A Scanning Transmission X-ray Microscopy Study of Cubic and Orthorhombic C(3)A and Their Hydration Products in the Presence of Gypsum

This paper shows the microstructural differences and phase characterization of pure phases and hydrated products of the cubic and orthorhombic (Na-doped) polymorphs of tricalcium aluminate (C(3)A), which are commonly found in traditional Portland cements. Pure, anhydrous samples were characterized using scanning transmission X-ray microscopy (STXM), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) and demonstrated differences in the chemical and mineralogical composition as well as the morphology on a micro/nano-scale. C(3)A/gypsum blends with mass ratios of 0.2 and 1.9 were hydrated using a water/C(3)A ratio of 1.2, and the products obtained after three days were assessed using STXM. The hydration process and subsequent formation of calcium sulfate in the C(3)A/gypsum systems were identified through the changes in the L(III) edge fine structure for Calcium. The results also show greater Ca L(II) binding energies between hydrated samples with different gypsum contents. Conversely, the hydrated samples from the cubic and orthorhombic C(3)A at the same amount of gypsum exhibited strong morphological differences but similar chemical environments.