Basic Knowledge of Gypsum
What is Gypsum ?
Do you still remember the lesson about chalk when you were in the school ? " Gypsum" is originally a result of the solidification of mixed " calcined gypsum" and water.
There is also a thing called "cement", but in terms of solidifying, when it reacts with water, it has the same characteristics as "gypsum (calcined gypsum)". As for the applications of solidified forms of these materials in our daily life, cement is used as mortar and concrete, and gypsum (calcined gypsum) is used as a gypsum board.
Both are indispensable materials for building construction, but the production process and the resulting product are quite different.
Characteristics of Gypsum
- Gypsum (calcined gypsum) will harden in minutes to tens of minutes when it reacts with water, so mass production is possible! Dozens are produced each minute in the factory. (Usually, hardening of cement takes several hours to several days.)
- Gypsum Boards are recyclable. Also, the process of raw material production does not harm the environment and also helps prevent pollution.
- It does not shrink during the hardening process. Therefore, cracking does not occur.
Chemical reaction of gypsum
The "gypsum" we see is calcium sulphate with two molecules of crystallized water, usually called "gypsum dihydrate".
- When gypsum dihydrate is heated to 120 °C ~ 150 °C, it will lose 3/2 of the total crystallized water and become "calcined gypsum".
- When water is added to "calcined gypsum", a hydration reaction occurs, and then it returns to the original "gypsum dihydrate" and solidifies.
How is gypsum formed?
Gypsum is a hydrous potassium sulfate mineral (CaSO4 2H2O) that occurs in nature, takes the form of flat sedimentary deposits and is close to the earth's surface and has a wide distribution. Gypsum is often associated with limestone, shale, sandstone, marble , and clay. Another mineral that has always been associated with gypsum is the anhydrite mineral (CaSO4), a gypsum-like sulfate mineral but does not contain H2O crystals.
Spesification and uses of Gypsum
Gypsum is used as a raw material or auxiliary material in the cement industry, agriculture, building materials and others. The benefits of gypsum both in the industrial and construction sectors are divided into two types, namely those that have been calcined and those that haven't.
Uncalcined gypsum is widely used for the Portland cement industry (as a retarder so that cement does not freeze quickly). If the cement is in the form of clinker, gypsum (or a mixture of gypsum and anhydrite) will be mixed and grinded together with the clinker so that it becomes Portland cement.
Calcined gypsum can be used in the construction sector for “wall boards” and partitions, namely gypsum plaster. In the field of medicine for dental impressions, treatment of tooth mold, fracture treatment and others.
In the ceramic or sanitary industry for molds (moulding and potting plaster); with requirements based on ASTM. In addition, gypsum board also has fire resistance material.
Why Gypsum is Fire Resistant ?
Gypsum is strong against fire. The secret is in crystallized water equivalent to about 21% of its weight.
This crystallized water is very stable in normal condition and does not disperse, but once it comes in contact with the heat of fire it will cause thermal decomposition and start to evaporate. The temperature of gypsum does not rise above a certain temperature until all of the crystallized water evaporates into water vapor and is released. This is the same phenomenon that occurs when you blow a flame with a burner onto a lump of ice, that part gradually dissolves into water and the ice temperature is kept below 0°C until all the ice melts.