Abstract
The effects of the quality of gypsum on the grindability of cement were studied. Mixtures of normal portland cement clinkers and natural or by-product gypsums (SO3-1.75% in the resulting cement) were ground to the Blaine fineness 3, 200 cm2/g in a test mill at various grinding temperatures, and the time required for grinding, the amounts of coating on the grinding media and of flaked products, dehydration of gypsum during grinding, and fineness of the resulting cements were determined.
The results obtained are summarized as follows :
1. High-grade natural or by-product gypsums are inferior to low-grade natural gypsum in the grindability. This fact is due to the presence of impurities in low-grade natural gypsum which act as a good grinding agent.
2. The main component of impurities in natural gypsums consists of chlorite. This impurities prevent from the formation of coating on the grinding media.
3. The grindability of high-grade natural or by-product gypsums and of anhydrite is improved by adding low-grade natural gypsum.
4. It is probable that the primary dehydration temperature of gypsums during grinding is about 130°C, and the secondary dehydration temperature is about 160°C.
