Myths about TMT bar

1. TMT has higher bond
Process of making TMT as such has no role in bond strength between rebar and concrete. Factors responsible for higher or lower bond are Rib geometry and concrete properties.
Rib geometry
-transverse rib height
-transverse rib length
-transverse rib angle of inclination
-transverse rib spacing
Concrete properties
-use of chemical ingredient
Bond strength of any type of rebar in concrete can be tested with pull out test

2. TMT is corrosion resistant
in fact reverse is the truth. TMT bars are highly prone to corrosion due to its dual microstructure ie. Martensite and Perlite, Which provides galvanic coupling for corrosion. TMT bars at site shows corroded layer on outer surface.

3. TMT bar once in concrete never corrode
This is equally false belief that TMT bars gets corroded in outer atmosphere only and not inside concrete. As concrete is permeable to corrodents like moisture, oxygen, chloride etc Rate of corrosion can be different based on severity of atmosphere

4. TMT never fails in bend/strength
Every material has a defined range of properties which is prescribed in various nation/international standards beyond which it fails.

5. Any water-cooled bar are TMT
Water cooling hot bars are critical part of TMT bar processing but the process is called Quenching and is carried out under certain range of temperature to get desired microstructure which is responsible for higher strength of TMT bar. Water quenching if not done properly creates two process issues
Improper or peripheral quenching- this creates bar with variable mechanical properties in the bar, which is an safety hazard.
Tempering-this process imparts ductility and stress relieving effects to bar which harmonizes properties of rebar

6. TMT bars are earth quake resistant
In case of earthquake combined effects of concrete and TMT bar plays important role, TMT bar alone can’t resist forces of earthquake. Hence judicious selection of properties and integration of both is required

7. Scrap heated and rolled into bars are also TMT
Any scrap without known material history does not provide physical and mechanical properties defined in rebar standard, it may provide such wide variation that structural design requirement becomes first casualty and hence a safety concern.

8. TMT is the only rebar used in RCC

Now a days lot of innovations are happening in rebar field. Variety of Bars depending on site and environmental concerns are deployed. Some of the widely used type are Stainless steel, FRP, basalt, galvanized bars, epoxy coated bars

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