Chloride transport in estuarine ship-lock concrete structure exposed to a unique seawater corrosive environment with low chlorine-salt concentrations and high-frequency drying‒wetting cycles: Experimental study and computational model

Estuarine ship-locks are the navigational structures closest to the sea, which can form a unique seawater corrosive environment characterized by low chlorine-salt concentrations and high-frequency drying‒wetting cycles. Such an environment is caused by the downstream saltwater tides infiltrating into the ship-lock chamber and coupled with the filling and drainage water processes during the ship-lock operation. This unique seawater corrosive environment can seriously threaten the durability of estuarine ship-locks concrete structures. Currently, the chloride transport mechanisms in concrete for estuarine ship-locks under such a unique seawater corrosive environment remain elusive. Particularly, the transport characteristics of chloride invasion into estuarine ship-lock concrete structures, driven by drying-wetting cycle environmental factors, necessitate further study. This paper investigates the effects of drying‒wetting cycle environmental factors of the unique seawater corrosive environment, including the environmental chloride salt concentration, the drying‒wetting frequency, and the drying‒wetting ratio, on the chloride transport in estuarine ship-lock concrete structure by carrying out a physical experimental study. Results indicated an "M"-shaped trend in chloride concentration, surface chloride concentration, and chloride diffusion coefficient of concrete with an increasing drying-wetting ratio. Additionally, the aforementioned chloride transport parameters exhibited a positive correlation with the increase of drying-wetting frequency and environmental chlorine-salt concentration. Notably, the environmental chlorine-salt concentration had the greatest influence on chloride transport, whereas the high-frequency drying-wetting cycles can diminish the promotion degree of environmental chlorine-salt concentration on chloride transport behaviors in concrete. Furthermore, the time-varying patterns of surface chloride concentration and apparent chloride diffusion coefficient in the estuarine ship-lock concrete structures, subjected to different drying-wetting ratios under low chlorine-salt concentrations and high-frequency drying‒wetting cycles, were quantified, and the mathematical relationship between the drying-wetting ratios and ship-lock structural elevation was derived. On the basis of Fick's second law, a computational model of chloride transport in estuarine ship-lock concrete structure was developed, incorporating the influence of structural elevation, i.e., drying-wetting ratios.