Hydration products in sulfoaluminate cements: Evaluation of amorphous phases by XRD/solid-state NMR

The hydration of four sulfoaluminate cements have been studied: three sulfoaluminate systems, having different content of sulfate and silicate, and one blend Portland-CSA-calcium sulfate binder. Hydration was followed up to 90 days by means of a combination of X-ray diffraction and solid state MAS-NMR; Differential scanning calorimetry and Scanning electron microscopy were also performed in order to help the interpretation of experimental data. High amount of amorphous phases were found in all the four systems: in low-sulfate cements, amorphous part is mainly ascribed to monosulfate and aluminium hydroxide, while strätlingite is observed if belite is present in the cement; in the blend system, C-S-H contributes to the amorphous phase beyond monosulfate.