Fabrication and characterization of calcium aluminates cement via microwave-hydrothermal route: Mayenite, katoite, and hydrocalumite

In response to the growing interest in functional building materials, the microwave-hydrothermal (M-H) technique was employed to prepare calcium aluminate-based cement. In this study, aqueous solutions containing active lime and alumina were treated using M-H method for one hour at temperatures of 100°, 120°, and 140 °C. Various starting compositions with calcia to alumina molar ratios (C/A) of 1, 1.3, 1.5, 2, 3, and 4 were investigated. Subsequently, the hydrothermally synthesized powders at 140 °C were subjected to calcination for 2hr at 1150°, and 1350 °C to obtain anhydrous phases. The formed powders were characterized using X-ray diffraction (XRD), differential thermogravimetric analysis (TG-DTG), Raman spectroscopy, and scanning- or transition- electron microscopy (SEM & TEM). The results revealed that for starting C/A molar ratio of 1.00–2.00, M-H treated samples at 100°–140 °C produced stable phases such as katoite and hydrocalumite. As the lime content increased in the C/A mixtures up to a molar ratio of 3.00, the tri-calcium aluminate hydrate was an abundant phase, with its crystallinity increasing with higher hydrothermal temperatures. The M-H treated samples at 140 °C, calcined for 2hr at 1150°, and 1350 °C, yielded mayenite powder (C12A7) with varying degrees of crystallinity. These findings provide valuable insights into the preparation of calcium aluminate-based cement using the microwave hydrothermal method.