A new fractal model for flow-solid-chemical multi-field coupling in underground engineering

The permeation diffusion behavior of chloride ions with seawater is one of the key factors causing damage to reinforced concrete structures due to seawater erosion of steel bars. This study establishes a new mathematical model for chloride ion transport in reinforced concrete structures exposed to seawater. The model captures the effect of chloride ions on underwater tunnel structures effectively and provides a valuable theoretical basis for the maintenance and safety of these structures. The proposed model uniquely incorporates the microscopic pore structure characteristics of concrete and the effects of static water pressure and porosity on chloride ion diffusion. The results show that: (1) the diffusion coefficient of chloride ions first increases rapidly, then remains basically unchanged and gradually decreases; (2) there is a non-linear positive correlation between porosity, static water pressure, and maximum corrosion thickness; and (3) the fractal dimension of pore curvature is opposite to the fractal dimension of pore size and crack length.