Corrosion Propagation Phase Modeling of Cracked In-Ground Reinforced Concrete Elements for a 100-Y Design Life Available to Purchase

Cracking up to 1.5 mm was predicted for two zones of the reinforced concrete (RC) piles of a 100-y design life major new road infrastructure project in Australia, where the piles had moved more than the structural design limits during construction. In-ground exposure conditions for the piles were saline groundwater, and conventional carbon steel reinforcement at crack locations was therefore exposed to higher levels of chloride than would be expected during the future 100-y design life of the structure. To determine whether the RC substructure elements of this section of the project could meet a 100-y design life without remedial works in aggressive, marine salinity, in-ground exposure conditions, desktop deterministic corrosion propagation modeling at crack locations was undertaken during construction. Both microcell corrosion and macrocell corrosion can occur for conventional steel in cracked marine concrete. Each of these forms of corrosion was examined in turn for the steel reinforcement in high-performance, blended cement-based, 75 mm minimum cover, cracked concrete (of anticipated surface crack widths of up to 1.5 mm) under buried (in rock), saline (essentially seawater), groundwater conditions. While microcell and macrocell corrosion may act together, it was proposed that macrocell corrosion takes over and dominates until ongoing (long-term) corrosion means that anodes will extend, and macrocell corrosion will eventually evolve into microcell corrosion. Microcell section losses were also judged not to be added to predicted macrocell section losses. The maximum predicted section losses due to pitting were therefore considered as worst-case for a 100-y design life period. Two (2) microcell deterministic corrosion models and one (1) macrocell deterministic corrosion model were considered during the desktop assessment, namely: for microcell corrosion: oxygen diffusion control and crack resistance control models, and for macrocell corrosion assessment: an oxygen diffusion control model. Microcell corrosion deterministic desktop modeling predicted the worst-case likely local reinforcing steel section loss for affected RC pile tops and pile toes to be 2.1 mm at 0.15 mm to 0.7 mm surface cracked locations over the 100-y structure design life. For 0.7 mm to 1.5 mm cracked locations, microcell corrosion deterministic modeling then predicted the worst-case likely local reinforcing steel section loss for affected RC pile tops and pile toes to be 3.2 mm over the 100-y structure design life. Macrocell corrosion deterministic desktop modeling, on the other hand, predicted the worst-case likely local section reinforcing steel loss for affected RC pile tops and pile toes in both 0.15 mm to 0.7 mm and 0.7 mm to 1.5 mm surface cracked concrete to be 7.1 mm over the 100-y structure design life. Because of the desktop deterministic corrosion propagation modeling, a local reinforcing steel section loss (not full circumference) of up to 7.1 mm was therefore allowed by the structural designers for pile top and pile toe sections over the 100-y design life of the project. Furthermore, the desktop corrosion assessment provided the structural designers, constructors, project verifiers, and structure owner authority with sufficient information to make suitably informed decisions and approve the 100-y durability design for the structure.