Active sulfate-rich belite sulfoaluminate cement

This work focuses on the activation of belite to improve the strength development of sulfate-rich belite sulfoaluminate cements. Borax was used to act as an activator to promote stabilisation of high-temperature belite polymorphs. The phase compositions of clinkers were analysed by using quantitative X-ray powder diffraction. The transformation of β-belite (C₂S) to α′-C₂S mainly depends on the dosage of borax, and the change in polymorphs is almost complete when the dosage of borax reaches 5%. The formation of α′-C₂S can significantly increase the compressive strength and the concentration of borax has a great effect on the strength development of the activated cements. The hydration products of activated cements were also investigated. The results show that the activation of belite can promote the formation of ettringite. Moreover, the crystallisation of ettringite is also affected by the polymorphs of belite, and a fine microstructure of ettringite is found in the activated cement paste.