Corrosion Performance of Epoxy-Coated Reinforcement

The long-term corrosion resistance of fusion-bonded epoxy-coated reinforcement in concrete exposed to chlorides has recently been questioned. Damage to coating, primarily during fabrication, handling, and construction, is considered to be the most serious factor affecting performance. In this study, the integrity of epoxy-coated bars in various corrosive environments was examined. The effects of coating damage, exposure conditions, and cracking due to structural loading on corrosion performance of coated bars were investigated experimentally.

The level of damage to the coating governed the resistance to corrosion. The larger the areas damaged and percentage of damage on a bar surface, the higher was the corrosion rate. Bent bars with damage concentrated at the bends exhibited extensive debonding of the coating from the bar and widespread corrosion on the steel substrate. Concrete cracking, regardless of the width, led to an accummulation of chlorides at the bar surface and accelerated initiation of corrosion. Significant pitting corrosion was observed on stressed coated bars with 3% surface damage embedded in concrete beams with crack widths about 0.33 mm (0.013 in.). Electrical continuity between coated and uncoated bars located in different chloride environments, or exposure of damaged coated bars to chloride concentration cells, promoted macrocell activity. Also, variations in concrete consolidation around coated bars facilitated initiation of corrosion and increased probability of void formation at the underside of the bar where corrosion spotting was noted most.

The epoxy coating, however, improved the performance of reinforcement in concrete exposed to chloride compared with bare reinforcement. Corrosion initiation was delayed and the severity of bar suface degradation and metal loss was reduced on coated bars compared to uncoated bars. Corrosion-induced deterioration of concrete members with coated reinforcement was reduced. Patching of damaged areas reduced corrosion activity but did not stop it completely. The performance of coated bars will be improved by coating after fabrication, minimizing damage to coating, avoiding mixing coated and uncoated reinforcement, improving coating repair materials and application, tightening current specification requirements regarding coating quality and acceptable damage limits, and improving concrete consolidation around bars.