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 lath-like.
– 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, Butterworth-Heinemann.https://en.wikipedia.org/wiki/Calcium_aluminoferrite