Impact of supplementary cementitious materials on the solid–liquid equilibrium curve of calcium in cement hydrates

The leaching of calcium in cement hydrates, particularly in harsh environments, significantly affects the durability of cement-based materials. Understanding the solid–liquid equilibrium of calcium is essential to elucidate the leaching mechanism and leachability for developing accurate degradation models of cementitious materials under chloride exposure. In this study, the effects of different types and proportions of supplementary cementitious materials (SCMs) on the calcium leaching process were investigated. This was achieved by simulating pore solutions at various leaching degrees. Key parameters of the equilibrium curves were extracted and analyzed at different leaching stages. Additionally, a functional relationship between these parameters and the proportions of various SCMs was established. The leachability was assessed by comparing the saturated concentration of calcium ions, the total concentration of solid-phase calcium, and the relative content of calcium hydroxide (CH) and calcium silicate hydrate (C–S–H). It was found that composite binder pastes containing 50% slag demonstrated the best performance in terms of calcium leaching resistance. This research provides valuable insights for the design of anti-leaching cementitious materials and contributes to the development of precise deterioration models for concrete exposed to aggressive environments.