Tricalcium aluminate

Properties: Tricalcium aluminate forms from a mixture of calcium oxide and aluminum oxide at temperatures above 1300°C. The crystals are cubic with a unit cell dimension of 1.5263nm. It has a density of 3064kg/m³ and melts at 1542°C. The structure of pure liquid tricalcium aluminate consists mostly of AlO tetrahedra in an infinite network. In Portland cement clinker, it occurs as an interstitial phase and has several polymorphs. Effect on cement properties: Tricalcium aluminate reacts strongly with water and generates a large amount of heat, leading to flash set. It forms AFm phases contributing little to strength development. It can cause heat release and sulfate attack in concrete, reducing durability. Alkaliloaded polymorphs are more reactive and can make set control difficult. The presence of tricalcium aluminate in concrete can lead to delayed ettringite formation. Hydration: Tricalcium aluminate hydrates in the formation of Portland cement. Two hydrates form during hydration: C3AH6 and C4AH19. In the presence of gypsum, the sulfate forms C4ASH12. References: Kosmatka, Steven (2012). Cement. KirkOthmer Encyclopedia of Chemical Technology. Mondal, P.; Jeffery, J. W. (1975). The Crystal Structure of Tricalcium Aluminate. Drewitt, James W. E.; et al. (2017). Structure of liquid tricalcium aluminate.