seminar report on fiber rainforced concrete

7/21/2019 Seminar Report On Fiber Rainforced Concrete

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FIBRE REINFORCED CONCRETE

Chapter- 1

INTRODUCTION

INTRODUCTION

Fibre reinforced concrete (FRC) may be defined as a composite materials made with ortland

cement! a""re"ate! and incorporatin" discrete discontin#o#s fibres$

ortland cement concrete is considered to be a relati%ely brittle material! with a low tensile

stren"th and a low strain capacity$ &hen s#b'ected to tensile stresses! nonreinforced concrete

will crac and fail$ *ince mid +,--.s steel reinforcin" has been #sed to o%ercome this

problem$ /s a composite system! the reinforcin" steel is ass#med to carry all tensile loads$

Fibre reinforced concrete (FRC) is ortland cement concrete reinforced with more or less

randomly distrib#ted fibers$ In FRC! tho#sands of small fibers are dispersed and distrib#ted

randomly in the concrete d#rin" mi0in"! and th#s impro%e concrete properties in all

directions$ Fibers help to impro%e the post pea d#ctility performance! precrac tensile

stren"th! fati"#e stren"th! impact stren"th and eliminate temperat#re and shrina"e cracs$

The role of randomly distrib#tes discontin#o#s fibres is to brid"e across the cracs that

de%elop pro%ides some post cracin" 1d#ctility2$ If the fibres are s#fficiently stron"!

s#fficiently bonded to material! and permit the FRC to carry si"nificant stresses o%er a

relati%ely lar"e strain capacity in the postcracin" sta"e$

The real contrib#tion of the fibres is to increase the to#"hness of the concrete (defined as

some f#nction of the area #nder the load %s$ deflection c#r%e)! #nder any type of loadin"$ That

is! the fibres tend to increase the strain at pea load! and pro%ide a "reat deal of ener"y

absorption in postpea portion of the load %s$ deflection c#r%e$ &hen the fibre reinforcement

is in the form of short discrete fibres! they act effecti%ely as ri"id incl#sions in the concrete

matri0$ hysically! they ha%e th#s the same order of ma"nit#de as a""re"ate incl#sions3 steel

fibre reinforcement cannot therefore be re"arded as a direct replacement of lon"it#dinal

reinforcement in reinforced and prestressed str#ct#ral members$ 4owe%er! beca#se of the

inherent material properties of fibre concrete! the presence of fibres in the body of the

concrete or the pro%ision of a tensile sin of fibre concrete can be e0pected to impro%e the

resistance of con%entionally reinforced str#ct#ral members to cracin"! deflection and otherser%iceability conditions$

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Figure1. The load vs. deflection curve

The fibre reinforcement may be #sed in the form of three dimensionally randomly distrib#ted

fibres thro#"ho#t the str#ct#ral member when the added ad%anta"es of the fibre to shear

resistance and crac control can be f#rther #tili5ed$ On the other hand! the fibre concrete may

also be #sed as a tensile sin to co%er the steel reinforcement when a more efficient two 6dimensional orientation of the fibres co#ld be obtained$ Fibre reinforced concrete (FRC) is

concrete containin" fibro#s material which increases its str#ct#ral inte"rity$ Fibres incl#de

steel fibres! "lass fibres! synthetic fibres and nat#ral fibres$ &ithin these different fibres that

character of fibre reinforced concrete chan"es with %aryin" concretes! fibre materials!

"eometries! distrib#tion! orientation and densities$

Fibre reinforced is mainly #sed in shotcrete! b#t can also be #sed in normal concrete$ Fibre

reinforced normal concrete are mostly #sed for on"ro#nd floors and pa%ements! b#t can be

considered for a wide ran"e of constr#ction parts (beams! pliers! fo#ndations etc) either alone

or with handtied rebars$


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Chapter- 2

I!TOR" OF D#$#%O&'#NT OF FI(R# R#INFORC#D CONCR#T#

I!TOR" OF D#$#%O&'#NT OF FI(R# R#INFORC#D CONCR#T#

The #se of fibres to reinforce and enhance the properties of constr#ction materials "oes bac

at least 78-- years! when straw was #sed to reinforce s#nbaed brics in 9esopotamia$

E"yptians also #sed straw to reinforce m#d brics! b#t there is e%idence that asbestos fiber

was #sed to reinforce clay posts abo#t 8--- years a"o$ Cementbo#nd prod#cts ha%e been

reinforced by %ario#s types of fibre at least since the be"innin" of the last cent#ry! and steel

and synthetic fibres ha%e been #sed to impro%e the properties of concrete for the past 7- or :-

years$ ortland cement concrete is considered to be a relati%ely brittle material$ &hen

s#b'ected to tensile stresses! nonreinforced concrete will crac and fail$ *ince mid +,--.s

steel reinforcin" has been #sed to o%ercome this problem$ /s a composite system! the

reinforcin" steel is ass#med to carry all tensile loads$

The problem with employin" steel in concrete is that o%er time steel corrodes d#e to the

in"ress of chloride ions$ In the northeast! where sodi#m chloride deicin" salts are commonly

#sed and a lar"e amo#nt of coastal area e0ists! chlorides are readily a%ailable for penetration

into concrete to promote corrosion! which fa%ors the formation of r#st$ R#st has a %ol#me

between fo#r to ten times the iron! which dissol%es to form it$ The %ol#me e0pansion

prod#ces lar"e tensile stresses in the concrete! which initiates cracs and res#lts in concretespallin" from the s#rface$ /ltho#"h some meas#res are a%ailable to red#ce corrosion of steel

in concrete s#ch as corrosion inhibiti%e admi0t#res and coatin"s! a better and permanent

sol#tion may be replace the steel with a reinforcement that is less en%ironmentally sensiti%e$

Fibre Reinforced Concrete (FRC) was in%ented by French "ardener ;oseph 9onier in +,:$

9ore recently micro fibres! s#ch as those #sed in traditional composite materials ha%e been

introd#ced into the concrete mi0t#re to increase its to#"hness! or ability to resist crac

"rowth$

*e%eral different types of fibres! both manmade and nat#ral! ha%e been incorporated intoconcrete$ ?se of nat#ral fibres in concrete precedes the ad%ent of con%entional reinforced

concrete in historical conte0t$ 4owe%er! the technical aspects of FRC systems remained

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essentially #nde%eloped$ *ince the ad%ent of fibre reinforcin" of Concrete in the +


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Chapter-

#FF#CT OF FI(R#! IN CONCR#T#

#FF#CT OF FI(R#! IN CONCR#T#

Fibres are #s#ally #sed in concrete to control plastic shrina"e cracin" and dryin" shrina"e

cracin"$ They also lower the permeability of concrete and th#s red#ce bleedin" of water$

*ome types of fibres prod#ce "reater impact! abrasion and shatter resistance in concrete$

Aenerally fibres do not increase the fle0#ral stren"th of concrete! so it cannot replace moment

resistin" or str#ct#ral steel reinforcement$ *ome fibres red#ce the stren"th of concrete$

The amo#nt of fibres added to a concrete mi0 is meas#red as a percenta"e of the total %ol#me

of the composite (concrete and fibres) termed %ol#me fraction ( f)$ ftypically ran"es from

-$+ to 7$ /spect ratio (ld) is calc#lated by di%idin" fibre len"th (l) by its diameter (d)$Fibres with a noncirc#lar cross section #se an e#i%alent diameter for the calc#lation of

aspect ratio$ If the mod#l#s of elasticity of the fibre is hi"her than the matri0 (concrete or

mortar binder)! they help to carry the load by increasin" the tensile stren"th of the material$

Increase in the aspect ratio of the fibre #s#ally se"ments the fle0#ral stren"th and to#"hness

of the matri0$ 4owe%er! fibres which are too lon" tend to 1ball2 in the mi0 and create

worability problems$It is important to #nderstand the effect of fibers in concrete mechanism$

The composite will carry increasin" loads after the first cracin" of the matri0 if the p#llo#t

resistance of the fibers at the first crac is "reater than the load at first cracin"$ /t the

craced section! the matri0 does not resist any tension and the fibers carry the entire load

taen by the composite$ &ith an increasin" load on the composite! the fibers will tend to

transfer the additional stress to the matri0 thro#"h bond stresses$ This process of m#ltiplecracin" will contin#e #ntil either fibers fail or the acc#m#lated local debondin" will lead to

fiber p#llo#t$ Fibres s#ch as "raphite and "lass ha%e e0cellent resistance to creep! while the

same is not tr#e for most resins$ Therefore! the orientation and %ol#me of fibres ha%e a

si"nificant infl#ence on the creep performance of rebarstendons.It has been reco"ni5ed that

the addition of small! closely spaced and #niformly dispersed fibres to concrete wo#ld act as

crac arrester and wo#ld s#bstantially impro%e its static and dynamic properties$ Reinforced

concrete itself is a composite material! where the reinforcement acts as the stren"thenin" fibre

and the concrete as the matri0$ It is therefore imperati%e that the beha%ior #nder thermal

stresses for the two materials be similar so that the differential deformations of concrete and

the reinforcement are minimi5ed$

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Chapter:

FCTOR! #FF#CTIN/ &RORTI#! OF FI(R# R#INFORC#D CONCR#T#

0. FCTOR! #FF#CTIN/ &RORTI#! OF FI(R# R#INFORC#D

CONCR#T#

Fibre reinforced concrete is the composite material containin" fibres in the cement matri0 in

an orderly manner or randomly distrib#ted manner$ Its properties wo#ld ob%io#sly! depends

#pon the efficient transfer of stress between matri0 and the fibres$ The factors are briefly

disc#ssed below

Relative fi+re 'atri !tiffness

The mod#l#s of elasticity of matri0 m#st be m#ch lower than that of fibre for efficient stress

transfer$ Gow mod#l#s of fibre s#ch as nylons and polypropylene are! therefore! #nliely to

"i%e stren"th impro%ement! b#t the help in the absorbsion of lar"e ener"y and therefore!

impart "reater de"ree of to#"hness and resistance to impart$ 4i"h mod#l#s fibres s#ch as

steel! "lass and carbon impart stren"th and stiffness to the composite$

Interfacial bond between the matri0 and the fibre also determine the effecti%eness of stress

transfer! from the matri0 to the fibre$ / "ood bond is essential for impro%in" tensile stren"th

of the composite$ The interfacial bond co#ld be impro%ed by lar"er area of contact! impro%in"

the frictional properties and de"ree of "rippin" and by treatin" the steel fibres with sodi#m

hydro0ide or acetone$


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Figure. Reinforceent in a concrete atri

$olue of Fi+res

The stren"th of the composite lar"ely depends on the #antity of fibres #sed in it$ Fi"#re 8

and = show the effect of %ol#me on the to#"hness and stren"th$ It can see from Fi"#re 8 that

the increase in the %ol#me of fibres! increase appro0imately linearly! the tensile stren"th and

to#"hness of the composite$ ?se of hi"her percenta"e of fibre is liely to ca#se se"re"ation

and harshness of concrete and mortar$


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Figure0. !tress v3s !train on fi+re volue curve

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Figure4. #ffect of volue of fi+res Figure5. #ffect of volue of fi+res

In fleure in tension

spect Ratio of the Fi+re

/nother important factor which infl#ences the properties and beha%ior of the composite is the

aspect ratio of the fibre$ The /spect Ratio of a fibre is the ratio of its len"th to its He#i%alent@

diameter$ /s lon" as a fibre@s basic shape! tensile stren"th! dosa"e and anchora"e mechanismremain the same! a hi"her aspect ratio will res#lt in a steel fibre reinforced concrete element

ha%in" a hi"her postcrac load carryin" capacity$ This impro%ed performance is d#e to the

increased fibre co#nt i$e$ there are more fibres pro%idin" tensile capacity at each craced

section$ The /spect Ratio of the fibres chosen for a partic#lar application is a f#nction of

economics and performance$

It has been reported that #p to aspect ratio of >8! increase on the aspect ratio increases the

#ltimate concrete linearly$ Beyond >8! relati%e stren"th and to#"hness is red#ced$ Table +$+

shows the effect of aspect ratio on stren"th and to#"hness$


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8


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Ta+le1. spect ratio of the fi+re

spect

T*pe of concrete

Ratio

Relative strength

Relative toughness

lain concrete

0

+

+

&ith

8

+$8

$-

Randomly

8-

+$=

,$-

Dispersed fibres

>8

+$>

+-$8

+--

+$8,$8


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Orientation of Fi+res

One of the differences between con%entional reinforcement and fibre reinforcement is that in

con%entional reinforcement! bars are oriented in the direction desired while fibres are

randomly oriented$ To see the effect of randomness! mortar specimens reinforced with -$8

%ol#me of fibres were tested$ In one set specimens! fibres were ali"ned in the direction of the

load! in another in the direction perpendic#lar to that of the load! and in the third randomly

distrib#ted$

It was obser%ed that the fibres ali"ned parallel to the applied load offered more tensile

stren"th and to#"hness than randomly distrib#ted or perpendic#lar fibres$

6or7a+ilit* and Copaction of Concrete

It is well nown that the addition of any type of fibers to plain concrete red#ces the

worability$

Incorporation of steel fibre decreases the worability considerably$ This sit#ation ad%ersely

affects the consolidation of fresh mi0$ E%en prolon"ed e0ternal %ibration fails to compact the

concrete$ The fibre %ol#me at which this sit#ation is reached depends on the len"th and

diameter of the fibre$ *ince fibres impart considerable stability to a fresh concrete mass! the

sl#mp cone test is not a "ood inde0 of worability$

For e0ample! introd#ction of +$8 %ol#me percent steel or "lass fibres to a concrete with --

mm of sl#mp is liely to red#ce the sl#m of the mi0t#re to abo#t 8 mm! b#t the placeability

of the concrete and its compactability #nder %ibration may still be satisfactory$

Therefore! the ebe test is considered more appropriate for e%al#atin" the worability of

fibrereinforce concrete mi0t#res$ /nother conse#ence of poor worability is non#niform

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distrib#tion of the fibres$ Aenerally! the worability and compaction standard of the mi0 is

impro%ed thro#"h increased water cement ratio or by the #se of some ind of water red#cin"

admi0t#res$

!i8e of Coarse ggregate

9a0im#m si5e of the coarse a""re"ate sho#ld be restricted to +-mm! to a%oid appreciable

red#ction in stren"th of the composite$ fibres also in effect! act as a""re"ate$ /ltho#"h they

ha%e a simple "eometry! their infl#ence on the properties of fresh concrete is comple0$ The

interparticle friction between fibres and between fibres and a""re"ates controls the

orientation and distrib#tion of the fibres and conse#ently the properties of the composite$

Friction red#cin" admi0t#res and admi0t#res that impro%e the cohesi%eness of the mi0 can

si"nificantly impro%e the mi0$

'iing

9i0in" of fibre reinforced concrete needs caref#l conditions to a%oid ballin" of fibres!

se"re"ation and in "eneral the diffic#lty of mi0in" the materials #niformly$ Increase in the

aspect ratio! %ol#me percenta"e and si5e and #antity of coarse a""re"ate intensify the

diffic#lties and ballin" tendency$ *teel fibre content in e0cess of by %ol#me and aspect

ratio of more than +-- are diffic#lt to mi0$

9i0in" of FRC can be accomplished by many methods$ The mi0 sho#ld ha%e a #niform

dispersion of the fibres in order to pre%ent se"re"ation or ballin" of the fibres d#rin" mi0in"$

9ost ballin" occ#rs d#rin" the fibre addition process$ Increase of aspect ratio! %ol#mepercenta"e of fibre! and si5e and #antity of coarse a""re"ate will intensify the ballin"

tendencies and decrease the worability$ To coat the lar"e s#rface area of the fibres with

paste! e0perience indicated that a water cement ratio between -$: and -$=! and minim#m

cement content of :-- "m7 are re#ired$ Compared to con%entional concrete! fibre

reinforced concrete mi0es are "enerally characteri5ed by hi"her cement factor! hi"her fine

a""re"ate content! and smaller si5e coarse a""re"ate$

/ fibre mi0 "enerally re#ires more %ibration to consolidate the mi0$ E0ternal %ibration is

preferable to pre%ent fibre se"re"ation$ 9etal trowels! t#be floats! and rotatin" power floats

can be #sed to finish the s#rface$It is important that the fibres are dispersed #niformly

thro#"ho#t the mi03 this can be done by the addition of the fibres before the water is added$

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&hen mi0in" in a laboratory mi0er! introd#cin" the fibres thro#"h a wire mesh baset will

help e%en distrib#tion of fibres$ For field #se! other s#itable methods m#st be adopted$

The t*pical proportion for fi+re reinforced concrete is given +elo,9

Cement content 78 to 88- "cm

&C ratio -$: to -$=

of sand to total a""re"ate 8- to +--

9a0im#m a""re"ate si5e +- mm

/ircontent = to


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Chapter-4

DIFF#R#NT T" OF FI(R#!

DIFF#R#NT T" OF FI(R#!

Followin" are the different type of fibres "enerally #sed in the constr#ction ind#stries$

*teel fibre Reinforced Concrete

olypropylene fibre Reinforced (FR) cement mortar Jconcrete

Alassfibre Reinforced Concrete

/sbestos fibres

Carbon fibres

Or"anic fibres

!teel fi+re Reinforced Concrete

/ n#mber of steel fibre types are a%ailable as reinforcement$ Ro#nd steel fibre the commonly#sed type are prod#ced by c#ttin" ro#nd wire in to short len"th$ The typical diameter lies in

the ran"e of -$8 to -$>8mm$ *teel fibres ha%in" a rectan"#lar cs are prod#ced by siltin" the

sheets abo#t -$8mm thic$ Fibre made from mild steel drawn wire$ Conformin" to I* ,-

+= with the diameter of wire %aryin" from -$7 to -$8mm ha%e been practically #sed in

India$ Ro#nd steel fibres are prod#ced by c#ttin" or choppin" the wire! flat sheet fibres

ha%in" a typical cs ran"in" from -$+8 to -$:+mm in thicness and -$8 to -$


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formin" and stora"e of classical reinforcement frames! riss of spallin" d#rin" transportation

and layin")$

Figure:. Different t*pe of steel fi+re

*tr#ct#ral #se of *FRC /s recommended by /CI Committee 8::! Hwhen #sed in str#ct#ral

applications! steel fibre reinforced concrete sho#ld only be #sed in a s#pplementary role toinhibit cracin"! to impro%e resistance to impact or dynamic loadin"! and to resist material

disinte"ration$ In str#ct#ral members where fle0#ral or tensile loads will occ#r the reinforcin"

steel m#st be capable of s#pportin" the total tensile load@$ Th#s! while there are a n#mber of

techni#es for predictin" the stren"th of beams reinforced only with steel fibres! there are no

predicti%e e#ations for lar"e *FRC beams! since these wo#ld be e0pected to contain

con%entional reinforcin" bars as well$

For beams containin" both fibres and contin#o#s reinforcin" bars! the sit#ation is comple0!

since the fibres act in two ways

They permit the tensile stren"th of the *FRC to be #sed in desi"n! beca#se the matri0 will nolon"er lose its loadcarryin" capacity at first crac$

They impro%e the bond between the matri0 and the reinforcin" bars by inhibitin" the "rowth


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of cracs emanatin" form the deformations (l#"s) on the bars$

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4owe%er! it is the impro%ed tensile stren"th of *FRC that is mostly considered in the beam

analysis! since the impro%ements in bond stren"th are m#ch more diffic#lt to #antify$ *teel

fibres ha%e been shown to increase the #ltimate moment and #ltimate deflection of

con%entionally reinforced beams3 the hi"her the tensile stress d#e to the fibres! the hi"her the

#ltimate moment$

&ol*prop*lene Fi+re Reinforced ;&FR< ceent

olypropylene fibre reinforced concrete or mortar is an additi%e to concrete and mi0es which

considerably red#ces the ris of dryin" cracs$ The plastic fibres consist of polypropylene

fibres which are resistant in alaline en%ironments and the len"th and dosa"e of which can

%ary dependin" on what properties are re#ired$

olypropylene fibre was first #sed to reinforce concrete in the +


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olypropylene fibre reinforced concrete or mortars are #sed for

Considerably red#cin" the ris that dryin" cracs will arise d#rin" dry! windy and hot

weather$

Impro%in" the cohesion between fresh concrete batches$

Impro%in" the ability to p#mp thro#"h pipes and hoses of smaller dimensions and thro#"h

"reater p#mpin" distances$

Impro%in" worability while po#rin"$

/reas of application

?sed in concrete and mortar where there is a ris of dry cracin"$ Dryin" cracs are most

often formed in the case of concrete po#rin" that is carried o#t witho#t protection d#rin"

weather that is dry! windy or hot$ Castin" of slabs! beams and cast on str#ct#res that are

partic#larly %#lnerable$ It can be diffic#lt to protect concrete or mortar a"ainst dry cracin"

immediately after po#rin" has been completed$ In s#ch sit#ations! the plastic fibre

reinforcement is a simple and effecti%e aid! #ntil the s#rface can be protected by #sin"

con%entional methods s#ch as water! wellf#nctionin" c#rin" membranes or co%erin"s$

9i0in" in plastic fibre reinforcement does not replace normal c#rin" methods

Figure=. &ol*prop*lene fi+re reinforced ceent-ortar > concrete


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/lass-fi+re Reinforced Concrete

Alass fibre is made #p from --:-- indi%id#al filaments which are li"htly bonded to mae

#p a stand$ These stands can be chopped into %ario#s len"ths! or combined to mae cloth mat

or tape$ ?sin" the con%entional mi0in" techni#es for normal concrete it is not possible to

mi0 more than abo#t (by %ol#me) of fibres of a len"th of 8mm$

The first research on "lass fibres in the early +


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s+estos fi+res

The nat#rally a%ailable ine0pensi%e mineral fibre! asbestos! has been s#ccessf#lly combined

with ortland cement paste to form a widely #sed prod#ct called asbestos cement$ /sbestos

fibres here thermal mechanical J chemical resistance main" them s#itable for sheet prod#ct

pipes! tiles and corr#"ated roofin" elements /sbestos cement board is appro0imately two or

fo#r times that of #nreinforced matri0$ 4owe%er! d#e to relati%ely short len"th (+-mm) the

fibre ha%e low impact stren"th$

Figure1@. s+estos fi+res

Car+on fi+res

Carbon fibres are man#fact#red by carboni5in" s#itable or"anic materials in fibro#s forms at

hi"h temperat#res and then ali"nin" the res#ltant "raphite crystallites by hotstretchin"$ The

fibres are man#fact#red as either Type I (hi"h mod#l#s) or Type II (hi"h stren"th) and are

dependent #pon material so#rce and e0tent of hot stretchin" for their physical properties$

Carbon fibres are a%ailable in a %ariety of forms and ha%e a febrile str#ct#re similar to that ofasbestos$

Carbon fibre made from petrole#m and coal pitch is less e0pensi%e than the con%entional

carbon fibre made from fibro#s materials$ The Type I and II carbon fibres prod#ced by

carboni5in" s#itable or"anic materials other than petrole#mbased materials are - to :-

times stron"er and ha%e a mod#l#s of elasticity #p to +-- times "reater than the pitchbased

carbon fibre$

Carbon fibres from the most recent J probability the most spectac#lar addition to the ran"e of

fibre a%ailable for commercial #se$ Carbon fibre comes #nder the %ery hi"h mod#l#s of

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elasticity and fle0#ral stren"th$ These are e0pansi%e$ Their stren"th J stiffness characteristics

ha%e been fo#nd to be s#perior e%en to those of steel$ B#t they are more %#lnerable to dama"e

than e%en "lass fibre! and hence are "enerally treated with resi"n coatin"$ Tensile creep is

red#ced sli"htly! b#t fle0#ral creep can be s#bstantially red#ced when %ery stiff carbon fibres

are #sed

Figure11. Car+on fi+res

Carbon fibre cementmatri0 composites are str#ct#ral materials that are "ainin" in importance

#ite rapidly d#e to the decrease in carbon fibre cost and the increasin" demand of s#perior

str#ct#ral and f#nctional properties$ These composites contain short carbon fibres! typically 8

mm in len"th! as the short fibres can be #sed as an admi0t#re in concrete (whereas contin#o#s

fibres cannot be simply added to the concrete mi0) and short fibres are less e0pensi%e than

contin#o#s fibres$ 4owe%er! d#e to the wea bond between carbon fibre and the cement

matri0! contin#o#s fibres KL:M are m#ch more effecti%e than short fibres in reinforcin"

concrete$ *#rface treatment of carbon fibre (e$"$ by heatin" or by #sin" o5one ! silane ! *iO

particles or hot NaO4 sol#tion ) is #sef#l for impro%in" the bond between fibre and matri0!

thereby impro%in" the properties of the composite$ In the case of s#rface treatment by o5oneor silane! the impro%ed bond is d#e to the enhanced wettability by water$ /dmi0t#res s#ch as

late0 methylcell#lose and silica f#me also help the bond

The effect of carbon fibre addition on the properties of concrete increases with fibre %ol#me

fraction! #nless the fibre %ol#me fraction is so hi"h that the air %oid content becomes

e0cessi%ely hi"h $(The air %oid content increases with fibre content and air %oids tend to ha%e

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a ne"ati%e effect on many properties! s#ch as the compressi%e stren"th$) In addition! the

worability of the mi0 decreases with fibre content$

9oreo%er! the cost increases with fibre content$ Therefore! a rather low %ol#me fraction of

fibres is desirable$ / fibre content as low as -$ %ol$ is effecti%e! altho#"h fibre contents

e0ceedin" + %ol$ are more common$ The re#ired fibre content increases with the particle

si5e of the a""re"ate! as the Fle0#ral stren"th decreases with increasin" particle si5e$

Effecti%e #se of the carbon fibres in concrete re#ires dispersion of the fibres in the mi0$ The

dispersion is enhanced by #sin" silica f#me (a fine partic#late) as an admi0t#re KL:M$ /

typical silica f#me content is +8 by wei"ht of cement$ The silica f#me is typically #sed

alon" with a small amo#nt (-$: by wei"ht of cement) of methylcell#lose for helpin" the

dispersion of the fibres and the worability of the mi0$ Gate0 (typically +8L - by wei"ht of

cement) is m#ch less effecti%e than silica f#me for helpin" the fibre dispersion! b#t it

enhances the worability! Fle0#ral stren"th! Fle0#ral to#"hness! impact resistance! frost

resistance and acid resistance$ The ease of dispersion increases with decreasin" fibre len"thThe impro%ed str#ct#ral properties rendered by carbon fibre addition pertain to the increased

tensile and fle0ible stren"ths! the increased tensile d#ctility and fle0#ral to#"hness! the

enhanced impact resistance! the red#ced dryin" shrina"e and the impro%ed free5e thaw

d#rability$

Figure12. Figure of Car+on Fi+re


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Organic fi+res

Or"anic fibre s#ch as polypropylene or nat#ral fibre may be chemically more inert than either

steel or "lass fibres$ They are also cheaper! especially if nat#ral$ / lar"e %ol#me of %e"etable

fibre may be #sed to obtain a m#ltiple cracin" composite$ The problem of mi0in" and

#niform dispersion may be sol%ed by addin" a s#per plastici5er$

Figure1. Organic fi+re


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Chapter-5

CURR#NT D#$#%O&'#NT IN FI(R# R#INFORC#D CONCR#T#

CURR#NT D#$#%O&'#NT IN FI(R# R#INFORC#D CONCR#T#

There is a new "eneration of hi"h performance fiberreinforced composites$ In many of these

materials the stren"th! to#"hness! and d#rability are si"nificantly impro%ed which were not

easily achie%ed by normal fibre reinforced concrete$ 4ere some new type of fibre reinforced

concrete disc#ssed

Compact Reinforced Composites

Reacti%e owder Concrete

*l#rryInfiltratedfibred concrete

En"ineered Cementitio#s Composite (EEC)

5.1. Copact Reinforced Coposites ;CRC8mm thicness. of con%entionally reinforced concrete slab! a +8-mm

thic crimpedend FRC slab was #sed to o%erlay an e0istin" asphaltic pa%ed aircraft parin"

area$ FRC pa%ements are now in ser%ice in se%ere and mild en%ironments$

T#nnel Ginin" and *lope *tabili5ation

*teel fibre reinforced shotcrete (*FR*) are bein" #sed to line #nder"ro#nd openin"s and roc

slope stabili5ation$ It eliminates the need for mesh reinforcement and scaffoldin"$

Blast Resistant *tr#ct#res

&hen plain concrete slabs are reinforced con%entionally! tests showed that there is no

red#ction of fra"ment %elocities or n#mber of fra"ments #nder blast and shoc wa%es$

*imilarly! reinforced slabs of fibro#s concrete! howe%er! showed - percent red#ction in

%elocities! and o%er ,- percent in fra"mentations$

Thin *hell! &alls! ipes! and 9anholes

Fibro#s concrete permits the #se of thinner flat and c#r%ed str#ct#ral elements$ *teel fibro#s

shotcrete is #sed in the constr#ction of hemispherical domes #sin" the inflated membrane

process$ Alass fibre reinforced cement or concrete (AFRC)! made by the spray#p process!

ha%e been #sed to constr#ct wall panels$ *teel and "lass fibres addition in concrete pipes and

manholes impro%es stren"th! red#ces thicness! and diminishes handlin" dama"es$

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Figure10. !egents Figure14. (ea

Dam sand 4ydra#lic *tr#ct#re

FRC is bein" #sed for the constr#ction and repair of dams and other hydra#lic str#ct#res to

pro%ide resistance to ca%itation and se%ere erosion ca#sed by the impact of lar"e water born

debris$

Other /pplications

These incl#de machine tool frames! li"htin" poles! water and oil tans and concrete repairs$


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Chapter-1@ FI(R# R#INFORC#D CONCR#T# $#R!U! CON$#NTION%%"

R#INFORC#D CONCR#T#

1@. FI(R# R#INFORC#D CONCR#T# $#R!U! CON$#NTION%%"

R#INFORC#D CONCR#T#

?nreinforced concrete has a low tensile stren"th and a low strain capacity at fract#re$ These

shortcomin"s are traditionally o%ercome by addin" reinforcin" bars or prestressin" steel$

Reinforcin" steel is contin#o#s and is specifically located in the str#ct#re to optimi5e

performance$

Reinforced concrete itself is a composite material! where the reinforcement acts as the

stren"thenin" fibre and the concrete as the matri0$ It is therefore imperati%e that the beha%ior#nder thermal stresses for the two materials be similar so that the differential deformations of

concrete and the reinforcement are minimi5ed$

Fibres are discontin#o#s and are "enerally distrib#ted randomly thro#"ho#t the concrete

matri0$ /ltho#"h not c#rrently addressed by /CI Committee 7+,! fibres are bein" #sed in

str#ct#ral applications with con%entional reinforcement$ Beca#se of the fle0ibility in methods

of fabrication! fibre reinforced concrete can be an economic and #sef#l constr#ction material$

For e0ample! thin (+ to 7: in$ K+7 to - mmM thic)! precast "lass fibre reinforced concrete

architect#ral claddin" panels are economically %iable in the ?$*$ and E#rope$ In slabs on

"rade! minin"! t#nnelin"! and e0ca%ation s#pport applications! steel and synthetic fibre

reinforced concrete and shotcrete ha%e been #sed in lie# of welded wire fabric reinforcement$

/ccordin" to the report by /CI Committee 88: the total ener"y absorbed in fibre debondin"

as meas#red by the area #nder the loaddeflection c#r%e before complete separation of a beam

is at least +- to :- times hi"her for fibrereinforced concrete than for plain concrete$

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Coparison of &erforance of !tandard Concrete and Fi+re Reinforced

!tandard Concrete #posed To #levated Teperatures

#periental &rograe

Ta+le 2- 'aterial used during eperient

+)$ /n increase in compressi%e stren"th and tensile stren"th has been obser%ed for both

standard concrete and fibre reinforced standard concrete when e0posed to a temperat#re of

8--C$

)$ In the ran"e of 8- to ,--C the split tensile stren"th of both standard concrete and fibre

reinforced standard concrete is same$

7)$ Fle0#ral stren"th of standard concrete is e#al to that of the fibre reinforced standard

concrete in ran"e of 8--C,--C$

:)$ Beyond 8--C! both standard concrete and fibre reinforced standard concrete are fo#nd to

loose compressi%e stren"th "rad#ally$

8)$ Fibre reinforced standard concrete is fo#nd to e0hibit more compressi%e stren"th splittensile stren"th and fle0#ral stren"th than standard concrete at all temperat#res$

=)$ The difference between compressi%e stren"th of fibre reinforced standard concrete and

standard concrete %aries in the ran"e of =+-percenta"e$

>)$ The difference between split tensile stren"th of fibre reinforced standard concrete and

standard concrete %aries in the ran"e of -+ percenta"e$

,)$ The difference between fle0#ral stren"th of fibre reinforced standard concrete and

standard concrete %aries in the ran"e of -- percenta"e$


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D$NT/#! ND DI!D$NT/#! OF FI(R# R#INFORC#D

CONCR#T#

Fibre reinforced concrete has started to find its place in many areas of ci%il infrastr#ct#re

applications where the need for repairin"! increased d#rability arises$ /lso FRCs are #sed in

ci%il str#ct#res where corrosion can be a%oided at the ma0im#m$ Fibre reinforced concrete is

better s#ited to minimi5e ca%itationserosion dama"e in str#ct#res s#ch as sl#iceways!

na%i"ational locs and brid"e piers where hi"h %elocity flows are enco#ntered$ / s#bstantial

wei"ht sa%in" can be reali5ed #sin" relati%ely thin FRC sections ha%in" the e#i%alent

stren"th of thicer plain concrete sections$

FRC controls cracin" and deformation #nder impact load m#ch better than plain concrete

and increased the impact stren"th 8 times$

&hen #sed in brid"es it helps to a%oid catastrophic fail#res$ /lso in the #ae prone areas the#se of fibre reinforced concrete wo#ld certainly minimi5e the h#man cas#alties$ In addition!

polypropylene fibres red#ce or relie%e internal forces by blocin" microscopic cracs from

formin" within the concrete$

The main disad%anta"e associated with the fibre reinforced concrete is fabrication$

The process of incorporatin" fibres into the cement matri0 is labor intensi%e and costlier than

the prod#ction of the plain concrete$

The real ad%anta"es "ained by the #se of Fibre Reinforced Concrete o%errides this

disad%anta"e$


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Chapter-11

!U''#R" ND DI!UC!!ION

!U''#R" ND DI!UC!!ION

/ brief stateoftheart report on fiber reinforced concrete is presented$ O#r #nderstandin" of

fibermatri0 interaction! reinforcement mechanisms and performance characteristics is fairly

ad%anced$ The theory! properties! and typical applications of concrete reinforced with the

%ario#s fibres ha%e been described$ nowled"e of the theory of the different fibre types and

cate"ories is necessary to #nderstand the appropriate testin" and de"ree of #ality

controlass#rance necessary to ens#re that desi"n re#irements are satisfied$

The #sef#lness of fiber reinforced concrete (FRC) in %ario#s ci%il en"ineerin" applications is

indisp#table$ Fiber reinforced concrete has started to find its place in many areas of ci%il

infrastr#ct#re applications where the need for repairin"! increased d#rability arises$ /lso FRC

are #sed in ci%il str#ct#res where corrosion can be a%oided at the ma0im#m$Fiber reinforced

concrete has so far been s#ccessf#lly #sed in slabs on "rade! shotcrete! architect#ral panels!

precast prod#cts! offshore str#ct#res! str#ct#res in seismic re"ions! thin and thic repairs!

crash barriers! footin"s! hydra#lic str#ct#res and many other applications$FRC is slowly

becomin" a well accepted mainstream constr#ction material$

There are c#rrently --!--- metric tons of fibers #sed for concrete reinforcement$ *teel fiberremains the most #sed fiber of all (8- of total tonna"e #sed) followed by polypropylene

(-)! "lass (8) and other fibers (8)$

seminar report on fiber rainforced concrete

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