Hydration of calcium [alumino] ferrite with limestone

Ferrite has the lowest embodied CO2 among the four major phases found in Portland cement, so increasing the ferrite content of the clinker would improve its CO2 footprint. Ferrite hydration is known to depend on the cooling regime during the production, Al/Fe ratio, and minor element uptake, and thus, their effects have to be fully understood to increase the composition of this phase in the Portland cement and assure their good hydration properties. Here, ferrites with different Al/Fe ratios (0, 0.5, 1, and 2), and minor elements (Zn) has been synthesized at two different burning temperatures, 1250 °C and 1350 °C and hydrated in presence of excess CaCO3 for 1 and 3 days. The ferrite with Al/Fe = 0 did not form any hydration product after 3 days of hydration, while Al-monocarbonate was the only hydration product in the other systems. The hydration kinetics increased with Al/Fe ratio, and when the burning temperature was increased. Comparing XRD and TGA data, the Al-monocarbonate formed from the ferrite with Al/Fe = 2 was found to be more amorphous than other ferrites. ZnO doping up to 2 wt.% had no prominent effect on hydration, implying that raw materials with Zn can be utilised in high-ferrite cement. These results indicate that high-ferrite limestone cement could be a promising solution to reduce cement the CO2 emission.