Ceramics-Silikáty 66, (4) 527 - 539 (2022)

This paper presents a study on the influence of different amounts of alkalis (K₂O and Na₂O) on clinker phase formation, microstructure, phase composition and reactivity of belite-sulfoaluminate cement clinker. Using X-ray powder diffraction and scanning electron microscopy with energy dispersive spectrometry, it was found that the amount of C₂S and C₄AF increases with the incorporation of alkalis, while the amount of C₄A₃S and CS decreases. In addition to the major phases, the samples with alkalis also consist of minor phases such as C₃A (tricalcium aluminate), KS (arcanite), and KC₂S₃ (Ca-langbeinite). The major ions in the major phases were substituted by alkali cations and some other ions (Ca²⁺, Al³⁺, Fe³⁺, S^2-, S⁶⁺, Si⁴⁺). The alkalis also affect the microstructure of the clinker, e.g., the shape of the grains. Consequently, isothermal calorimetry was used to detect differences in hydration kinetics. The clinker with 2 wt. % K₂O content was the most reactive, while the sample with 0.5 wt. % Na content was the least reactive. The latter was primarily influenced by the content of the main and minor phases of the clinker.