Investigation of the accelerating effect of water pressure immersion on chloride ion erosion in concrete

In complex marine environments, concrete structures are subjected to long-term immersion under water pressure, which inevitably affects their durability. To investigate the influence of water pressure on the chloride ion transport mechanism in concrete, long-term seawater immersion tests and comparative immersion tests considering the effect of water pressure were designed. The results indicate that: (1) Under the influence of water pressure, the chloride ion erosion rate increases significantly with prolonged immersion time, with the erosion depth increasing by 7.14–50.00 %. This effect is particularly pronounced during the early stages of immersion. At the same diffusion depth, the chloride ion concentration increases with immersion time, with the difference being especially significant in the shallow region of the concrete (1–20 mm). (2) As seawater immersion time increases, the microstructure deterioration of the concrete progresses through three stages. First, water pressure promotes the formation of expansive products (e.g., gypsum and ettringite), reducing porosity. Second, water pressure enhances the transport of aggressive ions (such as Cl - , SO₄² - ), accelerating the formation of expansive products in pores, which induces the propagation of microcracks in the stress concentration areas of the concrete. Third, after long-term seawater immersion, the internal pore size of the concrete stabilizes. (3) Based on Fick's second law, a chloride ion transport model incorporating the influence of water pressure was developed. Numerical simulation was employed to validate the chloride ion transport behavior in concrete under the influence of water pressure. The proposed methodology and findings provide a theoretical basis for analyzing the chloride ion migration mechanism in concrete exposed to water pressure environments.