Debashis Wadadar

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FIBER REINFORCED CONCRETE

CE 613: Mtech Seminar Report

Submitted By:

DEBASHIS WADADAR

Roll No 113040029

Under the supervision of:

PROF. PRAKASH NANTHAGOPALAN

Department Of Civil Engineering

Indian Institute of Technology Bombay

Powai, Mumbai 400076.

September, 2011


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ACKNOWLEDGEMENT

First and foremost, I would like to thank The Almighty for being as kind on me

during the process of completing this report as He always has been during my best

and worst days. My family members, specially my parents, deserve big thanks. The

values and beliefs they inculcated have inspired me throughout my life.

I express my sincere gratitude to my guide and mentor, Prof Prakash

Nanthagopalan , Department of Civil Engineering, IIT Bombay, for his kind and

valuable guidance during the preparation of this report. I take this opportunity to

thank him for devoting his precious time for the preparation of the report and the

critical suggestions he gave me for its improvement.

The others who have helped me during the process are my friends. They have been

my pillars of strength in every situation.

I am thankful to the librarians of the Central library, for helping me with the most

appropriate books and journals whenever I needed them.

Every other person involved directly or indirectly with this report deserves a

mention.

With regards,

Debashis Wadadar,

M.tech, 1st year,

Date: 30.09.2011 IIT Bombay,

Place: Mumbai Roll No-113040029


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CONTENTS

1. Introduction

1.1.What is a fiber?1.2.What is fiber reinforced concrete?

1.3.History of fiber reinforced concrete1.4.Reinforcement mechanism

2. Different types of fiber used in fiber reinforced concrete

2.1.Steel fiber reinforced concrete

2.2.Polypropylene / Nylon FRC2.3.Asbestos FRC

2.4.Glass FRC

2.5.Carbon FRC

3. Comparison of fiber types and properties4. Why FRC?

5. Factors affecting strength and resistance to crack in FRC

6. Properties of fibers and matrices7. Steel fiber reinforced concrete

7.1.General idea

7.2.Properties

7.3.Applications8. Polypropylene /Nylon Fiber reinforced concrete

8.1.General idea

8.2.Properties8.3.Applications

9. Asbestos fiber reinforced concrete10.Glass fiber reinforced concrete

10.1. Introduction10.2. Benefits of GFRC

11.Natural fiber reinforced concrete

11.1 Introduction11.2 Types

12.Carbon FRC

13.Some developments in fiber reinforced concrete

14.Merits and demerits of using fiber reinforced concrete15.Mixing , placing and finishing fiber reinforced concrete

16.Some specific applications of FRC

Applications in civil infrastructure

17.Conclusion18.References


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1.Introduction1.1.What is a fiber? Fibersare a particular class ofmaterials that are slender, elongated and

threadlike. In fiber reinforced concrete small pieces of reinforcing material possessing

certain characteristic properties are used to enhance or modify properties of concrete.These fibers can be circular or flat. The parameter used to describe fiber is called

Aspect ratio. Aspect ratio is ratio of its length to its diameter. Typical aspect ratio for

fibers ranges from 30 to 150.1.2.What is fiber reinforced concrete? Compared to other building materials such as

metals and polymers, concrete is significantly more brittle and exhibits a poor tensile

strength. Based on fracture toughness values, steel is at least 100 times more resistant to

crack growth than concrete. Concrete in service thus cracks easily, and this crackingcreates easy access routes for deleterious agents resulting in early saturation, freeze-thaw

damage, scaling, discoloration and steel corrosion. The concerns with the inferior

fracture toughness of concrete are alleviated to a large extent by reinforcing it with fibers

of various materials. The resulting material with a random distribution of short,discontinuous fibers is termed fiber reinforced concrete (FRC) and is slowly becoming

a well accepted mainstream construction material. Significant progress has been made inthe last thirty years towards understanding the short and long-term performances of fiber

reinforced cementitious materials. Steel fiber remains the most used fiber of all,

followed by polypropylene, glass and other fibers.

1.3.History of fiber reinforced concrete: The use of fibers in brittle matrix materials has along history. Historically, horsehair was used in mortar and straw in mud bricks. In

1910, porter put the idea that concrete can be strengthened by the inclusion of fibers. In

the early 1900s, asbestos fibers were used in concrete. There was a need to find areplacement for the asbestos used in concrete and other building materials once

the health risks associated with the substance were discovered.Till 1963, there was onlyslow progress on fiber reinforced concrete (FRC). Romualdi and Batson gave rise to

FRC by conducting numerous experimental works to determine the basic engineeringproperties such as compressive and tensile strength of FRC.

1.4.Reinforcement mechanism: Concrete carries flaws and micro-cracks both in the

material and at the interfaces even before an external load is applied. These defects andmicro-cracks emanate from excess water, bleeding, plastic settlement, thermal and

shrinkage strains and stress concentrations imposed by external restraints. Under an

applied load, distributed micro-cracks propagate coalesce and align themselves to

produce macro-cracks. When loads are further increased, conditions of critical crackgrowth are attained at the tips of the macro-cracks and unstable and catastrophic failure

is precipitated.The micro and macro-fracturing processes described above, can favourably be modified

by adding short, randomly distributed fibers of various suitable materials. Fibers notonly suppress the formation of cracks, but also abate their propagation and growth. Soon

after placement, evaporation of the mix water and the autogenous process of concrete

hydration creates shrinkage strains in concrete. With large surface areas, fibers engagewater in the mix and reduce bleeding and segregation. The result is that there is less

water available for evaporation and less overall free shrinkage.
http://en.wikipedia.org/wiki/Materialhttp://en.wikipedia.org/wiki/Asbestoshttp://en.wikipedia.org/wiki/Carcinogenhttp://en.wikipedia.org/wiki/Carcinogenhttp://en.wikipedia.org/wiki/Asbestoshttp://en.wikipedia.org/wiki/Material


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On the other hand, in the hardened state, when fibers are properly bonded, they interact

with the matrix at the level of micro-cracks and effectively bridge these cracks therebyproviding stress transfer media that delays their coalescence and unstable growth. If the

fiber volume fraction is sufficiently high, this may result in an increase in the tensile

composite. Once the tensile capacity of the composite is reached, and coalescence and

conversion of micro-cracks to macro-cracks has occurred, fibers, depending on theirlength and bonding characteristics continue to restrain crack opening and crack growth by

effectively bridging across macro-cracks. This post-peak macro-crack bridging is the

primary reinforcement mechanism in the majority of commercial fiber reinforcedconcrete composites.

2.Different types of fibers used in fiber reinforced concrete :Although every type of fiber has been tried out in cement and concrete, not all of them can beeffectively and economically used. Each fiber has some characteristic properties and

limitations.

Fibers used are-

Steel fibers

Polypropylene, nylons

Asbestos, Coir

Glass

Carbon

Natural fibers

Steel fibers are available in round, flat, reimped, deformed forms. Steel fibers were used in

different structural elements in various zones and investigated its performance. Now-a-days

synthetic fibers have become more attractive and used for the reinforcement of cementitiousmaterials.


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3. Comparison of fiber types and properties:

Material or

fiber

Relative

density

Dia or

thickness()

Length

(mm)

Elastic

Modulus(Gpa)

Tensile

Strength(Mpa)

Failure

Strain(%)

Volume

in

composite(

Mortar matrix 1.8-2.0 300-5000 - 10-30 1-10 0.01-0.05 85-97

Concretematrix

1.8-2.4 10000-20000

- 20-40 1-4 0.01-0.02 97-99.9

Asbestos 2.55 0.02-30 5-40 164 200-1800 2-3 5-15

Carbon 1.16-

1.95

7-18 3-cont. 30-390 600-2700 0.5-2.4 3-5

Cellulose 1.5 20-120 0.5-5 10-50 300-1000 20 5-15

Glass 2.7 12.5 10-50 70 600-2500 3.6 3-7

Polypropylenechopped film

0.91 20-100 5-50 5 300-500 10 0.01-1

Polyvinylalcohol

1-3 3-8 2-6 12-40 700-1500 - 2-3

Steel 7.86 100-600 10-60 200 700-2000 3-5 0.3-2

TABLE 1


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4. Why FRC?

The main objectives of the modern engineer in attempting to modify the properties of concreteby the inclusion of fibers are as follows:

To improve the rheology or plastic cracking characteristics of the material in the freshstate or up to about 6 hours after casting.

To improve the tensile or flexural strength.

To improve the impact strength and toughness.

To control cracking and the mode of failure by means of post-cracking ductility.

To improve durability.

They also lower the permeability of concrete and thus reduce bleeding of water.

Some types of fibers produce greater impact, abrasion and shatter resistance inConcrete.

The material ductility is increased by the addition of fibers. High-performance fiber-reinforced concrete used in bridges found to provide residual

strength and control cracking. The residual strength is directly proportional to the

fiber content.

Generally fibers do not increase the compressive strength of concrete. Fibers cannotreplace moment resisting or structural steel reinforcement.

5.Factors affecting strength and resistance to crack in FRC :The most significant factors affecting resistance to crack propagation and strength of the fibrous

concrete and mortar are

Shape and bond at fiber matrix interface

Volume fraction of fibers

Fiber aspect ratio and Orientation of fibers

Workability and Compaction of Concrete

Size of Coarse Aggregate

Mixing

SHAPE AND BOND AT FIBER MATRIX INTERFACE :The modulus ofelasticity of matrix must be much lower than that of fiber for efficient stress transfer. Low

modulus of fibers such as nylon and polypropylene are therefore unlikely to give strengthimprovement, but they help in the absorption of large energy and therefore impart greater degree

of toughness and resistance to impact. High modulus fibers such as steel, glass and carbon impart


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strength and stiffness to the composite. Interfacial bond between the matrix and the fibers also

determine the effectiveness of stress transfer, from the matrix to the fiber. A good bond is

essential for improving tensile strength of the composite.

VOLUME FRACTION OF FIBER :The strength of the composite depends largely on

the quantity of fibers used in it. The increase in the volume of fibers, increase approximatelylinearly, the tensile strength and toughness of the composite. Use of higher percentage of fiber is

likely to cause segregation and hardness of concrete and mortar.

FIBER ASPECT RATIO :Fiber aspect ratio is defined as the ratio of fiber length to theequivalent fiber diameter. In order to utilize fracture strength of fibers fully, adequate bond

between the matrix and the fiber has to be developed.

ORIENTATION OF FIBERS: One of the differences between conventionalreinforcement and fiber reinforcement is that in conventional reinforcement bars are oriented inthe direction desired while fibers are randomly oriented. It was observed that in fiber reinforced

mortar the fibers aligned parallel to the applied load offered more tensile strength and toughnessthan randomly distributed or perpendicular.

WORKABILITY AND COMPACTION OF CONCRETE: Incorporation of steelfiber decreases the workability considerably and even prolonged external vibration fails to

compact the concrete. This situation adversely affects the consolidation of fresh mix. The fiber

volume at which this situation is reached depends on the length and diameter of the fiber andnon-uniform distribution of the fibers. Generally, the workability and compaction standard of the

mix are improved through increased water/cement ratio or by the use of water reducing

admixtures. The overall workability of fresh fibrous mixes is largely independent of the fibertype. Crimped fibers produce slightly higher slumps, and hooked fibers are more effective than

straight and crimped ones.

MIXING: Mixing of fiber reinforced concrete needs careful conditions to avoid balling of

fibers, segregation, and difficulty of mixing the materials uniformly.

6. Properties of fibers and matrices :The performance of the composite is controlled mainly by the volume of the fibers, the physical

properties of the fibers and the matrix, and the bond between the two. It is apparent from Table 1that the elongations at break of all the fibers are two or three orders of magnitude greater than thestrain at failure of the matrix and hence the matrix will usually crack long before the fiber

strength is approached. On the other hand, the modulus of elasticity of the fiber is generally less

than five times that of the matrix and this, combined with the low fiber volume fraction, meansthat the modulus of the composite is not greatly different from that of the matrix.


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7.Steel fiber reinforced concrete :7.1 General idea: Steel fiber is one of the most commonly used fibers. Generally, round

fibers are used. The diameter may vary from 0.25 to 0.75 mm. The steel fiber is likely

to get rusted and lose some of its strength. But investigations have shown that the

rusting of the fibers take place only at the surface. Use of steel fibers make

significant improvements in flexural, impact and fatigue strength of concrete, it hasbeen extensively used in various types of structures, particularly for overlays of roads,

airfield pavements and bridge decks. Thin shells and plates have also been

constructed using steel fibers.

Fig-17.2 Properties:

Steel fibers provide virtually no increase in the compressive or uniaxial tensile strength ofconcrete. The main benefits in uniaxial tension result from the control of crack widths

due to shrinkage or thermal effects in slabs and tunnel linings.

Longer fibers give better reinforcement but reduce the workability so that a compromisemust be reached usually at equivalent l/d ratios between 40 and 80 with fiber lengthsbetween 20 mm and 60 mm.

Free water cement ratios of less than 0.55 are preferable and workability is commonly

improved by the addition of plasticizers or superplasticizers to give slumps of more than

100 mm.


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Steel fibers are generally well protected in uncracked concrete where the high alkalinityprovides a passive layer on the fiber surface. Even when the fibers are near the surface in

a carbonated zone, serious corrosion takes many years to occur and surface spalling israre. The main durability problem is likely to occur where load-bearing carbon steel

fibers are exposed across cracked sections in the presence of chlorides, where they will

readily corrode and it would be wise in such conditions to use stainless steel fibers.

7.3 Applications:

A major use of steel fibers is to use them as a replacement for conventional steel mesh in

industrial ground-floor slabs. Fiber dosages of between 15 kg/m3 and 60 kg/m3 are

commonly used in floors with slab thicknesses between 120 mm and 200 mm.

Used for-overlays of roads, airfield pavements, bridge decks.

8. Polypropylene /Nylon Fiber reinforced concrete :8.1 General idea :Polypropylene (PP) is a versatile thermoplastic material, which is producedby polymerizing monomer units of polypropylene molecules into very long polymer molecules

or chains in the presence of a catalyst under carefully, controlled heat and pressure. Propylene is

an unsaturated hydrocarbon, containing only carbon and hydrogen atoms.

8.2 Properties: A summary of the mechanical properties of nylon fiber alone is given below:

Tensile Strength: 25-33 Mpa

Flexural Modulus: 1.2-1.5 Gpa

Elongation at break: 150-300%

Strain at yield: 10-12%

Polypropylene fibers are added to the concrete in several different forms and by usingvarious techniques. The fibers can be incorporated into concrete as short discrete chopped

fibers, as a continuous network of fibrillated film, or as a woven mesh.

Polypropylene Fibers (Fig-2)


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Polypropylene fibers are synthetic types of fibers. Synthetic fibers are gradually replacingsteel fibers due to the fact that they are cost effective, can be used in low volume

fractions and there is no risk of corrosion by their use in concrete.

8.3 Applications:

Several manufacturers currently produce polypropylene fiber specifically for use inconcrete as a form of reinforcement as they possess many properties that make them

particularly adaptable for use in concrete . Polypropylene has ,for polymers, a high

melting point (165C) and it is chemically inert. The chemical inertness makes the fibers

resistant to most chemicals. Any chemical that will not attack the concrete will have noeffect on the fiber either . Polypropylene has a hydrophobic surface that prevents it frombeing wetted by the cement paste. Since they are non-polar the bundles of polypropylene

fibers do not cling or ball together . The hydrophobic nature of the polypropylene fiber

does not affect the mixing water requirements of the concrete.

Polypropylene fibers that are added to the concrete for reinforcement contributes for the

post peak ductility of the FRCs.

9. Asbestos fiber reinforced concrete : Mineral fiber, most successful of all as it can be mixed with portland cement.

Tensile strength of asbestos varies between 560 to 980 N/mm2.

Asbestos cement paste has considerably higher flexural strength than portland cementpaste.

10.Glass fiber reinforced concrete : The glass fibers are primarily used for glass fiberreinforced cement (GFRC) sheets. Regular E-Glass fibers were found to deteriorate in

concrete. Glass-fiber reinforced concrete or G.F.R.C, also referred to as G.R.C., is a cement

mixture that also contains alkali resistant glass fibers. The use of alkali resistant glass fibersis the industry standard for G.F.R.C. as it demonstrates higher resistance to environmentaldeterioration and strength retention than the less expensive E-glass glass-fibers, which are

used in polyester resins and gypsum.

Glass fibers (Fig-3)


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Benefits of GFRC:

There are lots of good reasons to use GFRC for thin sections of concrete:

Lighter weight: With GFRC, concrete can be cast in thinner sections and is therefore as

much as 75% lighter than similar pieces cast with traditional concrete. An artificial rockmade with GFRC will weigh a small fraction of what a real rock of similar proportions

would weigh, allowing for lighter foundations and reduced shipping cost.

High strength: GFRC can have flexural strength as high as 4000 psi and it has a very high

strength-to-weight ratio.

Reinforcement: Since GFRC is reinforced internally, there is no need for other kinds ofreinforcement, which can be difficult to place into complex shapes.

Consolidation: For sprayed GFRC, no vibration is needed. For poured, GFRC, vibrationor rollers are easy to use to achieve consolidation.

Toughness: GFRC doesn't crack easilyit can be cut without chipping.

Durability: According to ACI 544.1R-96, State of the Art Report on Fiber Reinforced

Concrete, "The strength of fully-aged GFRC composites will decrease to about 40percent of the initial strength prior to ageing." Durability has been increased through theuse of low alkaline cements and pozzolans.

Cost: GFRC as a material, however, is much more expensive than conventional concreteon a pound-for-pound basis. But since the cross sections can be so much thinner, that cost

is overcome in most decorative elements.

11.Natural fiber reinforced concrete :Introduction:

The oldest forms of fiber reinforced composites were made with naturally occurring fiber such asstraw and horse hair. The Roman Coliseum was built with fiber reinforced concrete. A pueblo

house built in 1540 with straw reinforced adobe brick is believed to be the oldest house in the

US. Modern technology has made it possible to extract fibers economically from various plants,such as jute and bamboo to use in cement composites. The unique aspects of this fiber is the low

amount of the energy required to extract these fibers. The primary problem with use of these

fibers in concrete is their tendency to disintegrate in an alkaline environment. Effects are being

made to improve durability of this fiber in concrete by using admixture to make the concrete less

alkaline and subjecting the fibers to special treatment.

Types:

Natural fibers used in Portland cement composite includes akwara, bamboo, coconut, jute, sisal,sugarcane, wood, and others .Mechanical properties of some of these fibers are presented in the

succeeding.


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AKWARA FIBERS:

Akwara is a natural fiber derived from a plant stem grown in large quantities in Nigeria. They are

made of a cellular core covered with a smooth sheath. Akwara fibers were found to be durable in

alkaline environment of cement matrix.

BAMBOO FIBERS:

Bamboo, which is a member of the grass family, grows in tropical and subtropical region. Plants

can grow up to a height of 15 m. their hollow stalks have intermediate joints, the diameters of

these stalks range from 0.4 to 4.0 inch (1 to 10 cm). Bamboo fibers are strong in tension, but

have a relatively low modulus of elasticity. Their tendency to absorb water adversely affects the

bonding between the fibers and the mixture during the curing process.

COCONUT FIBERS:

A mature coconut has an outer fibrous husk. Coconut fibers, called coir, can be extracted simplyby soaking the husk in water or, alternatively, by using mechanical processes. Coir has a low

elastic modulus and is also sensitive to moisture changes.

FLAX AND VEGETABLE FIBERS:

Flax is grown for its fiber. Flax fibers are strong under tension and also possess a high modulus

of elasticity. Fibers extracted from other plant such as elephant grass, water reed, plantain, andmusamba have also been tried as reinforcements for concrete. Most of these fibers are removed

from the stems of the plants manually.

12.Carbon FRC :As for brittle materials in general, concrete is strong under compression and weak under tension

orflexure. This problem may be alleviated by the addition of short carbon fibers (typically - 10

pm in diameter). Almost all the early works on carbon fiber reinforced concrete showed that theuse of carbon fibers in the amount of 2 vol.% approximately doubled the flexural strength .

Recent work performed in U.S.A. by Zheng and Chung showed the approximate doubling of the

flexural strength with only 0.3% carbon fibers - an improvement resulting from the use ofchemical agents. Early works on short carbon fiber reinforced concrete used isotropic pitch-

based carbon fibers, which are the least expensive form of commercially available carbon fibers.

Their tensile strength and modulus are much lower than those of continuous pitch-based or PAN-based carbon fibers that are used for aircrafts. The price of short pitch-based carbon fibers has


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been steadily decreasing. This price decrease is giving much impetus to the use of carbon fibers

in concrete.The technique of dispersing carbon fibers randomly in the concrete mix is critical to the success

of the carbon fiber reinforced concrete technology. Two options are possible. One is to mix the

fibers with cement and fine aggregate in the dry state . The other option is to first disperse the

fibers in water and then pour the dispersion into the slurry with cement and fine aggregate .

As per Dr. Deborah D.L Chung (Ref: Transportation Research Board Index: SHRP-ID/UFR-92-

605, accession number - 00622531),

Wet Mix is an effective method only if a dispersant and a de-foamer are used.

Carbon fibers increase the freeze-thaw durability ofconcrete.

The use of short pitch-based carbon fibers along with methylcellulose dispersants, waterreducing agent, and silica fume increases the flexural strength of concrete to a great

extent.

13.Some developments in fiber reinforced concrete :ECC: Engineering cementitious composite is one of the latest inclusions in FRC technology.

ECC looks similar to OPC, only difference is that it does not include coarse aggregate

and can deform or bend under strain.

The unique feature of ECC is its ultra high ductility. This implies that structural failure byfracture is significantly less likely in comparison to normal concrete or FRC.

Reduction or elimination of shear reinforcement: ECC has excellent shear capacity.Under shear, ECC develops multiple cracking with cracks aligned normal to the principal

tensile direction. Because the tensile behaviour of ECC is ductile, the shear response is

correspondingly ductile. As a result, R/ECC elements may need less or no conventional

steel shear reinforcements. There are a number of characteristics of ECC that make it attractive as a repair material.

ECC can eliminate premature delamination or surface spalling in an ECC concrete

repaired system (Lim and Li 1997). Interface defects can be absorbed into the ECC layer,and arrested without forming spalls, thus extending the service life.

ECC also has good freeze-thaw resistance and restrained shrinkage crack control.

SIFCON:

Slurry infiltrated fiber concrete (SIFCON) is a relatively new special type of high

performance (steel) fiber-reinforced concrete (HPFRC). SIFCON is made by pre-placingshort discrete fibers in the moulds to its full capacity or to the desired volume fraction,

thus forming a network. The fiber network is then infiltrated by a fine liquid cement-based slurry or mortar. The fibers can be sprinkled by hand or by using fiber-dispending

units for large sections. Vibration is imposed, if necessary, during placing the fibers and

pouring the slurry. The steel fiber content can be as much as 30 % by volume. Inconventional fiber reinforced concrete (FRC), where fibers are mixed together with other


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ingredients of concrete, this percentage is limited to only about 2 % for practical

workability reasons.

Because of its high fiber content, SIFCON has unique and superior mechanical propertiesin the areas of both strength and ductility. The main differences between FRC and

SIFCON, in addition to the clear difference in fiber volume fraction, lie in the absence of

coarse aggregates in SIFCON which, if used, will hinder the infiltration of the slurrythrough the dense fiber network. Furthermore, SIFCON contains relatively high cement

and water contents when compared to conventional concrete.

An example of failed preparation because of the lack of fluidity of slurry

The dense fiber network is also clear in the figure

(Fig-4)

14.Merits and demerits of using fiber reinforced concrete:Advantages:

Lowering the permeability of concrete.

Reducing bleeding of water.

It controls plastic shrinkage cracking and drying shrinkage cracking.


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It increases the strength of concrete.

It reduces the flexural creep.

It resists structures from aggressive environment, e.g. high temperatures, ingress of

chlorides and electrical fields.

Increased static and dynamic tensile strength.

Energy absorbing characteristics and better fatigue strength.

Uniform dispersion of fibers throughout the concrete provides isotropic properties.

Disadvantages:

The main disadvantage associated with the fiber reinforced concrete is fabrication. The process

of incorporating fibers into the cement matrix is labour intensive and costlier than the production

of the plain concrete. The real advantages gained by the use of FRC overrides this disadvantage.

15.Mixing , placing and finishing fiber reinforced concrete :Adding steel or synthetic fibers to concrete at low volume dosage rates provides benefits not

available in conventional concrete.

Mixing

Synthetic fibers: Synthetic fibers are packed loosely in degradable bags, which can be added tothe mix at the batch plant. Proper mechanical agitation is needed to ensure separation of the

fibers, thereby, virtually eliminating the formation of fiber balls in the concrete. It also

distributes the fibers in a thorough, uniform manner throughout the mix.

Steel fibers: Packaged in boxes and bags, steel fibers are manually added to the concrete at

either ready mix plants or jobsites. To prevent the formation of fiber balls, special adhesives are

added to glue a number of steel fibers together; during mixing, the glue degrades, dispersing thefibers throughout the concrete. The mixing of some uncollated steel fibers may require care to

prevent the development of fiber balls in the fresh concrete.

Placing

Both synthetic- and steel-fiber- reinforced concrete can be placed using conventional equipment

such as truck chutes, concrete buckets, conveyors, and pumps. The equipment should be clean

and in good condition to ensure that the fiber- reinforced concrete flows easily.

Finishing:

Though fiber- reinforced concrete finishing operations are very similar to those for plain

concrete, there are some differences.


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Strike-off operations: One key to finishing fiber- reinforced concrete is using external vibration

in the form of a vibratory truss screed. External vibration brings paste to the surface and buriesfibers located at the slab surface, encapsulating them in concrete and minimizing exposed fibers.

Bull-floating and re-straightening operations: As with air- entrainedconcrete, we should not

use woodfloats or other wooden tools. We have to use magnesium floats instead. Magnesiumfloats do an especially good job of establishing a high-quality surface and closing up any tears or

open areas caused by the screed.

Waiting period: In case of synthetic FRC, the millions of synthetic fibers in the concrete can

block or delay the appearance of bleed-water at the surface. Therefore, we have to be sure that all

the bleed-water has evaporated before getting on the concrete.

Final finishing operations: Synthetic fibers are compatible with almost all concrete surface

treatments and finishes, including pattern stamping, exposed aggregate, brooming, and hand or

power troweling. Steel fibers, however, are not compatible with pattern stamping or exposed-

aggregate finishes.

16. Some specific applications of FRC : Overlays of air-fields.

Road pavements.

Industrial flooring.

Bridge decks.

Canal lining.

Explosive resistant structure.

Refractory lining.

Fabrications of precast products like pipes, boats, beams, staircase steps, wall panels, roof

panels, manhole covers etc.

Manufacture of prefabricated formwork moulds of U shape for casting lintels and small

beams.


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Applications :

Road Pavement Bridge Deck

(Fig-5) (Fig-6)

Precast canal lining Manhole Cover

(Fig-7) (Fig-8)


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17. CONCLUSION:Fiber reinforced concrete is concrete containing fibrous materials which are incorporated in

concrete in order to enhance its structural integrity. Different types of fibers are available which

offer several advantages over ordinary concrete. The use of steel FRC increases structuralstrength, improves ductility and impact resistance. On the other hand polypropylene fibers, due

to their relatively low modulus of elasticity, have the most significant effect at early age and after

cracking. At early age, fibers decrease shrinkage significantly, and decrease cracking as well.Generally, at early age, all strength parameters are improved. However, after curing, the fibers

no longer have an impact on compressive strength, and flexure and tensile tests show only slight

improvements. Long term shrinkage similarly shows no major benefit. After cracking, the fibersare again beneficial. Ductility is substantially increased, as failures are no longer brittle. Crack

widths are greatly decreased, and impact resistance greatly increased. Polypropylene and

polyethylene fibers, then, are useful when early age properties need to be improved, or when

ductility is important. Blends of both steel and polymeric fibers are often used in construction

projects in order to combine the benefits of both the products. Fiber reinforced concrete hasstarted to find its place in many areas of civil infrastructure applications where the need forrepairing, increased durability arises. Also FRCs are used in civil structures where corrosion can

be avoided at the maximum. Fiber reinforced concrete is better suited to minimize cavitationdamage in structures such as sluice-ways, navigational locks and bridge piers where high

velocity flows are encountered. A substantial weight saving can be realized using relatively thin

FRC sections having the equivalent strength of thicker plain concrete sections. When used inbridges it helps to avoid catastrophic failures. Also in the quake prone areas the use of fiber

reinforced concrete would certainly minimize the human casualties. In addition, polypropylene

fibers reduce or relieve internal forces by blocking microscopic cracks from forming within the

concrete. Although the concept of FRC is not new, it is still a very expanding field. The newly

emerged ECC (unique feature is its ultra high ductility) & SIFCON adds new dimension to theFRC technology. Last but not the least, there is considerable scope for research on FRC using

industrial wastes .Very little work has been done in this field. With increase in population andindustrial activities, the quantity of waste fibers generated from different metal industries will

increase manifold in coming years. These industrial waste fibers can effectively be used for

making high strength, low-cost FRC after exploring their suitability.


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18.References:1. Song P.S. & Hwang S. (2004). Mechanical properties of high-strength steel fiber-

reinforced concrete .Elsevier

2. Soong W.H , Raghavan J & Rizkalla S.H. (2010)Fundamental mechanisms of bonding

of glass fiber reinforced polymer reinforcement to concrete Elsevier3. Li.Victor.C (2003) On Engineered Cementitious Composites (ECC) .A Review of the

Material and Its Applications. Japan Concrete Institute. Journal of Advanced ConcreteTechnology Vol. 1, No. 3, 215-230 November 2003.

4. ahmaran .M , Li.Victor.C & Arbor Ann Engineered Cementitious Composites: An

Innovative Concrete for Durable Structure (2009) ASCE

5. Fiber reinforcement of concrete structures Brown .R, Shukla A, Natarajan .R.K (2002)Uritc project no. 536101

6. Fibre reinforced cementitious composites, By Arnon Bentur, Sidney Mindess

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