The plain cement concrete is weak in tension, though it has enough strength in compression. Fresh concrete can be moulded into almost any shape and can be used in building construction. Due to little strength in tension , plain concrete as such is weak in bending, shear and torrosion. Hence the use of plain concrete is limited to applications where great compressive strength and weight are the principal requirements and where tensile stresses are either totally absent or are extremely low.
Concrete once set will take a superimposed load that compresses it, but , if used say as a beam will fail if heavily loaded , because it is weak in tension . Steel , on the other hand is strong in tension , so the two materials are combined to enable the concrete to perform well in tension as well as in compression by casting steel rods in the positions where reinforcing is necessary to improve tensile strength , especially in beams, lintels etc . Thus reinforcement is used to help resist compressive forces or to improve dynamic properties.
A reinforced concrete section where the concrete resist the compression and steel resists the tension can be made into almost any shape and size required construction. Unreinforced concrete cracks under relatively small loads or temperature change because of low tensile strength. The cracks are unsightly and can cause structural failure. To prevent cracking or to control the size of crack openings, reinforcement is incorporated in the concrete. Generally, steel wires or bars are used for reinforcement. The concrete so obtained is termed as reinforced cement concrete (RCC).
During construction, the bars are placed in a form and then concrete from a mixer is cast to embed them. After the concrete has hardened deformation is resisted and stresses are transferred from concrete to reinforcement by friction and adhesion along the surface to the reinforcement.
Reinforced concrete can be used to construct entire skeletal frames, floor, slabs, walls etc. either precast in a factory or on site where it will be permanently placed.
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