Concrete is a construction material that consists of, in its most common form, cement, gravel and sand, and water. Concrete is the most highly used manmade product on Earth. It is used to make pavements, building structures, foundations, motorways/roads, overpasses, parking structures, brick/block walls and

footings for gates, fences and poles. Approximately six billion cubic metres of concrete are produced every year, which is one cubic metre per person on Earth! Concrete commands a $35 billion worldwide industry and employs, in the United States alone, 2 million people.

The origins of concrete can be traced back to the Babylonians, who used a clay-mix similar to concrete. However, the modern-day form of concrete was not invented till 1756, when British engineer John Smeaton pioneered the use of cement in concrete. His ingredients included pebbles and powdered brick as

aggregate. Nowadays, recycled materials are becoming increasingly more popular as ingredients in concrete due to higher public awareness about ecological sustainability and environmental damage.

The composition of concrete is traditionally relatively simple. However, modern concrete is often a complicated mix, ensuring durability and longevity. Cement is the main ingredient in concrete. Portland cement is the most common cement in circulation, which is just a basic mix of mortar and plaster.

Water is another ingredient in the manufacture of concrete. The w/c ratio (mass ratio of water to cement) is the key factor that determines the strength of Concrete. A lower w/c ratio will yield a concrete which is stronger, while a higher w/c ratio yields a concrete with a lower strength. Water also affects the workability and consistency of a concrete.This water and cement paste hardens over time, and both fine and coarse aggregates are added to provide bulk. Widely used aggregates include sand, gravel and crushed stone. Decorative stones such as, small river stones or crushed glass are sometimes added to the surface of concrete for a decorative "exposed aggregate" finish, popular among landscape designers.

Ad mixtures are also added to a concrete mix to give it certain characteristics not obtainable by basic production. Admixtures come in powder or paste form and generally consist of no more than 5% of the entire mixture.Concrete has many characteristics including:

1)Workability: bility to mould to certain shapes

2)Curing: keeping concrete under certain conditions till it hydrates

3)Strength: high compressive strength, low tensile strength

4)Elasticity:relatively low

5)Expansion and shrinkage:provisions must be made for both

6)Cracking:abnormal drying rate will result in cracks

7)Creep:the permanent movement of a slab of concrete

Concrete is used for many structures. Mass concrete structures are structures built with one, giant concrete slab so that there are no weak points, such as dams or shelters. Reinforced concrete structures have bars of steel running through the concrete to ensure strength and stability. Pre stressed concrete

structures have a predetermined stress level which will never be exceeded, as they will only carry their own weight. Concrete is an amazingly versatile material. Whether you are building some of the largest structures in the world or a small pathway , the evolution and discovery of concrete has changed our world.