Chloride ion transport in coral aggregate concrete subjected to coupled erosion by sulfate and chloride salts in drying-wetting cycles

Some structures or components of coastal buildings are often in an unsaturated state between drying and wetting conditions, and their performance deterioration is extremely serious. This paper mainly studied Cl− diffusion of coral aggregate concrete under the coupled erosion of drying-wetting cycles, sulfate and chloride salts. Based on the microscopic morphology of corroded concrete, the erosion mechanism of the concrete under the coupled erosion of drying-wetting cycles sulfate and chloride salt was elaborated. The results indicated that, under the coupling erosion of sulfate and chloride salts, a large amount of Na2SO4 crystals will precipitate on the surface of concrete. The addition of mineral admixtures can not only improve the relative dynamic elastic modulus and relative compressive strength of coral aggregate concrete, but also improve its resistance to Cl− corrosion. SO42− reacts with cement hydration products to produce ettringite and gypsum, which hinder further Cl− corrosion during the early stage of erosion. However, as the erosion time increases, large numbers of erosion products lead to continuous expansion of cracks and accelerate Cl− transport. Finally, based on the transport mechanism of Cl− in the concrete, machine learning prediction models for Cl− content were established using CART, SVR, and XGBoost, respectively. It was found that the predicted values of the XGBoost model were in good agreement with the measured values, and the goodness of fit of the test set was R2 = 0.98, RMSE = 0.021%, MAE = 0.013%. This work can provide a new method for predicting chloride concentration in concrete under the coupling effect of multiple factors.