TMT Bars

Indian Scenario”

TMT Bar

Requirement of High Strength Rebars Problems associated with High Strength Rebars Technological developments in production processes of High Strength Rebars
Comparison of different processes for production of High Strength Rebars TMT Bars Manufacturing process TMT bars vs “Quenched & Tempered” bars
Advantages & Applications International Scenario Indian Scenario

Indian Scenario

Round plain steel ruled over this industry up to sixties.

In 1967, tor steel (trade name for deformed bars) was introduced in India and due to its advantageous properties, it completely replaced the mild steel except a few situations where acute bending was required in higher diameters of steel bars.

Tor steel, called grade Tor-40, with its characteristic strength of 415N/sq mm proved to be much economical than the conventional mild steel having a strength of 250 N/sq. mm only. While is a very small difference in their price-range, Tor steel is almost 65% stronger than mild steel and thus directly affects economy in RCC works.

Tor steel thus took over the scene in seventies and maintained its supremacy till nineties. Europe, where the CTD process was developed, gave up its use in the 1970s, a few years after its development. But in India, the story was different.

Introduced in 1970, the CTD bars gained a strong foothold in India despite the findings in Europe.

The closed market conditions prevailing at that time helped matters in this regard – it appears that we only appreciated the significant savings from use of CTD bars of 415 N/mm2 and ignored the drawbacks.

Mr. R. N. Raikar, President of the India Chapter of the American Concrete Institute, at his opening remarks in the seminar on ‘Reinforcement – Today & Tomorrow’ held in Mumbai in June 2003, lamented that “fewer repairs were required in buildings prior to the use of CTD bars. Today, the repair of buildings has become a specialised industry”.

One reason for delay in adopting this superior technology in India was the delay in amendment to Code IS 13920 for bars permitted to be used in seismic zones 3, 4 & 5. IS 13920 (before its amendment in March’02) stipulated that “ Steel reinforcement of grade Fe 415 (see IS 1786:1985) or less only shall be used.”

The reason apparently was that the IS 1786: 1985 specified minimum value of elongation as 12% & 8 % for Fe 500 & Fe 550 respecively; whereas this value was 14.5% for Fe 415 grade. This barred the use of Grade Fe-500 (& higher grade) even though they were available in the country with 18 per cent elongation since past 15-20 years.

It was only in March 2002 that an amendment no 2 was issued to IS 13920 which stipulated that “….high strength deformed steel bars, produced by thermo-mechanical treatment process, of grades Fe 500 & Fe 550, having elongation more than 14.5% and conforming to other requirements of IS 1786:1985 may also be used for the reinforcement.”

This delay only helped extend the life of CTD bars in India and as such it could not benefit from the introduction of superior quality rebars of higher strength and greater safety than CTD bars. Even so, many civil engineers were not aware of this amendment till as late as mid-2003.

However, the last decade has seen an extensive use of TMT steel and corrosion resistance steel thereby ushering in greater economy and longer life for RCC structures.

However, a bit of awareness on the part of civil engineers would certainly help in better harnessing of benefits from technological advances made in this field. This article aims at just that.

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References:
Latest developments on steel front” by Jagvir Goyal
Thermex Quenching and Tempering Technology” by R.K. Markan, the Chairman and Managing Director of H&K India
Websites of SAIL, Rajuri steel & Evcon

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