The Hydration Products of a Refractory Calcium Aluminate Cement at Intermediate Temperatures

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The major hydraulic phase in all the calcium aluminate cements including ciment fondue is CA (CaAl2O4). Once hydrated, it starts to form the hexagonal crystals of CAH10 and C2AH8 that depending on the time and temperature of hydration convert to the cubic crystals of C3AH6 and AH3. The nature, sequence, crystallinity and microstructure of hydrated phases of commercial refractory calcium aluminate cement were analyzed using differential scanning calorimetry (DSC), differential thermal analysis (DTA), X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results showed that the formation of different hydrated phases was temperature dependent. At 28 oC, the hydration products at the beginning of hydration were a gel phase, C2AH8 and gibbsite, while CAH10 also formed after four days of hydration, both C2AH8  and CAH10 were converted to  C3AH6 at latter ages. The rate of conversion of C2AH8 is dependent on the temperature  and  time  of  hydration  at  temperatures  higher  than  28 ºC  and  accelerates  with increasing temperature, but still takes several weeks for completion at 36 ºC.