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Thermo-Analytical Techniques on MX-80 Montmorillonite: A Way to Know the Behavior of Water and its Thermodynamic Properties during Hydration Dehydration Processes

Vieillard P, Tajeddine L, Gailhanou H, Blanc P, Lassin A and Gaboreau S

Thermoanalytical techniques, including differential thermal analysis (DTA) and thermogravimetric analysis (TGA), are considered as a way to determine the temperature history of concrete after fire exposure. TGA is essentially a means of observing the weight evolution of a sample as a function of temperature (dynamic heating) or time (isothermal heating). In its simplest form, the instrument used consists of a sensitive balance and a furnace arranged such that the sample holder sits inside the furnace. The system includes a thermocouple to monitor the sample temperature and a heating controller to maintain a constant temperature or change the temperature in a pre-determined fashion. DTA compares the temperature of a sample with that of a suitable reference material while both materials are heated at the same rate. Any difference in temperature between the two materials is detected by thermocouples whose signal is proportional to ∆T. To maintain the sample and reference material under similar conditions, both materials are embedded in a block of material with a large thermal mass. In theory, the temperature change in the sample should be proportional to the enthalpy change.