Combined effect of chloride and high temperature on corrosion of steel reinforcement in concrete

Understanding the impact of elevated temperatures on chloride-induced corrosion of reinforcing steel is critical for assessing the long-term durability of concrete structures in hot climates. In this study, concrete prisms reinforced with carbon–manganese steel rebars and cast with varying chloride concentrations were exposed to four temperatures (20 °C, 35 °C, 50 °C and 65 °C) for a period of 730 days. The results revealed a substantial increase in corrosion rates at temperatures above 50 °C. Detailed analysis of the corrosion products provided key insights into the mechanisms driving this accelerated degradation. X-ray diffraction analysis revealed that the akaganeite phase (β-FeOOH), present in corrosion products at lower exposure temperatures (20 °C, 35 °C and 50 °C), was absent at 65 °C. This disappearance is attributed to the transformation of akaganeite into the lepidocrocite phase (γ-FeOOH), which is believed to promote the corrosion process. Scanning electron microscopy examination further indicated exfoliation of the corrosion product layer formed at 65 °C, suggesting a breakdown in the protective barrier and an increased vulnerability to corrosion. These findings highlight the detrimental synergy between high temperature and chloride ingress on rebar corrosion in concrete structures.