About Gypsum in Cement

Gypsum is called the retarding agent of cement which is mainly used for regulating the setting time of cement and is an indispensable component. Without gypsum, cement clinker can condense immediately by mixing with water and release heat.
During cement manufacturing process upon cooling of clinker a small amount of gypsum is added during the final grinding process. Gypsum controls the setting of the cement and if not added the cement will set immediately leaving no time for concrete placing.

The cement manufacturing industry is the major consumer of gypsum, which is added to the clinker in a percentage of 3–5 wt% [1], [2], [3]. As it is well known, the workability property of cement solutions depends on reaction rate of C3A with water and to justify this, retarder raw materials are used. In cement industry, natural gypsum (CaSO4·2H2O) is the most effective raw material for this purpose.

Gypsum helps soil better absorb water and reduces erosion. It also cuts down on phosphorus movement from soils to lakes and streams and improves the quality of various fruits and vegetables, among other benefits. The chemical formula of Gypsum is CaSO4. 2H2O. It contains two moles of water in it. It can also be said as Calcium Sulphate dihydrate. 

Dissolving gypsum in water or soil results in the following reaction: CaSO4·2H2O = Ca2+ + SO42- + 2H2O. It adds calcium ions (Ca2+) and sulfate ions (SO42-), but does not add or take away hydrogen ions (H+). Therefore, it does not act as a liming or acidifying material. The hydroxamic acid and the named salts thereof have the ability to dissolve gypsum, and also the ability to convert gypsum not actually dissolved into a water dispersible sludge.

Gypsum is a pale, gray, veiled white with a red undertone. Physical and Chemical Properties of Gypsum Mineral. Gypsum is a mineral found in crystal as well as masses called gypsum rock. It is a very soft mineral and it can form very pretty, and sometimes extremely large colored crystals.

How many types of gypsum are there?

Gypsum rock is mined or quarried, crushed, or ground into a fine powder. The calcined gypsum becomes the base for gypsum plaster, gypsum boards, and other gypsum products. Another type of gypsum is synthetic gypsum. One example of synthetic gypsum is FGD gypsum.
There are five basic forms of gypsum: selenite (transparent and some of the largest crystals found on earth), satin spar (fibrous and silky), alabaster (fine-grained, translucent white, used in ornamental works), rock gypsum (the most common form), and gypsite (soft, earthy, impure form).