Corrosion Performance of ASTM A615 Carbon Steel Bars in Arabian Seawater Under Natural and Simulated Conditions

Reinforcing steel bars in coastal regions are frequently exposed to chloride-rich environments before the concrete placement, yet the mechanical consequences of this pre-embedding exposure are rarely quantified. This study experimentally investigates the corrosion progression and mechanical degradation of ASTM A615 grade 60 reinforcing steel bars subjected to natural marine exposure and accelerated simulated chloride conditions using real Arabian seawater. Bare bars of 10 mm diameter were exposed to outdoor coastal conditions in Karachi and to an electrically accelerated seawater environment. A periodic evaluation was carried out up to 270 days, including visual inspection, mass loss, diameter reduction, tensile testing, and microstructural characterisation using scanning electron microscopy (SEM). Natural exposure produced gradual general corrosion, corresponding to ~0.5% annual cross-sectional loss and minor reductions in tensile strength within experimental variability. In contrast, simulated chloride exposure markedly accelerated deterioration, causing diameter losses approaching 1 mm and reductions in yield and ultimate strength of up to 20-25% within 60 days. Strength degradation trends closely followed section loss, indicating cross-sectional reduction as the dominant observed factor. SEM observations showed porous and cracked corrosion products with limited protective capacity. A performance-based time equivalence between natural and simulated exposure was derived from degradation trends while acknowledging possible mechanistic differences. Regression models relating exposure parameters to residual strength showed strong agreement with experimental data. The findings demonstrate that pre-placement marine exposure can introduce measurable steel degradation, underscoring the need to account for construction-stage corrosion in durability management of reinforced concrete in coastal regions. The findings highlight the critical impact of pre-embedding chloride exposure on reinforcing steel performance and emphasise the need to incorporate construction-stage corrosion effects into durability-based design and marine construction practices.