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• A experimental study is conducted to investigate the mechanism of calcium leaching of cement hydrates exposed to the sodium sulfate solution. • The influences of sulfate ions concentration and environmental temperature are analyzed on calcium leaching process. • The solid–liquid equilibrium curve describing calcium leaching in deionized water is extended to sodium sulfate solutions. Calcium leaching from cement hydrates to pore solution increases the porosity and reduces the bonding strength of cement hydrates, accelerating the degradation of concrete. Calcium leaching can be quantified by solid–liquid equilibrium curves, which have been studied in deionized water or ammonium nitrate. The research of solid–liquid equilibrium curve of calcium under sulfate attack is limited and its mechanism is poorly understood. Reported here provide insights into the dissolution process of calcium from cement hydrates exposed to the sodium sulfate solution. The experimental programme examines the effects of sulfate ion concentration and temperature. An external sulfate attack (ESA) model considering the influence of calcium leaching is established and validated. The results show that, compared to deionized water, sulfate ions impact strongly the leaching process. Qualitatively, the dissolution of calcium in cement hydrates is accelerated by increasing the concentration of sulfate ions and decreasing the environmental temperature. Quantitatively, the presence of sulfate ions modifies the equilibrium curve describing calcium leaching in deionized water. In addition, the prediction results of the ESA model considering the influence of calcium leaching are in good agreement with the experimental results. [ABSTRACT FROM AUTHOR]

Assessing the long-term durability of concrete structures subjected to external sulfate attack (ESA) poses a significant challenge, primarily due to the lack of a well-defined quantitative metric for durability limit states. Traditional performance indicators such as compressive strength, mass loss, and expansion strain are insufficient for providing a comprehensive understanding of the extent of damage and are often difficult to measure accurately in practice. The primary objective of this study is to introduce a novel durability failure indicator, namely the failure thickness of concrete under ESA exposure, designed to quantitatively assess the ultimate limit state of concrete durability. Experiments were conducted and the results confirmed that the failure thickness can reliably reflect changes in both the elastic modulus and compressive strength of concrete exposed to ESA. A prediction model for estimating the failure thickness was subsequently developed, integrating key influencing factors like sulfate concentration, initial aluminate content, and sulfate ion diffusion coefficient. The established model exhibited a high degree of correlation between the predicted and experimental failure thickness values, with a low margin of error. The findings of this research contribute to serve as a foundation for both lifespan prediction and durability design of concrete structures exposed to sulfate-rich environments. • We propose a durability failure indicator based on critical sulfate concentration. • Concrete performance deterioration can be well characterized by failure thickness. • The validity of the prediction model of failure thickness was confirmed. [ABSTRACT FROM AUTHOR]

• The performance of concrete under sulfate attack and dry-wet cycles is investigated. • A newly defined index is proposed to describe the progress of sulfate attack. • A novel method is proposed to assess the performance of sulfate-attacked concrete. Sulfate attack is a major cause of concrete durability deteriorations. Mass loss, strength reductions, and expansive strain of concrete specimens are generally used in laboratory testing to identify the resistance of concrete materials to sulfate attack. However, these indicators cannot be directly used to quantitatively predict the bearing capacity of actual concrete structures under sulfate attack. There exists a significant size effect between laboratory and engineering size concrete components. In this study, the durability performance of concrete specimens, exposed to sulfate attack and dry–wet cycles, was investigated. Mass loss, dynamic elastic modulus, compressive strength, and sulfate ions distributions of deteriorated concrete were measured over time. Test results indicate that the newly defined integral area of sulfate ions distributions is a suitable index to describe the non-uniform deteriorations behavior of sulfate–attacked concrete; and a novel method based on the homogenizations theory is proposed to predict the deteriorations level of components of attacked concrete structures, which provides a potential use in assessing the loading capacity of actual concrete structures based on accelerated test results in a laboratory. [ABSTRACT FROM AUTHOR]