Evolution of rebars in India has been explained

1. Journey to TMT Bars
Dr.G.S.Suresh
Professor &Head
Civil Engineering Department
The National Institute of Engineering
Mysore

2. Introduction
• Reinforcement(Rebar)strengthens
concrete
• Concrete contracts and grips
rebar-Bond
• Rebars are rolled from billets that are obtained from a furnace.
• Rebars are generally rolled in round section.
• Ribs are indented on the surface of the deformed rebars or wires
during the process of rolling.
• The prime objective of such deformation is the enhancement of
bonding with concrete by mechanical interlocking.
• Plain mild steel (MS) rebars of grade Fe-250 were used widely till
about 1967
• Square twisted bars (deformed bars) were first introduced in
India in 1965.

3. Introduction Contd.
• The concept of reinforced concrete (RC) was first
initiated by Jean Louis Lambot in 1850 through
his rowboat
• The earliest civilian reinforced concrete
buildings were probably built in Bombay.
• In the suburb of Byculla a four-storey students
hostel built in 1907 for the Victoria Jubilee
Technical Institute is described as the «earliest
reinforced concrete structure in India

4. Introduction Contd.
• The Indian Cement Company was the first to start
producing cement, in 1914 at a factory in Porbander
on the Gujarat coast.
• In 1914 India manufactured 945 tons of cement and
imported 150,530 tons and the demand was such that
London agents were buying Germancement to re-
export to India
• The steel reinforcement was initially imported from
the UK though agents in Bombay and Calcutta
• Tata were the principle manufacturer of
reinforcement in India from 1914

5. Introduction Contd.
• In 1918, soon after the war, Indian Iron and Steel
Company (IISCO) was formed.
• The then Mysore government also decided to start an
iron works at Bhadravati.
• While IISCO started producing pig iron at Burnpur in
1922, the Mysore Iron and Steel Works took about 18
years to start its plant.
• Meanwhile, the Bengal Iron Works went into
liquidation and merged with IISCO.
• The Steel Corporation of Bengal (SCOB) formed in
1937, started making steel in its Asansol plant. Later
in 1953, SCOB merged with IISCO.

6. Introduction Contd.
• By the end of the second world war, deformed high
strength rebars started gaining momentum around
the world
• Cold twisted and hot rolled deformed rebars of proof
strength about 420 N/mm2 came out for wide usage
• However,in the Indian context, till about 1965, the
classical plain mild steel rebars of yield strength 250
N/mm2 constituted the reinforcement for the
concrete construction industry
• Winds of change were seen in this domain only after
1965.

7. Types of Rebars
• Mild Steel Bars
• Medium tensile steel
• Hot rolled deformed bars
• High yield strength deformed (HYSD)bars or
Cold twisted deformed bars (CTD)
• Thermo Mechanically treated bars
All bars have E= 200 kN/mm2

8. LIST OF BUREAU OF INDIAN
STANDARD CODE FOR REBARS
432 : Mild Steel and medium tensile steel bars and hard
drawn steel wire for concrete.
1786: Specifications for HYSD bars and wires for
reinforcement.
1566: Hard drawn steel wire fabrics for concrete
reinforcement.
2502: Code of Practice for bending and fixing of bars for
concrete reinforcement.
2751: Recommended practice for welding of mild steel
reinforcement
1139 : Hot rolled deformed bars.

9. History of Rebars in India
Introduction of square twisted rebars
• For the first time in India, on a small scale, square twisted
rebars with chamfered corners, Fig 2, were brought in to
market by IRC Steels, West Bengal with the collaboration of
BRC, UK. Since production of such rebars was quite an involved
process and since the rebars were not efficient enough, they
were phased out from the Indian market in a very short period.

10. History of Rebars in IndiaContd.
Production of cold twisted circular
rebars
• In 1967, Tor Isteg Steel Corporation of Luxumberg
introduced, in India, ‘cold twisted deformed circular
rebars’ of proof stress 420 N/mm2, which subsequently
became popular as Tor 40 rebars. The manufacturing
process essentially comprised of three stages:
(i) production of quality billets
(ii) passing the reheated billets through stands, to get
deformed rebars of desired diameters ; and
(iii) cold twisting the deformed rebars to the desired
Pitch.

11. History of Rebars in IndiaContd.
Production of cold twisted circular rebars
• Agarwal Hardwares, Kolkata; Mukund Steel, Mumbai, Rathi Steels,
Delhi; ISRM, Chennai were the first to produce these rebars in the
country in 1967. Hindustan Steels, (Presently SAIL) followed soon
after. By about 1970, these Tor 40 rebars (grade Fe 415) replaced the
classical plain mild steel rebars by about 50 percent in the country,
Fig 3.

12. History of Rebars in IndiaContd.
Production of cold twisted circular rebars
• In view of the simplicity in production, significant
savings in the consumption of rebars in
constructions and aggressive technical marketing
by the manufacturers and TOR ISTEG Steel
Corporation, classical plain mild steel rebars were
virtually replaced by these, by about 1975.

13. History of Rebars in IndiaContd.
Production of cold twisted circular rebars
• By about 1978, the industry decided to bring in
Fe 500 cold twisted rebars in consonance with
the trend in Europe. As a result, Tor 50 and
Tiscon 50 (grade Fe 500) were pushed in the
market
• Several major constructions came up around the
country with these higher grade rebars.

14. History of Rebars in IndiaContd.
Production of hot rolled rebars
• During the period when cold-twisted rebars were
being introduced, a few industrialists decided to
produce hot-rolled alloy rebars as well in our
country

15. History of Rebars in IndiaContd.
Production of hot rolled rebars
• It was by about 1968, that for the first time these
rebars were produced by Tata Steel and were
branded as Tistrong rebars
• Tata Steel, subsequently brought out cold twisted
deformed rebars with indigenous technical back
up, branding them Tiscon rebars

16. History of Rebars in IndiaContd.
Production of hot rolled rebars
• It was by about 1968, that for the first time these
rebars were produced by Tata Steel and were
branded as Tistrong rebars
• Tata Steel, subsequently brought out cold twisted
deformed rebars with indigenous technical back up,
branding them Tiscon rebars
• It was at this juncture that Tor Isteg Steel
Corporation handed over the mantle of ensuring
production of quality rebars to Torsteel Research
Foundation.

17. History of Rebars in IndiaContd.
Torkari rebars
In contrast to the cold twisting and thermo processing, a
new procedure for manufacturing high strength
deformed rebars was developed by Germans, branded as
Torkari rebars. The manufacturing procedure essentially
comprises of simultaneous cold reduction and cold
ribbing of wire rods. This process results in production of
rebars of proof strength upto 550 N/mm2. However, the
process is restricted to diameters up to 11 mm.

18. History of Rebars in IndiaContd.
Introduction of thermo processed (TMT) rebars
• In addition to Torsteel and Tiscon, several secondary
steel units, in the unorganised sector, also started
production of Fe-415 rebars, popularly termed as
CTD rebars.
• Between 1980 and 1985, new type of rebars termed
TMT rebars were developed around the world, for
the benefit of RC constructions. Notable amongst
them were Torsid from France, Tempcore from
Belgium and Thermex from East Germany.

19. History of Rebars in IndiaContd.
Introduction of thermo processed (TMT) rebars
• In addition to Torsteel and Tiscon, several secondary
steel units, in the unorganised sector, also started
production of Fe-415 rebars, popularly termed as
CTD rebars.
• Between 1980 and 1985, new type of rebars termed
TMT rebars were developed around the world, for
the benefit of RC constructions. Notable amongst
them were Torsid from France, Tempcore from
Belgium and Thermex from East Germany.

20. History of Rebars in IndiaContd.
Introduction of thermo processed (TMT) rebars
• The manufacturing process essentially comprised of
controlled quenching of rebars.
• The rebars heated up to a temperature of about 900o C,
when passed through quenching tubes — wherein the
volume and temperature of cooling water is controlled —
get quenched to a temperature of about 450oC in a few
seconds, This process results in enhancement of the
strength level of rebars, subject to precise control of all
parameters.
• These are essentially ‘dual phase rebars’, with tempered
martensite periphery and ferrite-pearlite core.

21. History of Rebars in IndiaContd.
Manufacturing Process of TMT Bars

22. History of Rebars in IndiaContd.
•In the initial years, the production
was restricted to rebars having
diameter higher than about 16 mm.
With experience and with the advent
of refinements in technology, smaller
diameters could be produced.

23. History of Rebars in IndiaContd.

24. History of Rebars in IndiaContd.
Other Development in Rebars
• Corrosion resistant rebars (CRS)
Modifications in chemical composition of the billets.
Manufactured by TATA, Vizag Steel and SAIL.
• Stainless steel rebars
Austenitic stainless steel rebars –expensive
Ferritic stainless steel rebars, - chromium content of 11 to 12%
both cost effective and corrosion resistant.

25. History of Rebars in IndiaContd.
Provisions in standards
A few prominent standards which cover the requirements
are:
Indian Standards – IS 1786
British Standards – BS 4449
American Standards – ASTM A615M and ASTM A706M
Euro norms – EN10080
and Asian Model Code 1999.

26. Standard Grade Yield
Strength(N/mm2)
min
UTS
(N/mm2)
%Elongation
min-mix
IS:1786-2008 Fe 415 450 540 18-22
IS:1786-2008 Fe 500 530 610 16-21
IS:1786-2008 Fe 550 580 640 16-20
Provisions in standards

27. Constituent
Carbon
Sulphur
Phosphorus
Sulphur &
Phosphorus
Fe
415
0.3
0.060
0.060
0.11
Fe
415D
0.25
0.045
0.045
0.085
Fe 500
0.3
0.055
0.055
0.105
Fe
500D
0.25
0.040
0.040
0.075
Fe 550
0.3
0.055
0.050
0.100
Fe
550D
0.25
0.040
0.040
0.075
Fe 600
0.3
0.040
0.040
0.075
Chemical Requirements
Maximum Limits as per IS1786-2008
Percent, Maximum
Note: The figures following Fe indicate the specified minimum 0.2% proof
stress or yield stress in N/mm2
The letter D following the strength grade indicates the category
with same specified minimum 0.2% proof stress/ yield stress but with
enhanced specified minimum percentage elongation

28. Requirements of Bond (IS:2770 part 1)
For high strength deformed bars/ wires, the mean
area of ribs (in mm2) per unit length (in mm) above the core
of the bar/wire, projected in on a plane normal to the axis
shall not be less than following values:
The mean projected area of transverse rib alone shall
be not less than one-third of the values given above.
When subjected to pullout testing in accordance with
IS 2770 part1, the bond strength calculated from the load at
measured slip of 0.025mm and 0.25mm for deformed bars/
wires shall exceed that of a plain round bar of the same
size by 40% and 80 % respectively.
0.12φ
0.15φ
0.17φ
For φ ≤ 10 mm
For φ more than 10mm and ≤
16mm
For φ > 16mm

30. History of Rebars in IndiaContd.
Sub-standard reinforcing bars
Inspite of the overall developments in the reinforcement field, the
construction industry is faced with the problem of substandard
reinforcements in the market which exhibit the following lacunae:
(i) brittle rebars with high carbon content,
(ii) low strength rebars with low carbon content,
(iii) bars marketed as TMT rebars, not being quenched at all; and
(iv) bars with inadequate quenching resulting in lower strength

31. History of Rebars in IndiaContd.
The defects which are generally observed in rebars from
the market are:
(i) underweight
(ii) defective geometry (over sized ribs and lugs or worn
out ribs and lugs)
(iii) rolling defects
(iv) twisting defects, and
(v) defects due to production from defective raw material
(pipings and inclusions).

32. History of Rebars in IndiaContd.
In the course of last two and a half years, about
18,000 rebar samples, sent by various consumers,
have been tested in Torsteel laboratories at
Bangalore, Chennai and Hyderabad in accordance
with stipulations in Indian Standards — IS 1608: 1995
and IS 1786 : 1985 (reaffirmed 2000). The physical
and chemical properties assessed included:
(i) 0.2 percent proof stress,
(ii) tensile strength
(iii) percentage elongation
(iv) type of fracture, and
(v) carbon content.

33. History of Rebars in IndiaContd.
The sub-standard rebars that were tested can be classified
into six specific categories. These categories are:
(i) TMT rebars with low carbon content
(ii) TMT rebars (?) quenched in water tank
(iii) TMT rebars with inadequate quenching in cooling tubes
(iv) TMT rebars (?) with no quenching at all
(v) CTD rebars – hot twisted, and
(vi) CTD rebars with high carbon content.

34. History of Rebars in IndiaContd.
CLOSE-UP OF TWO SUB STANDARD REBARS TESTED

35. History of Rebars in IndiaContd.
TMT REBARS QUENCHED IN WATER TANK: TYPICAL BRITTLE FRACTURE

36. History of Rebars in IndiaContd.
TMT REBARS THAT ARE INADEQUATELY QUENCHED

37. History of Rebars in IndiaContd.
TMT REBARS THAT ARE INADEQUATELY QUENCHED

38. History of Rebars in IndiaContd.
TMT REBARS WITH VERY LOW TENSILE STRENGTH

39. History of Rebars in IndiaContd.
STRESS-STRAIN DIAGRAM OF NORMAL AND SUBSTANDARD TMT BARS

40. 1. Concrete and Rebars are the two vital
components in any reinforced concrete
construction.
2. Safety and durability of such constructions is
directly dependent on the quality of Concrete
and / or Rebars.
3. The main problem in India today, is defective,
substandard and fake rebars in the market.
Field test for Checking TMT bars

41. The cursory test – outline of test
Whenever a rebar under a high temp is
quenched under controlled conditions and
cooled in air subsequently, due to metallurgical
transformation, two distinct phases (shades)
show out.
Tempered martensite in the form of a ring
with definite width forms the outer case (ring),
whereas the inner core remains pearlite / ferrite.
The outer case (ring) and inner core are
distinctly visible, when the cross-section of
rebar is etched.

42. Rebar before and after Thermo-Processing
C/s of a sample before
controlledquenching
Tempered martensite (outer
case)
Pearlite / ferrite
(inner core)

43. Following are the steps for carrying out the test;
1.Cut ‘small length samples’ from a few randomly
selected TMT rebars of any lot, preferably in a
cutting machine, if not, by hack-saw cutting.
2.Cross-sections of test samples shall be mirror
finished with any suitable polishing device.
An ideal polishing device is a unit with rpm of
about 3000, wherein an emery sheet can be
mounted on the rotating circular disc.
Polishing of cross-sections shall be done for
atleast about 10 minutes.
The Cursory Field Test - test procedure
Contd/….

44. Soon after etching, two distinct phases
(Shades) with uniform thickness are clearly visible
on the c/s, if the rebars are ‘Genuine TMT Rebars’.
If the two phases are not distinct, the rebars
are either ‘Substandard’ or ‘Fake’ TMT rebars.
Note: It is essential that the c/s be examined soon
after etching. In case of delay, etching to be redone.
The cursory field test – Test procedure (Contd/…..)
3. The c/s shall be smeared (etched) with drops of
‘Nitrol Solution’.
It is nothing but a synthesis of ’10 % of Conc.
Nitric Acid’ and ‘90 % of Ethyl Alcohol’.

45. Appearance of Genuine Thermo-processed
(TMT) rebars after etching with Nitrol

46. Appearance of Fake Thermo-processed
(TMT) rebars after etching with Nitrol

47. Appearance of (inadequately / inappropriately
quenched) Thermo-processed (TMT) rebars after
etching with Nitrol

48. Diameter
(mm)
12
16
25
% Carbon
0.174
0.152
0.160
0.2% Proof
Stress
(N/sq.mm)
602
567
513
Ultimate
Tensile
Strength
(N/sq.mm)
696
685
629
Elongation
over a gauge
length of ‘5
dia’ (%)
20
24
23
Chemical properties of Geniune Thermo-Processed
(TMT) Rebars
Note: The test results satisfy the requirements of
IS:1786-2008 for rebars.

49. Diameter
(mm)
12
16
20
% Carbon
0.204
0.186
0.198
0.2% Proof
Stress
(N/sq.mm)
353
314
390
Ultimate
Tensile
Strength
(N/sq.mm)
552
520
556
Elongation
over a gauge
length of ‘5
dia’ (%)
32
35
29
Chemical Properties of Fake Thermo-Processed (TMT)
Rebars
Note: The test results do not satisfy the requirements of
rebars as per IS:1786-2008

51. Twisting operation is not involved in the production of the TMT steel bar,so no residual
stresses involved in that , which in turn increases the corrosion resistance.
Rust and Corrosion Resistance :
The main reason for failure in any reinforcement concrete structure is due to corrosion of
TOR Steel in the concrete, where this steel corrodes in existence of chloride ions. TMT Bars,
due to its Thermo- mechanical treatment are very highly rust and corrosion resistant and is
best suited in the humid and coastal states like West Bengal and Orissa.
Uses:
TMT Bars are much superior to conventional TOR Steel by virtue of their various engineering
properties and can be used for Residential Buildings, Bridges, Drums, Industrial
Establishment and all types of concrete reinforcement purposes.
TMT Bars:
Grade - Fe 415
IS: 1786
Note:
The project designers use thermo mechanically treated bars (TMT) in place of torsteel and
even in TMT, the choice is increasingly focussed on that with higher tensile strength ( Fe-500
in lieu of Fe-415) and high corrosion resistant TMT (HCRM) which is specially meant for use
in coastal areas.