Methods of thermal analysis in the detection of thaumasite and its presence in the sulfate-attacked concrete

Thaumasite (3CaO(.)SiO(2.)SO(3.)CO(2.)15H(2)O, or Ca3Si(OH)(6)CO(3)SO(4.)12H(2)O - 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 degreesC 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 front-proposed stoichiometry of the decomposition of thaumasite.