Methods of Thermal Analysis in the Detection of Thaumasite and its Presence in the Sulfate-attacked Concrete

摘要

Thaumasite (3CaO.SiO_2.SO_3.CO_2.15H_2O, or Ca_3Si(OH)_6CO_3SO_4.12H_2O - in accord with the crystal structure) is by far not an entirely new mineral. However, it is a phase newly recognised in some sulphate-attacked building constructions. The problem with thaumasite is that it is a non-binder formed from the main cementitious binder hydrates. Multi-step thermal analysis combining dynamic and isothermal heating from ambient temperature to 1000°C in the atmosphere of N_2(g) gives characteristic and defined TG mass losses and DTA effects. A method relying on TG/DTA experiments is introduced and discussed as a tool for the estimation of thaumasite in building constructions. The key quantitative insight - estimation of the mole fraction of thaumasite in any inspected sample, is clearly evaluated as a ratio of the values of TG mass losses in individual steps and the data from proposed stoichiometry of the decomposition of thaumasite.