How Is Cement Powder Made?

Cement powder is a key component of concrete.

Four types of substances go into the making of portland cement: calcium, aluminum, iron and silicon. The primary material, calcium, typically comes from limestone. Sand or clay provide the silicon, while sources such as bauxite and iron oxide supply the aluminum and iron. All of these elements need processing at production facilities to create the strong binding material called portland cement.

Crushing

Cement manufacturers obtain the appropriate materials and collect them at their facilities. The limestone then undergoes a crushing process that shapes it into small pieces about six inches long. A second process reduces the size to about three inches long. The small pieces of limestone then move into a blender, which adds the other substances and mixes them with the limestone aggregate. Machines then grind the blended material into a powder to prepare it for the next step in the process.

Kiln

Heating the powder in kilns removes some of the water and carbon dioxide from the mixture and binds it together. The kiln, a large rotating pipe with flame jets on its lower section, reaches temperatures of about 2,700 degrees F., and changes the chemical makeup of the mix. About two-thirds of the original mixture remains once the process is complete. Called clinker, the treated mix takes the form of red-hot pellets.

Grinder

Once the clinker cools, it goes through a grinder that changes it back to powder form. The gray powder is quite fine; one pound of powder can contain 150 billion grains. During the grinding process manufacturers add a small amount of gypsum, a crystalline mineral that helps control the rate of hardening when the cement is used to make concrete. After the grinding finishes, the material now qualifies as portland cement.

Storage and Distribution

Manufacturers store the cement in silos as they wait to distribute it to their customers. They use a variety of methods for distribution, including the use of trucks specially designed for transporting cement, railroad cars and ships or barges. They also put some of the cement powder into bags for customers who want smaller amounts. Do-it-yourself homeowners purchase these bags when buying cement at the local home improvement store.

References

• BuildEasy: What is Cement and How is it Made?
• Portland Cement Association: How Portland Cement is Made
• Portland Cement Association: Frequently Asked Questions