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

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Calcium aluminates (CA) are the most important hydraulically setting cements used for preparing refractory castables, because they develop high strength at very early ages after placements.  The anhydrous phases of this kind of cements are CA, CA2 and traces of C12A7 and alpha-alumina. The major hydraulic phase in all of the CA cements including ciment fondue is CA. Once hydrated, it starts to form the hexagonal crystals of CAH10 and C2AH8 that depending on the time and temperature of hydration converts to the cubic crystals of C3AH6 and AH3. The nature of the calcium aluminate hydrates, their morphology and the way in which they are broken down, play an important roles in determining the properties of fired cement.  For this reason a series of investigations has been conducted on the hydration reactions of Secar 71, a commercial cement which can completely represents this type of cements, and hydration products were characterized by DTA, DSC, XRD and SEM. At 12 oC, the only hydration products were a gel phase, CAH10 and gibbsite, while the same hydrates were still predominant phases, C4ACH11 also formed as a result of carbonation of the pastes.