ABSTRACT

Corrosion inhibitors are used to prevent or delay corrosion in reinforced concrete structures. Available commercial products are based on nitrite or organic mixtures based on amines, alkanolamines, fatty acids and carboxylic substances. During the last 15 years, an intense experimental research has been carried out focused at identifying new organic substances or binary mixtures that might have inhibiting effectiveness on chloride-induced corrosion. The paper describes results of potentiodynamic and potentiostatic electrochemical tests carried out in alkaline solution, in the presence of chlorides, on binary mixtures with nitrite, dimethylethanolamine (DMEA), glutamine and benzoate. Some of the mixtures exhibited a marked synergistic effect in the potentiodynamic polarisation tests, with a clear increase in pitting potential. A certain effect on chloride threshold was also observed in potentiostatic polarisation. The best mixtures are able to increase the critical chloride content, then accordingly they can delay corrosion initiation on real reinforced concrete structures.

INTRODUCTION

Durability of reinforced concrete structures depends on carbon steel rebars corrosion. The two main causes of corrosion are concrete carbonation, due to the ingress of CO2, which reduces concrete pore solution pH to 8, and ingress of chlorides.1 In the latter case, corrosion occurs if at the rebar level, chloride concentration exceeds a threshold value, which is influenced by the chemical composition of the rebar, concrete pH and rebar electrochemical potential, as clearly described by the ”Pedeferri Diagram” for cathodic protection and prevention.2-3 Corrosion prevention is achieved during the design phase by making a high quality concrete mixture proportion, with a low water/cement ratio, by performing a correct curing and casting, and by using an appropriate cover. The European standards set out the threshold values of such parameters in relation to environmental aggressiveness.4-5 With regard to structures exposed to very corrosive environments, or for structures with a design life over 50 years, it would be appropriate to use additional protective methods: blended cements, corrosion- resistant reinforcements, inhibitors, concrete coatings and cathodic protection.

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