Local Al network and material characterization of belite-calcium sulfoaluminate (CSA) cements

The present study investigates the local Al network and material characterization of belite-calcium sulfoaluminate (CSA) cements to provide a comprehensive understanding of the hydration products and characteristics of CSA cements. In this context, the present study elucidates relationships between detailed Al network and microstructural characteristics which can offer an in-depth view of such binder systems. CSA cements having various molar ratios of calcium sulfate to ye'elimite were prepared by controlling the externally incorporated anhydrite dosages. Hydration products of the samples were explored using solid-state ²⁷Al MAS and CPMAS NMR spectroscopy methods and XRD, while MIP and compressive strength tests were used to characterize the samples. The NMR spectroscopy results revealed that the resonance characteristics arising in the tetrahedral Al environment of the samples were identical due to the small potential amounts of C–S–H and strätlingite, whereas Al incorporation in C–S–H was unclear. The MIP analysis showed that the formation of ettringite significantly altered the amount of micropores and mesopores volumes, an outcome which was found to be closely related to the development of compressive strength.