Sustainable sodium carboxylates as safe and effective corrosion inhibitors for reinforcing steel in chloride-contaminated simulated concrete: An integrated experimental and computational study

This study investigates the sustainable sodium carboxylates sodium octanoate (SO) and sodium citrate dihydrate (SC) as corrosion inhibitors for carbon steel in NaCl-contaminated SCPS representative of reinforced concrete environments. Notably, SO is evaluated in SCPS for the first time, and its performance is benchmarked against SC. A unified electrochemical approach combining LPR, EIS, and PDP was employed, alongside surface characterization using SEM, EDS, and 3D optical profilometry to establish structure performance relationships. The results showed that SO exhibited optimal inhibition at 208 ppm, reducing the corrosion rate by 90%, while SC achieved 88% efficiency at 368 ppm, highlighting the influence of molecular structure on inhibitor effectiveness. A 40-day immersion test confirmed the formation of a smooth, compact chemically stable Fe–O–Ca rich protective film with minimal chloride incorporation on inhibited steel, whereas untreated steel showed severe pitting and high surface roughness. Density functional theory identified carboxylate oxygen atoms as the primary electron-donating sites, and molecular dynamics simulations on Fe(110) revealed spontaneous adsorption for both inhibitors, with stronger interaction energies and flatter adsorption geometry observed for SO. The combined experimental and computational results establish clear structure-performance relationships between SO and SC through the first integrated evaluation of SO in NaCl-contaminated SCPS, providing quantitative dosage guidance for environmentally safer corrosion mitigation in reinforced concrete environments.