Corrosion response and microstructural evolution of reinforcement steel in the aggressive coastal seawater environment of Walvis Bay, Namibia

The coastal environment of Walvis Bay, Namibia, ranks among the most corrosive globally due to persistent salt-laden winds, high humidity, and temperature fluctuations. Prior to corrosion testing, the physicochemical properties of seawater were determined, as they directly influence the corrosion mechanisms and electrochemical behaviour of reinforcement steel; thus, their analysis provides essential baseline conditions for interpreting OCP and potentiodynamic polarisation results accurately. This study evaluates the corrosion behaviour of standard reinforcement steel bars of two diameters in two aggressive marine exposure sites: Berth #1 and the Syncrolift Berth. Potentiodynamic polarisation in natural seawater revealed that smaller rebars corroded more rapidly by ~ 10.9% at Berth #1 (0.331 ± 0.041 mm/year) and ~ 3.6% at the Syncrolift (0.336 ± 0.032 mm/year) compared to larger ones. SEM confirmed a ferrite–pearlite microstructure, while XRD identified Fe2O3, Fe3O4, γ-FeOOH, and α-FeOOH as dominant corrosion products, reflecting both uniform and localised attack. Vickers hardness values of 193.7 ± 2.2 HV3 for the smaller rebar and 298.0 ± 7.1 HV3 for the larger one suggest that lower hardness may contribute to enhanced corrosion susceptibility. These findings highlight the synergistic effects of geometry, microstructure, and mechanical properties on corrosion performance and underscore the need for targeted durability strategies in marine infrastructure exposed to splash, tidal, and atmospheric zones. Corrosion of two rebar types was studied in Walvis Bay seawater. Seawater showed high conductivity with elevated Cl⁻, SO4²⁻, and CO3²⁻ levels. Corrosion rates ranged from 0.295 ± 0.034 to 0.336 ± 0.032 mm/y. Uniform, pitting, and crevice corrosion dominated. Hardness ranged 193.7 ± 2.2 HV3 to 298.0 ± 7.1 HV3, with microstructural degradation. Results aid corrosion protection for marine steel infrastructure.