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Cement, How It Is Produced




Cement - The Short Version
Cement, or Portland cement, is defined as "a hydraulic cement, obtained by burning a mixture of lime and clay to form a clinker, then pulverizing the clinker into powder. The greenish gray powder is composed primarily of calcium silicates, calcium aluminates, and calcium ferrites. When mixed with water (Hydrated), it solidifies to an artificial rock, similar to Portland stone." A Portland Stone is a yellow limestone from the Isle of Portland, in Great Britain.

Historically, cement can be traced back to the early Roman Empire, and contributed to the building of the great structures of the Roman Empire. By varying the amounts and types of the same basic ingredients, cement with various properties may be obtained. By further varying the ingredients, even more differing cements are manufactured.

*"Cement manufacturing is the basic processing of selected and prepared mineral raw materials to produce the synthetic mineral mixture (clinker) that can be ground to a powder having the specific chemical composition and physical properties of cement." Cement manufacture, like many other manufacturing processes, begins at the mine, where the raw materials like limestone, silica, aluminates, feric minerals and others are obtained. Some typical materials used for calcium carbonate in cement manufacturing are limestone, chalks, marbles, marls, and oyster shell. Some typical materials used for alumina in the cement manufacturing are shale, clay, slags, fly ash, bauxite, alumina process waste, and granite. Some typical materials used for silica in cement manufacturing are sand, clay, claystone, shale, slag, and fly ash. Some typical materials used for iron in cement manufacturing are iron ores, blast furnace flue dusts, pyrite clinker, mill scale, and fly ash.


Ball Mill In A Cement Plant


 
The general mining methods are surface mining, while some silicates, such as sand, are commonly mined using dredges, from lakes, rivers and waterways. There are a few underground limestone mines, but most are pits on the surface. Cement plants are typically located central to the minerals required to make the cement, which saves the transportation costs and reduces the price of the cement. Once the ore material to be used for cement has been mined, it is transported to the crushing/screening plant, where it is crushed and screened, to produce the desired particle size. Ore from the mines are typically reduced to about inch and stored in a coarse stockpile. From there, the inch ore is typically reduced to a powder in a large ball mill.  



 
Sometimes, the raw materials are wet ground in the ball mill by adding water, and form a slurry. In either event, wet or dry, the ground powder is then blended, using the "Chemist's Secret Mixture", which can be a closely guarded "recipe", and are then transported to the rotary kiln for heat processing. In the rotary kiln, first the carbon dioxide is driven off of the calcium carbonates, then the raw material is fused at a temperature somewhere around 2,700 degrees F. The discharge from the kiln is called clinker, as it resembles small rocks or residue from a blast furnace. The clinker is the cement in "lump" form. The particle size range for clinker is from about 2 inches to about 10 mesh. The clinker is then ground in a ball mill and shipped to users as Portland Cement.

 
There are five general types of cement.
First, Type 1 cement is general cement for general use, typically the type used in construction.

Type 2 cement is still a general cement, but it has resistance to sulfates and heat of hydration.

Type 3 cement is for high strength properties in the early stages of the cement's life. I.e., immediately after curing.

Type 4 cement is used where very low heats of hydration are desired.

And Type 5 cement is used where a very high sulfate resistance is required.

In the United States, the American Society of Testing Materials, the American Association of State Highway Officials, the American Concrete Institute, the US Corps of Engineers are generally the primary driving force of the cement quality and technology standards and specifications.

Concrete is a mixture of gravel, sand and cement. Concrete is NOT cement, but it is made with cement.

* - Industrial Minerals and Rocks 4th Edition

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