Influence of gypsum additive on the gyrolite formation process

The influence of gypsum additive on the gyrolite formation process and a sequence of intermediary compounds formation in the CaO–SiO2·nH2O–H2O system was examined and explained. The synthesis has been carried out in unstirred suspensions. The molar ratios of primary mixtures were CaO/SiO2 = 0.66. The amount of sulphate ions to be added to a raw mixture was 1–10%. The duration of isothermal curing at 200 °C was 4, 8, 16 and 72 h. It was determined that the quantity of sulphur which penetrates into the crystalline structure of gyrolite depends not only on the synthesis conditions but also on the composition of initial mixture. A larger amount of sulphate ions stimulate the formation not only of gyrolite, but also of CaSO4. Gypsum additive has no influence on the re-crystallization temperature of C–S–H(I), Z-phase and gyrolite into wollastonite. The composition of initial mixtures is recommended to calculate according to molar ratios. In other cases, upon increasing the amount of sulphate ions, the basicity of the mixture decreases and gyrolite forms more difficult.