Behavior in Cements
Calcium aluminoferrite has little effect upon the physical properties of cement. On hydration it forms 4CaO⋅Al2O3⋅nH2O and hydrated iron oxide gel. In principle, this is a fast and energetic reaction, but precipitation of an insoluble layer of hydrated iron oxide upon the calcium aluminoferrite crystal surface forms a barrier to further reaction. In the case of Portland cement, subsequent slow reaction with dissolved sulfate forms an AFm phase, which has negligible strength-giving properties. In the case of calcium aluminate cements, the situation is less clear-cut, but there is little contribution to early strength. Calcium aluminoferrite is also present in sulfoaluminate cements, and again contributes no strength.
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