Coupled effect of drying-wetting cycle and sustained load on chloride ion transport behavior of waterborne polyurethane-modified concrete

Concrete structures are relatively common in marine engineering. Considered the actual status of concrete structure working in marine environment, the chloride ion transport behavior of WPUMC is explored under the coupling effect of sustained load and drying-wetting cycle. The results indicate that under the same depth and sustained load, the maximum concentration of free chloride ion and chloride ion diffusion coefficient of WPUMC initially decreases and then increase as the polymer-cement ratio increases. It reaches the minimum value under the polymer-cement ratio of 0.4 %. The maximum concentration of free chloride ion of WPUMC increases with the increase of drying-wetting cycles, while the chloride ion diffusion coefficient of WPUMC decreases. The apparent chloride ion diffusion coefficient is roughly linear with the number of drying-wetting cycles. When the number of drying-wetting cycles and polymer-cement ratio remain constant, the chloride ion permeability firstly decreases and then increases with the increase of stress level. Compared to single factor, chloride penetration of WPUMC is enhanced under the coupled effect of drying-wetting cycle and sustained load. Finally, based on Fick's second law, a chloride ion transport model of WPUMC is established by comprehensively considering the effects of polymer-cement ratio, sustained load and drying-wetting cycle. The accuracy and reasonability of the chloride ion transport model are validated by comparing the theoretical values and the experimental values.