ctep - unit - i - admixtures & construction chemicals
TRANSCRIPT
ADMIXTURESADMIXTURES
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BY K.R.SHANKAR M.E.,
ASSISTANT PROFESSOR DEPARTMENT OF CIVIL ENGINEERING
EBET GROUP OF INSTITUTIONS TRIPPUR DISTRICT
TAMUL NADU, INDIA – 638108 Email ID – [email protected]
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.
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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
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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
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TYPES OF ADMIXTURESTYPES OF ADMIXTURES
Air entraining agents – AEAAir entraining agents – AEA
Water reducers Water reducers
PlasticisersPlasticisers
Super plasticisersSuper plasticisers
RetardersRetarders
AcceleratorsAccelerators
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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
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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
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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
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WATER REDUCERS / PLASTICISERSWATER REDUCERS / PLASTICISERS
Dispersion of cementDispersion of cement
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WATER REDUCERS / PLASTICISERSWATER REDUCERS / PLASTICISERS
Corresponding mixesCorresponding mixes
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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
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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)
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SUPERPLASTICISERSSUPERPLASTICISERS
Cement dispersionCement dispersion
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SUPERPLASTICISERSUPERPLASTICISER
Normal slump concrete with no Normal slump concrete with no SuperplasticisersSuperplasticisers
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SUPERPLASTICISERSUPERPLASTICISER
Concrete with Superplasticisers Concrete with Superplasticisers courtesy of MBT admixturescourtesy of MBT admixtures
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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
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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
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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
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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
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CONSTRUCTION CONSTRUCTION CHEMICALSCHEMICALS
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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
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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
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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.,
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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
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