HOW THINGS ARE MADE - What is cement and how is it made?

What is cement and how is it made?

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

Did you know? 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 (2.2 lbs) contains over 300 billion grains, although we haven't actually counted them to see if that is completely accurate! The powder is so fine it will pass through a sieve capable of holding water.

Tip: Cement should be stored in a dry area. If it gets wet or damp the powder will turn into a hard lump.

An example of how cement can be 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.