A

PAPER PRESENTATION

ON TOPIC

“BENEFITS OF STEEL FIBER REINFORCED CONCRETE”

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CONTENTS

1. ABSTRACT 2. INTRODUCTION 3. FIBER REINFORCED CONCRETE

4. WHY USE STEEL FIBER 5. BENEFITS OF STEEL FIBER REINFORCED CONCRETE 6. NEED FOR THE USE OF SFRC 7. APPLICATION OF SFRC 8. EFFECTS OF STEEL FIBER IN CONCRETE 9. PROPERTIES OF SFRC 10. CONCLUSION 11. SFRC CONCLUSION 12. REFERENCES

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1. ABSTRACT

The word concrete comes from the Latin

word "concretus" which means "to harden"

Concrete- the world’s most widely used structural

material cracks for a variety of reasons. These

reasons may be attributed to structural,

environmental factors etc. But most of the cracks are

formed due to the inherent weakness of concrete to

restrain tension. Shrinkage and restrains create crack

in concrete.

Extensive Research and

Development to overcome the weakness of concrete

led to the introduction of Steel Fiber Reinforcement

as a viable solution to the problem of cracking by

making concrete tougher and more ductile.

Comprehensive field trialaover three decades have

proved that addition of steel fibers to conventional

plain or reinforced and pre-stressed concrete

members at the time of mixing/ production imparts

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higher strength, improves performance and durability

of concrete

2. INTRODUCTION

Portland cement concrete is considered to

be a relatively brittle material. When subjected to

tensile stressed, unreinforced concrete will crack and

fail. Since the mid 1800's steel reinforcing has been

used to overcome this problem. As a composite

system, the reinforcing steel is assumed to carry all

tensile loads. When fiber reinforcing is added to the

concrete mix, it too can add to the tensile loading

capacity of the composite system. In fact, research

has shown that the ultimate strength of concrete can

be increased as much as 5 times by adding fiber

reinforcing.

The main properties influencing toughness

and maximum loading of fiber reinforced concrete

are;

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Type of fibers used.

Volume percent of fiber.

Aspect ratio (the length of a fiber divided by

its diameter).

Orientation of the fibers in the matrix.

Materials used in fiber reinforcing

including acrylic, asbestos, cotton, glass, nylon,

polyester, polyethylene, polyperpylane, rayon,

rockwool and steel. Of these, steel fiber have

received the most attention. The percent of fiber in

the concrete mix is based on volume and is expressed

as a percent of the mix. Tests ranging from 1.7% to

2.7% are common.

3. WHAT IS FIBER REINFORCEDCONCRETE

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Plain cement concrete is considered to be

a brittle material because of its low tensile strength

and impact resistance. Now it has established that by

addition of small diameter, short length, and

randomly distributed fibers it is possible to bring

about marked improvements in the tensile strength

and impact resistance properties of concrete.

Concrete with fiber is termed as fiber reinforced

concrete. The improvements in the properties

depends upon various factors like material of fiber,

their shape, size, pattern of distribution and

magnitude in the concrete mix.

In other words Fiber reinforced concrete is a

mixture of A

Conventional Concrete (cement, water, rock and

sand) + Fibers.

. Types of Fibers

Steel fibers Synthetic organic polymer fibers such as

polypropylene, nylon, polyester, polythylene, cellulose acetate.

Carbon fibers Natural fibers Asbestos fibers Glass fibers

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4 .WHY USE STEEL FIBER

1. Steel Fibres are generally distributed throughout a given cross section whereas reinforcing bars or wires are placed only where required

2. Steel fibres are relatively short and closely spaced as compared with countinuous reinforcing bars of wires.

3. It is generally not possible to achieve the same area of reinforcement to area of concrete using steel fibres as compared to using a network of reinforcing bars of wires.

Steel Fibers are typically added to concrete in low volume dosages (often less than 1%), and have been shown to be effective in reducing plastic shrinkage cracking.

Steel Fibers typically do not significantly alter free shrinkage of concrete, however at high enough dosages they can increase the resistance to cracking and decrease crack width (Shah, Weiss, and Yang 1998).

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STEEL FIBERS IN CONCRETE MAY IMPROVE:

Crack, Impact and Fatigue Resistance

Shrinkage Reduction

Toughness- by preventing/delaying crack

propogation from micro-cracks to macro-

cracks.

5. BENIFITS OF STEEL FIBER

REINFORCED CONCRETE

SFRC distributes localized stresses.

Reduction in maintaince and repair cost.

Provides tough and durable surfaces.

Reduces surface permeability, dusting and

wear.

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Cost saving

They act as crack arrestor.

Increases tensile strength and toughness.

Resistance to impact.

Resistance to freezing and thawing

6. NEED FOR THE USE OFSTEEL FIBER REINFORCED

CONCRETE

The two main disadvantages of

reinforced concrete beams are the potential

corrosion of the reinforcement and the high self

weight. The latter in particular is an important issue

given the fact that 75-80% of the material that

contributes to the weight (concrete in the tensile

zone) does not directly contribute to the overall load

carrying capacity. The low cost of concrete is

probably the main reason that this has not been a

major issue in the past.

It is now well established that one of

the important properties of steel fibre reinforced

concrete (SFRC) is its superior resistance to cracking

and crack propagation. As a result of this ability to

arrest cracks, fibre composites possess increased

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extensibility and tensile strength, both at first crack

and at ultimate, particular under flexural loading; and

the fibres are able to hold the matrix together even

after extensive cracking. The net result of all these is

to impart to the fibre composite pronounced post –

cracking ductility which is unheard of in ordinary

concrete. The transformation from a brittle to a

ductile type of material would increase substantially

the energy absorption characteristics of the fibre

composite and its ability to withstand repeatedly

applied, shock or impact loading.

7. APPLICATION OF STEELFIBER REINFORCED

CONCRETE

7.1 STEEL FIBER FOR PRE-CAST APPLICATION:

Manholes, Risers, Burial Vaults, Septic Tanks, Curbs, Pipes, Covers, Sleepers

7.2 APPLICATION:

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A) Highway And Airfield Pavements: Repair of existing pavement.

Reduction in pavement thickness.

Increase in resistance to impact.

Increase in transverse and longitudinal joint

spacing

Smooth riding surface.

B) Hydraulic Structures:

Resistance to cavitations or erosion damage.

Repair of spilling basin.

C) Fiber Shotcrete (FRS):

The inclusion of steel fibres in shotcrete improves

many of the mechanical properties of the basic

material viz the toughness, impact resistance, shear

strength, flexural strength, and ductility factor.FRS

has been used for

Rock stabilization, tunnels, dams, mines.

Bridges arches, dome structures, power-house

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Stabilization of slopes to prevent landslides

repair of deteriorated concrete surface, water

channel etc.

8. EFFECTS OF STEEL FIBERSIN CONCRETE

Steel Fibers are usually used in concrete to

control plastic shrinkage cracking and drying

shrinkage cracking. They also lower the permeability

of concrete and thus reduce bleeding of water. Steel

fibers produce greater impact, abrasion and shatter

resistance in concrete. Generally fibers do not

increase the flexural strength of concrete, so it cannot

replace moment resisting or structural steel

reinforcement. Steel fibers reduce the strength of

concrete.

The amount of fibres added to a concrete mix is

measured as a percentage of the total volume of the composite

(concrete and fibres) termed volume fraction (Vf). Vf typically

ranges from 0.1 to 3%. Aspect ratio (l/d) is calculated by

dividing fibre length (l) by its diameter (d). Fibres with a non-

circular cross section use an equivalent diameter for the

calculation of aspect ratio. If the modulus of elasticity of

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the fibre is higher than the matrix (concrete or mortar

binder), they help to carry the load by increasing the tensile

strength of the material. Increase in the aspect ratio of the

fibre usually segments the flexural strength and toughness of

the matrix. However, fibres which are too long tend to "ball"

in the mix and create workability problems.

9. PROPERTIES OF STEEL FIBERREINFORCED CONCRETE

9.1.SFRS PROPERTIES: (General)

Factors affecting performances of SFRS:

1)Volume fraction of constituent materials e.g.properties generally improve as fiber content increase

2)Physical properties of fibers and matrix

3)Bond strength between constituents (Transmission of forces between fibers and matrix) (Weak link that governs most SFRS mechanical properties)

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4)Matrix cracks long before fiber fractures

10. CONCLUSION

Steel Fiber Reinforced Concrete will play a

major role in the of civil engineering structures in the

21st century.

The high strength to weight ratio and non

corrosive characteristics of these materials could be

utilized to built innovative structures that cannot be

build using the current conventional materials.

SFRC could be used to build light, yet more

durable and economic structures. Designers should

be encouraged to utilized these materials based on its

unique characteristics rather than a replacement for

the current conventional materials.

The steel fibre reinforced concrete have high

initial investment during construction because of

which it is not possible to use this concrete in each

and every part of a country.

Steel Fibre reinforced concrete is design for

reasonably high value of strength. The successful

performance of a steel fibre reinforced concrete very

much depends on ensuring that the design

requirements are met by the steel fibre reinforced

concrete as constructed. A very good quality control

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is, therefore a prime need. Quality control consists of

ensuring that the materials that go into production of

concrete are of the required specifications and that

the concrete as produced and laid is also of specified

quality and strength.

11. SFRC CONCLUSION

BEAM CONSTRUCTED

Using Plain Concrete

Using Steel Fiber Reinforced Concrete

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12. REFERENCES

1)Concrete Technology- M. S. Shetty-Chapter10 Testing of Concrete

2)Journal of concrete Technology- Properties of concrete

3)I.S.516-1959- Tests on concrete

4)www.google.com- Steel Fiber reinforced concrete

5)www.wikepedia.com – Reinforcement using Fiber

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