Admixture 04

8/16/2019 Admixture 04

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ADMIXTURE


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ADMIXTURES• A m xtures are c em ca a e to

concrete, mortar or grout at the

time of mixing to modify

properties either in the wet state

or after mix has hardened

• Can a be a single chemical orblend

• Usually in solutions with typically

35-40 acti!e mineral compounds

• Amount added is less than 5 of

cement "mostly # $%


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Why Are They Used?

• &o modify properties of fresh ' hardened

concrete

• &o ensure the (uality of concrete during

mixing, transporting, placing ' curing

• &o o!ercome certain unexpected

emergencies during concrete operations

"i) e) set retarders%How Applied?

• *ost admixtures are supplied in a ready-to-useform and added at plant or +ob site)

• igments and pumping aids are batched by hand in./ small amounts for


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MINERAL ADMIXTURE


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nera m xtures

Mineral admixtures are incorporated in concrete to:

•

Increase the compressive strength, other mechanicalproperties and duraility!

• Improve the rheological ehaviour in the "resh state!

• #orrect de"iciencies in the pac$ing

aggregates and%or increase the

paste

density o"

the content

withoutincreasing the cement dosage &i!e!, as a "iller'!

• (ecrease the heat o" hydration!

• (ecrease the environmental impact o" concrete &i!e!,y saving cement and%or utilising a waste product'


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MI)*+A A(MI-TU+*./#A..*.• Cementitious

• )atural cements• Hydraulic lime• 0last1"urnace slag &220.'

• Pozzolanic• Materials o" natural

originsuch as crushed

diatomites, volcanic ashes and meta$aolin• 3ly ash• Microsilica or silica "ume

• Materials of lo or ne!li!i"le reacti#it$• imestone, 4uart5 or other roc$ dust• 0entonite• Hydrated lime


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Supplementary Cementitious Materials


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6o55olanic +eaction

Amorp%ous & calcium %$droxide & ater ' calcium silicate%$drate

silica

S & C( & ( ' C)S)(

*re+uentl$, reacti#e alumina is also present in a pozzolan, %ic% leads

to an analo!ous reaction to produce calcium aluminate %$drates-

A & C( & ( ' C)A)(

Calcium aluminate %$drates can react expansi#el$ it% sulp%ate to

form ettrin!ite-


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Silica *ume ---

7ery "ine amorphous &noncrystalline' silica produced in electric arc

"urnaces as a yproduct o" the production o" elemental silicon or

alloys containing silicon8 also $nown as condensed silica "ume or

microsilica!

.ilica "ume is a yproduct o" producing silicon metalor "errosilicon alloys in an electric1arc "urnace!

Has an amorphous .i9: content ; !

Metals that produce silica "ume/• .ilicon metal 1 typically greater than @> silicon• 3errosilicon alloys 1ranging "rom B to

B>

alloyed with iron


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.ilica 3ume/ 6hysical properties

C D E m•Particle size (typical)

• Bulk density as- produced slurry

densified

•Specific gravity

•Surface area (BET)

DFB to FB $g%mF

DF:B to DB $g%mF


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.ilica 3ume/ *""ects in #oncrete

• 6hysical e""ect/ Acts as a

micro1"iller due to its smallparticle si5e

• #hemical e""ect/ Has high

po55olanicity


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C./SE0UE/CE .* SI1ICA *UME: *RES(

C./CRETE IS M.RE C.(ESI2E

• *ore strength gain

• 1ncrease 2uidity• *aes concrete sticyand cohesi!e

• ften cause bleeding


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Aggregate1paste inter"ace

Transition 3oneIn usual concrete, 5one o"

B!B= to D mm thic$ness

contains large crystals o"

#a&9H':reason and pores!9ne

"or the higher porosity o" this 5one is the

accumulation o" leed

water at the sur"ace o"

coarse aggregate particles!


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#onse4uence in Hardened #oncrete/ 0etter aggregate1

paste inter"ace

The wea$est 5one in usual concrete is the Inter"acial Transition Gone &ITG'

etween the hydrated cement paste &H#6' and the aggregate sur"ace!

This 5one is improved signi"icantly y silica "ume incorporation!

3l A h 9 i i


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3ly Ash/ 9rigin• It is the ash precipitated "rom the exhaust gases o"

coal1

"ired power plants!

• The particles are spherical and have high "ineness!

• The particle si5es are etween less than D m and DBB m!

The 0laine speci"ic sur"ace is usually etween :=B and BBm:%$g!

*l A % . i i


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*l$ As%: .ri!in• #ommon "ly ash derived "rom ituminous coal, is

mainly

siliceous &A.TM #lass 3'!

• .u1ituminous coal and lignite result in high1lime "ly ash

&A.TM #lass #'!

• #lass 3 "ly ash is po55olanic, has a comined silica,

alumina and "erric oxide content o" at least @B>, a

maximum .9F content o" => and maximum loss on ignition

o" >! The "ineness, caron content and colour varies "rom

plant to plant!

• #lass # "ly ash may have a lime content as high as :>! It

has some cementitious properties! The caron content is

low, the "ineness is high and the colour is light!


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Influence of *l$ As% on *res%

Concrete• The setting time is increased!

• Wor$aility and "low o" concrete are increased due to thespherical shape o" the "ly ash particles, which has a Jall1

earingK e""ect! There"ore, the paste demand decreases!

• 0leeding and segregation are usually reduced "or well1proportioned "ly ash concrete!


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In"luence o" 3ly Ash on Hardened #oncrete

• 6o55olanic activity is proportional to the amount o"

particlesunder DB m in diameter !

• .trength gain o" "ly ash concrete is slower than normal

concrete! Ultimate strengths are reached much a"ter :< days!

This leads to lower thermal crac$ing!

• #reep and shrin$age o" "ly ash concrete are typically lower

than normal concrete ecause o" the lower amount o" paste in

the concrete!• +esistance against corrosion, al$ali aggregate reaction and

sulphate attac$ is increased due to a less permeale and

porous microstructure and reduced portland cement content!


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2round 2ranulated 0last13urnace .lag

&220.'• 0last "urnace slag is a y1product o" the extraction o"

pig

iron "rom iron ore!

• #o$e and limestone are added as "luxes inside the last

"urnace! The impurities in iron ore comine with the lime

and rise up to the sur"ace o" the last "urnace as slag, while

the heavier molten iron stays at the ottom!

• The slag is suse4uently granulated and can e ground

later to the desired "ineness &usually greater than F=B

m:%$g'!


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When 4uenched "rom its molten state, granulated slag

remain in a meta1stale amorphous state, which gives it

hydraulic 4ualities! &.low air1cooled slag is hydraulically

inert!'

Luenched slag is a glass containing #a9, .i9: and Al:9F!

It is reactive, "orming an aluminum1sustituted #1.1H/

#.A N H O #.H

The hydraulicity o" slag is activated y calcium

hydroxide in

concrete!

445S: Structure and Action


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I/*1UE/CE .* 445S ./ *RES(

C./CRETE

• 6or7a"ilit$ is impro#ed-

• 5leedin! and se!re!ation are usuall$

reduced-

• Some earl$ slump loss-

• T%e settin! time is increased-


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Influence of 445S on (ardened Concrete• The microstructure is denser because less lime

is• produced

• !eat development is lo"ered

• !igher long-term strength gain# especially "hen the $$BS has a

high fineness• %esistance against corrosion is increased due to a

less

• permeable and porous microstructure

• %esistance to sulphate attack is improved due tolo"er calcium hydro&ide content

• 'lkali aggregate reactivity is lo"ered due to the reduction in the

alkali mobility by the lo"er permeability


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#hemical Admixtures/ .igni"icance


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#hemical Admixtures/ .igni"icance

• Water1solule materials that are added to concrete,

at dosages o" less than B1B> o" the cement

weight, are generically called chemical admixtures!

• #hemical admixtures are now common and, in

many cases, essential components o" high14uality

concrete!• Aout B1=> o" the concrete produced in several

countries incorporates some type o" admixture!

• #hemical Admixtures have led to the developmento" several high per"ormance concretes8 e!g!,

shortcrete and .el"1#ompacting #oncrete!


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Factors that Affect the Action of the

Chemical Admixture

• (osage and addition procedures• #haracteristics o" the cement

and aggregates

• *nvironmental conditions&temperature'

The dosage o" the admixtures should

e prescried and controlled rigorously!

Admixture dosage


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• Admixtures should comply with )ational

.tandards

• (osage and type o" admixture shouldcon"orm

with design speci"ications and codes

•

Admixtures dispensers should e• Accurate, calirated

• *nsure complete dosage is delivered to

concrete

•Time o" addition should e "ixed &neveradded to

dry material'

• +edosing should e supervised

• Health sa"et and environmental

Admixture dosage


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Tyes of Chemical Admixtures

• Admixtures t%at mainl$ affect t%e fres% state• Water1reducing agents

• .uperplastici5ers

+educe the amount o" water needed "or increasing

the wor$aility or yield higher wor$aility without

any change in the water content!

• Admixtures t%at mainl$ affect t%e settin! sta!e• .et1accelerators

• .et1retarders+educe%increase rate o" reactionetween

cement

the initial

and water! This causes a

reduction%increase in the time ta$en y

mortars and concrete to pass "rom the plastic to

solid state!


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• Admixtures t%at mainl$ affect t%e %ardenin! state• Hardening accelerators

Accelerate the development o" early strength!

• Admixtures t%at mainl$ affect t%e %ardened state• Air1entraining agents

#ause the "ormation o" uni"ormly distriutedmicroscopic ules o" air in the concrete or mortar!These ules remain a"ter hardening and lead to

higher "ree5e1thaw resistance!

Admixture "$ action


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Admixture "$ action• 6ater reducer and plasticizer

• Superplasticizer

• Set retarder

• Set accelerator

• Air entertainin! a!ent

• 6ater repellin! admixture

• 2iscosit$ modifier

• Corrosion resistant admixture

• Cold %et%er admixture

• S%rin7a!e reducer


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Water +educers

•

Admixture that reduces the water content o" amortar or concrete "or a given wor$aility! Usually

has a secondary e""ect o" retarding the setting o"

the concrete!

• Mainly ased on pure or modi"ied lignosul"onicacids and their salts, hydroxycaroxylic acid and

hydroxylated polymers!

• ignosul"onates have een used since the DFBsin concrete!


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1i!osulfonates

•

ignin ma$es up :B> o" the composition o" wood!

• (uring paper1ma$ing, products o" lignin are

otained as y1products!

• A"ter processing, lignosul"onates are produced!

• #ommercial lignosul"onates used in admixtures

are mainly calcium or sodium ased with sugar

contents o" D1FB>!


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Action o" Water1+educing Admixtures

• When the admixture is added to the concrete mix,

a part o" it is adsored y the cement and thehydration products, with the initial hydrationproducts having the higher adsorption capacity!

• There is a modi"ication o" the normal process o"ettringite "ormation and a delay in the #F.

hydration!

• The "inal hydration products are not signi"icantlya""ected y the presence o" the admixture!However, the morphologies o" the #1.1H gel and#a&9H': are sometimes modi"ied!


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Effect of 6ater8Reducin!

Admixtures• Wor$aility increases with the incorporation o" thewater1reducing admixture!

• +eduction in w%c

• Initial setting time o" cement can e extended y

several hours, depending on the dosage!

•

(rying shrin$age and creep seem to increase withwater1reducing admixture addition!


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!uerlastici"er


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Usage ofSuperplasticizers

Constant 9c:

Increase

in t%e or7a"ilit$

Constant or7a"ilit$:

1oer 9c

same or7a"ilit$

LOWER WATER CONTENT

Lower w/c

M1S SM* SC/o

admixture

MEC(A/ISMS .* ACTI./, D.SA4E

A/D USE


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Mechanisms o" Action

Types o" interaction etween cementparticles and the superplastici5er

P(SICA1

Adsorption andgeneration o"

repulsive "orcesetween cement

particles

C(EMICA1

#hemisorption,"ormation o"

admixture1#a:Ncomplexes and

interaction with the

hydration

reactions


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Chemical Formulation

• .ulphonate &.9F1'

• #aroxylate ϟ',

• Hydroxide &9H1' or

• 6hosphonate &69F1'

.ur"actants solule in water, with di""erent

"unctional groups/• Modified 1i!nosulp%onates ;M1S<• Salts of nap%t%alene sulp%onate and

formalde%$de condensates ;SNF)

• Salts of melamine sulp%onate andformalde%$de condensates

;SMF)

• Com"8t$pe pol$mers

Hydrophilic group

Hydrophobic group


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.uperplastici5er Action

*locculation in t%e a"senceof superplasticizer

Entrapped

ater

6ater Cement

particle

6ater Cement

particle

Effect of t%e superplasticizer


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Consequences of Superplasticizer Usage

•+educes placing and compaction time, leadingto lower construction costs!

• 3acilitates the casting o" elements with

complex shapes and dense rein"orcement!

sur"ace "inish o" the concrete• Improves

theelements!

• eads to superior strength and duraility

with

lower cement contents!


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Consequence of

Superplasticizer Action

Decrease in t%e entrapped air and ater contents of t%e

fres% paste leads to loer porosit$ and cr$stallinit$ of t%e%$drated cement paste

Un%$drated

cement !rains

6ater

9c =

>-?@

9c =

>-@

APtcin


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Applications where a

.uperplastici5er is *ssential

• 3luid%3lowing%6umpale concrete

• .hotcrete

• .el"1compacting concrete

• High1strength concrete

• High1duraility concrete

• #oncrete with low shrin$age and creep


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#ommon high1range water reducers &or .uperplastici5ers'/

Dst generation/ ignosulphonates at high dosages:nd generation/

6olysulphonates

1 .ulphonated melamine "ormaldehyde &.M3'1 .ulphonated naphthalene "ormaldehyde &.)3'

Frd generation/

1 6olycaroxylates

1 6olyacrylates

1 Monovinyl alcohols


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SET8RETARDERS


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*""ect o" .et1+etarding Admixtures• When

system,

a retarder is added to cement1water

physical adsorption andchemicalreactions generally occur with the #F A and #F.!

The result is the retardation o" setting o" the

cement and hardening o" the concrete!

• The initial and "inal setting times are increased!

• Wor$aility is maintained longer!• Heat o" hydration and

temperature

rise o" concretes are lesser at early ages!


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Effect of Set8Retardin! Admixtures in %ardened

concrete• When there is plastici5ing e""ect in addition to

retardation, strength increases as water content isconse4uently reduced!

• .et retardation generally leads to slower

"ormation o" more ordered, smaller and denser

hydration products! This results in higher long1

term strength!

• (ue to the extended plastic stage, the concrete

should e protected against shrin$age and cured

longer!


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SET8ACCE1ERAT.RS

B

(ARDE/I/48ACCE1ERAT.RS


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Types of Accelerators

• #hloride1ased

• #alcium chloride a#l:' is the most common

accelerator! Has een used since D


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Effect of Accelerators

• The rates o" hydration o" #F A and%or #F. are generally

increased!

• #alcium chloride decreases the dormant period o" #F.,accelerates the hydration o" #:., and the reaction

etween #F A and gypsum! It may also comine with #F Aand gypsum!

• #alcium "ormate increases the

hydration

rate o" #F.!However, it is not as e""ective as calcium chloride!

#F A, and•

Triethanolamine accelerates the hydrationo"

retards the hydration o" #F. and #:.!• Higher early strength results "rom the increased amount o"

hydration products!

Ad t d Di d t


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Ad#anta!e and Disad#anta!e

• 6rimary application is in cold1weather concreting!

• 3or improving the onding o" shotcrete to the ase or

previously1placed layers!• Used "or otaining higher early1age strengths!• increase the corrosion• reduce the resistance against sulphate attac$

• #an cause stains on the concrete sur"ace due

to e""lorescence

• reduce the long1term strength


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AIR E/TRAI/I/4

A4E/TS

*reezin! and T%ain! of Concrete


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*reezin! and T%ain! of Concrete• When the temperature o" concrete drops to elow BQ#, the

water does not all "ree5e immediately!

• Water in smaller pores will need a lower temperature to "ree5e

&e!g!, water in DB nm pores will not "ree5e until 1 =Q#, and

pores o" F!= nm will not "ree5e until 1 :BQ#8 gel water will not

"ree5e until 1@


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Effect of Air

Entraining Admixtures

A sur"actant used to produce air ules and dispersethem throughout the cement paste!

Air entraining sur"actant

Mehta and Monteiro


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Freezing and Thawingof Concrete

Mehta and Monteiro


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Applications o" Air *ntraining Agents

•

6rotection against the damage produced inthe concrete y "ree5e1thaw!

• +eduction o" leeding and improvement o"

the uni"ormity o" the concrete, as well asthe wor$aility and consistency!

• owering the density o" concrete!


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C.RR.SI./8I/(I5ITI/4

ADMIXTURES


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DAMP8PR..*ERS

6ATER8REPE11I/4ADMIXTURES

A i f % D f


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Action of t%e Damp8proofer • 6rovides a thin hydrophoic layer within the pores

and voids, and on the sur"ace o" the concrete y/ – +eaction with the cement hydration products,

– #oalescence "rom emulsion "orm, or

– Incorporation in a very "inely divided "orm!

• Those that react with the hydration products are ased on

li4uid "atty acids, such as stearic acid and utyl stearate!

• Those that coalesce on contact with the

hydration products are "ine wax emulsions!• Those that are "ine hydrophoic materials are ased

on

calcium and aluminium stearates!

+ixom and Mailvaganam


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2ISC.SIT8E/(A/CI/4A4E/TS

2ISC.SIT8M.DI*I/4

A4E/TS


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Action of t%e 2iscosit$ Modif$in! A!ent

• Induces cohesion ut does not inhiit the "low signi"icantly!

Its "low ehavior is pseudoplastic &i!e!, has a decreasing

viscosity with higher shear rate'!

• The cohesion increases due to/

– The increase in the viscosity o" water &water1solule

organic polymers such as Welan gum, starch,

cellulose ethers and polyacrylamide', or

– Higher interparticle attraction a"ter the admixture is

adsored on the cement particles &organic water1

solule "locculants such as styrene copolymers'

+ixom and Mailvaganam


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Action of the iscosity Modifying Agent

)agata$i

Underwater test


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Applications o" 7iscosity1Modi"ying Agents

•Underwater concrete• *acilitates sufficient mo"ilit$ of t%e

concrete

under ater it% little loss of cement-

• .el"1compacting concrete

• 1eads to %i!% floa"ilit$ it% no se!re!ation!

•

2routing• Eliminates t%e mi!ration of ater from t%e!rout due to t%e differential pressure-

• (elps maintain t%e cement particles in

suspension once inection ceases-


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C.1D 6EAT(ER

ADMIXTURE SSTEMS

Action of Cold 6eat%er Admixture


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Action of Cold 6eat%er Admixture

S$stems ;C6AS<

•

#WA. can e developed "rom existing admixtures "orconcretes to e placed at temperatures down to 1= R#!

They help protect the concrete against "ree5ing and

maintain productivity!

• 2enerally, setting time doules "or each DB R# drop in

temperature! However, the #WA. should not allow the set

retardation to occur! Also, the water in the concrete should

not e allowed to "ree5e!

• #WA. can consist o" accelerating admixtures, corrosion

inhiitors and water1reducing admixtures! Theaccelerating admixtures and corrosion inhiitors tend to

depress the "ree5ing point o" the concrete!


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S(RI/A4E8REDUCI/4

ADMIXTURES

S%rin7a!e Mec%anisms


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S%rin7a!e Mec%anisms

• Plastic s%rin7a!e: Due to t%e loss of ater in t%e

plastic state due to e#aporation-• Auto!enous s%rin7a!e: Chemical shrinkage ;loer

#olume of %$drates t%an cement and ater< & Self-

desiccation ;reduction in t%e pore ater due to

%$dration


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Shrinkage

%ours da$s ee7s mont%s $ears

Time

Plastic

T%ermal;contraction<

Auto!enous

Dr$in!

Car"onation

.h i $ + d i Ad i t &.+A'


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.hrin$age +educing Admixture &.+A'

*irst used in apan, in t%e FGH>s-

It acts y reducin! t%e surface tension o" theevaporale water in the pores!

eads to lower capillar$ stresses during

drying!

Cement particle

6ater


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• To satis"y the growing demands o" the society

and the construction sector!

• To provide etter staility under

certain environmental conditions!

• To increase the productivity%e""iciency

during "arication, transport and placing!

The capacity o" traditional materials to satis"y

these demands is limited!


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END

Admixture 04

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