Steel reinforcements are provided in RCC to resist tensile stresses.The quality of steel used in RCC work is as important as that of concrete. Steel bars used in RCC should be clean and free from dust and impurities.
As per clause 5.6 of IS 456, steel reinforcment used in concrete may be of the following types:
- Mild steel and medium tensile steel bars.
- High yield strength deformed bars.
- Hard drawn steel wire fabric.
- Structural steel.
Mild Steel Bars: These bars which are produced by hot rolling, are generally not used in RCC as they have smooth surface and hence their bond strength is less comapared to deformed bars. They are used only as ties in columns or stirrups in beams. Mild steel bars have characteristic yield strength ranging from 240MPa to 350MPa.
High-yield strength-deformed bars: (HYSD bars) These bars were introduced in India in 1967. They completely replaced mild steel bars except in few situations where bending of bars greater than 30 mm was required. They were produced initially by cold twisting and later by heat treatment.
Thermo-mechanically treated reinforcement bars (TMT): These are a class of hot rolled HYSD bars, which are rapidly cooled to about 450ºC from 950ºC by a controlled quenching process using water when they are leaving the mill. TMT bars can be welded and no extra precautions are required.