ctep - unit - i - admixtures & construction chemicals

ADMIXTURESADMIXTURES

11

BY K.R.SHANKAR M.E.,

ASSISTANT PROFESSOR DEPARTMENT OF CIVIL ENGINEERING

EBET GROUP OF INSTITUTIONS TRIPPUR DISTRICT

TAMUL NADU, INDIA – 638108 Email ID – krs.civil@ebet.edu.in

ADMIXTURESADMIXTURES

DefinitionDefinition

Proprietary mixture of chemicals added at Proprietary mixture of chemicals added at

the mixing stage to concrete to alter or the mixing stage to concrete to alter or

improve the properties of fresh or hardened improve the properties of fresh or hardened

concrete.concrete.

22

ADMIXTURES USESADMIXTURES USES

When properties cannot be made by varying the composition When properties cannot be made by varying the composition

of basic materialof basic material

To produce desired effects more economicallyTo produce desired effects more economically

Unlikely to make a poor concrete better Unlikely to make a poor concrete better

Not a substitute for good concrete practiceNot a substitute for good concrete practice

Required dose must be carefully determined and administeredRequired dose must be carefully determined and administered

33

USE OF ADMIXTURESUSE OF ADMIXTURES

Check job specificationCheck job specification Use the correct admixture Use the correct admixture

never use one from an unmarked container. never use one from an unmarked container. keep containers closed to avoid accidental contamination.keep containers closed to avoid accidental contamination.

Add the correct dosage.Add the correct dosage. avoid adding 'a little bit extra' avoid adding 'a little bit extra' use a dispenseruse a dispenser–wash thoroughly at the end the daywash thoroughly at the end the day

Best if added to the mixing waterBest if added to the mixing water Manufacturer's recommended dosage is usually adequateManufacturer's recommended dosage is usually adequate Trial mixes are important to determine most effective dosageTrial mixes are important to determine most effective dosage

44

TYPES OF ADMIXTURESTYPES OF ADMIXTURES

Air entraining agents – AEAAir entraining agents – AEA

Water reducers Water reducers

PlasticisersPlasticisers

Super plasticisersSuper plasticisers

RetardersRetarders

AcceleratorsAccelerators

55

AIR ENTRAINING AGENTSAIR ENTRAINING AGENTS

Foaming agents, gas producing chemicalsFoaming agents, gas producing chemicals– introduces millions of tiny, stable bubbles of uniform introduces millions of tiny, stable bubbles of uniform

size that are uniformly distributed throughout the mix size that are uniformly distributed throughout the mix (usually about 5% of the volume). (usually about 5% of the volume).

Improves properties of fresh concreteImproves properties of fresh concrete– workability, cohesion workability, cohesion – reduces segregation and bleeding .reduces segregation and bleeding .Properties of hardened concreteProperties of hardened concrete– For every 1% of air there is a 4% loss in strength.For every 1% of air there is a 4% loss in strength.

Minimised by the reduction in water contentMinimised by the reduction in water content– Improves durabilityImproves durability

frost, de-icing saltsfrost, de-icing salts66

AIR ENTRAINING AGENTSAIR ENTRAINING AGENTS

–Improves durabilityImproves durabilityfrost, de-icing saltsfrost, de-icing salts

77

WATER REDUCERS & PLASTICISERSWATER REDUCERS & PLASTICISERS

PropertiesProperties

increases the dispersion of cement particles and a increases the dispersion of cement particles and a

reduction in viscosityreduction in viscosity

Improve workability with same waterImprove workability with same water

Reduce water required for equal slumpReduce water required for equal slump

Do not affect shrinkageDo not affect shrinkage

88

WATER REDUCERS / PLASTICISERSWATER REDUCERS / PLASTICISERS

MechanismMechanism

CementCement 300 kg300 kg 300 kg300 kg 300 kg300 kg 270 kg270 kg

StoneStone 10001000 10001000 10101010 10251025SandSand 870870 870870 880880 895895WaterWater 180 180 180 180 162 162 162 162 WRDAWRDA 00 1.0 L1.0 L 1.0 L1.0 L 0.9 L0.9 Lw/c ratiow/c ratio 0.600.60 0.600.60 0.540.54 0.60.6

slumpslump 75 mm75 mm 130 mm130 mm 75 mm75 mm 75 mm75 mm

strengthstrength 30 MPa30 MPa 30 MPa30 MPa 36 MPa36 MPa 30 MPa30 MPa

cost cost $ 100$ 100 $ 102$ 102 $ 102$ 102 $ 95$ 95

99

WATER REDUCERS / PLASTICISERSWATER REDUCERS / PLASTICISERS

Dispersion of cementDispersion of cement

1010

WATER REDUCERS / PLASTICISERSWATER REDUCERS / PLASTICISERS

Corresponding mixesCorresponding mixes

1111

SUPERPLASTICISERSSUPERPLASTICISERS

PropertiesPropertiesProduce flowing concreteProduce flowing concrete– no reduction in strengthno reduction in strength– Assist placing when heavy reinforcementAssist placing when heavy reinforcementflowing characteristicsflowing characteristics– short duration (30 mins) old technologyshort duration (30 mins) old technology– New generation can tailor madeNew generation can tailor madeUsually added at site immediately before placingUsually added at site immediately before placingCan produce high strength concreteCan produce high strength concrete

reduce w/c ratio reduce w/c ratio maintain the same workabilitymaintain the same workability

1212

SUPERPLASTICISERSSUPERPLASTICISERS

PropertiesProperties

Amount of fines in mix usually increasedAmount of fines in mix usually increased

Take care with rapid pouring in high walls Take care with rapid pouring in high walls

(hydraulic pressure)(hydraulic pressure)

1313

SUPERPLASTICISERSSUPERPLASTICISERS

Cement dispersionCement dispersion

1414

SUPERPLASTICISERSUPERPLASTICISER

Normal slump concrete with no Normal slump concrete with no SuperplasticisersSuperplasticisers

1515

SUPERPLASTICISERSUPERPLASTICISER

Concrete with Superplasticisers Concrete with Superplasticisers courtesy of MBT admixturescourtesy of MBT admixtures

1616

RETARDERSRETARDERS

PropertiesPropertiesLonger setting timesLonger setting timesSlower strength gainsSlower strength gainsPrevents the formation of cold jointsPrevents the formation of cold jointsAssist with long transit timesAssist with long transit timesMain usesMain uses– large concrete pourslarge concrete pours– sliding formworksliding formwork– hot weather concretinghot weather concretingRetarding water-reducing admixtures are also availableRetarding water-reducing admixtures are also availableOverdosing can cause problemsOverdosing can cause problems– Excessive retardationExcessive retardation– Excessive bleedingExcessive bleeding

1717

ACCELERATING AGENTSACCELERATING AGENTS

PropertiesProperties

Quicker setting timesQuicker setting times

Higher early strength developmentHigher early strength development

TypesTypes

CaClCaCl2 2 most effective most effective

Chloride free use inChloride free use in

Main usesMain uses

winter conditionswinter conditions

emergency repair workemergency repair work

early removal of formworkearly removal of formwork1818

ACCELERATING ACCELERATING AGENTSAGENTS

DisadvantagesDisadvantages

increased drying shrinkageincreased drying shrinkage

reduced resistance to sulphate attackreduced resistance to sulphate attack

CaClCaCl2 2 high-risk of corrosion of steel - not permitted in RC high-risk of corrosion of steel - not permitted in RC

Cl freeCl free

– more expensivemore expensive

– less effectiveless effective

1919

DAMP PROOFING ADMIXTURESDAMP PROOFING ADMIXTURES

Reason for using admixtureReason for using admixture

– to resist when subjected to presence of waterto resist when subjected to presence of water

– to protect the absorption of surface water by capillary actionto protect the absorption of surface water by capillary action

– it will reduces permeabilityit will reduces permeability

They are available in Powder and Liquid formThey are available in Powder and Liquid form

They will fill pores and make concrete as water repellantThey will fill pores and make concrete as water repellant

Its property of making impermeable depends on uniform Its property of making impermeable depends on uniform

spreading of admixturesspreading of admixtures

2020

Materials used in pore filling is silicates of soda, Aluminium Materials used in pore filling is silicates of soda, Aluminium

sulphate, Zinc Sulphate, Aluminium Chloride and Calcium sulphate, Zinc Sulphate, Aluminium Chloride and Calcium

chloridechloride

Mineral oil free fatty or vegetable oils are also usedMineral oil free fatty or vegetable oils are also used

2121

CONSTRUCTION CONSTRUCTION CHEMICALSCHEMICALS

2222

ReasonReason

– To prevent the loss of water from surface due to evaporationTo prevent the loss of water from surface due to evaporation

Loss of water depends onLoss of water depends on– Air temperatureAir temperature

– Relative humidityRelative humidity

– Fresh concrete temperatureFresh concrete temperature

– Wind velocityWind velocity

CONCRETE CURING COMPOUNDSCONCRETE CURING COMPOUNDS

2323

COMPOUNDS USED:COMPOUNDS USED:

Resin & WaxResin & Wax– placed on surface of concrete for 28 days and peel offplaced on surface of concrete for 28 days and peel off

AcrylicAcrylic

– placed on surface of concrete and need not to be removed placed on surface of concrete and need not to be removed

because it will provide good adhesion for plasterbecause it will provide good adhesion for plaster

Chlorinated RubberChlorinated Rubber– placed on surface of concrete for 28 days and peel offplaced on surface of concrete for 28 days and peel off

– It will provide good surface finishIt will provide good surface finish

2424

POLYMER BONDING AGENTSPOLYMER BONDING AGENTS

ReasonReason

– To place new concrete over old concreteTo place new concrete over old concrete

– To have better bonding between two of themTo have better bonding between two of them

– Used in repair works such as ceiling of concrete roof, hydraulic Used in repair works such as ceiling of concrete roof, hydraulic

structures, prefabricated members, pipes, poles etc.,structures, prefabricated members, pipes, poles etc.,

It will be mixed new concrete while mixing and it will also It will be mixed new concrete while mixing and it will also

increases workability and reduces shrinkageincreases workability and reduces shrinkage

Products used are Roof Bond ERB, Nit bond PVA, etc.,Products used are Roof Bond ERB, Nit bond PVA, etc.,

2525

WATERPROOFING CHEMICALS WATERPROOFING CHEMICALS

Damp proof compounds will alter the permeability of concrete to Damp proof compounds will alter the permeability of concrete to

make it as impermeablemake it as impermeable

But these are chemicals which are used for water proofing But these are chemicals which are used for water proofing

Compounds such as acrylic based polymer, mineral based polymer, Compounds such as acrylic based polymer, mineral based polymer,

chemical DPC, waterproofing adhesive for tiles, silicon based water chemical DPC, waterproofing adhesive for tiles, silicon based water

repellent materials, injection grout, joint sealants, protective and repellent materials, injection grout, joint sealants, protective and

decorative coatings decorative coatings

2626