Synthetic Preparation of Thaumasite – Several Possible Routes for Thaumasite Formation

Presented work is a part of an experiment where limestone is partially replaced by fluidized fly ash during cement manufacturing. Hydration of this type of cement is connected to formation of AFt phases – thaumasite and ettringite that cause serious damage to cement stone. Thaumasite (CaSiO3·CaCO3·CaSO4·15H2O) is less known and less common. It forms especially at lower temperatures. During its growth C-S-H phases are built into thaumasite unite cell, therefore, cement stone decomposes. To preclude thaumasite formation, further research of this mineral is necessary; therefore, its synthetic preparation in sufficient quality is important. The aim of this work was to verify several routes for thaumasite synthetic preparation. In the beginning, burning of mixtures prepared on stoichiometric proportions of compounds in thaumasite was done then two methods used in literature were tried and in the end a new method based on main calcium silicate phases was realized.