507 33 Powerpoint-slides Ch1 DRCS

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Oxford University Press 2013. All rights

Design ofDesign of

ReinforcedReinforcedConcreteConcrete

StructuresStructures

N. Subramanian


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Chapter 1Chapter 1

Introduction toIntroduction to

Reinforced ConcreteReinforced Concrete


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Concrete is used in nearly every type of construction.

raditionally! concrete has "een pri#arily co#posed ofce#ent! $ater! and aggregates.

Concrete is not a ho#ogeneous #aterial! and its

strength and structural properties #ay vary greatlydepending upon its ingredients and #ethod of#anufacture.

%teel reinforce#ents are often included to increase thetensile strength of concrete& such concrete is calledreinforced cement concrete '(CC) or si#plyreinforced concrete '(C).

As of 200*! a"out +., "illion cu"ic #etres of concrete

-ntroduction


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lo"al Annual Consu#ption of%tructural /aterials

Material Unit Weight(g!m"#

Million$onnes

$onnes!%erson

%tructural steel +,0 12 0.1

Ce#ent 10 300 0.

Concrete 200 1!000 2. '0 litres)

i#"er +00 2++ 0.0

4rin5ing$ater

1000 ,132 0.+3 '+30 litres)

Table 1.1 Annual consumption of major structural materials in the world


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Case %tudy


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1. /oulded to any shape

2. 6asy availa"ility of #aterials 'for #anufacturing concrete)

3. 7o$ #aintenance

. 8ater and 9re resistant

,. ood rigidity

*. :igh co#pressive strength

+. 6cono#ical

. 7o$;s5illed la"our re


7/94 Oxford University Press 2013. All rights

1. 7o$ tensile strength 'one;tenth of its co#pressivestrength)

2. (e



Portland ce#ents are also referred to as hydrauliccements! as they not only harden "y reacting $ith$ater "ut also for# a $ater;resistant product. he ra$#aterials used for the #anufacture of ce#ent consistof li#estone! chal5! seashells! shale! clay! slate! silica

sand! alu#ina and iron ore.

$o di?erent processes! 5no$n as dry and wet! areused in the #anufacture of Portland ce#ent!

-n addition! a se#i;dry process is also so#eti#ese#ployed in $hich the ra$ #aterials are ground dry!#ixed $ith $ater! and then "urnt in the 5ilns. /ost

#odern ce#ent factories use either a dry or a se#i;dry

/anufacturing Process ofPortland Ce#ent

/ f i P f



/anufacturing Process ofPortland Ce#ent

Fig. 1.1 Schematic representation of dry process of cement manufacture



Fig. 1.2 Cement, water, fine and course aggregate, chemical and mineral

admitures are combined to form present!day concrete

Concrete -ngredients



Portland Ce#ent

Portland cement (OPC) is the #ost co##on type ofce#ent in general use around the $orld.

Ordinary Portland ce#ent is the #ost i#portant ce#entand is often used! though the current trend is to use PPC.

he speci9c gravity of Portland ce#ent is approxi#ately3.1,.

he silicates C3% and C2% are the #ost i#portantco#pounds and are #ainly responsi"le for the strength of

the ce#ent paste. hey constitute the "ul5 of theco#position.



e# ca o#pos on oOPC

@Ce#ent che#ists use the follo$ing shorthand notation C B CaO! % B %iO 2! A B Al2O3! B e2O3! /

B /gO! : B :2O!

D B Da2O! E B E2O! % B %O3.

S.

No.

Compound Cement

ChemistNotation

(CCN#&

$'pical

Compositionas

Mineral

%hase

1. ricalciu# silicate3'CaO)F%iO2

C3% ,;*, Alite

2. 4icalciu# silicate2'CaO)F%iO2

C2% 1,;30 Gelite

3. ricalciu# alu#inate3'CaO)FAl2O3

C3A ,;10 Alu#inate

. etracalciu# alu#inoferrite'CaO)FAl2O3Fe2O3

CA ,;1, errite

,. ypsu# Ca%OF2 :2O 2;10

Table 1.2 Chemical composition of "#C $%ogue&s Compounds'


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he G-% has classi9ed OPC into the follo$ing threerades

33 rade OPC! -% 2*1

3 rade OPC! -% 1121 ,3 rade OPC! -% 122*1+

he nu#"er in the grade indicates 2 day co#pressivestrength of ce#ent in DH##2

Dote 33 grade is not availa"le in the #ar5etI

hree rades of OPC

Ad t f P tl d P l



Advantages of Portland PoJJolanaCe#ent

1. 6cono#ical than OPC as the costly clin5er is replaced"y cheaper poJJolanic #aterial

2. Converts solu"le calciu# hydroxide into insolu"lece#entitious products! thus i#proving per#ea"ility

and dura"ility

3. Consu#es calciu# hydroxide and does not produce as#uch calciu# hydroxide as OPC

. -#proves pore siJe distri"ution and reduces #icro;

crac5s at the transition Jone due to the presence of9ner particles than OPC

,. (educes heat of hydration and ther#al crac5ing

*. :as high degree of cohesion and $or5a"ility in

concrete and #ortar

4i d t f P tl d



1. he rate of develop#ent of strength is initiallyslightly slo$er than OPC.

2. he e?ect of reducing the al5alinity #ay reduce theresistance to corrosion of steel reinforce#ent.

4isadvantages of PortlandPoJJolana Ce#ent



Portland %lag Ce#ent

P%C is o"tained either "y inti#ateinter;grinding of a #ixture ofPortland ce#ent clin5er and

granulated slag $ith the additionof gypsu# or calciu# sulphate or

"y an inti#ate and unifor#

"lending of Portland ce#ent and9nely ground granulated slag.

A t P t %


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1. UtiliJation of slag ce#ent in concrete not only lessens

the "urden on land9lls& it also conserves a virgin#anufactured product 'OPC) and decreases thee#"odied energy re


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. he lighter colour of slag ce#ent concrete also helpsreduce the heat island e?ect in large #etropolitanareas.

,. -t has lo$ heat of hydration and is relatively "etterresistant to soils and $ater containing excessivea#ounts of sulphates and is hence used for #arine

$or5s! retaining $alls! and foundations.

A vantages o Port an % agCe#ent


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Aggregates

he 9ne and coarse aggregates occupy a"out *0=+, percent of the concrete volu#e '+0=,> "y #ass) and hencestrongly inKuence the properties of fresh as $ell ashardened concrete! its #ixture proportions! and the

econo#y.

Aggregates #ust "e clean! hard! strong! and dura"le&they should "e free fro# coatings of clay! a"sor"edche#icals! and other 9ne #aterials that could a?ect thehydration and "ond of the ce#ent paste.


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Aggregates are co##only classi9ed into 9ne and coarse

aggregates. )ine aggregates generally consist ofnatural sand or crushed stone $ith particle siJe s#allerthan a"out , ##. Coarse aggregates consist of one ora co#"ination of gravels or crushed stone $ith particle

siJe larger than , ##.

4epending on the source! they could "e eithernaturall' occurring 'gravel! pe""les! sand! etc.) or

s'ntheticall' manufactured '"loated clay aggregates!sintered Ky ash aggregate! etc.).

4epending on the "ul5 density! aggregates can either

"e normal *eight '1,20=1*0 5gH#3

)! light*eight3

Classi9cation of Aggregates


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AggregatesS. No. )actors In,uence on Concrete %ropert'

1. %peci9cgravityHPorosity

%trengthHA"sorption of $ater

2. Crushing strength %trength

3. Che#ical sta"ility 4ura"ility

. %urface texture Gond grip

,. %hape 8ater de#and 'strength)

*. radation or particlesiJedistri"ution

8ater de#and 'strength)! cohesion!"leeding! and segregation

+. /axi#u# siJe of

aggregate

%trength and $ater de#and

. Presence of deleterious#aterials such as dust!clay!silt! or #ud

8ater de#and 'strength)! cohesion!"ond! and dura"ility

Table 1.( Factors of aggregates that may affect properties of concrete


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8ater8ater plays an i#portant role in the $or5a"ility!

strength! and dura"ility of concrete.

oo #uch $ater reduces the concrete strength! $hereastoo little $ill #a5e the concrete un$or5a"le.

he $ater used for #ixing and curing should "e cleanand free fro# inLurious a#ounts of oils! acids! al5alis!

salts! sugars! or organic #aterials! $hich #ay a?ect theconcrete or steel. -n general! sea $ater should not "eused for #ixing or curing concrete.


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Che#ical Ad#ixturesChe#ical ad#ixtures are #aterials in the for# of

po$der or Kuids that are added to the concretei##ediately "efore or during #ixing in order to i#provethe properties of concrete.

he co##on types of ad#ixtures are as follo$s

1. Accelerators

2. (etarders

3. 8ater;reducing ad#ixtures

. Air entraining ad#ixtures

,. Corrosion inhi"itors


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/ineral Ad#ixtures/ineral ad#ixtures are inorganic #aterials that also

have poJJolanic properties. hese very 9ne;grained#aterials are added to the concrete #ix to i#prove theproperties of concrete '#ineral ad#ixtures) or as areplace#ent for Portland ce#ent '"lended ce#ents).

%o#e of the #ineral ad#ixtures are listed as follo$s

1.ly ash

2. round granulated "last furnace slag

3.%ilica fu#e

. (ice hus5 ash '(:A)

,. :igh;reactivity /eta5aolin ':(/)


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Concrete /ix

Concrete #ix design is the process ofproportioning various ingredients

such as ce#ent! ce#entitious

#aterials! aggregates! $ater! andad#ixtures opti#ally in order to

produce a concrete at #ini#al cost

and $ill have speci9ed properties of$or5a"ility and ho#ogeneity in thegreen state and strength and

dura"ility in the hardened state.

ropor on ng o oncre e


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he #ain o"Lective of any concrete #ix proportioning#ethod is to #a5e a concrete that has the follo$ingfeatures

1. %atis9es $or5a"ility re


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/ix Proportioning Procedure

1. Calculate the target #ean co#pressive strength for#ix proportioning.

2. %elect the $Hc ratio.

3. %elect the $ater content.

. Calculate the content of ce#entitious #aterial.

,. 6sti#ate the proportion of coarse aggregate.

*. -dentify the co#"ination of di?erent siJes of coarseaggregate fractions.

+. 6sti#ate the proportion of 9ne aggregate.

. Perfor# trial #ixes.

ropor on ng o oncre e


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ropor on ng o oncre e/ixes

S. No. Nominal Ma-imum Sie of

/ggregate0 mm

Ma-imum Water Content0

g

1. 10 20

2. 20 1*

3. 0 1*,Table 1.) *aimum water content per cubic metre of concrete for nominal maimum si+e of

$angular' aggregateNominal

Ma-imumSie of

/ggregate0mm

olume of Coarse /ggregate %er Unit olume of $otal/ggregate for Di2erent 3ones of )ine /ggregate (for

*!c Ratio 4 5.6#

3one I 3one III 3one II 3one I

10 0.,0 0. 0.* 0.

20 0.** 0.* 0.*2 0.*0

0 0.+, 0.+3 0.+1 0.*

Table 1. -olume of coarse aggregate per unit olume of total aggregate for different +ones of

fine aggregate


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:ydration of Ce#ent

8hen Portland ce#ent is #ixed $ith $ater! a series ofche#ical reactions ta5es place! $hich results in thefor#ation of ne$ co#pounds and progressive setting!hardening of the ce#ent paste! and 9nally in the

develop#ent of strength. he overall process is referredto as ce#ent hydration.

:ydration involves #any di?erent reactions! oftenoccurring at the sa#e ti#e. 8hen the paste 'ce#ent and$ater) is added to aggregates 'coarse and 9ne)! it acts asan adhesive and "inds the aggregates together to for#

concrete.


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7eat of h'dration8 8hen Portland ce#ent is #ixed$ith $ater! heat is li"erated as a result of the exother#icche#ical reaction. his heat is called the heat ofhydration. he heat generated "y the ce#entNs hydration

raises the te#perature of concrete. A very highte#perature rise $ill result in the crac5ing of theconcrete.

/ineral ad#ixtures 'e.g.! Ky ash)! can signi9cantlyreduce the rate and a#ount of heat develop#ent. curing$ith $ater helps to control te#perature increases and is

"etter than other curing #ethods.

:ydration of Ce#ent


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ypes of Concrete 4epending on $here it is #ixed! concrete #ay "e

classi9ed as site9mi-ed concreteor read'9mi-ed(factor'9mi-ed# concrete (RMC#.

Concrete $ithout reinforce#ent is called plainconcrete and $ith reinforce#ent is called RCCor RC.

4epending on the strength it #ay attain in 2 days!concrete #ay "e designated as ordinar' concrete!standardor normal strength concrete (NSC#!high9strength concrete 7SC! and ultra9high9

strength concrete (U7SC#.


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Concrete $ith enhanced perfor#ance characteristics iscalled high9performance concrete (7%C#. Self9compacting concrete (SCC#is a type of :PC! in$hich #axi#u# co#paction is achieved using special

ad#ixtures and $ithout using vi"rators.

8hen 9"res are used in concrete! it is called :bre9

reinforced concrete ()RC#. :igh;perfor#ance (Csare called ductile :bre9reinforced cementitiouscomposites (D)RCCs#& they are also called ultra9high9performance concretes (U7%Cs# or

engineered cementitious composites (;CCs#.

ypes of Concrete


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(eady;#ixed Concrete

(eady;#ixed concrete is a type of concrete that is#anufactured in a factory or "atching plant! "ased onstandardiJed #ix designs! and then delivered to the $or5site "y truc5;#ounted transit #ixers.

/ost of the (/C plants are located in seven large citiesof -ndia! and they contri"ute to a"out 30=*0 per cent of

total concrete used in these cities. he fraction of (/C tototal concrete "eing used is 2., per cent. (/C is "eingused for "ridges! Kyovers! and large co##ercial andresidential "uildings.


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/d+antage

his type of concrete results in #ore precise #ixtures!$ith strict


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4e9nition of :igh;perfor#anceConcrete

:igh;perfor#ance concrete #ay "e de9ned as any

concrete that provides enhanced perfor#ancecharacteristics for a given application.

AC- has adopted the follo$ing "road de9nition of :PC


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he :PCs are #ade $ith carefully selected high;


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%ropert' Criteria that ma' be speci:ed

:igh strength +0=10 /Pa at 2=1 days

:igh early co#pressivestrength

20=2 /Pa at 3=12 hours or 1=3 days

:igh early Kexural strength 2= /Pa at 3=12 hours or 1=3 days

:igh #odulus of elasticity /ore than 0 Pa

A"rasion resistance 0=1 ## depth of $ear

7o$ per#ea"ility ,00=2000 Coulo#"s

Chloride penetration 7ess than 0.0+> Cl at * #onths%ulphate attac5 0.10> or 0.,> #axi#u# expansion at *

#onths for#oderate or severe sulphate exposures

7o$ a"sorption 2=,>

7o$ di?usion coeMcient 1000 101 #Hs(esistance to che#icalattac5

Do deterioration after 1 year

7o$ shrin5age %hrin5age strain less than 0.0> in 0 days

7o$ creep 7ess than nor#al concreteTable 1./ 0esired characteristics of #Cs


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%elf;co#pacting Concrete

%CC is a highly $or5a"le concrete that can Ko$ throughdensely reinforced and co#plex structural ele#ents underits o$n $eight and ade


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%elf;co#pacting Concrete%everal ne$ tests have evolved for testing the suita"ility

of %CC 'see ig. 1.3 in the follo$ing slide). heyessentially involve testing the follo$ing

1. lo$a"ility 'slu#p Ko$ test)

2. illing a"ility 'slu#p Ko$ test! Q;funnel! and Ori#et)

3. Passing a"ility '7;"ox! R;ring! $hich is a si#plersu"stitute for U;"ox)

. (o"ustness

,. %egregation resistance or sta"ility 'si#ple colu#n"ox test sieve sta"ilit test

lf i


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%elf;co#pacting Concrete

Fig. 1.( Tests on self!consolidating concrete $a' Slump flow test $b' !bo $c' 3!ring $d' -!funnel

$e' 4!flow test

ruc ura g $e g


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ruc ura g $e gConcrete

%78C is #ade $ith light$eight coarse aggregates such

as natural pu#ice or scoria aggregates and expandedslags& sintering;grate expanded shale! clay! or Ky ash&and rotary;5iln expanded shale! clay! or slate.

Advantages

1. he use of %78C allo$s us to reduce the dead$eightof concrete ele#ents! thus resulting in overall

econo#y.2. %eis#ic perfor#ance is also i#proved "ecause the

lateral and horiJontal forces acting on a structureduring an earth


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-nternal Curing

An e?ective techni


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i"re;reinforced Concrete

i"res are added to concrete to control crac5ing caused"y plastic shrin5age and drying shrin5age.

he addition of s#all closely spaced and unifor#ly

dispersed 9"res $ill act as crac5 arresters and enhancethe tensile! fatigue! i#pact! and a"rasion resistance ofconcrete.hey also reduce the per#ea"ility of concrete.

hough the Kexural strength #ay increase #arginally!9"res cannot totally replace Kexural steel reinforce#ent.

i" i f d C t


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i"re;reinforced Concrete

Fig. 1.) Fibres used in concrete $a' 0ifferent types and shapes of steel fibres

$b' Fine fibrillated polypropylene fibres $c' 5lass fibres

4uctile i"re;reinforced


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4uctile 9"re;reinforced ce#entitious co#posite is a"roader class of #aterials that has properties andsuperior perfor#ance characteristics co#pared toconventional ce#entitious #aterials such as concrete and

(C.

4(CCs have uni


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Classi9cation of Ce#entitious/aterials

Fig. 1. Classification of cementitious materials



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;ngineered Cementitious Composites6CC are a special type of :P(CC that has "een #icro;structurally tailored "ased on #icro;#echanics.

6CC is syste#atically engineered to achieve highductility under tensile and shear loading.

Gy e#ploying #aterial design "ased on #icro;#echanics! it can achieve #axi#u# ductility in excess ofthree per cent under uniaxial tensile loading $ith only t$o

per cent 9"re content "y volu#e.

4uctile i"re reinforcedCe#entitious Co#posites



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Ultra9high %erformance ConcreteU:PCis a high;strength! high;sti?ness! self;consolidating! and ductile #aterial! for#ulated "yco#"ining Portland ce#ent! silica fu#e!


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Slurr' In:ltrated )ibrous Concrete(SI)C?N#

%-COD is produced "y in9ltrating ce#ent slurry into

pre;placed steel 9"res 'single plain or defor#ed 9"res) ina for#$or5. -t has to "e noted that it does not contain anycoarse aggregates "ut has a high ce#entitious content.

Slurr' in:ltrated mat concrete (SIMC?N# is si#ilarto %-COD! "ut uses pre;placed 9"re #at instead of steel9"res.

4uctile i"re reinforcedCe#entitious Co#posites

t


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erroce#enterroce#ent is a thin (C #ade of rich ce#ent #ortar

'ce#ent to sand ratio of 13) "ased #atrix reinforced $ithclosely spaced layers of relatively s#all dia#eter $ire#esh! $elded #esh! or chic5en #esh.

Fig. 1./ Ferrocement

t


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erroce#ent

he #ortar #atrix should have excellent Ko$characteristics and high dura"ility. he use of poJJolanic#ineral ad#ixtures such as Ky ash ',0> ce#entreplace#ent $ith Ky ash is reco##ended) and use of

superplasticiJers $ill not only per#it the use of $ater="inder ratio of 0.0=0., "y #ass "ut $ill also enhancethe dura"ility of the #atrix.

Applications of ferroce#ent include "oats! "arges! $atertan5s! pipes! "iogas digesters! septic tan5s! toilet "loc5s!and #onolithic or prefa"ricated housing.

P l C t


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Poly#er Concrete%ol'mer concrete is o"tained "y i#pregnating

ordinary concrete $ith a #ono#er #aterial and thenpoly#eriJing it "y radiation! "y heat and catalyticingredients! or "y a co#"ination of these t$o techni


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(einforcing %teel%teel reinforce#ents are provided in (CC to resist tensile

stresses. he


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(einforcing %teel

%teel reinforce#ent used in concrete #ay "e of thefollo$ing types

1. /ild steel and #ediu# tensile steel "ars '/% "ars)

2. :igh;yield strength;defor#ed steel "ars ':S%4 "ars)

3. :ard dra$n steel $ire fa"ric

. %tructural steel confor#ing

Corrosion of (e"ars


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Corrosion of (e"ars

he pri#ary factors controlling the corrosion rate ofsteel re"ars"are the availa"ility of oxygen! electricalresistivity and relative hu#idity of the concrete! p:! andprevailing te#perature.

Car"onation is another cause for corrosion. Car"onation;induced corrosion often occurs in "uilding facades that

are exposed to rainfall! are shaded fro# sunlight! andhave lo$ concrete cover over the reinforcing steel.

Corrosion of (e"ars


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Corrosion of (e"arsCorrosion can also occur $hen t$o di?erent #etals are

in contact $ithin concrete.

8hen corrosion ta5es place! the resulting rust occupies

#ore than three ti#es the original volu#e of steel fro#$hich it is for#ed creating tensile stresses in theconcrete! $hich can eventually cause crac5ing!dela#ination! and spalling of cover concrete.

he presence of corrosion also reduces the e?ectivecross;sectional area of the steel reinforce#ent and leads

to the failure of a concrete ele#ent and su"se


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/itigating Corrosion

/itigation #easures to reduce the occurrence of corrosioninclude the follo$ing

1. 4ecreasing the $Hc or $Hc# ratio of concrete andusing poJJolans and slag to #a5e the concrete less

per#ea"le2. Providing dense concrete cover using controlled

per#ea"ility for#$or5 'CP)! thus protecting thee#"edded steel re"ars fro# corrosive #aterials

3. -ncluding the use of corrosion;inhi"iting ad#ixtures. Providing protective coating to reinforce#ent

,. Using of sealers and #e#"ranes on the concretesurface



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ollo$ing reinforce#ents can "e used to #itigatecorrosion

1.)usion9bonded epo-'9coated reinforcing barsused in (C "ridges $ith a satisfactory perfor#ance

@.Aal+anied reinforcing bars $hose protectiveJinc layer does not "rea5 easily and results in "etter

"ond

".Stainless steel bars $hose initial cost is high "utthe life cycle cost is lo$er



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B. )ibre9reinforced pol'mer bars ()R% bars# areara#id 9"re 'A(P)! car"on 9"re 'C(P) or glass9"re '(P) reinforced poly#er rods. hey are non;#etallic and hence non;corrosive.

6. asalt bars are #anufactured fro# continuous"asalt 9la#ents and epoxy and polyester resins

using a pultrusion process o?ering a corrosion;resistant alternative to steel reinforce#ent.

Concrete /ixing! Placing!


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Concrete /ixing! Placing!Co#pacting! and Curing

he #ixing of #aterials should ensure that the #ass"eco#es ho#ogeneous! unifor# in colour andconsistency. /achine #ixing is to "e adopted for "etter


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Concrete /ixing! Placing!Co#pacting! and Curing

he concrete should "e deposited and co#pacted"efore the co##ence#ent of initial setting of concreteand should not "e distur"ed su"se


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(e#oval of or#s-t is advantageous to leave for#s in place as long as

possi"le to continue the curing period.

he vertical supporting #e#"ers of for#$or5 'shoring)should not "e re#oved until the concrete is strong

enough to carry at least t$ice the stresses to $hich theconcrete #ay "e su"Lected to at the ti#e of re#oval offor#$or5.

%ince the #ini#u# stripping ti#e is a function ofconcrete strength! the preferred #ethod of deter#iningstripping ti#e in other cases is to "e deter#ined "ased onthe tests of site cured cu"es or concrete in place.

8or5a"ility of Concrete


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8or5a"ility of Concrete8or5a"ility #ay "e de9ned as the property of the

freshly #ixed concrete that deter#ines the ease andho#ogeneity $ith $hich it can "e #ixed! placed!co#pacted! and 9nished.

he #ain factor that a?ects $or5a"ility is the $atercontent 'in the a"sence of ad#ixtures). he otherinteracting factors that a?ect $or5a"ility are aggregatetype and grading! aggregateHce#ent ratio! presence of

ad#ixtures! 9neness of ce#ent! and te#perature.

8or5a"ility should "e chec5ed fre


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8or5a"ility of Concrete

Fig. 1.7 Slump testing $a' Typical mould for slump test $b' *easuring slump $c' Types of slump

Co#pressive %trength


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Co#pressive %trength

Co#pressive strength at a speci9ed age! usually 2days! #easured on standard cu"e or cylinder speci#ens!has traditionally "een used as the criterion for theacceptance of concrete.

his is very i#portant for the designer "ecause concreteproperties such as stress=strain relationship! #odulus of

elasticity! tensile strength! shear strength! and "ondstrength are expressed in ter#s of the uniaxialco#pressive strength.

Cu"e and Cylinder ests


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Cu"e and Cylinder ests1. he concrete is poured in the cu"e or cylinder #ould in

layers of ,0 ## and co#pacted properly "y either hand or avi"rator so that there are no voids.

2. he top surface of these speci#ens should "e #ade evenand s#ooth "y applying ce#ent paste and spreading

s#oothly on the $hole area of the speci#en.

3. he test speci#ens are then stored in #oist air of at least 0per cent relative hu#idity and at a te#perature of 2+TC

2TC for 2 hours. After this period! the speci#ens are #ar5edand re#oved fro# the #oulds and 5ept su"#erged in clearfresh $ater! #aintained at a te#perature of 2+TC 2TC untilthey are tested.



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. hese speci#ens are tested "y a co#pression testing#achine after + days of curing or 2 days of curing.

,. he average of three speci#ens gives the co#pressivestrength of concrete.



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Fig. 1.8 Cube testing and failure of concrete cubes $a' Cubes in testing machine $b' Failure ofconcrete cubes

actors A ect ng Co#press ve


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g p%trength

1. $Hc or $Hc# ratio 'inversely related to concrete

strength and directly lin5ed to the spacing "et$eence#ent particles in the ce#ent paste)

2. ype of ce#ent

3. Use of supple#entary ce#entitious #aterials

. ype of aggregates

,. Vuantity and


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g p%trength

*. /oisture and te#perature conditions during curing

+. Age of concrete

. (ate of loading during the cu"e or cylinder test 'the#easured co#pressive strength of concrete increases$ith increasing rate of loading)

. %iJe of speci#en

%tress=%train Characteristics


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%tress=%train Characteristicsypical stress=strain curves of nor#al $eight concrete of variousgrades! o"tained fro# uniaxial co#pression tests! are sho$n in ig.1.10. %uch a #athe#atical de9nition of stress=strain curve is re


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ensile %trength

Concrete is very $ee5 in tension! and direct tensilestrength is only a"out =11 per cent of co#pressivestrength for concretes of grade /2, and a"ove.

he use of poJJolanic ad#ixtures increases the tensilestrength of concrete. Although the tensile strength ofconcrete increases $ith an increase in co#pressive

strength! the rate of increase in tensile strength is of thedecreasing order.

ensile %trength


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ensile %trength

Eno$ledge of tensile strength is re


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ensile %trength

Shear StrengthPure shear is a rare occurrence& usually a co#"ination ofKexural and shear stresses exists! resulting in a diagonaltension failure.

ond Strength

he co##on assu#ption in (C that plane sections re#ain

plane after "ending $ill "e valid only if there is perfect"ond "et$een concrete and steel reinforce#ent. Gondstrength depends on the shear stress at the interface"et$een the reinforcing "ar and the concrete and on the

geo#etry of the reinforcing "ar.

/odulus of 6lasticity


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/odulus of 6lasticity

he #odulus of elasticity of concrete is a 5ey factor for

esti#ating the defor#ation of "uildings and #e#"ers as$ell as a funda#ental factor for deter#ining the modularratio.he SoungNs #odulus of elasticity #ay "e de9nedas the ratio of axial stress to axial strain! $ithin the elastic

range.

8hen linear elastic analysis is used! one should use thestatic #odulus of elasticity.Qarious de9nitions of #odulus

of elasticity are sho$n in ig. 1.11 'in the follo$ing slide).

he dyna#ic #odulus of elasticity of concretecorresponds to a s#all instantaneous strain. -t has to "e

used $hen concrete is used in structures su"Lected to

Qarious 4e9nitions of /odulus


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of 6lasticity of Concrete

Fig. 1.11 -arious definitions of modulus of elasticity of concrete

4yna#ic /odulus


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he dyna#ic #odulus of elasticity of concretecorresponds to a s#all instantaneous strain.

Used $hen concrete is used in structures su"Lected todyna#ic loading.

4eter#ined "y the non;destructive electro;dyna#ic#ethod.

4yna#ic /odulus

PoissonNs (atio


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Poisson s (atio

%oisson>s ratio is de9ned as the ratio of lateral strain tothe longitudinal strain! under unifor# axial stress.

8idely varying values (ange of 0.1,=0.2,.

Goth D%C and :%C use 0.2.

or light$eight concretes -t has to "e deter#ined fro#

tests.

reng un er o# ne


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g%tresses

%tructural #e#"ers are usually su"Lected to aco#"ination of forces! $hich #ay include axial force!

"ending #o#ents! transverse shear! and t$isting#o#ents.

Any state of co#"ined stress acting at any point in a#e#"er #ay "e reduced to three principal stresses

acting at right angles to each other on an appropriatelyoriented ele#entary cu"e in the #aterial.

8hen one of these three principal stresses is Jero! a

reng un er o# ne


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g%tresses

-n #ost of the situations! only the uniaxial strength

properties are 5no$n fro# si#ple tests.

:o$ever! the strength of concrete for "iaxial state of

stress has "een esta"lished experi#entally "y Eupfer! etal. ig. 1.12 'in the follo$ing slide) sho$s that under"iaxial tension! the strength is close to that of uniaxialtension.

8hen one principal stress is tension and other isco#pressive! the concrete crac5s at a lo$er stress than it

$ould have in uniaxial tension or co#pression.

reng un er o# ne


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g%tresses

Fig. 1.12 Strength of concrete in biaial stress

%hrin5age 6?ects


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%hrin5age 6?ects

he total shrin5age strain in concrete is co#posed of thefollo$ing

1. Autogenous shrin5age! $hich occurs during the

hardening of concrete

2. 4rying shrin5age! $hich is a function of the#igration of $ater through hardened concrete

%hrin5age 6?ects


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%hrin5age 6?ects

he #ost i#portant factors that inKuence shrin5age inconcrete are as follo$s

1.ype and content of aggregates

2.$Hc ratio

3.6?ective age at transfer of stress

.4egree of co#paction

,.6?ective section thic5ness

*.A#"ient relative hu#idity

+.Presence of reinforce#ent

e#perature 6?ects


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e#perature 6?ectsConcrete expands $ith rise in te#perature and

contracts $ith fall in te#perature. o li#it thedevelop#ent of te#perature stresses! expansion Lointsare to "e provided.

e#perature stresses #ay "e critical in the design ofconcrete chi#neys and cooling to$ers. (oof sla"s #ayalso "e su"Lected to ther#al gradient due to solar

radiation.

he coeMcient of ther#al expansion depends on the

type of ce#ent and aggregate! ce#ent content! relative

Creep of Concrete


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Creep of ConcreteCreep in concrete is the gradual increase in defor#ation

'strain) $ith ti#e in a #e#"er su"Lected to sustainedloads. he creep strain is #uch larger than the elasticstrain on loading 'creep strain is typically t$o to fourti#es the elastic strain).

Creep occurs under "oth co#pressive and tensilestresses and al$ays increases $ith te#perature. :%Cs

creep less than D%Cs.

he #ain factors a?ecting creep strain are the concrete

#ix and strength! the type of aggregate used! curing!

Creep of Concrete


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Creep of Concrete

Fig 1.1( Typical creep cure

Don;destructive esting


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Don destructive estingDon;destructive tests are used to 9nd the

strength of existing concrete ele#ents.

Fig. 1.1) ;on!destructie testing



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Don destructive esting

hey are classi9ed as follo$s1. :alf;cell electrical potential #ethod to detect the

corrosion potential of reinforcing "ars in concrete

2. %ch#idtH(e"ound ha##er test to evaluate thesurface hardness of concrete

3. Car"onation depth #easure#ent test to deter#ine

$hether #oisture has reached the depth of thereinforcing "ars! there"y leading to corrosion



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. Per#ea"ility test to #easure the Ko$ of $ater throughthe concrete

,. Penetration resistance or 8indsor pro"e test to#easure the surface hardness and hence the strength ofthe surface and near;surface layers of the concrete

*. Cover#eter test to #easure the distance of steelreinforcing "ars "eneath the surface of the concrete andthe dia#eter of the reinforcing "ars



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+.(adiographic test to detect voids in the concrete andthe position of prestressing ducts

. Ultrasonic pulse velocity test #ainly to #easure the

ti#e of travel of ultrasonic pulse passing through theconcrete and hence concrete


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10. o#ographic #odelling! $hich uses the data fro#ultrasonic trans#ission tests in t$o or #ore directions! todetect voids in concrete

11. -#pact echo testing to detect voids! dela#ination!and other ano#alies in concrete

12. round penetrating radar or i#pulse radar testing to

detect the position of reinforcing "ars or stressing ducts

13. -nfrared ther#ography to detect voids! dela#ination!and other ano#alies in concrete and also to detect $ater

entry points in "uildings


4ura"ility of Concrete


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4ura"ility of Concrete4eteriorating concrete structures not only a?ect the

productivity of the society "ut also have a great i#pacton our resources! environ#ent! and hu#an safety.

he deterioration of concrete structures is due to the

#ain e#phasis given to #echanical properties and thestructural capacity and the neglect of construction


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u a" y o Co c e e)actors /2ecting the Durabilit' of Concrete

1.6nviron#ent

2.Concrete cover to the e#"edded steel

3.Vuality and type of constituent #aterials

.Ce#ent content and $Hc ratio of concrete

,.4egree of co#paction and curing of concrete

*.%hape and siJe of #e#"er

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