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Chemical composition of cement:
1. C3S - Tri calcium silicate
2. C2S - Di Calcium Silicate
3. C3A - Tri calcium Aluminate
4. C4AF - Tetra calcium alumino ferrate.
Calcium sulfoaluminate cements (CSA) are a promising low-CO2 alternative to ordinary 9 Portland cements and are as well of interest concerning their use as binder for waste 10 encapsulation. In this study, the hydration of two CSA cements has been investigated 11 experimentally and by thermodynamic modelling at between 1 hour and 28 days at w/c ratios 12 of 0.72 and 0.80, respectively. 13 The main hydration product of CSA is ettringite, which precipitates together with amorphous 14 Al(OH)3 until the calcium sulfate is consumed after around 1-2 days of hydration. Afterwards, 15 monosulfate is formed. In the presence of belite, strätlingite occurs as an additional hydration 16 product. The pore solution analysis reveals that strätlingite can bind a part of the potassium 17 ions, which are released by the clinker minerals. The microstructure of both cements is quite 18 dense even after 16 hours of hydration, with not much pore space available at a sample age of 1928 days. 20 The pore solution of both cements is dominated during the first hours of hydration by 21 potassium, sodium, calcium, aluminium and sulfate; the pH is around 10-11. When the 22 calcium sulfate is depleted, the sulfate concentration drops by a factor of 10. This increases 23 pH to around 12.5-12.8.
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