Study of Hydration of Belite-Based Cement with High Gypsum Content

Belite-based binders offer major advantages over Ordinary Portland Cement with high Alite content in terms of durability, low heat evolution, and low carbon footprint during production. To gain these advantages, activation of the most active polymorphs of Belite by the addition of mineralizers and rapid cooling is needed. However, the reaction rates and hydration products of pure Belite paste are still not well understood. This is due to factors such as i) the effect of mineralizers incorporated in Belite crystals on hydration; ii) the role of residual mineralizers left outside of Belite; iii) the effect of sulfate’s addition on Belite hydration. In this study, a clinker with a high content of α-Belite was prepared. The variable parameter was the amount of Gypsum added during the stage of cement preparation, which ranged from 0 to 30%. The results of the study confirmed that the reactivity of cement based on Belite is highly dependent on the content of sulfates. As sulfate content increases, the degree of hydration increases at an early age but decreases at later ages. It has also been found that Gypsum reacts during the Belite hydration and forms atypical new hydration products such as aluminate-free Ettringite and Apatite. The results of this research reveal a high potential for a new type of low-carbon binder system based on α-Belite with high Gypsum content.