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Steel embedded in concrete is normally in a passive state against corrosion due to a thin iron oxide layer that forms on the steel surface and remains stable in the high alkaline environment of the concrete. This protective film must be destroyed (depassivation) and this can be mainly done in two ways: by the attack of chlorides on the steel (seawater, de-icing salt, unwashed sea sand, admixtures etc.) or by carbonation. Corrosion inhibitors may be a good alternative to protection steel against corrosion due to its lower cost and easy application. Many researchers are inclined to use surface applied corrosion inhibitors and prefer to use the Cl-/inhibitor parameter as an indication of chloride inhibitor threshold level. The objective of this study was to fill the gap left by public research in developing methods of corrosion control of reinforcement in concrete by synthetic solutions to emulate concrete environment. Three inhibitors were distinguished as passivation inhibitors in real solution extract and synthetic. In this study the tests with calcium nitrite (CNI), sodium monoflurophosphate (MFP) and ethanolamine based inhibitors showed reductions in the overall rates of corrosion after the inhibitive treatments.

The study of the corrosion inhibition of armatures made of steel conceived for reinforced concrete by sodium phosphate is the aim object of our experimental tests. Gravimetric and electrochemical measurements were carried in three different Mediums contaminated by chlorides (3% NaCl) with addition of increasing concentrations of sodium phosphate. Inhibitory efficiency reached 80% at an optimal concentration of 7,5 × 10 -3 M, the results obtained using the gravimetric measurements are in good agreement with those obtained by electrochemical methods. However, the monitoring of the pH evolution after 24h shows in the three studied environments, that the pH decreases slightly at 24 hours from the initial pH at t 0 , due to the presence of corrosion products which change the state of the final solution. Also, scanning electron microscopy revealed the existence of layers of apatite on the metal surface previously treated with the sodium phosphate which confirms the formation of a protective film around the surface of the metal.

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