Leaf-based extracts of Nepal origin plants as efficient inhibitors for controlling rebar corrosion in concrete pore solution

Reinforced concrete foundation (RCF) faces the challenges of early reinforcement concrete corrosion. Understanding such concrete corrosion mechanisms and developing effective mitigation strategies is crucial to ensure the durability of the RCF. The study aimed to investigate the effectiveness of leaf extracts from Ziziphus budhensis (LEZB) and Tagetes erecta (LETE) as eco-friendly corrosion inhibitors in a saturated Ca(OH)2 solution with a pH of around 11.5, considered as SCP (simulated concrete pore) solution. The weight loss (WL) experiment lasted over four months to assess the ability of these leaf-based extracts to inhibit corrosion of mild steel rod (MiSR) in SCP solutions with 500 ppm, 1000 ppm, 2000 ppm, 4000 ppm LEZB and LETE at laboratory temperature (i.e., 25°C). The highest corrosion inhibiting efficiency percentage reached at 4000 ppm LEZB, with 91.22% and 81.48% efficacy measured by gravimetric and electrochemical (EC) methods, respectively. Corrosion current density decreases with increasing LEZB or LETE concentrations in the SCP, as revealed by the EC study. Both extracts contain phyto-molecules (polyphenols, alkaloids, and flavonoids), which adhere to the surface of MiSR in SCP solution, thus impeding cathodic, anodic, or both reactions. In addition to WL and EC analyses, we used scanning electron microscopy with energy dispersive X-ray (SEM/EDX) and white light interferometry (WLI) techniques to study changes in the surface morphology of a passive corrosion barrier film formed on MiSR surface after being immersed for approximately four months in SCP solution without and with LEZB or LETE.