Hydration Behavior and Thermodynamic Modeling of Ternesite-Modified Calcium Sulfoaluminate Cement

This study investigates the influence of ternesite ( C 5 S 2 S ¯ ) on the hydration behavior and microstructural evolution of calcium sulfoaluminate (CSA) cement. High-purity ternesite was synthesized through a chemical method, and a range of techniques, including thermogravimetric differential scanning calorimetry (TG-DSC), scanning electron microscope (SEM), and gibbs energy minimization selektor (GEMS) simulations, were used to thoroughly examine the reaction mechanisms and the evolution of both macro and micro properties of CSA cement incorporating ternesite. The results showed that the optimal incorporation of ternesite significantly enhances paste fluidity and accelerates early-stage heat release, while also improving both flexural and compressive strengths at 28 days. Ternesite promotes the formation of denser hydration products, particularly strätlingite, and works synergistically with the sulfoaluminate phases. Under the specific conditions investigated, a 20% ternesite content was identified, demonstrating that modifying CSA cement with ternesite is an effective strategy for improving late-stage strength and reducing the heat of hydration, offering valuable insights for the development of high-performance, low-carbon binders with strong practical applications.