Although the words "cement" and "concrete" are often used interchangeably, cement is actually an ingredient of concrete - usually 10 to 15 percent of the concrete mix by volume. Mixing cement with water, sand and gravel, forms concrete.
Portland 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. Cement is usually gray in color and it's extremely fine in texture.
How Cement is Made
Limestone is the primary ingredient for making cement; we begin the process by mining limestone from a quarry.
We transport boulder-size limestone rocks from the quarry to the cement plant. The big rocks are fed into a machine called a crusher which smashes the boulders into marble-size pieces.
We send the pieces of limestone through a large blender and mix them up with other raw materials, such as sand and clay. Limestone, sand, clay and an iron source, such as mill scale or slag contain the four essential elements required to make cement: Calcium, silicon, aluminum and iron.
We use big, heavy rollers and a rotating platform to grind up the mixture of raw materials into a powder.
We transfer the mixture into a rotating kiln where the raw materials become 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".
When the clinker cools, we grind it with gypsum, which provides "workability." The result is the fine, gray power we know as cement.
We store the cement in silos where it awaits distribution.
We ship it to our customers in bulk via tanker-type trucks, by rail or even by barge or ship. Some of our product is bagged for our customers who prefer small quantities.
Learn more about cement and the cement industry by visiting the Portland Cement site at www.cement.org.
Enjoy these fun animations describing how cement and ready-mixed concrete are made.