Cement is a fine, soft, powdery-type substance. It is made from a mixture of elements that are found in natural materials such as limestone , clay , sand and/or shale. When cement is mixed with water , it can bind sand and gravel into a hard , solid mass called concrete. Cement can be purchased from most building supply stores in bags
Four essential elements are needed to make cement. They are Calcium , Silicon , Aluminum and Iron. Calcium (which is the main ingredient) can be obtained from limestone , whereas silicon can be obtained from sand and/or clay. Aluminum and iron can be extracted from bauxite and iron ore , and only small amounts are needed.
Cement is usually gray. White cement can also be found but it is usually more expensive than gray cement. Cement mixed with water , sand and gravel , forms concrete. Cement mixed with water and sand , forms cement plaster. Cement mixed with water , lime and sand , forms mortar.
Cement powder is very , very fine. One kilo contains over 300 billion grains. The powder is so fine it will pass through a sieve capable of holding water.
Cement should be stored in a dry area. If it gets wet or damp the powder will turn into a hard lump.
How cement is made?
1. Limestone is taken from a quarry. It is the major ingredient needed for making cement. Smaller quantities of sand and clay are also needed. Limestone , sand and clay contain the four essential elements required to make cement. The four essential elements are calcium , silicon , aluminum and iron.
2. Boulder-size limestone rocks are transported from the quarry to the cement plant and fed into a crusher which crushes the boulders into marble-size pieces.
3. The limestone pieces then go through a blender where they are added to the other raw materials in the right proportion.
4. The raw materials are ground to a powder. This is sometimes done with rollers that crush the materials against a rotating platform.
5. Everything then goes into a huge , extremely hot , rotating furnace to undergo a process called "sintering". Sintering means: to cause to become a coherent mass by heating without melting. In other words , the raw materials become sort of partially molten. The raw materials reach about 2700° F (1480°C) inside the furnace. This causes chemical and physical changes to the raw materials and they come out of the furnace as large , glassy , red-hot cinders called "clinker".
6. The clinker is cooled and ground into a fine gray powder. A small amount of gypsum is also added during the final grinding. It is now the finished product: Portland cement.
The cement is then stored in silos (large holding tanks) where it awaits distribution. The cement is usually shipped in bulk in purpose-made trucks , by rail or even by barge or ship. Some is bagged for those who want small quantities.