Properties study of anhydrite(II) prepared from waste gypsums

Anhydrites(II)-β CaSO4 were prepared from two waste gypsums (PRECHEZA Přerov, FOSFA Postorna). The samples of anhydrites(II) with sulphate activators were tested on spillage, beginning and the end of setting time, bending and pressure strength. Both sodium and potassium sulphates accelerated setting of anhydrite, more impressively that prepared from Postorna gypsum. The addition of Na2SO4 influenced the strength of this anhydrite very favourably. On the contrary K2SO4 influenced favourably the strength of Přerov anhydrite. Results confirm the necessity to evaluate properties of such materials with respect to their origin.