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Calcium leaching from cement hydrates has been shown to decrease the durability and shorten the service life of the concrete. Earlier studies have focused on investigating the leaching progress in deionized water or ammonium nitrate solutions, neglecting the effects of aggressive ion concentrations, types, and temperatures. In addition, the current equilibrium curve of calcium leaching is based on experimental data in deionized water, and its applicability to calcium leaching in actual marine environments is controversial. In this study, a dissolution experiment was carried out to study the effects of chloride ion concentrations and environmental temperatures. The functional relationship of critical parameters (x1 , x2 , and Csatu) of the equilibrium curves with the chloride ion concentrations and temperatures was established. Furthermore, considering the influence of calcium leaching on porosity and the diffusion coefficient of cementitious materials, the calcium leaching model was established within a time and space framework. The results showed that calcium leaching was accelerated by the increased concentration of chloride ions and the decrease in environmental temperature. In the authors' view, this study lays a theoretical foundation for a transport-reaction-mechanical deterioration model of concrete. [ABSTRACT FROM AUTHOR]

• 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]