- SteelworldResearch Team

32 January 2020STEELWORLD

Infrastructure boom to supportrebar demand in India

Reinforcement steel

bar (rebar) is a steel

bar or mesh of steelwires

used in reinforced concrete

and masonary structures to

strengthen and hold the

concrete in tension. The

surface of rebar is often

patterned to improve the

quality of the bond with the

concrete.

Reinforcing bars in

masonry construction have

been used since at least the

15th century (2,500 meters

of rebar was used). During

the 18th century, rebar was

used to form the carcass of

the leaning tower of

Nevyanskin, Russia, built on

the orders of the

industrialist AkinfiyDemidov.

The cast iron used for the

rebar was of high quality,

and there is no corrosion on

the bars to this day. The

carcass of the tower was

connected to its cast iron

tented roof, crowned with

one of the first known

lightning rods. However, it

was not until the mid-19th

century that rebar displayed

its greatest strengths with

the embedding of steel bars

into concrete, thus

producing modern

reinforced concrete.

The need

Rebar's surface is often

"deformed" with ribs, lugs or

indentations to promote a

better bond with the

concrete and reduce the risk

of slippage. The most

common type of rebar is

carbon steel, typically

consisting of hot-rolled

round bars with deformation

patterns. Other readily

available types include

stainless steel, and

composite bars made of

glass fibre, carbon fibre or

basalt fibre. The steel

reinforcing bars may also be

coated in an epoxy resin

designed to resist the

effects of corrosion mostly

in saltwater environments,

but also land based

constructions.

Bamboo has been shown

to be a viable alternative to

reinforcing steel in concrete

construction. These

alternate types tend to be

more expensive or may have

lesser mechanical

properties and are thus

more often used in specialty

construction where their

physical characteristics fulfil

a specific performance

requirement that carbon

steel does not provide. Steel

and concrete have similar

coefficients of thermal

expansion, so a concrete

structural member

reinforced with steel will

experience minimal

differential stress as the

temperature changes.

Rebar is required to

compensate for the fact that

whilst concrete is strong in

compression, it is relatively

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34 January 2020STEELWORLD

weak in tension. By casting

rebar into concrete, it is able

to carry tensile loads and so

increase overall strength.

Steel reinforcement steel

bars that are provided in

combination with plain

cement concrete to make it

reinforced concrete. Hence

these structures form steel

reinforced cement concrete

structure (RCC).

Plain concrete is weak in

tension and strong in

compression. Tensile

property for concrete

structures is obtained by

incorporating steel

reinforcement which is

strong in both tension and

compression. The tensile

property provided by the

steel reinforcement

prevents and minimizes

concrete cracks under

tension loads. The

coefficient of thermal

expansion of steel

reinforcement and concrete

are similar in that they

undergo similar expansions

during temperature

changes.

This property will ensure

that the concrete is

subjected to minimal stress

during temperature

variations. The surface of

the steel reinforcement bars

is patterned to have a proper

bond with the surrounding

concrete material. The two

main factors that provide

strength to the concrete

structures are steel and

concrete.

The design engineer will

combine both the elements

and design the structural

element such a way that the

steel resists the induced

tensile and shear force,

while the concrete takes up

the compressive forces.

Use of high-quality

reinforcement steel

products in concrete

improves its properties.

Nowadays, reinforcement

steel products are some of

the most important

building materials used in

metal industry.

It is impossible to

imagine buildings or metal

constructions without

reinforcement steel. Thanks

to their excellent

performance and technical

properties, reinforcement

steel products are being

used in all fields of

construction. Choosing

quality steel rebars and coils

is a very important and

responsible task at the first

stage of construction.

The durability, safety

and service life of buildings

directly depend on the

quality of reinforcing

materials. Rebars may be

categorized by their profile:

there are round, smooth

and ribbed.

Nowadays, reinforced

concrete is being used on

almost all construction

sites, and it is one of the

predominating building

materials.

Steel rebars are a very

important component of

monolithic reinforced

concrete, as they improve

the concrete and reinforced

concrete construction

bending and shear behavior

and strength. The most

commonly used reinforcing

steel materials are flexible,

including rebars, welded

wire mesh and frames.

Nowadays, reinforced

concrete is being used on

almost all construction

sites, and it is one of the

predominating building

materials.

Types of rebars and their

applications

Steel is only used as

rebar because elongation of

steel due to high

temperatures (thermal

expansion coefficient)

nearly equals to that of

concrete. The surface of the

mild steel bars is plain and

round in shape. They are

available in various sizes of

6 mm to 50 mm. They are

used in concrete for special

purposes, such as dowels at

expansion joints, where bars

Nowadays,

reinforced

concrete is

being used

on almost all

construction

sites, and it is

one of the

predominating

building

materials.

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35 January 2020STEELWORLD

must slide in a metal or

paper sleeve, for contraction

joints in roads and runways,

and for column spirals.

They are easy to cut and

bend without damage.

Deformed steel bars

have ribs, lugs and

indentation on the surface

of the bar, which reduces

the major problem that is

faced by mild steel bar due

to slippage and good

bonding is achieved

between concrete and rebar.

The tensile property is

higher compared to other

rebars. These bars are

produced in sections from 6

mm to 50 mm dia.

Thermo mechanically

treated bars are hot treated

bars that are high in

strength used in reinforced

cement concrete (RCC)

work. It is the latest

induction in the mild steel

bars with superior

properties such as strength,

ductility, welding ability,

bending ability and highest

quality standards at

international level.

High strength deformed

bars are cold twisted steel

bars with lugs, ribs,

projection or deformation on

the surface. It the

extensively and majorly

used for reinforcement

purposes in a construction.

These bars are produced in

sizes or sections from 4 mm

to 50 mm in diameter.

European rebar is made

of manganese, which makes

them bend easily. They’re

not suitable for use in areas

that are prone to extreme

weather conditions or

geological effects, such as

earthquakes, hurricanes, or

tornadoes. The cost of this

rebar is low.

As the name represents,

it is made up of carbon steel

and is commonly known as

Black Bar due to carbon

colour. The main drawback

of this rebar is that it

corrodes, which adversely

effect the concrete and

structure. The tensile

strength ratio coupled with

the value makes black rebar

one of the best choices.

Epoxy-coated rebar is

black rebar with an epoxy

coat. It has the same tensile

strength, but is 70 to 1,700

times more resistant to

corrosion. However, the

epoxy coating is incredibly

delicate. The greater the

damage to the coating

indicates the less resistant

to corrosion.

Galvanized rebar is only

forty times more resistant to

corrosion than black rebar,

but it is more difficult to

damage the coating of

galvanized rebar. In that

respect, it has more value

than epoxy-coated rebar.

However, it is about 40%

more expensive than epoxy-

coated rebar.

Glass-Fiber-Reinforced-

Polymer (GFRP) is made up

of carbon fibre. As it is

made up of fibre, bending is

not allowed. It is very

resistant to corrosion and

is costly when compared to

other rebars.

Stainless steel rebar is

the most expensive

reinforcing bar available,

about eight times the price

of epoxy-coated rebar. It is

also the best rebar available

for most projects. However,

using stainless steel in all

but the most unique of

circumstances is often

overkill. But, for those who

have a reason to use it,

stainless steel rebar is 1500

times more resistant to

corrosion than black bar; it

is more resistant to damage

Stainless steel

rebar is the

most expensive

reinforcing bar

available, about

eight times the

price of

epoxy-coated

rebar.

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36 January 2020STEELWORLD

than any of the other

corrosive-resistant or

corrosive proof types or

rebar, and it can be bent in

the field.

Hot rolled deformed

bars are most commonly

used steel reinforcement

for RCC structures. As the

name says, the hot rolling

of the reinforcement is

undergone leaving certain

deformations on its surface

in the form of ribs. These

ribs help to form a bond

with the concrete. The

typical yield strength of hot-

rolled deformed bars is

60000psi.

A cold worked

reinforcement bar is

obtained by letting the hot

rolled steel bars to

undergo cold working. In

the cold working process,

the bars will undergo

twisting and drawing. The

process is performed at

room temperature. The

cold worked steel bars do

not undergo a plastic yield

thus has less ductility

when compared with hot

rolled bars.

Production and

consumption of rebars in India

Rebars have become the

preferred standard for

construction of private or

commercial building

structures, bridges and

many other business

structures for public or

private uses. The most

popular among them is the

thermo mechanically

treated (TMT) reinforced

bars. About 35% of the total

steel production in the

country was accounted by

the reinforced steel industry.

Usage of high strength

TMT steel rebars has

ensured rapid growth within

the construction sector.

India produces around 30

million tonnes of rebars

annually which are

consumed fully. Of late,

however, the slowdown in

infrastructure sector has hit

rebar industry as well with

both production and

consumption declined over

the last few years, albeit

marginally to create surplus

in the system.

Leading manufacturers,

meanwhile, have lowered

operating capacity to

control production and

thereupon, supply to suit

India’s domestic demand.

Many producers of rebar

have started selling under

branded product to fetch

premiums other such

products available.

Outlook

The outlook of rebar

manufacturers is bright

considering huge

infrastructure push initiated

by the government with a

massive fund allocation

plans to push construction

of bridges, modernising

railway stations and

creating additional handling

capacity of national

highways and airports.

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WORLDSTEEL

Usage of high

strength TMT

steel rebars

has ensured

rapid growth

within the

construction

sector.

In-Focus