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Title: Inhibition Mechanism of Amino Acids Against Carbonation-Induced Corrosion in Reinforced Concrete
Authors: Purnima
Supervisor: Goyal, Shweta
Luxami, Vijay
Keywords: Carbonation;corrosion Inhibitors;Reinforced Concrete;EIS;Inhibition Mechanism
Issue Date: 4-Nov-2023
Abstract: Deterioration of reinforced concrete (RC) structures, due to exposure of steel reinforcing bar (rebar) to aggressive environment, is a major cause of concern in terms of durability and overall structural integrity. The two main aggressive environments for rebar corrosion are the ingress of chloride ions and carbonation. While the former cause pitting corrosion and localized breakdown of passive film, the latter results in a uniform corrosion of the rebar surface. Protection of RC against corrosion can be done by employing various techniques. Amongst all, application of corrosion inhibitors is found to be one of the most effective in terms of cost, application, environment and ease of handling. Corrosion inhibitors are chemicals that can effectively reduce the corrosion rate even when used in small quantities. The inhibition characteristics depend on their molecular structure, polarity and presence of heteroatoms. On the basis of their mode of application, they are generally categorized as admixed inhibitor or surface applied inhibitors. The major advantage of using surface applied inhibitor is that, it does not cause any negative affect on the concrete properties. Another advantage of surface applied inhibitors is that they can be used as repair strategy (i.e., application after the steel has reached active corrosion state). Present study explores the potential of these surface applied inhibitor inhibitors to act as repair measure. Eight different amino acids, that are 100 % environmentally safe, economically viable, namely, Serine (Ser), Cysteine (Cys), Phenylalanine (Phe), Tryptophan (Trp), Aspartic Acid (Asp), Glutamic Acid (Glu), Asparagine (Asn) and Glutamine (Gln) were selected on the basis of the presence of heteroatoms in their molecular structure and their solubility in high pH simulated concrete pore solution. The effectiveness of the selected compounds to reduce the carbonation-induced corrosion rates was assessed by conducting tests on steel in simulated concrete pore solution as well as concrete. The study was divided into three levels; pore solution test, migration studies and eventual application on reinforced concrete (RC) surface. In Level 1, the corrosion inhibition efficiency and corrosion inhibition mechanism were determined by conducting electrochemical testing and surface analysis tests, respectively. In Level 2, the percolation ability of the amino acids and percolation of CO2 through concrete (in presence and absence of amino acids) was determined by conducting ultra-violet visible spectroscopic analysis and carbonation depth test, respectively. Finally, in Level 3, the efficient amino acids from Level 1 (that performed well during concrete simulated pore solution test) and Level 2 (that percolated well through concrete) were applied on RC specimens and their ability to re-passivate the corroding rebars was assessed. Accelerated carbonation tests on the specimens were carried out by placing them in carbonation chamber where CO2 concentration was 5 %, temperature was 30 °C and relative humidity was 60 – 70 %. The corrosion rate was determined at regular intervals and once, active corrosion of rebars was confirmed, amino acids were applied on the specimens and left in laboratory environment to ensure sufficient percolation for 15 days. The specimens were again kept in the carbonation chamber and corrosion rates were again monitored. The effectiveness of the repair system was also determined by applying the corrosion inhibitors on a carbonation-induced corroding site structure. An un-sheltered corroding RC slab situated at Civil Engineering Department, Thapar Institute of Engineering and Technology, Punjab, India was repaired. Results of the study conducted reveal that most of the amino acids when used as surface applied corrosion inhibitors are capable of reducing the corrosion rates under carbonation conditions in laboratory specimens as well as on-site.
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