Alite sulfoaluminate clinker: Rietveld mineralogical and SEM-EDX analysis

The effect of zinc oxide and calcium fluoride on the clinkering of alite-sulfoaluminate (ACSA) materials has been studied by laboratory X-ray powder diffraction (EDX) and scanning electron microscopy (SEM). ACSA clinkers without the addition of calcium fluoride did not contained C₃S, and showed CaO_free (5·0(1) wt%). However, by adding 0·25 wt% of calcium fluoride, the obtained clinker did not contain free lime and showed C₃S (20·0(2) wt%). The suitable clinkering temperature has been proved to be 1300°C, in order to avoid C₄A₃S decomposition. The optimum amount of zinc oxide was found to be 1·0 wt% as the maximum percentage of C₃S was formed. An ACSA clinker prepared at 1300°C with 1·0 wt% of zinc oxide and 1·0 wt% of calcium fluoride contained 34·2(2) wt% of C₃S coexisting with 15·2(2) wt% of C₄A₃S, determined by Rietveld methodology, including amorphous content. SEM-EDX results have been statistically analysed and particles have been univocally identified. It has been proved that zinc oxide is preferentially placed in C₃S.