Long term performance of corrosion inhibitors in concrete

Corrosion of rebars is one of the most important phenomena affecting durability of reinforced concrete structures. Corrosion inhibitors may be used both as a preventative technique, as well as a repair system. The performance of commercial inhibitors as well as the investigation on new organic and inorganic compounds have been studied in our research group since 1998. Nitrite-based commercial inhibitors confirmed the performances reported in literature: if properly dosed they delay the initiation of chlorides induced corrosion by increasing critical chloride threshold. Organic commercial inhibitors are based on mixture of amines, alkanol-amines and carboxylates. Admixed products are able to delay chloride-induced corrosion, a small increase in the critical chloride threshold was detected. Among the organic substances, the ones containing carboxylic group showed the best performance in solution. In concrete, only one amine and one amino acid showed good performance, increasing the critical chlorides threshold with respect to the reference condition. Recently, nitrate-based inhibitors have been proposed. Results showed that nitrates are able to delay concrete carbonation but they have no effect on corrosion rate.