Concrete is good in resisting compression but is very weak in resisting tension. Hence reinforcement is provided in the concrete wherever tensile stress is expected. The best reinforcement is steel, since tensile strength of steel is quite high and the bond between steel and concrete is good. As the elastic modulus of steel is high, for the same extension the force resisted by steel is high compared to concrete.
However in tensile zone, hair cracks in concrete are unavoidable. Reinforcements are usually in the form of mild steel or ribbed steel bars of 6 mm to 32 mm diameter. A cage of reinforcements is prepared as per the design requirements, kept in a form work and then green concrete is poured. After the concrete hardens, the form work is removed. The composite material of steel and concrete now called R.C.C. acts as a structural member and can resist tensile as well as compressive stresses very well.
Properties of R.C.C./Requirement of Good R.C.C.
1. It should be capable of resisting expected tensile, compressive, bending and shear forces.
2. It should not show excessive deflection and spoil serviceability requirement.
3. There should be proper cover to the reinforcement, so that the corrossion is prevented.
4. The hair cracks developed should be within the permissible limit.
5. It is a good fire resistant material.
6. When it is fresh, it can be moulded to any desired shape and size.
7. Durability is very good.
8. R.C.C. structure can be designed to take any load.
Uses of R.C.C.
It is a widely used building material. Some of its important uses are listed below:
1. R.C.C. is used as a structural element, the common structural elements in a building where
R.C.C. is used are:
(a) Footings (b) Columns
(c) Beams and lintels (d) Chejjas, roofs and slabs.
2. R.C.C. is used for the construction of storage structures like
(a) Water tanks (b) Dams
(c) Bins (d) Silos and bunkers.
3. It is used for the construction of big structures like
(a) Bridges (b) Retaining walls
(c) Docks and harbours (d) Under water structures.
4. It is used for pre-casting
(a) Railway sleepers (b) Electric poles
5. R.C.C. is used for constructing tall structures like
(a) Multistorey buildings (b) Chimneys
6. It is used for paving
(a) Roads (b) Airports.
7. R.C.C. is used in building atomic plants to prevent danger of radiation. For this purpose R.C.C. walls built are 1.5 m to 2.0 m thick.