrating the concrete) and in carbonated concrete. Two organic migrating inhibitors (amine and alkanolamines based) were applied on the surface of concrete following the manufacturers' recommendations. Free corrosion potential and corrosion rate of steel rebar were periodically monitored for five years. Results show that migrating inhibitors are not effective in reducing corrosion rate, both in chlorides and carbonation induced corrosion, while a certain effect was observed on the delay of corrosion initiation in the case of chlorides penetration.
Corrosion inhibitors are chemical compounds that delay initiation and/or propagation of corrosion of reinforcement in concrete structures. They may be used both as preventive measures for new concrete structures, directly added to the fresh concrete, as well as a repair techniques for existing structures. Obviously, the prevention of corrosion is primarily achieved in the design phase by using high quality concrete, adequate concrete cover and suitable casting and curing. Additional prevention methods are mandatory when severe environmental conditions occur or on structures requiring very long service life1. Among available methods, corrosion inhibitors can offer a simple and cost effective prevention technique to delay chloride induced corrosion and as a remedial job for carbonation 2
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While admixed corrosion inhibitors (ACIs), first inorganic (nitrites), are commercially available since 70's 2-5, migrating corrosion inhibitors (MCIs) for concrete structures were studied in the last 20 years.Proposed MCIs are both inorganic compounds (sodium-mono-fluoro-phosphate) 6-8 and organic aqueous mixtures based on a volatile amine constituents and non volatile ones, mainly a carboxylate compound or a P-containing compound 2, 9-12. They claim to inhibit corrosion by penetrating concrete and adsorbing on the metal surface. The proper mechanism by which these inhibitors provide corrosion protection hasbeen a point of discussion. Some researchers 13 suggest that they are able to form an adsorption layer on the steel surface, hindering steel dissolution. It has been suggested that organic inhibitors influence the kinetics of the anodic and cathodic reactions 14-15. The use of inhibitors may also affect the chloride threshold value. Some authors report that corrosion inhibitors help to decrease the free chloride content in concrete and/or decrease the rate of diffusion 11-12.
The effectiveness of MCIs is related to their capability to penetrate through the capillary structure of concrete to reach the rebars 2, 16-19. Inhibitors migration in concrete follows different mechanisms: capillary suction, diffusion or vapour phase transport. The effectiveness of different mechanisms depends on concrete cover, porosity, water content, solubility and volatility of the migrating inhibitor. Low concrete cover, or high W/C ratio, may favour penetration of inhibitors, but also of aggressive agents (carbonation and/or chlorides).
The corrosion behaviour of steel in the presence of MCI has been widely studied 2,9,15-16,20-27, however the published results are sometimes contradictory and there is an open discussion both on the inhibitor penetration into concrete and on the effectiveness on corrosion reductio