TMT reinforcement steel are used in reinforced concrete construction to provide better strength in tension, bending, shear as well as in compression. TMT steel means Thermo Mechanically Treated steel.
For years, bamboo has been used by man for construction activities, later it has been replaced by CTD (Cold Twisted Deformed steel rods) or TOR steel rods. The manufacturers adopted the “Cold Twisting Process” in which the naturally cooled rods were twisted by means of motors.
Thus the molecular structure of the core steel is weakened. Thus it should not be used for construction activities.
Now, the TMT reinforcing steel rods have emerged. This rod is not twisted; instead it is treated with the Water Jacketing Process and allowed to cool in the ambient condition.
Composition of TMT Reinforcement Steel
The composition of TMT reinforcement steel is:
|Chemical||BIS (Bureau of Indian Standards)||Rosun TMT|
|Carbon (Max%)||0.30||0.25 to 0.30|
|Manganese (%)||0.5 to 1.2||0.5 to 0.8|
|Sulphur & Phosphorous||as per IS:1786/85||as per IS:1786/85|
Manufacturing Process of TMT Reinforcement Steel
TMT reinforcement steel manufacturing process is shown below:
Water Jacketing Method
The steel rebar are at high temperature when they leave the last rolling stand. They are immediately passed through a predetermined quantity of a high-pressure water-cooling system. These instant cooling tempers the outer surface and it becomes very hard.
The next phase involves cooling at an ambient temperature that allows the hot core to temper the surface through thermal exchange. This result in a unique tempered structure of Martensite (outer) and a fine-grained Bainite-Ferrite / Pearlite (core) that is stronger, more flexible and far better suited for construction.
Comparison of TMT Steel with CTD Steel Bars
|Properties||CTD Bars||TMT Bars|
|Strength||High (Normally up to Grade Fe-415)||Very High as grades of Fe-500 & 550 are easily achievable|
|Elongation||As per IS: 1786/ ’85||Very High in all grades and over- achieves the elongation requirement in the recent amendment to IS: 1786 for earthquake resistance|
|Weldability||Preferably avoided as welded joints are weak||Better and no loss of strength|
|Formability||Bend 3D – 5D, Re-bend 5D – 8D||Excellent due to uniform elongation|
|Ductility & Fatigue Strength||High||Very High, Most suited for earthquake resistant structures|
|Fire Hazards||Loss of Strength on temperature rise||Negligible loss in strength up to 500 deg. C|
|Corrosion Resistance||Scale fall down during cold twisting||Pre-welded meshes can be used|
|Workability||Easy working at site||Availability of Grade Fe-500 & 550 results in steel saving|
|Overall Economy||Availability of Grades Fe-500 & 550 results in steel Saving|
Advantages of TMT Reinforcement Steel
- Savings of 14 – 19% steel
- Reduction in Costs
- Better safety of structures
- Easy working at site
- Better ductility & bendability
- Better Corrosion Resistance
- Good Weldability
- Resistant to fire hazards
Special Features of TMT Reinforcement Steel
- Higher strength with better elongation
- Excellent Weld-ability
- Resistance to fire hazards
- Excellent Ductility
- Higher Fatigue Strength
- Easy workability at site
- Better Bonding Strength
- Better Corrosion Resistance
- Achieves better results than BIS Standards