Mechanistic study of macrocell effect on corrosion initiation and propagation of reinforcement in submarine immersed tunnel

Submarine immersed tunnel (SIT) is generally in a specific corrosive environment with inner marine atmosphere and outer high-pressure seawater. In this work, a setup was designed to simulate the specific structure and corrosive environment of the SIT, and the mechanism of the macrocell corrosion of reinforcement in SIT was investigated. The chloride threshold value (CTV) and the corrosion rate of macrocell corrosion were obtained and mainly discussed. The results indicated that the anodic corrosion process could be accelerated by increasing SC/A and reducing the thickness of the concrete layer (d) at the cathode. The corrosion initiation was promoted drastically, and the corrosion current density was increased. A remarkable decrease of CTV was discovered in the condition of higher SC/A and reducing d (mainly to improve oxygen acquisition) coexistent. The time to onset of corrosion could be reduced by up to 33%, and the CTV was decreased from 0.749% to 0.562% (by weight). The corrosion will occur earlier, and the damage to the structure will be more severe where the macrocell effect exists in the reinforced concrete structure.