Calcium aluminoferrite

Properties of the pure phase: Calcium aluminoferrite forms a solid solution series with the formula Ca(Al1–x for x in the range 0–0.7. Compositions with x > 0.7 do not exist at ordinary pressures. The crystal structure is orthorhombic and lathlike. Density ranges from 4026kg·m (x = 0) to 3614kg·m (x = 0.7). All compositions melt incongruently in the range 1400–1450°C. Phases in Portland cement clinker: Calcium aluminoferrite occurs as an interstitial phase in cement clinker. It acts as a repository for minor elements like titanium, manganese, and zinc. The typical chemical composition is dominated by CaO, Al, and Fe. The presence of other oxides in the phase reduces its melting point. The sum of Al and Fe contents in calcium aluminoferrite remains constant. Behavior in cements: Calcium aluminoferrite has little effect on the physical properties of cement. On hydration, it forms hydrogarnet and hydrated iron oxide gel. The reaction is exothermic, but a barrier of iron oxide hinders further reaction. In Portland cement, slow reaction with sulfate forms AFm phases with low strength. In calcium aluminate cements, there is little contribution to early strength. See also: Main mineral phases of Portland cement clinker include Alite, Belite, and Tricalcium aluminate. Alite is also known as 3CaO·SiO2. Belite is also known as 2CaO·SiO2. Tricalcium aluminate is also known as 3CaO·Al2O3. References: Taylor H.F.W. (1990). Cement Chemistry, Academic Press. Hewlett P.C. (Ed.) (1998). Leas Chemistry of Cement and Concrete: 4th Ed, Arnold. Further reading: Taylor, Harry F. W. (1997). Cement Chemistry, Thomas Telford. Peter Hewlett; Martin Liska (2019). Leas Chemistry of Cement and Concrete, ButterworthHeinemann.