Admixture( Chap1 BEC210)

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DEFINITIONDEFINITION

A material, other than aggregates, cement, or A material, other than aggregates, cement, or

water, added in small quantities to the mix inwater, added in small quantities to the mix in

order to produce some desired modifications,order to produce some desired modifications,

either to the physical or chemical properties of either to the physical or chemical properties of

the mix or of the hardened product.the mix or of the hardened product.

The most common admixtures affect plasticity,The most common admixtures affect plasticity,

air entrainment and curing time.air entrainment and curing time.



These admixtures are often referredThese admixtures are often referred

to:to:

AcceleratorsAccelerators

Water-reducing admixturesWater-reducing admixtures

Air entraining admixturesAir entraining admixtures RetardersRetarders



ADVANTAGES OF ADMIXTUREADVANTAGES OF ADMIXTURE

Water reduction in the mixWater reduction in the mix High strength concreteHigh strength concrete Corrosion protectionCorrosion protection Set accelerationSet acceleration Strength enhancementStrength enhancement Crack control (shrinkage reduction)Crack control (shrinkage reduction) Protect against freeze thaw cycles-improveProtect against freeze thaw cycles-improve

durabilitydurability



TYPES OF ADMIXTURETYPES OF ADMIXTURE

PlasticizersPlasticizers

SuperplasticizersSuperplasticizers

Retarders and retarding plasticizersRetarders and retarding plasticizers

Accelerators ad accelerating plasticizersAccelerators ad accelerating plasticizers

Air-entraining admixturesAir-entraining admixtures

Pozzolanic or mineral admixturesPozzolanic or mineral admixtures

Damp-proofing and waterproofing admixturesDamp-proofing and waterproofing admixtures

Gas forming admixturesGas forming admixtures



TYPES OF ADMIXTURE (cont’d)TYPES OF ADMIXTURE (cont’d)

Air detraining admixturesAir detraining admixtures

Alkali-aggregate expansion inhibiting admixturesAlkali-aggregate expansion inhibiting admixtures

Workability admixturesWorkability admixtures

Grouting admixturesGrouting admixtures

Corrosion inhibiting admixturesCorrosion inhibiting admixtures

Fungicidal, germicidal, insecticidal admixturesFungicidal, germicidal, insecticidal admixtures

Colouring admixture.Colouring admixture.



Accelerators faisal Accelerators f aisal

Accelerating admixtures are added to concreteAccelerating admixtures are added to concrete

to increase the rate of early strengthto increase the rate of early strength

development in concrete to:development in concrete to: Permit earlier removal of formwork Permit earlier removal of formwork

Reduce the required period of curingReduce the required period of curing

Advance the time that a structure can be placed inAdvance the time that a structure can be placed in

serviceservice

Partially compensate for the retarding effect of lowPartially compensate for the retarding effect of low

temperature during cold weather concreting.temperature during cold weather concreting.

In the emergency repair work.In the emergency repair work.



Retarding admixture faisal Retarding admixture faisal

It is admixture that slows down the chemical process of It is admixture that slows down the chemical process of

hydration so that concrete remains plastic and workablehydration so that concrete remains plastic and workable

for a long time than concrete without retarder for a long time than concrete without retarder

Retarders are used to overcome the accelerating effectRetarders are used to overcome the accelerating effect

of high temperature on setting properties of concrete inof high temperature on setting properties of concrete in

hot weather concreting.hot weather concreting.

Retarders also can overcome the difficult conditionsRetarders also can overcome the difficult conditions

during transportation and placing especially for readyduring transportation and placing especially for ready

mixed concrete which the concrete manufactured inmixed concrete which the concrete manufactured in

central batching plant and transported over a longcentral batching plant and transported over a long

distance to the job sites.distance to the job sites.



Retarding admixture (cont’d) Retarding admixture (cont’d)

faosal faosal The most commonly known retarder is calciumThe most commonly known retarder is calcium

sulphates.sulphates.

Sugar is one of the most effective retarding agents.Sugar is one of the most effective retarding agents.

At normal temperatures addition of sugar 0.05% toAt normal temperatures addition of sugar 0.05% to0.10% have little effect on the rate of hydration, but if 0.10% have little effect on the rate of hydration, but if

the quantity is increased to 0.2%, hydration can bethe quantity is increased to 0.2%, hydration can be

retarded to such an extent that final set may not takeretarded to such an extent that final set may not take

place for 72 hours or more. place for 72 hours or more.



Plasticizers (water reducer) Plasticizers ( water reducer)

Plasticizers can help the difficult conditions for Plasticizers can help the difficult conditions for

obtaining higher workability without using excess of obtaining higher workability without using excess of

water water

The advantages are considerable in the former, concreteThe advantages are considerable in the former, concrete

are stronger, and in the latter they are workable.are stronger, and in the latter they are workable.



Plasticizers (water reducer) (cont’d) Plasticizers ( water reducer) (cont’d)

The basic products constituting plasticizers are asThe basic products constituting plasticizers are as

follows:follows: Anionic surfactants such as lignosulphonates and their Anionic surfactants such as lignosulphonates and their

modifications and derivatives, salts of sulphonatesmodifications and derivatives, salts of sulphonates

hydrocarbonshydrocarbons Nonionic surfactants, such as polyglycol esters, acid of Nonionic surfactants, such as polyglycol esters, acid of

hydroxylated carboxylic acids and their modifications andhydroxylated carboxylic acids and their modifications and

derivativesderivatives

Other products, such as carbohydrates etc.Other products, such as carbohydrates etc.

Among these, calcium, sodium and ammoniumAmong these, calcium, sodium and ammonium

lignosulphonates are the most used.lignosulphonates are the most used.



Plasticizers (water reducer) (cont’d) Plasticizers ( water reducer) (cont’d)

Plasticizers are used in the amount of 0.1% toPlasticizers are used in the amount of 0.1% to

0.4% by weight of cement.0.4% by weight of cement.

At these doses, at constant workability theAt these doses, at constant workability the

reduction in mixing water is expected to be of reduction in mixing water is expected to be of

the order of 5% to 15%. This naturallythe order of 5% to 15%. This naturally

increases the strength.increases the strength.



Air-Entraining AdmixturesAir-Entraining Admixtures

Air-entraining admixtures are used to stabilizeAir-entraining admixtures are used to stabilize

microscopic air bubbles in concrete. Proper microscopic air bubbles in concrete. Proper

air-entrainment, with appropriate volume andair-entrainment, with appropriate volume and

spacing factor, will dramatically improve thespacing factor, will dramatically improve the

durability of concrete exposed to moisturedurability of concrete exposed to moisture

during cycles of freezing and thawing.during cycles of freezing and thawing.

Entrained air also improves concrete’sEntrained air also improves concrete’sresistance to surface scaling caused byresistance to surface scaling caused by

chemical deicers.chemical deicers.



Air-Entraining Admixtures (cont’d)Air-Entraining Admixtures (cont’d)

Air-entrained concrete containsAir-entrained concrete containsminute air bubbles that areminute air bubbles that aredistributed uniformly throughoutdistributed uniformly throughoutthe cement paste. Entrained air the cement paste. Entrained air can be produced in concrete bycan be produced in concrete byuse of an air-entraining cement,use of an air-entraining cement,

by introduction of an air- by introduction of an air-entraining admixture, or by aentraining admixture, or by acombination of both methods. Ancombination of both methods. Anair-entraining cement is a portlandair-entraining cement is a portlandcement with an air-entrainingcement with an air-entrainingaddition interground with theaddition interground with theclinker during manufacture. Anclinker during manufacture. Anair-entraining admixture, on theair-entraining admixture, on theother hand is added directly to theother hand is added directly to theconcrete materials either before or concrete materials either before or during mixing.during mixing.



Admixtures Functions Typical compounds Applications Disadvantages

Accelerators i. more rapidgain of

strength

ii. more rapidsetting

Calcium chloride,sodium nitrite

Sodium sulphate,

sodiumaluminate,sodium silicate,

sodiumcarbonate,

potassium,

hydroxide

- normal rate of strengthdevelopment at low temperature

- shorter stripping times- plugging of pressure leakssprayed concrete

i. possible cracking due toheat evolution

ii. possibility of corrosion of

embedded reinforcement

Retartders Delay setting Hydroxycarboxilic

acids, sugars

- maintain workability at high

temperature- reduce rate of heat evolution- extend placing times

May promote bleeding

Accelerators water-reducing

Increaseworkabilitywith faster

gain of strength

Mixtures of sugars orhydroxycarboxylic acids and

lignosulphonate

Water reducers with faster strengthdevelopment

Risk of corrosion

CONCLUTIONS

Admixtures Functions Typical Applications Disadvantages



Admixtures Functions Typicalcompounds

Applications Disadvantages

Retarding water-reducing

Increaseworkability and

delay setting

Mixture of sugarsor

hydroxycarboxylicacids and

lignosulphonate

Water reducers with slower the loss of workability

Plasticizers (waterreducers)

Increaseworkability

Calcium andsodiumlignosulphonate

-higher workability with strengthunchanged-higher strength with workabilityunchanged-less cement for same strength andworkability

i.retardation at high dosagesii.tendency to segregateiii.premature stiffening under

certain conditions

Superplasticizers Greatly increase

workability

Sulphonate

melamineFormaldehyde

resin

Sulphonatednaphthalene-formaldehyderesin

-water reducers, but over a widerrange-facilitate production of flowingconcrete

i.tendency to segregate

ii.may increase rate of loss of workability

Air entraining Entrainments of

air into concrete

Wood resins, fats,

lignosulphonate

Increase durability to frost without

increasing cement content

Careful control of air content

and mixing time necessary

Admixture( Chap1 BEC210)

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