Anhydrite is a kind of sulfate mineral, the composition of which is anhydrous calcium sulfate. It is mainly used as building materials, chemical raw materials and fillers. Due to the further requirements of cement performance, it is necessary to further improve the production quality of cement. Adding anhydrite into cement production to form anhydrite cement, namely anhydrous gypsum cement, can improve the setting and hardening properties of cement, which is worthy of promotion and reference.
Gypsum is usually used to adjust the setting time of cement. The application of anhydrite in cement production can greatly improve the setting and hardening properties of cement, and has a very good help to the quality of cement production.
Anhydrite cement is a kind of material, which is produced by heating natural anhydrite or natural dihydrate gypsum to 4000-7500 ℃, and grinded together by adding appropriate amount of activator. It is also called anhydrite cement.
The insoluble anhydrite formed in the calcination process loses the ability of setting and hardening, but it can be hydrated and hardened by adding activator. The commonly used activators are: sulfate activator, such as the mixture of 5% sodium sulfate, sodium bisulfate, and 1% iron vanadium or copper vanadium; and there are alkaline activators, such as 1-5% lime, lime and a small amount of hemihydrate, calcined dolomite, basic granulated blast furnace slag, etc.
Water gypsum cement belongs to air hardening cementing material, the setting speed of which is slower than other building gypsum. The paste made of water gypsum cement with certain consistency needs less water and has smaller porosity after hardening. It is with good resistance to fire, acid and alkali erosion, which is suitable for indoor use, for example, used in board and other building products, and plastering mortar.
Anhydrite cement will disintegrate and pulverize when touching water, so it is not easy to be used in the wet places. Anhydrite cement can be made from anhydrite or natural anhydrite calcined artificially at 600-750 ℃ and mixed with proper amount of activator. Anhydrite cement is suitable for indoor use, mainly used in board or other products, also can be used for indoor plastering.