Chapter 1 Introduction of Concrete Technology

Concrete Technology Chapter 1

1. CONCRETETECHNOLOGY AND
MASONRYSTRUCTURE
Chapter1 Introduction

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CONCRETE
•Concreteisacompositematerialcomposedofcoarse
aggregatebondedtogetherwithafluidcementthathardens
overtime.
•Acompositematerialthatconsistsessentiallyofabinding
medium,suchasamixtureofPortlandcementandwater,
withinwhichareembeddedparticlesorfragmentsof
aggregate,usuallyacombinationoffineandcoarse
aggregate.
•Oneoftheveryimportantandwidelyusedmaterialin
construction
•TheGradeoftheconcreteisspecifiedbyits28day’scube
strength(E.g.M20meansthecubestrengthis 20N/mm2)
•ConcreteusedonworksisspecifiedaccordingtoIS456
(2000).

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AdvantagesofConcrete
•Highcompressivestrength.
•Locallyavailablematerialscanbeused.
•Can beeasilymouldedandhandled.
•Pumpingmakesconcretetobeplacedindifferent
difficult placesalso.
•Durableandfireresistant.
•Requirescomparativelylittlemaintenance.
•Can besprayedtofillthevoids.
•Chemicalresistant.
•Canchangethepropertiesbyusingadmixture.

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DisadvantagesofConcrete
•Lowtensilestrength.
•Fresh concrete shrinks on drying and hardened
concreteexpandonwetting.
•Expandsandcontractsaccordingtochangein
temperature.
•Maycauseefflorescence.
•Mayundergocreepandfatigue.
•Lackofductility.

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Uses ofConcreteinstructure
Concreteis used inwiderangein differenttypesof structuresin
variousforms:
•Building:Variousstructuralandnon structuralcomponents.
•Bridge:Includingpierandsuperstructures.
•SteelStructure:Foundationbase forvarioussteelstructures.
•Tunnel/Undergroundstructures.
•Slopestabilization:shotcreting/ground retainingstructures.
•Offshore structures: various marine structures for oil/gas
extraction.
•Nuclearshield:As concreteisexcellentinprotectionof
radiation.
•Fire proofing:widelyusedinfire proofingofsteelstructure.
•Used in reinforced/Precast/prestressedconcretecomponents.

8. PreparationofConcrete
8

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ConstituentsofConcrete
•Cement[14-21%]
•Aggregate (fineandCoarse)[60-70%]
•Water[7-15%]
•Entrained air[0-3%]
•Admixtures[AsperDesign]
Concreteconsistof:
1.Consists ofPortlandcement,water,andaggregate(Fine&Coarse)
2.Cement,waterandfineaggregate–mortar
3.Admixturesaddedforspecificpurposeslike
•Entrainnumerousmicroscopicairbubbles
•Retardtheinitialsetoftheconcrete
•Waterproofthe concrete,etc.

10. ConstituentsofCement
10

11. PropertiesofCement
exceed10mm.
11
PhysicalPropertiesofCement:
(i)Itgivesstrengthtothemasonry.
(ii)Itisanexcellentbindingmaterial.
(iii)Itiseasilyworkable.
(iv)Itoffersgoodresistancetothemoisture.
(v)Itpossessesagoodplasticity.
(vi)Itstiffensorhardensearly.
(vii)Athinpasteofcementwithwatershouldfeelstickybetween thefingers.
(viii)Acementthrowninwatershouldsinkandshouldnotfloatonthesurface.
(ix)Theparticlesshouldhaveuniformityoffineness.Togetanideaoffineness,specificsurfaceareaofcement
particlesiscalculated.Thespecificsurfaceareaisameasureofthefrequencyofparticlesofaveragesize,
whichshouldnotbelessthan2250cm
2/gm.
(x)TheconsistencyofcementshouldbecheckedwithVicatapparatus.Ifthesettlementofplungerisbetween5
mmto7mmfromthebottomofmould,thewateraddediscorrect,otherwiserepeattheprocesswith
differentpercentagesofwatertillthedesiredpenetrationisachieved.
(xi)Theinitialsettingtimeforordinarycementisabout30minutes.Theinitialsettingtimeistheinterval
betweentheadditionofwatertocementandthestagewhenthesquareneedleofVicatapparatusceasesto
penetratecompletely.
(xii)Thefinalsettingtimeforordinarycementisabout10hours.Thefinalsettingtimeisthedifferencebetween
thetimeatwhichwaterwasaddedtocementandtimerequiredforneedlewithannularcollarofVicat
apparatusceasestomakeanimpressionontestblock.
(xiii)ThecementshouldbetestedforsoundnessusingLeChatelierapparatus.Thistestistodetectthepresence
ofuncombinedlimeincement.Theexpansionofcementafterheatingandcoolingthemould,shouldnot

12. 12
Cont…
MechanicalPropertiesofCement:
(i)Thecompressivestrengthattheendof3daysshouldnotbelessthan11.5
N/mm
2
and thatattheendof7daysshouldnotbelessthan17.5N/mm
2
.
(ii)Thetensilestrengthattheendof3daysshouldnotbelessthan2
N/mm
2and thatat theendof7 daysshouldnotbelessthan2.50N/mm
2.
ChemicalPropertiesofCement:
(i)Theratioofpercentageofaluminatoironoxideshouldnotbelessthan
0.66.
(ii)Theratioofpercentageoflimetoalumina,ironoxideandsilica,knownas
LimeSaturationFactor(LSF)shouldnotbelessthan0.66andshouldnot
bemorethan1.02.
(iii)Totallossonignitionshouldnotbemore than4per cent.
(iv)Totalsulphurcontentshouldnotbemore than2.75percent.
(v)Weightof insolubleresidueshouldnotbemore than1.50percent.
(vi)Weightofmagnesia shouldnotexceed5 percent.

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16. ManufacturingProcess ofCement
16

17. TypesofCement
17

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19. •
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Aggregate
•Aggregateisa inert materialused forthe manufactureofmortarand concrete.
•Itmay benaturaland artificial.
•Artificialaggregate:Furnaceclinker,cokebreeze,sawdustandfurnaceslag.
FineAggregate
•The aggregate passing through 4.75 mm IS sieve and entirely retain on 75 micron
ISsieve .
•Itmaybenaturalsandorcrushed stone.
CoarseAggregate
•Aggregateofsize whoseparticlesarebigger than 4.75 mmbut smaller than 75mm.
•It may be crushed gravel or uncrushed gravel or partially crushed gravel.
All in oneaggregate
•Theallinoneaggregateconsist ofdifferentfractions offine and coarse aggregate.
•Itisgenerallynotusedforhighqualityconcrete.
•Theaggregateofroundedshapehave minimumvoidsranging from32to 33%.
•It givesminimumratioof surface areatothe volumethusrequiringminimum
cementpaste tomakegoodconcrete.

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Cont…
Accordingtoshape,Aggregateareclassifiedas:
•Rounded
•Angular
•Irregular
•Flaky(leastdimension<0.6timesofmean
dimension)
•Elongated(greatestdimension>1.8timesof
meandimension)
Aggregatearealsocanbeclassifiedontheir
density/unitweight.

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Desirablepropertiesof Aggregatefor
Concrete
•Size:Thesizeofcoarseaggregatedependsontheusetowhichtheconcrete
istobeput.Forordinaryconstructionofresidentialorotherbuilding,
20mmisthemaximumsizethatwillbeused.
•Shape:Theshapeofaggregateisanimportantcharacteristicasitaffectsthe
workabilityofconcrete.Angularaggregateshowsbetterinterlockingeffect,
whichgivesasuperiorconcrete.
•Surfacetexture:Thesurfaceoftheaggregatesmaybesmooth,polished,
roughordull.Aroughsurfaceprovidesmoreareaforbondingwithcement
pasteandgivesmorestrength.Roundedaggregatewithsmoothsurfacewill
requirelesscementpasteandhenceincreasetheyieldperbag.
•Waterabsorption:Thewaterabsorptionofcoarseaggregateismeasuredby
thepercentincreaseinweightofanovendrysampleafterimmersionin
waterfor24hours.Thisgivesmorerealisticresult.Waterabsorptionwill
decreasethewatercontentinconcreteandtheconcretewillrequirea
higher/cementratio.Thewaterabsorptionwilldependupontheporosityof
aggregate,andmorewaterabsorptionwillaffectbothworkabilityand
durabilityoftheconcrete.

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Cont….
•Soundness:Soundnesstotheresistanceofferedbythe
aggregates,toanytypeofvolumechange.Thechangemay
beintemperature,alternatewettinganddryinginpotable
water.Thesoundnessmeasuredbyimmersingtheaggregate
ineithersodiumormagnesiumsulphateandovendryingit
underspecifiedconditions.
•Specificgravity:Itisratioofdryweightofaggregatetothe
weightofequalvolumeofwater.Thespecificgravityof
aggregateisdeterminedalongwiththewaterabsorptionas
specifiedinIS2386partlll1963.
•Bulkdensity:Theratioofnetweightofaggregatetothe
volumeofaggregategivenbulkdensity.Thebulkdensityis
generallyexpressedaskg/liter.

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Water
•Generally,qualityofwaterforconstructionworksaresameas
drinkingwater.
•Thisistoensurethatthewaterisreasonablyfreefromsuch
impuritiesassuspendedsolids,organicmatteranddissolved
salts,whichmayadverselyaffectthepropertiesofthe
concrete,especiallythesetting,hardening,strength,durability,
pitvalue,etc.
•Thewatershallbecleanandshallnotcontainsugar,molasses
ortheirderivatives,orsewage,oils,organicsubstances.
•Ifthequalityofwatertobeusedformixingisindoubt,cubes
of75mmincementmortar1:3mixwithdistilledwaterand
withthewaterinquestionshallbemadeseparately.Thelatter
typeofcubesshouldattain90%ofthe7days’strength
obtainedincubeswithsamequantityofdistilledwater.

26. Cont…
LimitsofAlkalinity:
•Toneutralize200mlofsampleshouldnotrequiremorethan
10mlof0.1 normalHCIusingmethyl orangeasanindicator.
LimitsofAcidity:
•Toneutralize200mlsampleofwatershouldnotrequiremore
than2mof0.1normalNaOH(Causticsoda).ThepHvalueof
watershallgenerallybenotlessthan6.
TypeofSolidinwaterPermissibleLimitsforConstruction
•
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•Organicmatter200mg/l
•Inorganicmatter3000mg/l
•Sulphates(SO4)500mg/l
•Chlorides(Cl):1000mg/lforRCCworkand
PCCwork
Suspendedmatter20000 mg/l

27. Admixtures
27
•Anadmixtureisasubstancewhichcanbeaddedtoconcretetoachieveor
modifyitsproperties.Admixturesareaddedtotheconcrete,inadditionto
cement,waterandaggregate,typicallyimmediatelybeforeorduringthe
mixingprocess.
•Admixturescanbeusedtoreducethecostofbuildingwithconcrete,orto
ensurecertainrequiredpropertiesorqualityofthecuredconcrete.If
problemsarisewiththeconcreteduringtheconstructionprocess,
admixturescanbeusedasanemergencymeasuretotryandpreventfailure.
Inaddition,someofthemainfunctionsofusingadmixturesinclude:
•Water-reducing:Canreducethewatercontentneededtoreacharequired
slumpby5-10%.
•Retarding:Slowthesettingrateofconcrete,keepingitworkableandare
oftenusedtocounteracttheacceleratingeffectofhotweather.
•Accelerating:Increasetherateofearly-strengthdevelopmentandreduce
thetimerequiredforcuring.
•Superplasticizers:CanreSdaundceeeepwPaaratjeulri(BcEoCinvilt,eMnSctCbMy12-30%tomakeahighly
fluidbutworkableformof
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28. 28
Cont….
•Corrosion-inhibiting:Usedtoslowthecorrosionofreinforcingsteelinthe
concrete.Oftenusedinmarinestructures,bridgesandothersthatwillbeexposedto
chlorideinhighquantities.
•Air-entraining:Smallbubblesofairformeduniformlythroughtheconcretemixto
increasecohesionandresistancetofreeze-thawdegradation.
•Improvingthecuringoftheconcrete.
•Providingwaterproofingproperties.
•Toimprovehardness.
•Providingcolour.
•Offsettingorreducingachemicalreaction.
•Aerationtoreducetheweight.
•Offsettingorreducingshrinkage.
•Dispersingcementparticleswhen mixedwithwater.
•Alkali-silicareactivityreduction.
•Admixturesareusuallyprovidedinaliquidform.Someadmixtures,suchas
pigments,pumpingaidsandexpansiveagents,aretypicallyaddedmanuallyfrom
pre-measuredcontainersastheamountusedisverysmall.

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AnyQuestions?

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ThankYou