Corrosion non-uniformity of in-service reinforced concrete beams subjected to natural marine environment

Abstract

This study systematically investigates the non-uniform corrosion characteristics of reinforcements in eight reinforced concrete (RC) beams extracted from a marine platform after 26 years of natural exposure. High-precision 3-D Laser scanning was employed to obtain detailed morphological data, enabling analysis of corrosion patterns influenced by environmental exposure, chloride ingress, and stress distribution. The results show significant spatial variability in corrosion at multiple scales. Construction-induced reinforcement cage eccentricity reduced concrete cover thickness on specific sides, exacerbating asymmetric corrosion. Surface directly exposed to the marine environment suffers from higher-intensity wind-driven salt spray and moisture, leading to higher corrosion severity. Corner rebars exhibited average corrosion degrees up to 7.78 times those of side rebars due to bidirectional chloride attack. Longitudinal corrosion distribution along bottom rebars followed a parabolic pattern, with the most severe corrosion occurring at mid-span. This distribution is consistent with higher tensile stresses promoting concrete microcracking and pore connectivity, thereby accelerating corrosive agent ingress and demonstrating stress-corrosion synergy. Stirrups provided cathodic protection to longitudinal rebars at low-to moderate corrosion levels; but this effect diminished beyond a threshold. These findings indicate that traditional models based on accelerated uniform corrosion may underestimate risks, emphasizing the need for probabilistic approaches incorporating non-uniformity to improve safety assessments of in-service marine RC structures.