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Calcium aluminates phase diagram Crystal structure of dodecacalcium hepta-aluminate, 12CaO·7Al 2 O 3 (C 12 A 7). [1] Calcium aluminates are a range of materials [2] obtained by heating calcium oxide and aluminium oxide together at high temperatures. They are encountered in the manufacture of refractories and cements.
AFm form inter alia when tricalcium aluminate 3CaO·Al 2 O 3, or C 3 A in CCN, reacts with dissolved calcium sulfate (CaSO 4), or calcium carbonate (CaCO 3). As the sulfate form is the dominant one in AFm phases in the hardened cement paste (HCP) in concrete, AFm is often simply referred to as Aluminate Ferrite monosulfate or calcium aluminate ...
Calcium aluminates can form complex salts in combination with different types of anions.Two series of calcium aluminates are known in cement chemistry: AFm and AFt phases, being respectively mono- or tri-substituted with a given divalent anion X (e.g. SO 2− 4, CO 2− 3, or hosting a divalent impurity such as SeO 2− 4 [3]...), or with two units of a monovalent anion, e.g. OH −, Cl − ...
Calcium aluminoferrite (Ca 2 (Al,Fe) 2 O 5) is a dark brown crystalline phase commonly found in cements. In the cement industry it is termed tetra-calcium aluminoferrite or ferrite. In cement chemist notation (CCN), it is abbreviated as C 4 AF meaning 4CaO· Al 2 O 3 · Fe 2 O 3 in the oxide notation. It also exists in nature as the rare ...
So, CAC cement must not be confused with calcium sulfo-aluminate (CSA) cement containing calcium sulfate and invented later in 1936. [6] The main constituent, and also the most reactive phase, of calcium aluminate cements is the monocalcium aluminate (CaAl 2 O 4 = CaO · Al 2 O 3, also written as CA in the cement chemist notation).
Alteration of hardened cement paste composition, with monosulfate aluminates phase converting to ettringite and, in later stages, gypsum formation. The necessary additional calcium is provided by the calcium hydroxide and calcium silicate hydrate in the cement paste; The effect of these changes is an overall loss of concrete strength.