Strength Assessment of Cement-Based Materials under Marine Conditions Subjected to Sulfate and Chloride Attack Based on Ion Distributions

Sulfate and chloride in the marine environment threaten the lifespan of concrete structures. Predicting the strength of concrete under different degrees of ion erosion is essential for marine structure design and maintenance. In this paper, a novel method was developed to predict the compressive strength evolution due to sulfate and chloride attack. The degradation and ion diffusion behavior of cement-based materials was investigated by analyzing the visual appearance, compressive strength, porosity, and ion distributions of mortar soaked in sulfate and chloride solutions with different concentrations. The damage degree was observed to increase with sulfate concentration and decrease with chloride concentration. Additionally, it was discovered that chloride and sulfate ions inhibited the diffusion of each other, and a higher concentration resulted in a more substantial inhibition effect. The total effective sulfate and chloride intrusions were proposed to describe the erosion degree of mortar based on the evaluation of the ion distributions with Fick’s second law. A compressive strength assessment method was established based on the analysis of the correlation between the strength contribution of sulfate reaction and the total effective chloride and sulfate intrusions. This method exhibits the potential for estimating the concrete strength of actual marine structures damaged by sulfate and chloride with accelerated laboratory tests.