Calcium aluminoferrite (Ca 2(Al,Fe) 2O 5), typically abbreviated as C 4AF, is one of the four main mineral phases in Portland cement. This phase contributes less directly to the strength of cement compared to other phases like tricalcium silicate (Ca 3SiO 5) but plays a significant role in influencing the color and chemical properties of the final product. In terms of hydration, C 4AF reacts with water to form complex hydrates that are less significant for strength but improve the sulfate resistance and may influence the thermal properties of the cement.