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COMPOSITE MATERIALS - REINFORCED CONCRETE

V. Ryan 2010

 

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Concrete is made from small stones and gravel called aggregate, sharp sand, cement and water. The small stone and gravel (aggregate) is the reinforcement and the cement is the matrix that binds it together. Concrete has good ‘strength’ under compression but it is weak in tension. It can be made stronger under tension by adding metal rods, wires, mesh or cables to the composite. The concrete is cast around the rods. This is called reinforced concrete.

 
Concrete is strong when under a compressive force. This is the case in most buildings, for example, the foundation of a building. The weight of the walls press down on the concrete foundations, compressing the concrete. Concrete is the ideal material for the foundations because it can withstand this type of compressive force.
However, concrete is very weak when under a tension (also known as a tensile force). If a concrete beam was to be used as a lintel, above a door, it would not be able to support the weight of the bricks above. Consequently, it would fail and collapse. Study the diagram below.
 
 
 
However, concrete can be reinforced by adding steel rods to the concrete mixture, allowing the concrete to set solid. The steel rods ensures that reinforced concrete can withstand tensile forces. This makes reinforced concrete a versatile, composite material. It is used widely in the construction industry
Reinforced concrete has long steel rods passing through its length, adding great strength to the final composite material, especially the ability to resist tensile forces.
 
The drawing below shows the concrete as being transparent. This is so the grid of steel rods can be seen in position.
 
 
 
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