Monitoring long-term chloride penetration into wave power marine concrete structures under repeated air pressure

Abstract

An Oscillating Water Column (OWC) power plant is typically a partially immersed concrete structure that generates energy by moving waves, forcing air to flow back and forth through the turbine to produce a consistent amount of energy. Due to the repeated air pressure application, chloride penetration can be accelerated in the OWC structure. However, long-term studies on chloride penetration monitoring are lacking. Therefore, the water-soluble chloride content of concrete subjected to repeated air pressures was measured after 108 months of the OWC structure. The results were analyzed, along with measurements taken 31 months after OWC completion. Concrete powder samples were collected from three areas: the bypass room, which was subjected to repeated air pressure; the tidal zone, which was subjected to alternate dry/wet conditions of seawater; and the splash zone in the offshore atmosphere. The collected samples were then titrated. Fick ' s 2nd law was used to derive diffusion coefficients. The experimental results indicated that the concrete in the bypass room had the highest watersoluble chloride content. Compared with the results obtained 31 months after completion, the water-soluble chloride content and diffusion coefficient decreased over time. This is attributed to the relatively small effect of air pressure and the clogging of pores owing to the accumulation of chloride ions on the surface. Comparing the measurements in 2017 and 2023, the splash zone exhibits the highest increase over time. This is attributed to the lower initial chloride penetration, which makes diffusion easier owing to the higher concentration differences compared to other locations. In the future, ensuring the reliability of the chloride penetration behavior in concrete subjected to repeated air pressures through periodic monitoring of the chloride content will be crucial. Additionally, research is needed to establish the crystallization and pore-clogging phenomena in concrete subjected to repeated air pressures through microstructural and chemical analyses.