Content of this article :
Characteristics of an Ideal Reinforcing Material,Steel as Reinforcing Material has high tensile strength and elasticity.,Deformed Bars and Twisted Bars
Characteristics of an Ideal Reinforcing Material
The characteristics of an ideal reinforcing material are:
- It should be easily and cheaply available in bulk.
- It should possess high tensile stress and elasticity.
- Its thermal coefficient of expansion should be nearly equal to that of concrete to minimise thermal stress.
- It should have a long and durable life so that it can render service for longer time.
- It should be free from loose mill scales, loose rust and coat of paints, which reduce the bond.
- It should be capable of forming perfect bond or grip with concrete so that stresses are transferred from one material to the other.
Steel as Reinforcing Material
The steel is commonly used as reinforcing material due to its following qualities.
- It possesses high tensile strength and elasticity.
- Its thermal coefficient is nearly equal to that of concrete i.e. and respectively.
- It develops good bond with concrete.
- It is cheaply and easily available in bulk.
- It is economical comparing all the aspects.
Deformed and Twisted Bars
The smoothness and roughness of the surface of the reinforcing bars, play an important role in the formation of bond. On smooth surface, less friction develops and consequently less bond. On the other hand, the rough surface provides better bond. To achieve this, the surface of reinforcing bars is roughened before use.
Deformed bars. This type of bars have some- type of projections which act as keys for concrete and check the flipping of bars. The deformations are spaced along the bar at equal distances and thus the bar develops a greater bond by mechanical resistance to sliding.
Twisted bars. Bond may also be improved by using twisted bars which are cold worked. Cold twisted bars increase the yield stress by about 50% and thus save the reinforcing material by 33%. The increase in stresses is due to the path of twist. Most suitable pitch is 9 cm. to 12 cm. If the pitch exceeds 12 cm., the stress reduces. In twisted bars hooks are generally not provided and thus a saving in steel and labour. On account of increased bond strength, the structures do not experience cracks. This is why twisted reinforcement is very useful for water retaining structures. The size of the bars used as reinforcement are 5, 6, 8, 10,12, 16, 20, 22,25, 32, 36, 40, 45 and 50 mm. These should fulfill the requirements of IS:code