Nondestructive Evaluation for Hydration and Setting Time of Gypsum Modified Calcium Sulfoaluminate Cement Paste

Calcium sulfoaluminate (CSA) cement is a promising solution for reducing CO₂ emissions. While previous studies have attempted to investigate the usefulness of CSA cement via various approaches, early age nondestructive evaluations for the setting and hydration of CSA cement mixtures have not been reported. In this study, we measured the ultrasonic pulse velocity and electrical resistivity of early age CSA cement paste. Six types of samples were prepared according to different water-to-solid ratios and different amounts of gypsum. In addition, various microstructural analyses were performed to understand CSA cement hydration with the obtained nondestructive parameters. Consequently, the effect of added gypsum in CSA cement paste was discussed in terms of ye'elimite dissolution and the precipitation of ettringite, and different pore distributions produced by added gypsum were discussed in terms of compressive strength. The 5% addition of gypsum in CSA cement paste enhanced the hydration evolution, such as ettringite, and it can induce the faster setting time up to 6 h and strength development during 24 h.