Comprehensive analysis of early-stage hydration and microstructure evolution in Sufflaminate cement: Insights from low-field NMR and isothermal calorimetry

This study presented a comprehensive investigation of the early hydration reaction and microstructure evolution of sulfoaluminate cement (SAC) using low-field nuclear magnetic resonance (LF-NMR) and isothermal calorimetry (IC). LF-NMR, combined with total relaxation signal and transverse relaxation time (T2), was employed to characterize the evolution of evaporation water (EW) and the degree of hydration (alpha lf) during the initial stage of SAC hydration. The hydration process was divided into four phases. The relative content of different EW types within the paste was investigated, and the pore structure and specific surface area evolution of SAC paste were studied based on the T2. The heat release of hydration of SAC was measured using IC, and the hydration kinetics was fitted with the JMAK model. The results demonstrated that the early hydration reaction of SAC was a multidimensional controlled process influenced by various factors. Also, the crystallization nucleation rate of hydration products was inversely related to w/ c. Furthermore, a successful nonlinear fitting between the weighted average of T2 and the hydration degree (alpha t) obtained from IC was established, providing a standard reference curve for studying hydration degree and microstructure. Finally, the hydration products and microstructure were investigated using, SEM, and TG, and the evolution of the compressive strength of SAC was also analyzed. This work gave valuable insights into SAC's early hydration behavior and microstructural development, which can contribute to a better understanding of its performance and potential applications.