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Concrete

In construction, concrete is a composite building material made from the combination of aggregate and cement binder. The most common form of concrete is portland cement concrete, which consists of mineral aggregate (generally crushed stone), Portland cement and water. After mixing, the cement hydrates and eventually hardens into a stone-like material. When used in the generic sense, this is the material referred to by the term concrete. 

The Assyrians and Babylonians used clay as cement in their concretes. The Egyptians used lime and gypsum cement. In the Roman Empire cements made from pozzolanic ash were used to make a concrete very similar to modern portland cement concrete. In 1756, British engineer John Smeaton pioneered the use of portland cement in concrete, and used pebbles and powdered brick as aggregate. 

Concrete has great compressive strength, but little tensile strength. To overcome this limitation, concrete is most often constructed with the addition of steel bars (rebars), steel mesh, or cables, to produce reinforced concrete, a composite material with more balanced strength properties. 

Concrete is also made with asphalt or epoxy as a binder. 

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