Developing the inhibition mechanism for amide-based amino acids in carbonated concrete environment and assessing the migration ability in concrete

Abstract

The corrosion inhibition mechanism of amide-based amino acids, Asparagine (Asn) and Glutamine (Gln) for steel in concrete pore solution simulating carbonated environment was explored by the means of gravimetric, electrochemical and surface characterization techniques. Thereafter, percolation ability of Asn and Gln was assessed through OPC and PPC concretes by UV–visible spectroscopy technique for their application as migratory corrosion inhibitors in concrete. The results revealed that Asn as well as Gln can be efficiently used in carbonated corrosive environment for steel inhibition. The protection ability of Gln was however, higher than Asn. Gln exhibited 50% lower corrosion current density values than Asn. Also, the charge transfer resistance of Gln inhibited specimens was 3 times higher than Asn inhibited specimens. The layer developed on steel with Gln as corrosion inhibitor was thermodynamically more stable than Asn as equilibrium constant of adsorption (kads) was 2.11 times higher for Gln. Optical and SEM images revealed the formation of a thin layer in the case of Asn while a thick layer was seen to form on Gln inhibited specimens. Surface layer characterization by FTIR and XPS evinced the formation of Asn-Fecomplex and Gln-Fecomplex on steel surface. Both the compounds bound the Fe ions by chelation through O atom from amide and carboxylate functional groups. Higher efficiency of Gln was attributed to development of more adherent protective film due to its longer carbon chain length than Asn. Gln’s chelate ring experienced lower steric hindrance than Asn’s ring. Asn and Gln percolated through concrete and reached upto a depth of 25mm within 15 days of application. Conclusively, it can be said that Asn and Gln can be employed as corrosion inhibitors for concrete subjected to carbonation-induced corrosion.