1. Concrete & Reinforced Concrete

Concrete

Concrete is a stone like material obtained by permitting a carefully proportioned mixture of cement, sand or gravel or other aggregate and water to harden in forms of the shape and dimensions of the desired structure. Here, cement is a binding material and aggregate is filling material.

Properties of Concrete

i) It is strong in compression and suitable for member subjected to compression like column.

ii) It is relatively brittle in nature.

iii) Tensile strength is low as compared with its compressive strength.

Reinforced Concrete

When steel reinforcement is used in the concrete at the place where the section is subjected to tensile stress then it is called reinforced concrete.

The reinforcement usually round steel rods with appropriate surface deformation to provide interlocking. When the reinforcement completely surrounded by the hardened concrete mass. It forms an integral part of the member.

N.B.:Concrete is weak in tensile stress compared to its compressive stress. To offset this limitation, steel reinforcement is used in concrete.

Advantages of reinforced concrete

i) It has a good compressive strength.

ii) It has high tensile strength.

iii) It has good resistance to damage by fire.

iv) It protects steel bars from buckling and twisting at high temperature.

v) Much greater ductility and toughness of steel makes reinforced concrete to more suitable for use in different construction.

vi) Its maintenance cost is practically low.

vii) It can be molded to any desired shape safely.

viii) RCC is more durable than CC.

Disadvantages of reinforced concrete

i) It needs mixing, casting and curing, all of which affect the final strength of concrete.

ii) The cost of the forms used to cast concrete is relatively high.

iii) It has low compressive strength as compared to steel (The ratio about 1:10 depending on material) which leads to large sections in columns or beams of multi-storey building.

iv) Crack develops in the concrete due to shrinkage and application of live loads.

Reasons behind using mild steel as reinforcement in RCC

It is observed that all the requirements of a good reinforcing material are fulfilled by mild  steel. Thats why mild steel is used as common reinforcing material for RCC.

Requirements of a good reinforcing material

i) Should be able to develop perfect bond with concrete.

ii) Coefficient of thermal expansion should be nearly the same as that of concrete.

iii) Should have high tensile strength and long durability.

iv) Should easily be cut and bent.

v) Should not produce any harmful effect or reaction combining with concrete.

vi) Should be easily available.

Pre-stressed concrete

A special way has been found however to use steels and concrete of very high strength in combination. This type of combination structure is known as pre-stressed concrete.

The steel bars are embedded in the concrete under high tension that is held in equilibrium by compressive stress in the concrete after hardening. Because of this pre-compression, the concrete in a flexural member will crack on the tension side at a much higher load then when not so pre-compressed. So, pre-stressed greatly reduced both the deflection and tensile cracks.