Though concrete is manufactured, it is composed entirely of natural elements. Concrete is actually composed of three parts: aggregates, cement and water.

Aggregate is a mixture of mineral materials such as sand and stone. Sand is finely crushed rock and is much coarser than limestone. Stones add strength to the concrete, and a variety of stones are added depending on what the concrete is used for.

Cement is created from limestone. ("What is limestone?") Limestone is blasted from the earth using explosives. Then it is heated up, which causes it to produce a very fine gray dust called cement.

When the cement is added to water, it creates a sticky paste that holds the aggregate together. The most common type of cement is Portland cement. (Learn how Portland cement is made).

1. Mixing. All the solid ingredients are put into a large mixing bowl at the plant. The bowl spins as the stone and sand (the aggregate) is mixed with the cement.
2. Adding water. Water is then added to the mixture, making concrete.

The mixture is then put in the back of a large mixer truck. These trucks have a back part that turns, keeping the concrete from drying out and getting hard until it is ready to be poured. Concrete gets warm and thick when it is wet.

When concrete is ready to be poured, the truck drivers release the concrete from a chute on the front of their truck into a form that keeps it in place. Workers must work quickly to smooth out the concrete before it dries; when the concrete does start to dry, it is called curing. It usually takes a day for concrete to dry.

5600 B.C.	The first concrete is used to build.
3000 B.C.	The Egyptians used lime and gypsum as cement in building the Great Pyramids.
290 B.C.	The Romans began to use a type of cement mixed with volcanic ash to build structures throughout Rome, including the Appian Way and the Roman baths.
1774 A.D.	It was discovered that combining lime with other materials created a hard binding material.
1824 A.D.	Joseph Aspdin created Portland cement by burning ground limestone and clay together, which created a stronger cement than using limestone alone.

Concrete has been around for a long time. Today, concrete is one of the most commonly used building materials, but it is still being adapted to modern needs. Look at this link to learn more about the bendable concrete that was invented at the University of Michigan. The concrete is already being used in places like Japan and Australia.

Floating Concrete