Coconut dust extract as a pitting corrosion inhibitor for reinforcing steel in concrete in the presence of chlorides

Abstract This study aimed to evaluate the inhibitory effect of coconut dust extract on the pitting corrosion of reinforcing steel in concrete via potentiodynamic polarization (PDP), electrochemical impedance spectroscopy (EIS), and weight loss measurements. Different solvents (water, ethanol, methanol, and acetone) were used for the extraction of coconut dust, in which water indicated the most efficiency due to the highest of flavonoids, tannins, polyphenols, saponins, phlobatannins, and anthraquinones contents. Then, the obtained coconut dust extract was tested in two cases: (i) mixing with a water extract obtained from concrete with the addition of 3% NaCl and (ii) adding to the mortar-making process before immersing it in a 3% NaCl solution. In the first case, the highest protection degrees of ~95% (from PDP), ~99% (from EIS), and ~89% (from weight loss) were obtained using the inhibitor concentration of 1.5 g·L–1. In the second case, the protection degree was increased at inhibitor concentrations of ≥ 0.5 g·L–1. The highest protection degree is ~95% (from weight loss) and ~97% (from PDP) at a concentration of 2.0 g·L–1. The findings indicated the high potential of coconut dust extract as a green corrosion inhibitor for the corrosion of reinforcing steel in concrete in the presence of chlorides.