Effect of coating defects and initial rust on corrosion and strength of reinforcing steel in concrete

Abstract This study investigates the effect of coating defects and initial rust on the corrosion behavior and mechanical performance of reinforcing steel in concrete. A total of 24 cylindrical concrete specimens were prepared using rebars coated with three different materials from various sources: E (epoxy-based), Z1 (zinc-rich with 40% zinc), and Z2 (zinc-rich with 90% zinc). Local defects of 0.5 cm, 2 cm, and 6 cm were introduced to simulate practical defect scenarios, with additional variation in surface condition (clean vs. initial rusted). Accelerated corrosion was conducted using the current-induced method in a chloride-rich environment. Key parameters, including cracking time, corrosion current, theoretical and actual mass loss, and tensile strength, were assessed. Results showed that fully coated specimens and those with 0.5 cm defects exhibited strong corrosion resistance, with negligible losses in both mass and mechanical properties, regardless of coating type or rust presence. In contrast, larger defects (2 cm and 6 cm) significantly accelerated corrosion, especially when combined with pre-existing rust. Among the materials, Z1 showed the lowest mass loss, while Z2 experienced higher mass loss due to its low bond strength to coated steel rebars. The findings highlight the critical influence of defect size and initial rust on long-term performance, offering practical insights for improving durability design in aggressive environments.