Evidence from differential thermal analysis and infrared spectroscopy

2 Evidence from differential thermal analysis and infrared spectroscopy 

In the first effective studies of hydrated cements by DTA, Kalousek and co-workers (K27,K32,K33) observed the early formation of ettringite and its subsequent replacement by what was termed a solid solution, but which was probably a mixture of AFm phases. They found no CjAHg or other hydrogarnet phases. Quantitative or semiquantitative determinations of gypsum and ettringite indicated that less than half the total SO3 present could be accounted for by these phases. The authors concluded that the solid solution was eventually replaced by a product which they termed Phase X , and which was possibly a gel containing all the oxide components of the original cement. 

Infrared absorption spectra (B97) of unhydrated cements typically show moderate to strong bands at 525 and 925 cm due to alite, and at 1120 and 1145 cm from S-O stretching vibrations, and weak bands in the 1650 and 3500 cm regions due to H2O molecules. The early formation of ettringite 

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