Lessons learned from a case of concrete damage under cathodic protection of steel in concrete

Concrete bridge deck support beams with impressed current cathodic protection (ICCP) showed corrosion damage after about 12 years of operation. The CP design was based on activated titanium strips in horizontal slots cut in the sides of the beams. During execution the usual care was taken to secure steel continuity. The subsequent performance was satisfying based on the 100 mV depolarisation criterion. After 12 years cracking and a blue-green zone were observed, while depolarisation was still sufficient. Investigation in 2022 revealed that corrosion occurred on two parts of the upper reinforcement in one beam, with wide cracks and rust efflorescence. The corroding rebars were electrically non-continuous stirrups. During execution, continuity had been tested only in spalled parts, which missed discontinuous stirrups in non-damaged parts. The blue-green zone was a piece of copper anode cable, embedded in the same slot as the anode strip, that suffered corrosion due to anodic polarisation at a defect in the insulation. Finally, it appeared that some corrosion also occurred of rebars that were located deeper in the beams, which received insufficient protective current. The paper will give suggestions for design and execution of ICCP based on the “lessons learned” from this case.