Evaluation of inhibition efficiency of generic compounds with additional heteroatom in simulated concrete pore solution and migration potential in concrete

Abstract

In the present study, the performance of two generic compounds, namely 2-Aminopyridine (AP) and 4-Aminobenzoic acid (ABA) at varying concentrations in carbonated pore solution contaminated by chlorides was investigated by using electrochemical measurement technique (potentiodynamic polarization curves) and surface analysis technique (optical microscope, SEM, EDX, XRD and FTIR). The migration ability of the two compounds in concrete was also investigated by using thin layer chromatography (TLC) and ultraviolet–visible spectroscopy (UV–Vis). The test results in simulated pore solution showed that both AP and ABA lowered the rate of corrosion irrespective of the tested concentration levels. Surface analysis data shows that corrosion product on specimen immersed in contaminated environment contains FeOOH, Fe2O3 and Fe3O4. From the electrochemical data, it was confirmed that AP behave like mixed kind of inhibitor and blocks both the anodic and cathodic reactions on the surface of steel rebar; which is supported by surface analysis data showing the presence of Fe (88.07%) on the surface of specimen. ABA protected the steel rebar by forming a protective layer containing higher C and O content. The spectra band of the bar in ABA mixed solution obtained by FTIR confirmed the presence of protective film in the form of chelate ring formed by –COO- on the specimen surface. The mechanism of inhibition revolves around the presence of heteroatoms within the molecular structure. While AP retarded the corrosion of rebar by forming a thin adsorption layer and restricted the corrosion mechanism, ABA formed an adsorptive black layer over the exposed surface by chelation process. Selected compounds were further applied on the concrete surface to check its migration ability through the cover concrete. Overall, it can be concluded that both the compounds have the potential to act as migratory inhibitor to retard rebar corrosion in the dual corrosive environment of chlorides and carbonation.