Aluminate-gypsum system

In the conduction calorimetric curves of the aluminate-gypsum system,the first stage is characterized by a peak at 30 minutes for the formation of ettringite. In the second stage, the peak occurs at 24-48 hours when the monosulfate phase forms by the reaction between ettringite and aluminate. 

Ramachandran, V. S., Adsorption and Hydration Behavior of Tricalcium Aluminate-Water and Tricalcium Aluminate-Gypsum-Water Systems in the Presence of Superplasticizers, J. Am. Concr. Inst., 80 235-241 (1983)... 

The soluble sulfate versus time curve for the cement containing the natural anhydrite is radically changed when CLS is present [130, 131]. The rate of solution of natural anhydrite, which is much slower than that of gypsum or calcium sulfate hemihydrate, is further retarded in the presence of chemical admixtures, which leads to a sulfate-starved system in the concrete, often producing rapid set and an increase in rate of concrete slump loss (Fig. 7.42). Apparently the adsorption of the lignosulfonate by the natural anhydride plus the rapid reaction between the soluble SO and the tricalcium aluminate keeps the SO level near zero concentration for the first 10-20 min causing rapid stiffening and quick set (approximately 15 min). It is also reported that chemical... 

Ramachandran followed the hydration of CjA (with and without gypsum) containing triethanolamine. It was found that TEA accelerated the hydration of C3A to the hexagonal aluminate hydrate and its conversion to the cubic aluminate hydrate. The formation of ettringite was also accelerated in the C3A-g q)sum-H20 system. 

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