Synthetic Fiber Reinforced Concrete

7/27/2019 Synthetic Fiber Reinforced Concrete

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SYNTHETIC FIBER REINFOCED

CONCRETE

BY

FAWAD UL HAQ

SUBMITTED TO

Dr. AMJAD NASIR

Department Of Civil Engineering

University of Engineering And

Technollogy Peshawar


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INTRODUCTION

Concrete is a brittle when subjected to tensile stresses, it cracks. Concrete mayalready be crack before applying load because of shrinkage or thermal effects. For this reason

steel reinforcement has been used to overcome the low concrete tensile strength. As a

composite system, the reinforcing steel is assumed to carry all tensile load.

Another approach to limit concrete brittleness concern the used of discontinuous

fibers to produce fiber reinforced concrete. In fiber reinforced concrete thousands of small

fibers are dispersed and randomly distributed in the concrete matrix, therefore, they improve

concrete properties in all direction. Fibers enhance the post cracking strength in tension, the

fatigue strength the resistance to impact loading and reduce temperature and shrinkage

cracking.

fibers reinforced concrete finds application in many area of civil engineering

where needs for repairing and durability arises. Fiber used in concrete may be natural or

synthetics.in this project we will only discuse the types, properties, and effect on concrete of

synthetics fibers only.


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SYNTHETIC FIBERS:

Synthetics fibers are primarily developed by the petrochemicals and textile

industry. Synthetic fibers are nonmetallic fibers including polymers that are available in a

variety of formulations. Synthetic fibers are added to concrete before or during mixingoperation. The use of synthetic fibers of typical addition rate does not require any mix design

change.

TYPES OF SYNTHETICS FIBERS:

There are different types of synthetics fibers but the most commonly used are:

1.Polypropylene: it is manufactured from the homopolymer polypropylene resin.These fibers have a low modulus of elasticity and also a low melting point. Low melting

point of this fiber may be beneficial when used in fire resistance structure, because the

fibers are expected to melt and provide a system of relief channels to dissipate internal

pressure. Polypropylene fibers are hydrophobic, so they do not absorb water and have

no effects on concrete mixing water requirement.

Polypropylene may be fibrillated bundles or monofilament. to produce

fibrillated fibers manufacturer extrude the polypropylene in sheet that are stretched

and silt. The result is a mesh of interconnected fibers strands rectangular in cross

section. Manufacturers cut the strands to specified length and separate them into

bundles. Fibers length range from to 2 inches.when added to concrete during

mixing, the fibrillated fibers open into a network of linked fibers filament that

mechanically anchor to the cement paste.

Sometime graded fibrillated fibers are also used. Graded fibrillated fibers

have various length, size, and fibrillation patterns. The graded fibers disperse more

thoroughly into all areas of the cement paste during mixing.

Monofilament fibers are fine, cylindrical strands that separate during mixing

because monofilament fibers are smooth and have a small surface area they don not

anchor into the cement matrix as well, as fibrillated fibers. With fibrillated fiber, cement

paste penetrate into the network of fibers filament resulting in better mechanicals

anchoring to the concrete.

Research show that lower volume of fibrillated fibers than of monofilament

fibers are needed to improve the post cracking load carrying capacity and ductility of

concrete.

Monofilament fibers are good for relative short term benefits, such as

plastics shrinkage , cracks control during the first few hours after concrete placement.


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2.POLYESTER:Polyester fibers are available in monofilament form in length from to 2

inches. Like polypropylene, polyester fibers are hydrophobic. However, they have a

tendency to disintegrate in alkaline environment of Portland cement concrete. To retard

this degradation, manufacturer coat the fibers to resist alkali attack.

Polyester are temperature sensitive and above normal service temperature

their properties may be altered.

3.NYLONE:It is present only in monofilament form, unlike polypropylene and polyester

it is hydrophilic. It retains a moisture balance of 4.5%. Because of this strong affinity to

water, nylone fibers bond chemically to the concrete matrix. The bond of polypropylene

and polyester is only mechanical. Nylone fibere also have higher aspect ratio than those

of polypropylene. Therefore, it can be added in small dosage to produce the same

reinforcing effect. These fibers also exhibit good tensile strength, high toughness and

excellent elastic recovery.

4.CORBON: Corbon fibers are inert in nature these fiber have high modulus, thermalresistance and long term chemicals stability in alkaline and other chemically aggressive

environment . it is also improve mechanical properties.

5.POLYVINYL ALCOHOL:Polyvinyl alcohol (PVA) fibers are manufactured from PVA resin . A special

surface treatment allows for improved fibers dispersion in cementetious system.Unfortunately PVA fibers have a negative coefficient of thermal expansion, shrinking 4%

in length at 200C. PVA is generally resistant to alkaline and organic solvent.

TWO TYPES OF SYNTHETIC FIBER: MACRO VS MICRO:

There are two classes of synthetics fibers, macro fiber and micro fibers.

1. MICRO FIBERS:Micro fibers are usually with diameter less than 0.1mm. It is used at low

addition rate, usually below 0.1% by volume of concrete. Microfibers are used to reduce

plastics shrinkage cracking in concrete before hardens.

2. MACRO FIBERS:Macro fibers also called, structural synthetics fibers, are design to control

crack in harden concrete. These fibers are used to at high rate upto 1% by volume of

concrete, which provide increased flexural toughness, impact resistance and fatigue


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resistance to harden concrete. Fig 1f shows two examples of latest synthetic structural

fibers of blended polypropylene and polyethylene with different length and aspect ratio,

the composition and configuration of which are design to achieve optimal performance

for flooring and tunnel lining application respectively.

PROPERTIES OF SYNTHETIC FIBERS:Several different kinds of polymers have been investigated for their

suitability for used in concrete. In evaluating fibers the following aspect are of interest:

1)MECHANICAL PROPERTIES:Fibers mechanical properties determine its potential as concrete

reinforcing materials. Table 1 gives the properties of synthetics fibers used to reinforced

concerete . Except polyaramid synthetics fibers are characterized by low modulus of

elasticity and high elongation. Low modulus of elasticity of the fiber means that high

strength composite are not achievable with synthetic fibers. Their advantages lies in

increasing such properties as strain capacity, toughness and crack control, properties

that are more important for slab construction than strength.


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TABLE 1: SYNTHETICS FIBERS PROPERTIES

2)PHYSICAL PROPEERTIES:Table 1 also gives the physical properties of synthetics fibers. The fibers are

characterized by low density so that a low mass of fibers yield a high volume of fibers in

concrete. polymerics fibers are also very flexible, therefore, fiber breakage or mechanical

distortion, will not be a problem during concrete.

The relative low thermal stability of polymer could be disadvantage. melting

point are generally below 300C but service temperature are considerably lower, since the fiberstart to soften and loose their tensile properties at temperature considerably below the melting

point .t this behavior causes loss of reinforcing capabilities in structured exposed to high

temperature (e.g. fire).

The glass transition temperature represent change in consistency from rubbery

to brittle as the temperature is lowered. It should also be considered.


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3) CHEMICAL PROPERTIES:Cement paste developed a moist alkaline environment, dangerous to many

organic materials. The minimum pH in cement paste is about 12.3. howeve many modern

cement have high alkali(sodium and potassium) content, which can raise the pH to 13.5 or

greater when the cement is mixed with water. This high pH is detrimental to some polymers.

Polester, polyacrylics and polyamids are particularly sensitive so they can undergo alkaline

hydrolysis. Hydrolysis may be slow at room temperature, but may be significantly accelerated

at higher temparture.

In studies on polyacrylic fibers slight loss of strength at 20C was also observed

after 2 months.

By contrast , the hydrophobic nature of polypropylene and polyethylene makes

them quit resistant to alkaline condition. However these fibers are sensitive to oxidation,particularly in the presence of sunlight and are treated with anti-oxidant to reduce this

succeptibilty.

4)FIBERS GEOMETRY AND DIMENSION:Fibers are availables in many different geometry and dimension. Three

different types of fibers are available:

1. MONOFILAMENT:Monofilaments are usually single straight fibers made by drawing

molten polymers. Such fibers are usually round in cross-section , ranging in

diameter from 50 m to 0.5 mm. such fibers are usually strong since the drawing

process tends to align the polymers chains and induce crystallization, but smooth

surface may result in a low interfacial bond strength, which limits the reinforcing

capability of the fibers.

2. ROVING:Many polymers are spun in the form of filament whose dia varies from

5 to 15m. several thousands fibrils are spun simultaneously, by drawing them

from a single die and bundle together. The bundle is held intact either by sizing

materials or by twisting them into yarn. Roving are cut into short length (


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Fibrillated polymers are formed by splitting a polymers film

longitudinally and then cut it into suitable length and width, so that the fibers

can be considered as bundles of cross linked fibrils. When pull apart the

fibrillated fibers opens out into a mesh of connected fibrils. The geometry of a

fibrillated fiber can be described in term of the film thickness (generally 15 to100 m) and width of each fibril (100 to 600 m). This form of fibers is limited to

film forming polymers (polypropylene and polyethylene). During mixing, the

bundles are opend up by the aggregate to act as individuals fibrils, that each

contribute to the reinforcing action. The fibrs are easy to handle and to disperse

uniformly with in the concrete mix

EFFECTS OF SYNTHETICS FIBERS ON THE PROPERTIES OF

CONCRETE:

1)FLEXURAL TOUGHNESS:Toughness is the key propert in understanding the benefits of inclusion

of fibers in concrete. Toughness is the ability of concrete to retain structural

antegrity after it has nominally failed by being exposed to a load which exceeds its

flexural strength. Plain, unreinforced concrete, when subjected to a bending load,

will withstand that load with very little movement until the load exceeds its flexural

strength. At this point, the concrete will fail suddenly and catastrophically and fall to

pieces. This is the classic behavior of brittle materials possessing no toughness. That

is, it has no residual strength or post cracking strength after a sudden brittle failure.But in the presence of fibers, the difference become apparent immediately after

failure.at failure the concrete cracks but the crack width is initially so small that it

cannot be seen. The load has been transferred to the fibers. If concrete unit

continues to be loaded, then the fibers starts to pull out , and the cracks starts to

widen. At this stage the unit is broken, but still able to withstand a large proportion

of its maximum load. This ability to carry load after failure and to provide resistance

of additional opening of the cracks in the hardened concrete is called toughness.Toughness of fibers reinforced concrete can be affected by the

following factors:I. Dosage rate

II. Type of fibersIII. Elastic modulusIV. Fiber lengthV. Aspect ratio etc.


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Fig 2 shows equivalent flexural strength value (ASTM C 1018) of concrete

with different types of synthetics fibers. Recent study also indicates that the toughness of fiber

reinforced concrete would also be affected by the strength of concrete.

FIG 2:EFFECTS OF FIBER VOLUME OF EQUAVALENT FLEXURALS

TRENGHT

2)CONTROL OF SHRINKAGE CRACKS:Shrinkage cracksare short, irregular cracks that can develop in concrete with

the first 24 hrs after concrete placement. Shrinkage cracks usually pass throughthe entire depth

of slab. The cracks are generally caused by either plastic or drying shrinkage. Plastic shrinkage

occur before concrete reaches initial set, drying shrinkage occur after concrete set.

All concrete shrinks after placement due to a volume change caused by

moisture loss. If the shrinkage could take place without any restraint, the concrete would not

crack. But the slab-on-grade concrete is always subjected to at least some restraint, by either

the foundation, another part of the structure, or by reinforcing steel embedded in the concrete.Restraint also develops during differential shrinkage, when concrete of the surface shrinks

faster than the underlying concrete, if the tensile stress caused by restraint exceeds the tensile

strength of the concrete the concrete cracks.

Taking precautions can minimize the possibility of shrinkage cracking. But even

when you take precautions, shrinkage cracks can occur.


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Synthetic fiber also control cracks the fiber in the concrete of the

recommended dosages results in millions of fibers dispersed evenly throughout the concrete

matrix. This multidimensional reinforcement reportedly gives fresh more tensile capacity to

resist typically volume changes. It also helps distribute tensile stress more evenly. If shrinkage

cracks do form, fibers bridge these cracks helping reduce their length and width.

Various test, have been conducted on synthetic fiber to determine the effect of

fiber on plastic shrinkage cracks. Paul kraai, a professor at san jose university (California)

compared early cracking behavior of slab sample made with plan concrete , concrete reinforced

with welded wire fabrics and concrete containing propylene fibers at a rate of 1 pound per

cubic yard. The slabs were 2ft wide, 3ft long and 2inch thick with edge restraint by panels. Fan

blew air at high velocity over the surface of the slab to force rapid drying. The result showed

plastic shrinkage cracks reduction of 71.5% in the fiber reinforced sample composed with the

plain concrete sample. The sample containing welded-wire fabrics showed cracks reduction of

only 6.5%.

3) DURABILITY:Concrete products are susceptible to degradation as a result of sulphate

attacks, freeze-thaw cycling, alkali silica reaction, and corrosion of embedded

reinforcing bars, if present. In all of these cases permeability to water plays an

important part. Durability of concrete product is therefore influenced by the rate at

which water may enter. Result have indicated that permeability , in turn , depends

largely on cracking in concrete, and an increase in the cracks width will produce a

highly permeable concrete. Fibers reinforced improve cracking resistance increasethe surface roughness of cracks and promotes multiple-crack development, thereby

significantly reducing the permeability of concrete in service.

In case of stress and stress induced cracking , the permeability of plain

concrete , increase dramtically while the permeability of fiber-reinforced concrete remains for

below that of plain concrete under service condition. (Fig 3)

Corrosion of steel reinforcing bars in concrete remains a major concern chloride contomination

of concrete is usually to blame, and the mechanism by which chloride ios promotes reinforcing

bar corrosion in concrete are well understod. Unfortunately cracks in concrete permits ready

ingress of chloride and other deleterious chemicals and further promote corrosion , Because

chloride diffusion depends principally on water permeability in both stressed and unstressed

concrete and hence slow the rate of chloride diffusion. The inclusion of fiber in concrete could

be a feasible solution for prolonging the life of concrete structure. A recent study has indicated

that both cellulose and polyprophylene fibers might increase the co-efficient of apparent (total)


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chloride diffusion but decrease the co-efficient of effective (free) chloride diffusion. In other

words while greater amounts of chloride diffuse through fiber-reinforced concrete. Fiber

chemically combine with the passing chloride such that only limited amount of free chloride are

available for steel corrosion. This ability of fibers to bind the chlorides was further reinforced in

loaded reinforced concrete beam where corrosion was delayed significantly as a result of fiberreinforcement fig 4.

FIG: 3

FIG : 4


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APPLICATIONS:

Synthetic fiber reinforced concrete are used in different area of civil

engineering.

Synthetic fiber reinforced concrete are used in:

I. Overlay of airfieldII. Road pavement

III. IndustrialsIV. Bridge deckV. Precast concrete

VI. Canal liningVII. Refractory lining

VIII. Sewerage pipesIX. Fabrication of precast product like pipes, boats beams, staircase

steps, wall panel, roof panel, main hole etc.

REFRENCES

I. Nadeem ullah khan , Bazid khan , and Noor badshah, performance of polymericconcrete with synthetic fibers reinforcement against reflective cracking in rigid

pavement overlay.

II. Robert C.zellers, An overview of synthetic fiber reinforced concrete.III. M.J.Hasan , M.Afroz and H.M.I Mohmud, An experimental investigation on

mechanical behavior of placro synthetic fiber reinforced concrete.

IV. Jiang jiabio, Steven Loh, Joh gosho. Synthetic structure fibers for toughness andcrack control of concrete.

V. D.Ludirdja and J.F.Young Synthetic fiber reinforcement for concrete.VI. Cement and concrete institute Fiber reinforced concrete.

VII. Don wimpenny, peter Duxson, jony cooper, john prvis, and RoberZeuschnerFiber reinforced geopolymer concrete products for underground infrastructure.

VIII. Nemkumar banthia , vivek Bindiganavile, john jones, and jeff novak Fiberreinforced concrete in precast concrete application, Research leads to innovativr

products.

IX. Robert E.Xnorr and Scoff E.Nodes , P.E Polyprophylene fiber reinforce concretedetention ponds: Final report.


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X. Michael Mahoney Structural synthetic fibers for precast and slab-on-gradeconstruction.

XI. Anne Laning Synthetic fibers.XII. TUF-STRAND (SF) Structural synthetic fibers for concrete reinforcement. (report)

XIII.

Youjiang wang, Stanley backer, vector C.Li An experimental study of syntheticfiber reinforced cementitious composite.

XIV. N.Banthia Fiber reinforce concrete.XV. Concrete technology by MS shetty.

XVI. Concrete technology by AM Neville.XVII. Propreties of concrete by AM veville.

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Synthetic Fiber Reinforced Concrete