On the formation of thaumasite CaSiO₃·CaSO₄·CaCO₃·15H₂O: Part III

In the first part of this series, thermodynamic properties were reported for the mineral thaumasite [Advances in Cement Research, 2004, 16, No. 2, 55–60]. These data were used to calculate reaction paths that were relevant for formation of thaumasite during sulphate attack on concrete [Advances in Cement Research, 2004, 16, No. 3, 89–94 and 2005, 17, No. 1, 46]. Measurements and calculations are referred to a temperature of 8°C. The present paper evaluates the results. A calculation of possible errors in the measured thermodynamic properties demonstrates that deviations are mainly due to shortcomings in the underlying database and a possible deviation from thermodynamic equilibrium. The results obtained for different reaction paths were compared to the results of laboratory investigations. Most of these data were taken from the literature where reactions involving pure phases were studied. Some additional experimental investigations were performed and in most cases the results obtained by thermodynamic calculations were in agreement with the experiment.