Concrete Technology 5th semester Notes.pdf

BCV503 - Concrete Technology

1. Concrete Technology
(18CV44)

2. Module 1: Concrete Ingredients
Module 2: Fresh Concrete
Module 3: Hardened Concrete
Module 4: Concrete Mix Proportioning as per IS10262: 2019
Module 5: Special Concrete
Course Outline

3. ThreeInternalassessmentswillbeconductedfor30marksandaverageofallthe
performanceswillbeconsidered.
Assignmentswillcarry10marks
TotalIAmarkswillbeawardedfor40marks
Tenquestionswillbeaskedintheexamination;Twofromeachmodule.
Fivefullquestionshouldbeansweredselectingonefromeachmodule.
Codebooks–IS456:2000,IS10262:2019shallbereferredforthedesign
IA & Exam Pattern

4. Afterstudyingthiscourse,studentswillbeableto:
1.Relatematerialcharacteristicsandtheirinfluenceonmicrostructureofconcrete.
2.Distinguishconcretebehaviorbasedonitsfreshandhardenedproperties.
3.Illustrateproportioningofdifferenttypesofconcretemixesforrequiredfreshand
hardenedpropertiesusingprofessionalcodes.
4.Adoptsuitableconcretingmethodstoplacetheconcretebasedonrequirement.
5.Selectasuitabletypeofconcretebasedonspecificapplication
Course Outcomes

5. Module –1
Concrete Ingredients

6. •Introduction to Concrete Ingredients
•Cement
•Aggregates
–Fine Aggregates
–Coarse Aggregates
•Water
•Admixtures
–Chemical Admixtures
–Mineral Admixtures
Module Outline

7. •Concrete Ingredients
–Cement, Aggregates, Admixtures & water
•Cement –Binder
•Cement can be primary classified as 1) Natural cements and 2) Artificial cements
Natural Cements –Manufactured by burning & crushing of stones containing clay, CaCO
3&
MgCO
3
Module Outline

8. Artificial Cements –Manufactured by burning a mixture of Calcareous and Argillaceous
materials
Concrete Ingredients

9. Characteristics of cement
Thecolorofthecementisgreywithgreenishshade.Itgivesanindicationofexcesslimeor
clayandthedegreeofburning.
Itshouldfeelsmoothwhentouchedorrubbedinbetweenfingers.
Ifhandisinsertedinabagofcementorinaheapofcement,itshouldfeelcoolandnot
warm.
Itshouldbefreefromanyhardlumps.
Itshouldnotcontainanyexcessamountsilica,lime,aluminaandalkalies.
Concrete Ingredients

10. Properties of cement
Physical Properties:-
1. It gives strength to the masonry.
2. It is an excellent binding material.
3. It is easily workable.
4. It offers greater resistance to moisture.
5. It possesses a good plasticity.
6. A thin paste of cement held in water should feel sticky between the fingers.
Concrete Ingredients

11. Physical Properties:-
7. When cement thrown in water should sink and should not float on the surface.
8. The particles should have uniformity of fineness and surface area of should not be less than 2250
cm2/gm.
9. The standard consistency of cement should be checked with Vicatapparatus. If the settlement of
plunger is between 5 to 7mm from bottom of the mould
10. The initial setting time of ordinary cement is about 30minutes. This initial setting time is the interval
between the addition of water to cement and the stage when the square needle of Vicatapparatus ceases
to penetrate.
Concrete Ingredients

12. Physical Properties:-
11.Thefinalsettingtimeforordinarycementisabout10hrs.Thefinalsettingtimeisthedifference
betweenthetimeatwhichwaterwasaddedtocementandtimerequiredforneedlewithannularcollar
ofVicat’sapparatusceasestomakeanimpressionontestblock.
12.ThecementshouldbetestedforsoundnessusingLe-Chatelierapparatus.
Concrete Ingredients

13. Mechanical properties:-
1. The compressive strength at the end of 3 days should not be less than 11.5 N/mm2 and at the end of 7
days should not be less than 17 N/mm2.
2. The tensile strength at the end of 3 days should not be less than 2 N/mm2 and at the end of 7 days
should not be less than 2.5 N/mm2.
Concrete Ingredients

14. Chemical properties:-
1. Total loss of ignition should not exceed 4%.
2. Total sulphurcontent should not be more than 2.75%.
3. Weight of magnesia should not exceed 5%.
4. Weight of insoluble residue should not be more than 1.5%.
Concrete Ingredients

15. Chemical composition of cement
Approximate oxide composition limits of Ordinary Portland cement
Concrete Ingredients

16. Effect of ingredients on properties of cement
1. Lime -if = unsoundness and if = Strength decreases and helps in fast setting
2. Silica -if = Strength increases and Setting time will be delayed
3. Alumina -if = weakens the cement
4. Calcium sulphate -To alter the setting the time
5. Iron oxide –Color, hardness & Strength to the cement paste
Concrete Ingredients

17. Role of oxides on Strength of cement paste
6. Magnesia -if = hardness & color and if = unsoundness
7. Sulphur-if = unsoundness
8. Alkalies -if = Formation of AAR & efflorescence
Concrete Ingredients

18. Harmfulconstituentsofcement
(1)Alkalioxidek
2OandNa
2O:ifamountofthesealkalioxidesexceedsby1%,itleadsto
failureofconcrete.
(2)MagnesiumoxideMgO:ifitexceeds5%,itcausescracksinhardenedconcrete.
TheidentificationofmajorcompoundsofcementislargelybasedonBogue’sequationsand
henceitiscalledasBogue’scompounds.Thefourcompoundsareusuallyregardedasmajor
compoundsarelistedbelow
Concrete Ingredients

19. Bogue’s Compounds
Concrete Ingredients
Name of compound Formula Abbreviated formula
Percentage by mass in
cement
Tricalcium silicate3CaO.SiO
2 C
3S Alite 30-50
Dicalcium silicate 2CaO.SiO
2 C
2S Belite 20-45
Tricalcium
aluminate
3CaO.Al
2O
3 C
3A Celite 08-12
Tetracalcium
alminoferrite
4CaO.Al
2O
3.Fe
2O
3 C
4AF Felite 06-10

20. Hydrationofcement
•Anhydrouscementdoesnotbindthefineandcoarseaggregates.Itacquiresadhesive
propertyonlywhenitismixedwithwater.Thechemicalreactionthattakesplacebetween
cementandwaterisknownashydrationofcement.
•Whenanhydrouscementmixedwithwater,itstartstodissolveandchemicallycombines
withittoformproducts.Thoseproductsareknownashydratesandthesehydratesareless
solubleinwater.
Concrete Ingredients

21. Hydrationofcementcanbevisualizedintwoways.
(1)Throughsolutionmechanism:Inthismechanism,whencementismixedwithwater,cement
compoundsdissolvetoformsupersaturatedsolutionfromwhichdifferenthydratedproductsget
precipitated.
(2)Solidstatemechanism:Inthismechanism,waterattackschemicalcompoundsofcementswhichare
insolidstateandconvertingthemtohydratedproductsstartingfromsurfacetointeriorcompoundswith
time.
Thereisapossibilityofoccurrenceofbothstagesinsamecourseofreaction.Solutionphaseoccursfirst
onlywhenthereislargeavailabilityofwaterandthensolidstatemechanismoccursinthenextstage.
Concrete Ingredients

22. Note:23%ofwaterbyweightofcementisrequiredforchemicalreactionofcementwithwaterand
another15%ofwaterrequiredforfillingupgelpores.Thereforetotal38%ofwaterisrequiredfor
hydrationofcement.
Heatofhydration
Thequantityofheatevolvedincal/gmofcementaftercompletehydrationofcement.
For7days→89–90cal/gm
28days→90–100cal/gmofheatwillbeevolved.
Concrete Ingredients

23. StructureofCementHydratedPaste
•When water is mixed with cement, the chemical compounds react with water to form
hydrated products such as
•C
3S + H
2O → hydrated Tri-calcium silicate + Ca(OH)
2
•C
2S + H
2O → hydrated Di-calcium silicate + Ca(OH)
2
•C
3A + H
2O → hydrated Tri-calcium aluminate + Ca(OH)
2
Note:whencalciumsilicatesreactwithwater,itformsCalciumSilicateHydratesgelcalledC-
S-Hgel;C3AreactstoformCalciumAluminateHydratesC-A-HandC4AFreactstoform
HydratedCalciumFerriteC-F-H
Concrete Ingredients

24. Role of Bogue’s compounds with respect to strength and heat of hydration
•C
3S and C
2S(Tri Calcium Silicates and Di Calcium Silicates):-
2C
3S + 6H → C
3S
2H
3+ 3Ca(OH)
2
2C
2S + 4H → C
3S
2H
3+ Ca (OH)
2
Ca(OH)
2isnotdesirableinconcretebecauseitimpartslowdurabilitytoconcrete.
Ca(OH)
2readilyreactswithsulphatespresentinsoilorwatertocalciumsulphateswhichfurtherreacts
withC
3Aleadstodeteriorationofconcrete.Thisisknownassulphateattack
C
3S readily reacts with water to produce more heat of hydration & responsible for early strength. C
2S
hydrates are formed slowly, hence it is responsible for progressive strength
The quantity & density of product formed by C
3S is slightly inferior when compared to that of C
2S.
Concrete Ingredients

25. Role of Bogue’s compounds with respect to strength and heat of hydration
C
3A (Tri Calcium Aluminates):-
ThereactionofC
3Awithwaterisveryfastandmayleadtoanimmediatestiffeningofpaste,andthisprocessis
termedasflashset.
Topreventthisflashset,2to3%gypsumisaddedatthetimeofgrindingthecementclinkers.
Itprovidesearlystrengthtocementupto3days,butcausesdeteriorationofconcreteatlaterstages.
ThehydratesofC
3Adonotcontributetothestrengthofconcrete.
C
3AreactswithwatertoformC-A-Hgels.
ThecubiccompoundC
3AH
6isprobablytheonlystablecompoundformedwhichremainsupto225ºC.
Concrete Ingredients

26. Role of Bogue’s compounds with respect to strength and heat of hydration
C
4AF (Tetra Calcium Alumina Ferrite) :-
C
4AFhydratesrapidly.
AhydratedcalciumferriteoftheformC
3FH
6ismorestablebutdoesnotcontributeanythingtothestrengthof
concrete.
ThehydratesofC
4AFshowacomparativelymorestablethehydratesofC
3A.
ThehydratesofC
4AFshowacomparativelyhigherresistancetosulphateattackthanthehydratesofC
3A.
Concrete Ingredients

27. Types of Cements
Ordinary Portland Cement (OPC):
Thistypeofcementismanufacturedbymixinglimestoneandclayinproperproportionatveryhigh
temperatureofabout1400-1500ºCinkiln.
Theresultingmixtureisaddedwithsmallamountofgypsumtodelaythesettingaction.
Initialsettingtimeisnotlessthan30minandfinalsettingtimenotmorethan600minor10hrs.
Usedfortheconstructionof
•Roadpavements
•RCCstructures
•Watertanks,pipelines,culverts.
Concrete Ingredients

28. Types of Cements
Rapid Hardening Cement:
ThiscementissimilartothatofOPCbutwithhigherpercentageofTri-calciumsilicate(C
3S)andfinerthan
OPC.
ThefinalstrengthobtainedfromthiscementisalmostsameasthatofOPC.
Initialsettingtimeisnotlessthan30minandfinalsettingtimenotmorethan600minor10hrs.
Thiscementisusedwherearapiddevelopmentofstrengthisdesired(Bridgeandroadrepairworks)
Therapiddevelopmentofstrengthisaccompaniedbyhigherrateofheatofhydration,soitnotsuitablefor
massconcreting
Itisabout10%costlierthanOPC.
Concrete Ingredients

29. Types of Cements
Quick Setting Cement:
ThiscementsetsmuchfasterthanOPC.
ThiscementisproducedbymixingsmallpercentageofAluminiumsulphateandbyfinelygrindingthecement.
Percentageofgypsumtobeaddedisalsoreduced.
Initialsettingtimeis5minandfinalsettingtimeis30min.
Itisusedformakingconcretethatisrequiredtosetearlyasforlayingunderwaterorinrunningwater.
Concrete Ingredients

30. Types of Cements
HighAluminaCement:
Itismanufacturedbyfusingtogetheramixtureoflimestoneandbauxiteincorrectproportionatveryhigh
temperatureandresultingproductisgrindedfinely.
TheultimatestrengthismuchhigherthanOPCandcolorofthiscementisblackandprovestobecostlierthan
OPC.
Initialsettingtimeisnotlessthan30minandfinalsettingtimenotmorethan600minor10hrs.
Itcanbeusedinlowtemperatures.
Theyresistchemicalattacks.
Concrete Ingredients

31. Types of Cements
LowHeatCement:
ThiscementisobtainedbyincreasingtheproportionofC
2SanddecreasingC
3SandC
3A.
ThiscementgainsstrengthslowlybutultimatestrengthissameasthatofOPCandnotsuitableforordinary
structures.
Initialsettingtimeisnotlessthan60minandfinalsettingtimenotmorethan600minor10hrs.
Thiscementisusedonlywhentheshutteringhastobekeptforlongperiodandcuringisprolonged.
Concrete Ingredients

32. Types of Cements
SulphateResistingCement:
Thiscementismanufacturedfromwellgranulatedslag(80to85%)&calciumsulphate(10to15%)alongwith1to2%of
OPC.
Itgiveslessheatofhydration,resistancetosulphateattackandstrengthandphysicalpropertiesaresameasthatofOPC.
Initialsettingtimeis2.5to4hrsandfinalsettingtimeis4.5to7hrs.
Usedintheconstructionof
•Marineworks
•Massconcreting
•Undergroundwaterworksandsewerworks.
Concrete Ingredients

33. Types of Cements
PortlandSlagCement:
Thiscementismadebyinter-grindingfinelythemixtureofclinkers,gypsumandgranulatedslaginproper
portions.
ThiscementislessreactivethanOPCandgainsstrengthslowlyduring28daysandadequatecuringis
required.
Thiscementisusedformarineworks.
Concrete Ingredients

34. Types of Cements
PortlandPozzolanaCement:
ThiscementhassamepropertiesascomparedtothatofOPC.
Thiscementproduceslessheatofhydrationandmoreresistanttosulphateattack.
Thiscementcanbeusedinmarineworksandmassconcreting.
Thiscementismanufacturedbyinter-grindingofclinkersandPozzolanawiththeadditionofgypsum.
TimerequiredtogainthestrengthislittlemoreandultimatestrengthismorethanthatofOPC.
Concrete Ingredients

35. Types of Cements
WhiteCement:
ThiscementhaspurewhitecoloranditpossessamepropertiesasthatofOPC.
Thegreycolorofthecementisduetothepresenceofironoxide.
Soifthepercentageofironoxideiskeptveryless,thenthecolorofthecementwillbewhite.
Thiscementismanufacturebymixingwhitechalkandclaywhichisfreefromlimeandoilisusedinsteadof
coalforburningofthecement.
ThisiscostlierthanOPCandgenerallyusedforarchitecturalanddecorativepurposes.
Concrete Ingredients

36. Types of Cements
ColoredCement:
Coloredcementismanufacturedbyaddingsuitablemineralpigmentstoordinarycementatthetimeof
grinding.
Thepercentageofthesepigmentstobeaddedvariesfrom5to10%.
Pigmentsusedincementshouldbechemicallyinertanddurable.
Chromiumoxidegivesgreencolor,CobaltgivesbluecolorandIronoxideindifferentproportionsgivesbrown,
redoryellowcolor.
Thiscementisusedinflooring,exteriorsurfacesanddecorativepurposes.
Concrete Ingredients

37. Types of Cements
Airentrainingcement:
ThisismadebymixingasmallamountofairentrainingagentwithOPCatthetimeofgrinding.
Someoftheairentrainingagentsare
1.Alkalisaltsofwoodresin.
2.Calciumlingo-sulphate
Theseagentsinpowderorinliquidformareaddedtotheextentof0.1to0.25%byweightofcement.
Airentrainingcementwillproduceatthetimeofmixing,atough,tinydiscreteairbubblesintheconcrete
whichwillmodifythepropertiesofplasticconcretewrttoworkability,segregation,bleedingandhardness.
Concrete Ingredients

38. Manufacturing Process of OPC
Mixingofrawmaterials
Burning
Grinding
Concrete Ingredients

39. Manufacturing of cement by Wet process (old technology)
Concrete Ingredients

40. Manufacturing of cement by Dry process (modern technology)
Concrete Ingredients

41. Testing of cement
Field Test
Open the bag and take a good look at the cement. There should be no visible lumps.
The color of the cement should be greenish grey
When hand is inserted in cement bag it should feel cool.
Take a pinch of cement and feel between fingers. It should give a smooth feeling and not a gritty feeling.
Take a handful of cement and throw it on a bucketful of water, the particles should float on water for some time before they
sink.
Concrete Ingredients

42. Testing of cement
Field Test
Take about 100gms of cement, add some water and prepare a stiff paste.
From stiff paste, pat a cake with sharp edges.
Put it on a glass plate and slowly take it under water in a bucket.
The shape of the cake should not be disturbed, while taking it down to the bottom of the bucket.
After 24 hours the cake should retain its original shape and at the same time it should also set and gain some strength.
Concrete Ingredients

43. Testing of cement
Laboratory Test
Fineness test
Standard Consistency test
Initial setting time
Final setting time
Soundness of cement
Concrete Ingredients

44. Testing of cement
Laboratory Test
Fineness test
Weigh correctly 100gms of cement
Take it on a standard sieve of 90μ and breakdown the air set lumps in the sample by means of fingers.
Sieve the sample continuously for 15mins and weigh the residue left out on the sieve.
This weight should not exceed 10% of the sample for the OPC.
Concrete Ingredients

45. Testing of cement
Laboratory Test
Fineness test
Concrete Ingredients
•Putafilterpaperintothecellthenweight2.84gof
cementsampleintoit.
•Putanotherfilterpaperonitandcompresswiththe
plunger.
•AttachthecellontopoftheU-tubemanometer.
•Evacuatetheairinthemanometerthroughthesidetube
usingtheaspiratorbulbuntiltheoilreacheslevel1.
•Closethesidevalveandmonitortheoilasitstarttofall.
•Usingastopwatch,measurethetimetakenfortheoilto
fallfromlevel2tolevel3

46. Testing of cement
Laboratory Test
Standard Consistency
Concrete Ingredients
•Take about 400gm of cement
•Make the cement paste with a known quantity of water (let it be 24%)
•Fill this paste into the Vicatmould
•Shake the mould to expel the air
•Bring the mould near to the plunger of Vicatapparatus
•Release the plug in order to allow the plunger to penetrate through the paste
•If the reading is not within 33-35mm from top or 5-7mm from bottom, then
repeat the procedure with the increase in % of water by 2% of weight of cement
taken

47. Testing of cement
Laboratory Test
Initial Setting Time
Concrete Ingredients
•Mixaknown%ofwatertothecementtomakeacementpaste
simultaneousstartthestopclock
•FillthiscementpasteintotheVicatmould
•Releasetheneedlesothattheneedlefallfreely.
•Stopthestopclockuntiltheneedlefailstopiercethetestsblocktoa
point5±0.5mmfromthebottomofthemould

48. Testing of cement
Laboratory Test
Final Setting Time
Concrete Ingredients
•Mixaknown%ofwatertothecementtomakeacementpaste
simultaneousstartthestopclock
•FillthiscementpasteintotheVicatmould
•Releasetheneedlewithanattachmentsothatitfallsfreely
•Cementshallbeconsideredasfinallysetwhentheattachmentfailsto
makeanimpressiononthetestblock
Note
FalsesettingistherapiddevelopmentofrigidityinfreshlymixedPortland
cementpaste,mortar,orconcreteoccursafterfewminutesofmixing
cementwithwaterwithoutthegenerationofmuchheat.
FlashsettingisarapiddevelopmentofrigidityinfreshlymixedPortland–
cementpaste,mortar,orconcrete.

49. Testing of cement
Laboratory Test
Soundness Test
Concrete Ingredients
•Thecementpasteisprepared.The%ofwaterusedwillbeequalto%ofwater
determinebythestandardconsistencytest.
•Thecylinderisplacedonaglassplateandisfilledwithcementpaste.Itiscoveredat
topwithanotherglassplate.
•Asmallweightisplacedonthetopoftheglassplate.
•Thenwholeassemblyisplacedinwaterfor24hrsmaintainedat27+/-20
0
C
•Takeitoutandmeasurethedistancebetweenthetwoindicatorsusingmeasuringscale
•Themouldisagainimmersedinwaterandbroughttoboilin30minandafterboiling
for1hr,themouldisremovedandaftercoolingthedistancebetweentheindicatorsis
measuredagain.

50. Steps to reduce Carbon footprint in cement manufacturing process
Increasing energy efficiency by optimizing processes and modernizing factories.
Substituting fossil fuels with other energy sources.
Using additives in cement to develop a large range of products according to their application.
Concrete Ingredients

51. Aggregates
•Aggregates are defined as inert, granular and inorganic materials that normally consist of stone or stone like
solids.
•Aggregates can be used alone (in road bases and various types of fill) or can be used with cementing materials
(such as Portland cement or asphalt cement) to form composite materials or concrete.
•Since aggregates constitutes about 3/4th of the volume of concrete, it contributes significantly to the structural
performance of concrete especially strength, durability and volume stability.
•Aggregates are formed from natural sources by the process of weathering and abrasion or by artificially by
crushing a large parent rocks.
Concrete Ingredients

52. Classification of aggregates
a) In accordance with size:
Coarse aggregate: if particle size is greater than 4.75mm are regarded as coarse aggregates
Fine aggregates: if particle size in between 75μ & 4.75mm are regarded as fine aggregates
Concrete Ingredients

53. Classification of aggregates
b) In accordance with sources:
Natural aggregates: This kind of aggregates is taken from natural deposits without changing their nature
during the process of production such as crushing and grinding.
Some examples in this category are sand, crushed limestone and gravel.
Manufactured aggregates: This is a kind of man-made materials produced as main product or an industrial
by-product.
Some examples are blast furnace slag, lightweight aggregate (e.g. expanded perlite), and heavy weight
aggregates (e.g. iron ore or crushed steel)
Concrete Ingredients

54. Classification of aggregates
c) In accordance with unit weight:
Lightweightaggregates:theunitweightofaggregatesislessthan1120kg/m3.(Cinder,blast-furnaceslag,
volcanicpumice).
Normalaggregates:Theaggregateshaveunitweightof1520-1680kg/m3.
Heavyweightaggregate:Theunitweightisgreaterthan2100kg/m3.Thebulkdensityofthecorresponding
concreteisgreaterthan3200kg/m3.
Concrete Ingredients

55. Grading of aggregates
Particlesizedistributionofanaggregateisdeterminedbysieveanalysisisknownas‘gradingoftheaggregate’
Oneofthemostimportantfactorsforproducingworkableconcreteisgoodgradingofaggregates.
Gradingofaggregatesareof3types
Concrete Ingredients

56. Grading of aggregates
Goodgradedorwellgraded:Itimpliesthatagivensampleofaggregatescontainsallstandardfractionssuch
therewillbeminimumnumberofvoids.
Uniformlygradedorpoorgraded:Itcontainsaggregateparticlesthatarealmostofthesamesize.Thismeans
thattheparticlespacktogether,leavingrelativelylargevoidsintheconcrete.
Gapgraded:Itconsistsofaggregateparticlesinwhichsomeintermediatesizeparticlesaremissing.
Concrete Ingredients

57. Sieve: It is a circular disc consists of wire mesh of square aperture.
Sieve analysis: This is the name given to the operation of dividing the given sample of aggregates into various
fractions each consisting of particles of same size.
The sieve analysis is conducted to determine the particle size distribution in a sample of aggregates which is
also called as Gradation.
Concrete Ingredients

58. Theaggregatesusedformakingconcretearenormallyofthemaximumsize80mm,
40mm,20mm,10mm,4.75mm,2.36mm,600micron,300micronand150
micron.
Theaggregatefractionsfrom80mmto4.75mmaretermedascoarseaggregateand
thosefractionsfrom4.75mmto75micronaretermedasfineaggregate.
Sievesareplacedoneabovetheother,maximumsizeisplacedatthetopand
minimumsizeinthebottom.Sievingcanbedoneeithermanuallyorbymechanically
withsieveshaker.Fromthesieveanalysis,theparticlesizedistributioninasampleis
foundout;fromthisfinenessmoduluscanbedetermined.
Concrete Ingredients

59. FinenessModulus:Itisarelativeindexwhichindicatestheparticlesareeithercoarserorfiner.Thesumofcumulative
percentageretainedonthesievesdividedby100givesfinenessmodulusofgivensampleofaggregates.
Forsandthefollowinglimitsaretakenasguidelines
Finesand→2.2–2.6
Mediumsand→2.6–2.9
Coarsesand→2.9–3.2
Concrete Ingredients

60. TestsonFineaggregates
SpecificGravity:
Thespecificgravityofanaggregateistheratioofthemassofsolidinagivenvolumeofsampletothemassofequal
volumewateratthesametemperature.
Theyareoftwotypes1)absolutespecificgravityand2)apparentspecificgravity.
Absolutespecificgravityisdefinedasratioofmassorweightexcludingvoidsinthevolumeofmaterialofsolidtothe
massofequalvolumeofwater.
Apparentspecificgravityisdefinedasratioofmassorweightincludingvoidsinthevolumeofmaterialofsolidtothe
massofequalvolumeofwater.
Averagespecificgravityoftherocksvariesfrom2.6to2.8.
It’srequiredforcalculationofthequantityofaggregateforagivenvolumeofconcrete
Concrete Ingredients

61. TestsonFineaggregates
SpecificGravity:
Thespecificgravityofanaggregateistheratioofthemassofsolidinagivenvolumeofsampletothemassofequal
volumewateratthesametemperature.
Theyareoftwotypes1)absolutespecificgravityand2)apparentspecificgravity.
Absolutespecificgravityisdefinedasratioofmassorweightexcludingvoidsinthevolumeofmaterialofsolidtothe
massofequalvolumeofwater.
Apparentspecificgravityisdefinedasratioofmassorweightincludingvoidsinthevolumeofmaterialofsolidtothe
massofequalvolumeofwater.
Averagespecificgravityoftherocksvariesfrom2.6to2.8.
It’srequiredforcalculationofthequantityofaggregateforagivenvolumeofconcrete
Concrete Ingredients

62. TestsonFineaggregates
SpecificGravity:
DeterminationofSpecificgravityoffineaggregatesbyPycnometermethod
Procedure
•FindtheweightanemptyPycnometerwithstopper.LetitbeW1gms.
•Takeabout1/3rdthevolumeofPycnometerfullofsand.FindtheweightofPycnometerwithsandandletitbeW2gms.
•NowfillthePycnometertoitshalfwithwatersoastosubmergethesandinside.Allowtheentrappedairfromsandto
escape.ThenfillthePycnometerwithwater.ReplacethestopperandfindthetotalweightPycnometerwithitsconstituents
andletitbeW3gms.
•RemovetheconstituentsfromthePycnometerandcleanit.Fillcompletelywithwaterandreplacethestopper.Findthe
weightwithwaterandletitbeW4gms.
Concrete Ingredients

63. TestsonFineaggregates
SpecificGravity:
DeterminationofSpecificgravityoffineaggregatesbyPycnometermethod
Concrete Ingredients
Specific gravity=
(W
2−W
1)
(W
2−W
1)−(W
3−W
4)

64. TestsonFineaggregates
Bulkingofsand
Bulkingcanbedefinedasthatpropertyofsandbyvirtueofwhichitexpandsinvolumewhen
itiswet.
Thisisbecause,whenwaterisaddedtothesand,eachparticlewillbecoatedbyafilmof
waterandkeepsfarapartfromeachotherduetosurfacetension.
Bulkingincreaseswiththeincreaseinwatercontentupto4%byweightandthendecreases.
Bulkingalsoincreaseswithfinenessofparticles.
Concrete Ingredients

65. TestsonFineaggregates
Bulkingofsand
Procedure
Takeabout300gmsofdrysandandpouritintoameasuringjar.Notedowntheinitialvolumeof
sand.
Transferthesandintoanonabsorbentpanandadd2%(byweightofsand)ofwater.Mixthe
sandthoroughlywithaglassrodsothatauniformcolorisobtained.
Thenpourthewetsandintothemeasuringjarandnotedowntheriseinvolume.
Againtransferthesanintothepanandaddanother2%ofwaterbyweightofsand.Mix
thoroughlyandpourbackintothejarandnotedownthenewvolume.
Repeatthisprocessbyincreasingthewatercontentattherateof2%untilthevolumestarts
decreasing.
Plotagraphof%increaseinvolumeV/S%ofwateradded.
Concrete Ingredients

66. TestsonFineaggregates
Measurementofmoisturecontentforfineaggregate
Moisturecontentmeansfreewaterheldonthesurfaceofaggregatewhichincludesthe
absorbedwaterandthewaterheldintheinteriorportionoftheaggregate.
Dryingmethod:
Thedryingmethodiscarriedoutinaovenandthelossinweightbeforeandafter
dryingwillgivethemoisturecontentoftheaggregate.Ifdryingisdoneathigh
temperatureforlongtime,thelossinweightwillincludenotonlythesurfacewater
butalsosomeabsorbedwater.
Afairlyquickresultcanbeobtainedbyheatingtheaggregateinanopenpanandthe
processcanbespeedupbypouringinflammableliquidlikeacetoneontheaggregate
andignitingit.
Concrete Ingredients

67. TestsonFineaggregates
Measurementofmoisturecontentforfineaggregate
Displacementmethod:
Inthelaboratory,themoisturecontentofaggregatecanbedeterminedbymeansofPycnometer.
Specificgravityofnormalaggregateishigherthanthatofwaterandthatagivenweightofwetaggregatewilloccupya
greatervolumethanthesameweightofdryaggregate.
Byknowingthespecificgravityofdryaggregate,specificgravityofwetaggregatecanbecalculated.
Fromthedifferencebetweenspecificgravityofwetanddryaggregates,themoisturecontentoftheaggregatecanbe
calculated.
Concrete Ingredients

68. TestsonFineaggregates
Measurementofmoisturecontentforfineaggregate
CalciumCarbidemethod:
Aquickandreasonablyaccuratemethodofdeterminingthemoistureoffineaggregateistomixwithexcessamountof
calciumcarbideinastrongair-tightvesselfittedwithpressuregas.
Calciumcarbidereactswithsurfacemoistureintheaggregatetoproduceacetylenegas.Thepressureofacetylenegas
generateddependsuponthemoisturecontentoftheaggregates.
Thepressuregaugeiscalibratedbytakingameasuredquantityofaggregateofknownmoisturecontentandthensucha
calibratedpressuregaugecouldbeusedtoreadthemoisturecontentofaggregatedirectly.
Themethodisoftenusedtofindoutthemoisturecontentoffineaggregateatthesiteofwork.Theequipmentconsistsofa
smallbalance,astandardscoopandcontainerfixedwithdialgauge.
Concrete Ingredients

69. TestsonFineaggregates
Measurementofmoisturecontentforfineaggregate
CalciumCarbidemethod:
Theprocedureisasfollows;weigh6gmsofwetsandandpouritintothe
container.
Takeonescoopfullofcalciumcarbidepowderandputitintothecontainer.
Closethelidofthecontainerandshakeitrigorously.
Calciumcarbidereactswithsurfacemoistureandproducesacetylenegas,the
pressureofwhichdrivestheindicatorneedleonthepressuregauge.
Thepressuregaugeissocalibrated,thatitgivesdirectlythepercentageof
moisturepresentinthesample.
Thewholejobtakesonlylessthan5minsandassuch,thistestcanbedoneat
verycloseintervalsoftimeatthesiteofwork.
Concrete Ingredients

70. TestsonFineaggregates
Measurementofmoisturecontentforfineaggregate
Electricalmetermethod:
Recentlyelectricalmetershavebeendevelopedtomeasureinstantaneousorcontinuousreadingofthemoisturecontentof
theaggregate.
Theprinciplethattheresistancegetschangedwiththechangeinmoisturecontentoftheaggregatehasbeenmadeusein
somesophisticatedbatchingplant.
Electricalmetersareusedtofindoutthemoisturecontentandalsotoregulatethequantityofwatertobeaddedtothe
continuousmixture.
Thewholejobtakesonlylessthan5minsandassuch,thistestcanbedoneatverycloseintervalsoftimeatthesiteof
work.
Concrete Ingredients

71. TestsonFineaggregates
Measurementofmoisturecontentforfineaggregate
Automaticmeasurement:
Inmodernbatchingplantssurfacemoistureinaggregatesisautomaticallyrecordedbymeansofsomekindofsensor
arrangements.
Thearrangementismadeinsuchawaythat,thequantityoffreewatergoingwithaggregateisautomaticallyrecordedand
simultaneouslythatmuchquantityofwaterisreduced.
Thissophisticatedmethodresultsinanaccuracyof±0.2to0.6%.
Concrete Ingredients

72. Alternativestoriversand
•Sandisavitalingredientinmakingtwomostusedconstructionmaterialsviz.CementConcreteandmortar.
•TraditionallyRiversand,whichisformedbynaturalweatheringofrocksovermanyyears,ispreferredasfineaggregate.
•Theeconomicdevelopmentfuelingthegrowthofinfrastructureandhousinggenerateshugedemandforbuildingmaterials
likesand.
•Theindiscriminateminingofsandfromriverbedsisposingaseriousthreattoenvironmentsuchaserosionofriverbedand
banks,triggeringlandslides,lossofvegetationonthebankofrivers,loweringthegroundwatertableetc.
Concrete Ingredients

73. Alternativestoriversand
•Demandforsandisincreasingdaybydayandatthesametimeminingthreatscannotbeignored.
•Hence,sandminingfromriverbedsisbeingrestrictedorbannedbytheauthoritieslike
NationalGreenTribunal,
StateEnvironmentalImpactAssessmentAuthorityand
PollutionControlBoard
Concrete Ingredients

74. SomeoftheAlternativestoRiversand
•ManufactureSand
•ProcessesQuarrydust
•ProcessedCrushedrockfines
•OffshoreSand
•Processedglass
•Aluminumsawmillwaste
•Granitefinesslurry
•Washedsoil(filteredsand)
•Flyash(bottomash/pondash)
•Slagsand
•CopperSlagsand
•ConstructionDemolitionwaste.
Concrete Ingredients

75. ManufactureSand
Manufacturedsandiscrushedfineaggregateproducedfromasourcematerialanddesignedforuseinconcreteorforother
specificproducts.Onlysourcematerialswithsuitablestrength,durabilityandshapecharacteristicsshouldbeused.
Concrete Ingredients

76. Concrete Ingredients

77. CoarseAggregates
Importanceofsize,shapeandsurfacetextureofaggregatesonworkabilityandstrength
Sizeofaggregate:
•Biggerthesizeofparticleslesswillbethesurfacearea
•Lessamountofwaterisrequired
•Lesscementpasterequiredforlubricatingthesurfacesofaggregates
•Sobiggerthesize,giveshigherworkability
Concrete Ingredients

78. CoarseAggregates
Importanceofsize,shapeandsurfacetextureofaggregatesonworkabilityandstrength
Shapeofaggregate:
•Angular,elongatedorflakyaggregatesmaketheconcreteveryharshwhencomparedtoroundedorcubicalaggregates.
•Cubicalaggregateshavelesssurfacearea,lessvoids,thefrictionalresistancebetweentheaggregatesisalsoless.
•Hencetheworkabilitywillbemoreincaseofroundedthancomparedtoflakyaggregates.
•Hencethestrengthwillbemorebyusingroundedorcubicalaggregates.
Concrete Ingredients

79. CoarseAggregates
Importanceofsize,shapeandsurfacetextureofaggregatesonworkabilityandstrength
Surfacetexture:
•Surfacetextureistheproperty,themeasureofwhichdependsupontherelativedegreetowhichparticlesurfacearepolishedordull,
smoothorrough.
•Surfacetexturedependsonhardness,grainsize,porestructureandstructureoftherock
•Totalsurfaceareaofroughtextureaggregateismorethanthatofsurfaceareaofsmoothroundedaggregatesofsamevolume.
•Roughtexturedaggregateswillshowpoorworkabilityandsmoothtexturedaggregateswillgivebetterworkabilitybecauseof
lesserfrictionalresistanceofinnersurfaceparticle.
Concrete Ingredients

80. Testfordeterminationofflakinessindex
•Anaggregatehavingleastdimensionlessthan3/5thofmeandimensionistermedasflaky.
•Thistestisnotapplicabletoaggregateslessthan6.3mm.
•Thistestisconductedbyusingametalthicknessgauge.
•Asufficientqualityofaggregatesistakenie,aminimumof200piecesofanyfractiontobe
tested.
•Eachfractionisgaugedintermsofthicknessonmetalgauge.
•Thetotalamountofaggregatepiecespassingthrougheachgaugeisweighedaccurately.
•Flakinessindexiscalculatedbytakingtheratiooftotalweightofmaterialspassingthrough
thevariousthicknessgaugestothetotalweightofaggregatesampletaken.
Concrete Ingredients

81. Testfordeterminationofelongationindex
•Theelongationindexofanaggregateistheparticlehavinglargestdimension(length)is
greaterthan9/5thofmeandimension.
•Theelongationindexisnotapplicabletosizeslesserthan6.3mm.Thistestisconductedby
usingmetallengthgauge.
•Asufficientquantityofaggregateistakentoprovideaminimumnumberofpiecesof200of
anyfractiontobetested.
•Eachfractionshallbegaugedindividuallyforthelengthonmetalgauge.
•Theamountretainedbythegaugelengthshallbeweighedtoanaccuracyof0.1%ofthe
weightofsampletaken.
•Theelongationindexiscalculatedinpercentagebytakingtheratiooftotalweightof
materialsretainedonvariouslengthgaugestothetotalweightofaggregatesampletaken.
Concrete Ingredients

82. Testingofmechanicalpropertiesofaggregates
Testfordeterminationofaggregatecrushingvalue
•Theaggregatecrushingvaluegivesarelativemeasureoftheresistanceofanaggregateto
crushingunderagraduallyappliedcompressiveload.
•Apparatusrequiredforthistestareasfollows
1.Steelcylinder(dia-15.2cm,height-14cm)
2.Cylindricalmeasure(dia-11.5cm,height-18cm)
3.Steeltampingrod(dia-1.6cm,height-40to60cm)
4.Balance
5.Compressiontestingmachine
Concrete Ingredients

83. Procedure
1.Ovendryaggregatepassing12.5mmISsieveandretainedon10mmISsieveisselectedforthetest.
2.Thesampleaggregatesinfilledthreelayersandeachlayerbeingtamped25blowsbyroundedendofthetampingrod.
3.Aftertampingthethirdlayer,thetopsurfaceisleveledusingthetampingrodasstraightedge.ThetestsampleweightistakenasW1gms.
4.Thecylinderofthetestapparatusisplacedinpositiononthebaseplateandthetestsampleistransferredintothecylinderinthreelayersand
eachlayeristampedwith25blows.
Concrete Ingredients

84. Procedure
5.Thesurfaceoftheaggregateisleveledandtheplungerinserted.
6.ThecylinderwiththetestsampleandplungerinpositionisplacedonCTM.
7.Loadisthenappliedthroughtheplungeratauniformrateof4tones/minuntilthe
totalloadof40tonesandthentheloadisreleased.
9.Aggregatesincludingthecrushedportionareremovedfromthecylinderandsieved
ona2.36mmISsieve,thematerialwhichpassesthissieveiscollectedandtakenW
2
gms.
Aggregatecrushingvalue=
�
�
�
�
����
AccordingtoIndianroadcongress&ISIhasspecifiedthataggregatecrushingvalueof
thecoarseaggregateusedforcementconcretepavementsshouldnotexceed30%and
usedforconcreteotherthanwearingsurfaceshouldnotexceed45%.
Concrete Ingredients

85. To determine the aggregate impact value
The aggregate impact value gives the relative measure of the resistance of an aggregate
to sudden shock or impact.
Apparatus required for the experiment are as follows
1. Impact testing machine
2. Cylindrical measure
3. Tamping rod
4. Balance
Concrete Ingredients

86. Procedure
1.Ovendryaggregatepassingthrough12.5mmISsieveandretainedin10mmISsieveareselected
forthetest.
2.Thecylindricalmeasureisfilledbythesampleaggregatesinthreelayersandeachlayerbeing
tampedby25blowswithroundedendofthetampingrod.
3.Aftertampingthethirdlayer,thetopsurfaceisleveledusingthetampingrodasstraightedge.The
testsampleweightistakenasW1gms.
4.Thecupofthetestapparatusisplacedinpositiononthebaseplateandtestsampleistransferredto
thecupinasinglelayerandbeingtamped25blowsandtopsurfaceisleveled.
Concrete Ingredients

87. Procedure
5.Thehammerisraiseduntilitslowerfaceis38cmabovetheuppersurfaceoftheaggregateinthe
cup,andallowedtofallfreelyonaggregatefor15timesatanintervalnotmorethan2secondsand
notlessthan1second.
6.Thecrushedaggregateisthenremovedfromthecupandthewholesampleissievedon2.36mmIS
sieve,thematerialwhichpassesthissieveiscollectedandtakenW2gms.
Aggregateimpactvalue=
��
�
�
����
Note:AccordingtoISspecification,theaggregateimpactvalue
<10%→exceptionallystrong
10–20%→strong
20–30%→satisfactoryforroadsurfacing
>30%→weakforroadsurfacing
Concrete Ingredients

88. Testforthedeterminationofaggregateabrasionvalue
Apparatusrequiredfortheexperimentareasfollows
1.Los-Angelesmachine
2.Steelballs(dia-48cm,weight-390to445g)
3.Balance
4.Sieves
Concrete Ingredients

89. Procedure
1.Cleandryaggregate,confirmingtoanyoneofthegradingAtoGisusedforthetest.Aggregate
weighing5kgforgradingA,B,CorDand10kgforgradingEandforGmaybetakenastest
specimenandplacedinthecylinderandisnotedasW1gms.
2.Theabrasivechargeisalsochosendependingupontheaggregateandisplacedinthecylinderof
themachine;thecoveristhenfixeddusttight.
3.Themachineisrotatedfor500revolutionsforgradingA,B,CandD&forgradingE,FandGit
shallberotatedfor1000revolutions.
4.Afterthedesirednumberofrevolutions,machineisstoppedandthematerialisdischargedfromthe
machinetakingcaretotakeoutentirestonedust.
5.Using1.7mmISsievethematerialissievedandthecoarsermaterialisretainedonthesieveis
takenasW2gms.
Percentagewear=
&#3627408406;&#3627409360;
&#3627408406;&#3627409359;
&#3627408407;&#3627409359;&#3627409358;&#3627409358;
Concrete Ingredients

90. No. Sieve size Weight (in gms) and grading of test samples
Passing on
mm
Retained on
mm
A B C D E F G
1 80 63 - - - - 2500 - -
2 63 50 - - - - 2500 - -
3 50 40 - - - - 5000 5000 -
4 40 25 1250 - - - - 5000 5000
5 25 20 1250 - - - - - -
6 20 12.5 1250 2500 - - - - -
7 12.5 10 1250 2500 - - - - -
8 10 6.3 - - 2500 - - - -
9 6.3 4.75 - - 2500 - - - -
10 4.75 2.36 - - - 5000 - - --
Number of spheres to be used 12 11 8 6 12 12 12
Number of revolutions 500 1000
No. Type of surface Maximum abrasion values
1 W.B.M subsurface course 60
2 W.B.M base course with bituminous surfacing 50
3 W.B.M surface course 40
4 Cement concrete surface course 35
5 Bituminous / Asphalt concrete surface course 30

91. TesttodetermineSpecificGravityofcoarseaggregatebywirebasketmethod
1.Takeabout5kgofcoarseaggregatesretainedon4.75mmsieve.
2.Washthoroughlytoremovedust,drytoconstantmassatatemperatureof105±5ºC.
3.Immersethesampleinwaterat22to32ºCforaperiodof24±1/2hours(30mininpractice).
4.Removetheaggregatesfromwater&rollthesameinalargepieceofanabsorbentclothuntilallvisiblefilmsofwaterareremoved,
althoughthesurfaceoftheparticleswillstillappearstobedamp.
5.Now,weigh3kgofthissampleintheinthesaturateddryconditionandnotedownthemassasW
1gm.
6.Placetheweighedaggregateimmediatelyinthewirebasket&dipitwater.Weighthisbucketwithaggregates,keepingitinwaterwiththe
helpofabalance.NotedownthemassasW
3gm.
Concrete Ingredients

92. TesttodetermineSpecificGravityofcoarseaggregatebywirebasketmethod
7.NotedowntheweightofsuspendedemptywirebasketinwaterwithoutaggregatesandnotedownthemassasW2gm.
8.Drythesampletotheconstantweightatthetemperatureof100to110ºCfor24±1/2hours.
9.Cooltoroomtemperatureandweighit&notedownthemassasW4gm.
10.Calculatespecificgravityandrepeattheprocedureforfreshsampleofaggregates.
Weightofovendryaggregate(C)=W4gm.
Weightofsaturatedsurfacedryaggregate(B)=W3gm.
Weightofbasket&aggregatesinwater(A1)=W2gm.
Weightofemptybasketsubmergedinwater(A2)=W1gm.
ActualSpecificgravity=&#3627408386;/(&#3627408385;−&#3627408384;)
Apparentspecificgravity=&#3627408386;/(&#3627408386;−&#3627408384;)
Waterabsorption=&#3627409359;&#3627409358;&#3627409358;??????(&#3627408385;−&#3627408386;)/&#3627408386;
WhereA=weightofsaturatedaggregateinwater=A1–A2.
Concrete Ingredients

93. RecycledAggregates
•WorldisgrowingandurbanizingataveryfastrateandsoisIndia.
•Thiseffectofrapidurbanizationisalsoseeninconstructionindustry.
•However,withurbanizationcomesthemoralresponsibilityofsustainingtheenvironment.
•Concreteisthefavoritechoiceasaconstructionmaterialamongcivilengineersaroundtheglobefordecades.
•Itispreferredforitsbetterperformance,longerlifeandlowmaintenancecost.
•Toachieverapidurbanizationeveryyearsmallerstructuresaredemolishedandnewerandbiggeronesareconstructed.
Concrete Ingredients

94. RecycledAggregates
•Thesedemolishedmaterials(majorityofwhichisusuallyconcrete)areoftendumpedonlandandisnotreusedforanypurpose.
•Thispracticeeffectsthefertilityofland.
•Onesuchmaterialisrecycledaggregateconcrete.
•AggregateswhichareobtainedfromdemolishedconcretestructuresarereferredasRecycledaggregates.
•ASTM(AmericanSocietyforTestingandMaterials)hasclassifiedtheseaggregatesasArtificialaggregates.
•Ithaslowstrength,loweryoung’smodulus,lowdensity,highdryingshrinkage,higherporosityandhigherabsorptioncapacity.
•Itproducesaconcreteoflowdensitythancomparedtoconventionalaggregates.
•Itisanaddedadvantageifitissaturated.Becauseithelpsininternalcuring.
Concrete Ingredients

95. ManufacturingofRecycledAggregates
Concrete Ingredients

96. ManufacturingofRecycledAggregates
•EvaluationofSourceconcrete:
ThefirststepinproductionofRACistodeterminethequalityofthesourceconcrete.Propertiesandrecordsofsourceconcretelikestrength,
durabilityandcompositionarelookedintofordecidingthepropersourceconcrete.
•Crushingofdemolishedconcrete:
Thesimpleprocessinvolvescrushingconcreteintospecifiedsizeandquality(usuallyofsize20mm–50mm).
•RemovalofContaminants:
Contaminantslikereinforcingsteel,foundationmaterials,asphaltconcreteshoulders,soil,etc.areremoved.Itcanbeachievedbymany
methodsincludingscreeningorairseparation,demolition,usingelectromagnets,etc.SomecontaminantsdependingontheuseofRCAcan
alsobeprocessedseparately
Concrete Ingredients

97. AdvantagesofRecycledAggregates
•Reducestheamountofvirginaggregatestobecreated,hencelessevacuationofnaturalresources.
•Whilebeingcrushedintosmallerparticlesalargeamountofcarbondioxideisabsorbed.ThisreducestheamountofCO2is
theatmosphere.
•Costsaving–fewresearchstudieshaveshownasignificantreductioninconstructioncostsifRACisused.
•Conserveslandfillspace,reducestheneedfornewlandfillsandhencesavingmorecosts.
•Createsmoreemploymentopportunitiesisrecyclingindustry.
Concrete Ingredients

98. DisadvantagesofRecycledAggregates
•Downgradingofqualityofconcrete.
•Increaseinwaterabsorptioncapacityrangingfrom3%to9%
•Decreaseincompressivestrengthofconcrete(10-30%)
•Reducesworkabilityofconcrete.
•Lackofspecificationsandguidelines.
•LessdurabilityofRAC,howeverfewpapershaveshownanimprovementinthedurabilitybymixingitwithspecial
materialslikeflyash
Concrete Ingredients

99. ApplicationsofRecycledAggregates
•Canbeusedforconstructinggutters,pavementsetc.
•Largepiecesofcrushedaggregatecanbeusedforbuildingrevetmentswhichinturnisveryusefulincontrollingsoil
erosion.
•Recycledconcreterubblescanbeusedascoarseaggregateinconcrete.
Concrete Ingredients

100. BlendingofAggregates
•Sometimesaggregatesavailableatsitesmaynotbeofspecifiedordesirablegrading.
•Insuchcasestwoormoreaggregatesfromdifferentsourcesmaybecombinedtogetthedesiredgrading.
•Often,mixingofavailablefineaggregatewithavailablecoarseaggregateinappropriatepercentagesmay
producedesirablegrading.
•Butsometimestwoormorefractionsofcoarseaggregatesismixedfirstandthenthecombinedcoarse
aggregateismixedwithfineaggregatetoobtaindesirablegrading.
Concrete Ingredients

102. Water
SomeoftheQualitiesofwatercanusedformixingare
•Theuseofportablewaterisgenerallysafeformixingofconcrete.
•AnywaterwithapHof6to8whichdoesnottastesalineissuitableforusetomixtheconcrete.
•Seawatercontainslargequantitiesofchloridestendstocausepersistentdampnessandefflorescence.
•InRCC,seawaterincreasestheriskofcorrosionofthereinforcement.
•Watercontaininglessthan2000ppmofdissolvedsaltscangenerallybeusedsatisfactoryformakingconcrete.
•Presenceofzinc,copper,tin,manganeseandleadreducetheconcretestrength.
•Sodiumphosphate,sodiumborateetc.,actsasretarderswhichresultsinlossofstrength.
•Sugarupto0.05%byweightofwaterisharmless.
•Sugarupto0.05%byweightofcementretardthesettingtime,reducetheearlystrengthandincreases28daysstrength.
•Sugarupto0.2%causesquicksettingofcement.
Concrete Ingredients

103. Useofseawaterformixingconcrete
•Seawaterhasasalinityofabout3.5%.
•About78%isNaCland15%ischloridesandsulphatesofmagnesium.
•Seawateralsocontainssmallquantitiesofsodiumandpotassiumsalts.
•Thiswillreactwithaggregatesandcementusedformixing.
•Henceseawatershouldnotbeusedformixingconcrete.
•Itisseenthatuseofseawaterformixingconcretedoesnotappreciablyreducethestrengthofconcretebutit
mayleadtocorrosionofreinforcement.
•Seawaterslightlyacceleratestheearlystrengthofconcretebutitreduces28daysstrengthofconcretebyabout
10-15%.
Concrete Ingredients

104. Admixtures
•Admixturesarechemicalormineralsubstancesotherthanfineaggregates,coarseaggregates,cement
andwater,whichareaddedinsmallamountbeforeoratthemixingstagetotheconcreteproduct.
•Theycanalsobeblendedatthetimeofgrindingofclinkerincementmanufacturingprocess.
•Addedonlywhenpropertiesoffreshorhardenedconcreteneedtobemodified.
Concrete Ingredients

105. MostcommonlyusedChemicaladmixturesare
•Plasticizers
•Superplasticizers
•RetardersandRetardingplasticizers
•AcceleratorsandAcceleratingplasticizers
•Air-entrainingAdmixtures
•DampproofingandWaterproofingAdmixtures
•GasformingAdmixtures
•AirdetrainingAdmixtures
•WorkabilityAdmixtures
•BondingAdmixtures
•ColoringAdmixtures
Concrete Ingredients

106. HowChemicalAdmixturesact?
Reactionofchemicaladmixtureswithcementtakesplaceinthreedifferentstages
1.PhysicoChemicalreaction:-
Inthisstage,C3S&C3Aareformedearlywhenwaterisaddedtothecementandbecauseofadhesivepropertyof
cement,anintermolecularforceofattractionwillbecreatedbetweenthecementgrainsasaresultcementflocwill
beformedinthecementpaste.
Concrete Ingredients

107. HowChemicalAdmixturesact?
Reactionofchemicaladmixtureswithcementtakesplaceinthreedifferentstages
2.Chemicaladsorptionandinteraction:-
•Whenchemicaladmixturesareaddedtothecement,itgetsadsorbedoncementcompoundsorcementgrains
andontheproductsofhydration(especiallyonC3A),whichstiffensthehydratedcompounds.
•Butsometimesitalsoinitiatesveryearlystiffening.
•Theyreallycombineandneverslowdownsthesettingbutinitiateslongtermhydration.
Concrete Ingredients

108. HowChemicalAdmixturesact?
Reactionofchemicaladmixtureswithcementtakesplaceinthreedifferentstages
3.DeflocculationorDispersion:-
•Flocculatedcementcompoundsconsistsofcertainamountofwaterinit.
•Butduetotheattackofadmixtures,itdeflocculatesordispersesthecementgrainsbycreatingan
intermolecularrepulsionbetweenthecementgrainswhichreleasesthewaterinthecementpasteasaresult,
workabilityofconcreteincreases.
•Theintermolecularrepulsionbetweenthecementgrainsisknownas“ZetaPotential”.
Concrete Ingredients

109. Plasticizers(Waterreducers):-
•Workabilityistheinherentpropertyofconcrete.Highdegreeofworkabilityisrequiredindeepbeams,thinwalls,column-
beamjunctionsandinRMC’s.
•Plasticizerhelpsinprovidinghighworkabilityevenindifficultsituations.
•Additionofextrawaterwillonlyimprovethefluiditybutnotworkability.
•Additionofplasticizerswillimprovetheplasticpropertiesofconcrete.
•Itreducesthewater-cementratioforagivenworkability,whichincreasesstrengthanddurability.
•Usedtoreducethecementcontentandheatofhydrationinmassconcreting.
Concrete Ingredients

110. Superplasticizers:-
•Thesearechemicallydifferentformnormalplasticizers.
•Reduceswatercontentupto30%withoutreducingtheworkability.
•Usedforproducingselfleveling,flowing,selfcompactingandhighperformanceconcrete.
•Canreducew/cratioforagivenworkability.
•Canreducecementcontentforgivenw/cratio.
•Provideshomogenouscohesiveconcretebutnotendencyofsegregationandbleeding.
Concrete Ingredients

111. Superplasticizers:-
Commonlyusedasbaseforsuperplasticizerare
•SulphonatedMelanie–Formaldehydecondensates(SMF)
•SulphonatedNaphthalene–Formaldehydecondensates(SNF)
•ModifiedLignosulphonate(MLS)
•PolyCarboxylatedEther(PCE)
Concrete Ingredients

112. Retarders:-
•Itisanadmixturewhichslowdownsthehydrationprocessandconcreteremainsplasticforlongtime.
•Usetoovercometheacceleratedeffectofhightemperatureonsettinginweatherconditions.
•Calciumsulphatesarethebestretardingadmixtureswhichretardssettingofconcrete
•Sometimescommonsugarisalsousedtodelaysettingofconcrete.
Concrete Ingredients

113. RetardingPlasticizers:-
•Weknowthatplasticizersandsuperplasticizersshowcertainextentofretardation.
•RetardingplasticizersaremixedinRMC’sforretainingslumplossincaseoflongdistancetransportation.
•Whenconcreteisbeingplacedortransportedunderconditionsofhighambienttemperature.
•Incaseoflargeconcretepoursd)Concreteconstructioninvolvingslidingformwork
Concrete Ingredients

114. Modeofaction
•ItisthoughtthatretardingadmixturesareabsorbedontotheC3Aphaseincementformingafilmaroundthe
cementgrainsandpresentingorreducingthereactionwithwater.
•Afterawhilethusfilmbreaksdownandnormalhydrationproceeds.
Commonlyusedchemicals
Unrefinedlignosulphonatescontainingsugar
Hydroxylcarboxylicacidandtheirsalts
Carbohydratesincludingsugar
Solublezinc
Solubleboratesetc.
Concrete Ingredients

115. Accelerators:-
•Addedtoincreasetheearlystrengthdevelopmentinconcrete.
•Allowsearlierremovalofformwork
•Reducerequiredperiodofcuring
•Usedinemergencyrepairworks
Commonlyusedchemicalsare
Calciumchlorides
Sulphates
Aluminates
•ButCaCl2isnotdesirableforconcretebecauseitleadstocorrosionofreinforcementinRCC.
Concrete Ingredients

116. AcceleratingPlasticizers:-
•Whenacceleratedsuperplasticizersareaddedtotheconcrete,itincreasesthestrength.
•Commonlyusedchemicalsare
Tri-ethanolaminechlorides
Nitratesandfluorosilicates
Concrete Ingredients

117. Airentrainingadmixtures
•Mixingsmallquantityofairentrainingagentswillincreasesthevoidsorairbubblesinconcretewhichimprovesthe
plasticandhardenedpropertiesandhaveimprovedresistanceagainstfrostactionandpermeability.
•Airvoidsinconcretecanbebroughtintotwogroups
Entrappedairisduetoinsufficientcompactionofconcrete
Entrainedairisintentionallyaddedanddistributeduniformly.
•SomeofthechemicalairentrainingagentsareNaturalwoodresins,Animalandvegetablefatsandoils
Concrete Ingredients

118. Mineraladmixtures
Mineraladmixturesareinorganic,finelygrainedmaterialshavingPozzolanicpropertiesaddedtotheconcretemix
inordertoimprovethepropertiesofconcrete.
SourceofMineralAdmixtures
a)Raworcalcinednaturalminerals
b)Industrialbyproducts
Concrete Ingredients

119. ClassificationofMineralAdmixture
ASIMspecificationC618recognizesthefollowingthreeclassesofmineraladmixtures.
a)ClassN—Raworcalcinednaturalpozzolanicsuchasdiatomaceousearths,clayandshales,tuffsand
volcanicashes.
b)ClassF—Flyashproducedfromburninganthraciteorbituminouscoal.
c)ClassC—Ashnormallyproducedfromligniteorsub-bituminouscoalwhichmaycontainanalyticalCaO
higherthan10%.
Concrete Ingredients

120. Reasonsforusingmineraladmixtures
a)Inrecentyears’considerableeffortshavebeenmadebythecementindustryworldwidetoreduceenergy
consumptioninthemanufactureofPortlandcement.Therefore,apartialreplacementofPortlandcementby
mineraladmixtureswhichcanbeoftheorderof50–60%byweightoftotalcementitiousmaterial,represents
considerableenergysavings.
b)Theabilityofcementandconcreteindustriestoconsumemithionsoftonsofindustrialbyproductscontaining
toxicmetalwouldqualifytheseindustriestobeclassifiedasenvironmentallyfriendly.
Concrete Ingredients

121. Reasonsforusingmineraladmixtures
SincenaturalPozzolanaandindustrialbyproductsaregenerallyavailablesubstantiallylowercoststhanPortland
cement,theexploitationofthePozzolanicandcementitiouspropertiesofmineraladmixturesareusedasapartial
replacementofcementcanleadtoaconsiderableeconomicbenefit.
Possibletechnologicalbenefitsfromtheuseofmineraladmixturesinconcreteincludeentrancementof
impermeabilityandchemicaldurability,improvedresistancetothermalcrackingandincreaseinultimatestrength.
Concrete Ingredients

122. TypesofMineraladmixtures
FlyAsh
GGBS
SilicaFume
Metakaolin
RiceHuskAsh
Concrete Ingredients

123. Flyash:-
•Aby-productofcoalfiredelectricgenerationplant,usedforpartiallyreplacingcementupto60%bymass.
•ItisobtainedbyElectrostaticprecipitator.
•ItisproducedinlargequantityinIndia.
•InIndia,FlyashisclassifiedasClassFbecauseitcontainslesscalcium.
•Itcontributesstrengthanddurabilityandenhancesworkabilityduetosphericalnature.
Concrete Ingredients

124. Flyash:-
•TherearetwotypesofFlyash
LowlimeFlyash→producescementitiouspropertybecauseoflimeorcement
Highlimeflyash→Exhibitcementitiouspropertybyitself
Applications:-Buildingblocks,Fineaggregate,Blendingcements,geotechnicalapplicationsetc.
Concrete Ingredients

125. EffectsofFlyAshonFreshConcrete:
Reductionofwaterdemandfordesiredslump.
Withthereductionofunitwatercontent,bleedinganddryingshrinkagewillalsobereduced.
EffectsofFlyAshonHardenedConcrete:
Contributestothestrengthofconcreteduetoitspozzolanicreactivity.
Continuedpozzolanicreactivityconcretedevelopsgreaterstrengthatlateragenotatinitialstage.
Resultingindecreaseofwaterpermeability
Concrete Ingredients

126. GroundGranulatedBlastFurnaceSlag(GGBFS/GGBS):-
Itisaby-productofsteelproduction
Usedtopartiallyreplacecementby80%bymass.
Concrete Ingredients

127. Effectsonfreshconcrete:
Itreducestheunitwatercontentnecessarytoobtainthesameslump.
Waterusedformixingisnotimmediatelylost,asthesurfacehydrationofslagisslightlyslowerthanthatof
cement.
Itreductionofbleeding.
Effectsonhardenedconcrete:
ItReducedheatofhydration.
Refinementofporestructuresgreatlyreducedpermeabilitytotheexternalagenciesandincreasedresistanceto
chemicalattack.
Concrete Ingredients

128. SILICAFUME:
Itisaproductresultingfromreductionofhighpurityquartzwithcoalinanelectricarcfurnaceinthe
manufactureofsiliconorferrosiliconalloy.
Containsatleast85%SiO2contentwithMeanparticlesizebetween0.1and0.2micron.
Minimumspecificsurfaceareais15,000m2/kg.ParticleshapeisSpherical.
Concrete Ingredients

129. Effectonfreshconcrete:
Freshconcretestickyinnatureandhardtohandle.
Causeslargereductioninbleedingandconcretewithmicrosilicacouldbehandledandtransportedwithout
segregationtoplasticshrinkagecracking.
Effectonhardenedconcrete:
Modulusofelasticityofmicrosilicaconcreteisless.
ItcausesimprovementindurabilityofconcreteandResistanceagainstfrostdamage.
Concrete Ingredients

130. Application:
Conservecement
Produceultrahighstrengthconcreteoftheorderof70to120Mpa.
Increaseearlystrengthofflyconcrete.
Controlalkali-aggregatereaction.
Reducesulfateattack&chlorideassociatedcorrosion.
Concrete Ingredients

131. RICEHUSKASH:
RicehuskashisobtainedbyBurningricehuskinacontrolledmanner.
Materialoffutureasmineraladditives.Itisaddedto10%byweightofcement.
Itgreatlyenhancestheworkabilityandimpermeabilityofconcrete.
ItcontainsAmorphoussilica(90%SiO2)inveryhighproportionwhenburntincontrolledmanner,5%carbon,
2%K2O.
Concrete Ingredients

132. Effects:
Itreducessusceptibletoacidattackandimprovesresistancetochloridepenetrationandreduceslargeporesand
porosityresultingverylowpermeabilityandfreelimepresentinthecementpaste.
ItDecreasesthepermeabilityofthesystemandImprovesoverall
resistancetoCO2attackImprovescapillarysuctionandacceleratedchloridediffusivity.
ItalsoEnhancesresistancetocorrosionofsteelinconcrete.Reducingmicrocrackingandimprovingfreeze-
thawresistance.
Concrete Ingredients

133. METAKAOLIN:
HighlyreactiveMetakaolinismadebywaterprocessingtoremoveunreactiveimpuritiestomake100%reactive
pozzolanicSuchaproduct,whiteorcreamincolor,purified,thermallyactivatediscalledHighReactive
Metakaolin(HRM)
Concrete Ingredients

134. EffectsofMetakaolin:
HighreactiveMetakaolinshowshighpozzolanicreactivityandreductioninCa(OH)2evenasearlyasoneday.
Thecementpasteundergoesdistinctdensification.
Densificationincludesanincreaseinstrengthanddecreaseinpermeability.
ThehighreactiveMetakaolinishavingthepotentialtocompetewithsilicafume.
Concrete Ingredients

135. MODULE –2
FRESH CONCRETE

136. Introduction
Thecementconcreteisamixtureofcement,sand,pebblesorcrushedstonesandwater.Whenthismixtureis
placedandallowedtocure,becomeshardlikeastone.
Fresh Concrete

137. Introduction
•Thepotentialstrengthanddurabilityofconcreteofagivenmixproportionisverydependentonthedegreeofits
compaction
•Itisvital,therefore,thattheconsistencyofthemixbesuchthattheconcretecanbetransported,placed,andfinished
sufficientlyearlyenoughtoattaintheexpectedstrengthanddurability.
Significance
•Thefirst48hoursareveryimportantfortheperformanceoftheconcretestructure.
•Itcontrolsthelong-termbehavior,influencef'c(ultimatestrength),Ec(elasticmodulus),creep,anddurability.
Fresh Concrete

138. Fresh Concrete

139. Propertiesofgoodconcrete
•Ithashighcompressivestrength.
•Itisfreefromcorrosionandlesseffectedbyatmosphericagents.
•Ithardenswithageandprocessofhardeningcontinuesforalongperiodoftimeafterconcretehas
attainedsufficientstrength.
•Itisprovedtobemoreeconomicalthansteel.Thisisduetothefactthat,theaggregatesconstitutesabout
80–90%ofvolumeofconcreteandisavailableatreasonablerates.
Fresh Concrete

140. •Itbindsrapidlywithsteelandasitisweakintension,thesteelreinforcementisplacedincementconcrete
structureatsuitableplacestotakeuptensilestresses.ThisistermedasReinforcedCementConcrete(RCC).
•Underthefollowingtwoconditions,ithasatendencytoshrink:
Thereisaninitialshrinkageofcementconcretewhichismainlyduetothelossofwaterthroughforms,
absorptionbysurfacesofforms.
Theshrinkageofcementconcreteoccursasithardens.Thistendencyofcementconcretecanbeminimizedby
propercuringofconcrete.
Fresh Concrete

141. •Ithasatendencytobeporousinnature.Thisisduetothepresenceofvoidswhichareformedduring
andafteritsplacing.Thetwoprecautionsnecessarytoavoidthistendencyareasfollows:
Thereshouldbepropergradingandconsolidationofaggregates.
Theminimumwater-cementratioshouldbeadopted.
•Itformsahardsurfaceandoffersresistancetoabrasion.
Fresh Concrete

142. Factors affecting Strength of concrete
•Water-Cement ratio -It is water cement ratio that basically governs the property of strength. Lesser
the water cement ratio, greater will be strength
•Type of cementing material –It affects the hydration process and therefore strength of concrete.
•Amount of cementing material -It is the paste that holds or binds all the ingredients. Thus greater
amount of cementing material greater will be strength.
•Type of aggregate -Rough and angular aggregates are preferable as they provide greater bonding
Fresh Concrete

143. Air content –The amount of air improves the concrete resistance on freezing and thawing. But in
excess lead to failure
Admixtures -Chemical admixtures like plasticizers reduce the water cement ratio and increase the
strength of concrete at same water cement ratio. Mineral admixtures affect the strength at later stage and
increase the strength by increasing the amount of cementing material.
•Once the mixing was completed the mixture is said to be Fresh concrete which is in plastic state and
can be moulded in any forms whereas the Hardened concrete is the one which is fully cured
Fresh Concrete

144. For fresh concrete to be acceptable, it should:
1. Be easily mixed and transported.
2. Be uniform throughout a given batch and between batches.
3. Be of a consistency so that it can fill completely the forms for which it was designed.
4. Have the ability to be compacted without excessive loss of energy.
5. Not segregate during placing and consolidation.
6. Have good finishing characteristics.
Fresh Concrete

145. Fresh Concrete

146. Workability
•Thepropertyofconcretedeterminestheamountofinternalworkrequiredtoproducefullcompaction.
Or
•Itistheeasewithwhichtheconcretecanbecompacted100%andcanbedeposited/transportedorplacedin
requiredposition.
•Ingeneral;easytomix,easytohandleandeasytoplaceisreferredasworkabilityofconcrete
Fresh Concrete

147. Factorsaffectingworkability
1.Watercontent:
•Thewatercontentinagivenvolumeofconcretewillhavesignificantinfluenceonworkabilityofconcrete.
•Higherthewatercontentpercubicmeterofconcrete,higherwillbethefluidity.
•Itshouldbenotedthatfromthedesirablepointofview,increaseinwatercontentwillbethelastresourcefor
improvingtheworkabilityincaseofuncontrolledconcrete.
•Butforcontrolledconcretewecannotincreasethewatercontent.
•Ifwewanttoincreasethewatercontent,simultaneouslywehavetoincreasethecementinordertomaintain
water-cementratioasconstantandstrengthoftheconcreteremainssame.
Fresh Concrete

148. Factorsaffectingworkability
2.Mixproportion:
•Aggregatetocementratioisanimportantratioinfluencingworkability.
•Highertheaggregatetocementratio,leanerwillbetheconcretemix.
•Incaseofleanconcretelessquantityofpasteisavailableforlubricatingthesurface.
•Hencethereischanceofmobilityofaggregates.
•Ontheotherhandincaseofrichmixwithloweraggregatetocementratio,morepasteisavailabletomakethe
mixcohesiveandalsogivesbetterworkability.
Fresh Concrete

149. Factorsaffectingworkability
Sizeofaggregate:
•Biggerthesizeofparticleslesswillbethesurfaceareaandhencelessamountofwaterisrequiredandalsoless
cementpasterequiredforlubricatingthesurfacesofaggregates.
•Sobiggerthesize,giveshigherworkability.
Fresh Concrete

150. Factorsaffectingworkability
Shapeofaggregate:
•Angular,elongatedorflakyaggregatesmaketheconcreteveryharshwhencomparedtoroundedorcubical
aggregates.
•Contributiontobetterworkabilityofroundedaggregatewillcomefromthefactthatforagivenvolumeor
weight.
•Itwillhavealesssurfaceareaandlesservoids.
•Notonlyisthatbeinginroundedinshape,thefrictionalresistancebetweentheaggregatesalsoreduced.
•Hencetheworkabilitywillbemoreincaseofroundedthancomparedtoflakyaggregates.
•Hencethestrengthwillbemorebyusingroundedorcubicalaggregates.
Fresh Concrete

151. Factorsaffectingworkability
Surfacetexture:
•Theinfluenceofsurfacetextureontheworkabilityisduetothefactthat,totalsurfaceareaofroughtexture
aggregateismorethanthatofsurfaceareaofsmoothroundedaggregatesofsamevolume.
•Roughtexturedaggregateswillshowpoorworkabilityandsmoothtexturedaggregateswillgivebetter
workabilitybecauseoflesserfrictionalresistanceofinnersurfaceparticle.
Fresh Concrete

152. Factorsaffectingworkability
Gradingofaggregates:
•Thisisoneofthefactorwillhavemaximuminfluenceonworkability.
•Awellgradedaggregatewillgiveleastamountofvoidsforgivenvolumeofaggregates.
•Whenthevoidsareless,excesspastewillbeavailabletogivebetterworkability.
•Betterthegrading,lesserwillbethevoidsandgreaterwillbetheworkability.
Useofadmixtures:
•Likeplasticizersandsuperplasticizersgreatlyimprovestheworkabilityofconcrete.
Fresh Concrete

153. HowToimprovetheworkabilityofconcrete
•increasewater/cementratio
•increasesizeofaggregate
•usewell-roundedandsmoothaggregateinsteadofirregularshape
•increasethemixingtime
•increasethemixingtemperature
•usenon-porousandsaturatedaggregate
•withadditionofair-entrainingmixtures
Fresh Concrete

154. MeasurementofWorkability
Thefollowingtestsarecommonlyemployedtomeasureworkability.
SlumpTest
CompactingFactorTest
Vee-BeeConsistometerTest
FlowTest
Fresh Concrete

155. ConcreteConsistency
•Consistencyorfluidityofconcreteisanimportantcomponentofworkabilityandrefersinawaytothewetnessofthe
concrete.
•Wetterthemixthemoreworkableitis.Ifamixistoowet,segregationmayoccurwithresultinghoneycomb,excessive
bleeding,andsandstreakingontheformedsurfaces
Fresh Concrete

156. Consistencyofconcrete
Ontheotherhand,ifamixistoodryitmaybedifficulttoplaceandcompact,andsegregationmayoccurbecause
oflackofcohesivenessandplasticityofthepaste.
Fresh Concrete

157. Fresh Concrete

158. SlumpTest
•Aslumptestisamethodusedtodeterminetheconsistencyofconcrete.
•Theconsistency,orstiffness,indicateshowmuchwaterhasbeenusedinthemix.
•Thestiffnessoftheconcretemixshouldbematchedtotherequirementsforthefinishedproductquality
Slumpisameasurementofconcrete’sworkability,orfluidity.
It’sanindirectmeasurementofconcreteconsistencyorstiffness.
Principle
•Theslumptestresultisameasureofthebehaviorofacompactedinvertedconeofconcreteundertheactionofgravity.It
measurestheconsistencyorthewetnessofconcrete
Fresh Concrete

159. Toolsandapparatususedforslumptest(equipment):
1.Standardslumpcone(100mmtopdiameterx200mmbottomdiameterx300mmhigh)
2.Smallscoop
3.Bullet-nosedrod(600mmlongx16mmdiameter)
4.Rule
5.Slumpplate(500mmx500mm)
Fresh Concrete

160. Procedure
•Thebaseisplacedonasmoothsurfaceandthecontainerisfilled
withconcreteinthreelayers,whoseworkabilityistobetested.
•Eachlayeristemped25timeswithastandard16mm(5/8in)
diametersteelrod,roundedattheend.
•Whenthemoldiscompletelyfilledwithconcrete,thetopsurfaceis
struckoff(leveledwithmoldtopopening)bymeansofscreeningand
rollingmotionofthetempingrod.
•Themoldmustbefirmlyheldagainstitsbaseduringtheentire
operationsothatitcouldnotmoveduetothepouringofconcreteand
thiscanbedonebymeansofhandlesorfoot–restsbrazedtothe
mold.
Fresh Concrete

161. Procedure
•Immediatelyafterfillingiscompletedandtheconcreteisleveled,the
coneisslowlyandcarefullyliftedvertically,anunsupportedconcrete
willnowslump.
•Thedecreaseintheheightofthecenteroftheslumpedconcreteis
calledslump.
•Theslumpismeasuredbyplacingtheconejustbesidestheslump
concreteandthetempingrodisplacedovertheconesothatitshould
alsocomeovertheareaofslumpedconcrete.
•Thedecreaseinheightofconcretetothatofmouldisnotedwith
scale.(usuallymeasuredtothenearest5mm(1/4in).
Fresh Concrete

162. Precautions
•Inordertoreducetheinfluenceonslumpofthevariationinthe
surfacefriction,theinsideofthemoldanditsbaseshouldbe
moistenedatthebeginningofeverytest,andpriortoliftingofthe
moldtheareaimmediatelyaroundthebaseoftheconeshouldbe
cleanedfromconcretewhichmayhavedroppedaccidentally.
Fresh Concrete

163. TypesOfSlump
Theslumpedconcretetakesvariousshapes,andaccordingtothe
profileofslumpedconcrete,theslumpis
termedas;
•CollapseSlump
•ShearSlump
•TrueSlump
Fresh Concrete

164. Typesofslump
CollapseSlump
•Inacollapseslumptheconcretecollapsescompletely.
•Acollapseslumpwillgenerallymeanthatthemixistoowetorthatit
isahighworkabilitymix,forwhichslumptestisnotappropriate.
Fresh Concrete

165. Typesofslump
ShearSlump
•Inashearslumpthetopportionoftheconcreteshearsoffandslips
sideways.ORIfone-halfoftheconeslidesdownaninclinedplane,
theslumpissaidtobeashearslump.
•Ifashearorcollapseslumpisachieved,afreshsampleshouldbe
takenandthetestisrepeated.
•Iftheshearslumppersists,asmaythecasewithharshmixes,thisis
anindicationoflackofcohesionofthemix.
Fresh Concrete

166. Typesofslump
TrueSlump
•Inatrueslumptheconcretesimplysubsides,keepingmoreorlessto
shape
•Thisistheonlyslumpwhichisusedinvarioustests.
•MixesofstiffconsistencehaveaZeroslump,sothatintheratherdry
rangenovariationcanbedetectedbetweenmixesofdifferent
workability.
Fresh Concrete

167. Uses
•Theslumptestisusedtoensureuniformityfordifferentbatchesofsimilarconcreteunderfieldconditionsandtoascertainthe
effectsofplasticizersontheirintroduction.
•Thistestisveryusefulonsiteasacheckontheday-to-dayorhour-to-hourvariationinthematerialsbeingfedintothemixer.
•Anincreaseinslumpmaymean,forinstance,thatthemoisturecontentofaggregatehasunexpectedlyincreases.
•Othercausewouldbeachangeinthegradingoftheaggregate,suchasadeficiencyofsand.
•Toohighortoolowaslumpgivesimmediatewarningandenablesthemixeroperatortoremedythesituation.
•Thisapplicationofslumptestaswellasitssimplicity,isresponsibleforitswidespreaduse.
Fresh Concrete

168. Fresh Concrete

169. Fresh Concrete

170. CompactionFactorTest
•Thistestmeasurethedegreeofcompaction.
•Thetestrequiremeasurementoftheweightofthepartiallyandfullycompactedconcreteandtheratiothe
partiallycompactedweighttothefullycompactedweight,whichisalwayslessthanone,isknownas
compactedfactor.
•Forthenormalrangeofconcretethecompactingfactorliesbetween0.8-0.92
Fresh Concrete

171. CompactionFactorTest
Apparatus
•Trowels
•HandScoop(15.2cmlong)
•Rodofsteelorothersuitablematerial(1.6cmdiameter,61cmlong
roundedatoneend).
•Balance.
Fresh Concrete

172. Procedure
1)Ensuretheapparatusandassociatedequipmentarecleanbeforetestandfreefromhardened
concreteandsuperfluouswater.
2)Weighthebottomcylindertonearest10gm,putitbackonthestandandcoveritupwithapair
offloats.
3)Gentlyfilltheupperhopperwiththesampledconcretetotheleveloftherimwithuseofa
scoop.
4)Immediatelyopenthetrapdooroftheupperhopperandallowthesampledconcretetofallinto
themiddlehopper.
5)Removethefloatsontopofthebottomcylinderandopenthetrapdoorofthemiddlehopper
allowingthesampledconcretetofallintothebottomcylinder.
6)Removethesurplusconcreteabovethetopofthebottomcylinderbyholdingafloatineach
handandmovetowardseachothertocutofftheconcreteacrossthetopofcylinder
Fresh Concrete

173. Procedure
1)Wipecleantheoutsideofcylinderofconcreteandweightonearest10gm.
2)Subtracttheweightofemptycylinderfromtheweightofcylinderplusconcreteto
obtaintheweightofpartiallycompactedconcrete
3)Removetheconcretefromthecylinderandrefillwithsampledconcreteinlayers.
4)CompacteachlayerthoroughlywiththestandardCompactingBartoachievefull
compaction.
5)Floatoffthesurplusconcretetotopofcylinderandwipeitclean.
6)Weighthecylindertonearest10gmandsubtracttheweightofemptycylinderfromthe
weightofcylinderplusconcretetoobtaintheweightoffullycompactedconcrete
Fresh Concrete

175. Vee-BeTimeTest
Itisbasedonmeasuringthetime(CalledVEBEtime)neededtotransfertheshapeofa
concretemixfromafrustumconetoacylinder(theseshapesarestandardizedbythe
apparatusofthistest),byvibratingandcompactingthemix.ThemoreVEBEtime
neededthelessworkablethemixis.Thismethodisveryusefulforstiffmixes.
Fresh Concrete

176. Vee-BeTimeTest
Apparatus
•Cylindricalcontainerwithdiameter=240mm,andheight=200mm
•Mould:thesamemouldusedintheslumptest.
•Disc:Atransparenthorizontaldiscattachedtoarodwhichslidesvertically
•VibratingTable:380*260mm,supportedbyfourrubbershockabsorbers
•TampingRod
•Stopwatch
Fresh Concrete

177. Procedure
•Slumptestasdescribedearlierisperformed,placingtheslumpconeinsidethesheet
metalcylindricalpotoftheconsistmeter.
•Theglassdiscattachedtotheswivelarmisturnandplaceonthetopoftheconcretein
thepot.
•Theelectricalvibratoristhenswitchedonandsimultaneouslyastopwatchstarted.
•Thevibrationiscontinuedtillsuchtimeastheconicalshapeoftheconcretedisappears
andtheconcreteassumeacylindricalshape.
•Thiscanbejudgebyobservingtheglassdiscfromthetopdisappearanceof
transparency.
•Immediatelywhentheconcretefullyassumeacylindricalshape,thestopwatchis
switchedoff
Fresh Concrete

178. •Thetimerequiredfortheshapeofconcretetochangefromslumpconeshapeto
cylindricalshapeinsecondisknownasVibeDegree.
•Thismethodisverysuitableforverydryconcretewhoseslumpvaluecannotbe
measurebyslumptest,butthevibrationistoovigorousforconcretewithslump
greaterthanabout50m.
•ThetestfailsifVee-BeTimeislessthan5seconds..Andthetestmustberepeated
whennocollapseorshearsslumpinconcrete
Fresh Concrete

179. FlowTest
Theflowtabletestorflowtestisamethodtodeterminetheconsistenceoffreshconcrete.
Application
•Whenfreshconcreteisdeliveredtoasitebyatruckmixeritissometimesnecessarytocheckitsconsistencebeforepouringitinto
formwork.
•Iftheconsistenceisnotcorrect,theconcretewillnothavethedesiredqualitiesonceithasset,particularlythedesiredstrength.Ifthe
concreteistoopasty,itmayresultincavitieswithintheconcretewhichleadstocorrosionoftherebar,eventuallyleadingtothe
formationofcracks(astherebarexpandsasitcorrodes)whichwillacceleratethewholeprocess,ratherlikeinsufficientconcretecover.
•Cavitieswillalsolowerthestresstheconcreteisabletosupport.
Fresh Concrete

180. FlowTest
Equipment
•Flowtablewithagripandahinge,70cmx70cm.
•Abramscone,openatthetopandatthebottom-30cmhigh,17cmtopdiameter,25cm
basediameter
•Waterbucketandbroomforwettingtheflowtable.
•Tampingrod,60cmheight
•Scaleformeasurement
Fresh Concrete

181. Procedure
•Theflowtableiswetted.
•Theconeisplacedontheflowtableandfilledwithfreshconcreteintwolayers,each
layer25timestampwithtampingrod.
•Theconeislifted,allowingtheconcretetoflow.
•Theflowtableisthenliftedupabout12.5mmandthendroppedfor15timesin15
seconds,causingtheconcreteflowalittlebitfurther.
•Afterthisthediameteroftheconcreteismeasuredina6differentdirectionandtakethe
average.
Fresh Concrete

183. Segregation
Segregationiswhenthecoarseandfineaggregate,andcementpaste,becomeseparated.Segregationmayhappenwhenthe
concreteismixed,transported,placedorcompacted
Segregationmakestheconcrete
•Weaker,
•Lessdurable,
•andwillleaveapoorsurfacefinish
Fresh Concrete

184. Segregation
Segregationmaybeofthreetypes
•firstly,thecoarseaggregateseparatingoutorsettlingdownfromtherestofthemixing
•Secondly,thepasteormatrixseparatingawayfromcoarseaggregateand
•thirdly,waterseparatingoutfromtherestofthematerialbeingamaterialoflowestspecificgravity.
Fresh Concrete

185. ToAvoidSegregation
•Ifplacingconcretestraightfromatruck,pourverticallyandneverlettheconcretefallmorethanone-and-a-half
meters.
Fresh Concrete

186. ConcreteBleeding
•Thisreferstotheappearanceofwateralongwithcementparticlesonthe
surfaceofthefreshlylaidconcrete.
•Thishappenswhenthereisexcessivequantityofwaterinthemixordue
toexcessivecompaction.
•Bleedingcausestheformationofporesandrenderstheconcreteweak.
•Bleedingcanbeavoidedbysuitablycontrollingthequantityofwaterin
theconcreteandusingfinergradingofaggregates.
Fresh Concrete

187. The effects of water gain:
•The water gain which causes voids and reduces the bond between the cement and aggregates.
•Water gain below the reinforcement especially at cranked portion reduces the bond between reinforcement and
concrete.
•Water while traversing from bottom to top make a channel and if water-cement ratio greater than 0.7 is used,
channel becomes continuous and responsible for permeability of concrete.
Fresh Concrete

188. Water gain can be avoided by
1. Proper mix proportion
2. Proper mixing
3. By using finely divided pozzolanic material
4. By using finer cement or cement with less alkali content
5. By re-vibration of concrete
6. By using air entraining agents
Fresh Concrete

189. ProcessofManufactureofConcrete
•Itisinterestingtonotethattheingredientsofgoodconcreteandbad
concretearethesame.
•Ifmeticulouscareisnotexercised,andgoodrulesarenotobserved,the
resultantconcreteisgoingtobeofbadquality.
•Withthesamematerialifintensecareistakentoexercisecontrolatevery
stage,itwillresultingoodconcrete.
Fresh Concrete

191. ProcessofManufactureofConcrete
Thevariousstagesofmanufactureofconcreteare:
(a)Batching
(b)Mixing
(c)Transporting
(d)Placing
(e)Compacting
(f)Curing
(g)Finishing
Fresh Concrete

192. Batching
Themeasurementofmaterialsformakingconcreteisknownasbatching.Therearetwomethodsofbatching:
•Volumebatching
•Weighbatching
Fresh Concrete

193. Batching
VolumeBatching:
•Volumebatchingisnotagoodmethodforproportioningthematerialbecauseofthedifficultyitofferstomeasure
granularmaterialintermsofvolume.
•Volumeofmoistsandinalooseconditionweighsmuchlessthanthesamevolumeofdrycompactedsand.
•Theeffectofbulkingshouldbeconsiderformoistfineaggregate.
•Forunimportantconcreteorforanysmalljob,concretemaybebatchedbyvolume.
Fresh Concrete

195. Batching
WeighBatching:
•Weighbatchingisthecorrectmethodofmeasuringthematerials.
•Useofweightsysteminbatching,facilitates,accuracy,flexibilityandsimplicity.
•Largeweighbatchingplantshaveautomaticweighingequipment.
•Onlargeworksites,theweighbuckettypeofweighingequipment'sareused.
Fresh Concrete

197. Batching
•Cementisalwaysmeasuredbyweight.
•Itisnevermeasuredinvolume.
•Generally,foreachbatchmix,onebagofcementisused.
•Thevolumeofonebagofcement(50kgs)istakenasthirtyfive(35)liters.
Measurementofwater:
•whenweighbatchingisadopted,themeasurementofwatermustbedoneaccurately.
•Additionofwaterbygraduatedbucketintermsofliterswillnotbeaccurateforthereasonofspillageofwater.
•Itisusualtohavewatermeasuredinahorizontalorverticaltank
•Thesetanksarefilledupofteneverybatch.
Fresh Concrete

198. Mixing
•Thoroughmixingofthematerialsproductionofuniformconcrete.
•Themixingshouldensurethatisessentialforthemassbecomeshomogeneous,uniformin
colourandconsistency.
•Therearetwomethodsadoptedformixingconcrete:
(i)Handmixing(ii)Machinemixing
Fresh Concrete

199. Mixing
Handmixing
•Handmixingispracticedforsmallscaleunimportantconcreteworks.
•Asthemixingcannotbethoroughandefficient,itisdesirabletoadd10per
centmorecementtocaterfortheinferiorconcreteproducedbythis
method.
•Handmixingshouldbedoneoveranimperviousconcreteorbrickfloorof
sufficientlylargesizetotakeonebagofcement.
•Spreadoutthemeasuredquantityofcoarseaggregateandfineaggregatein
alternatelayers.
Fresh Concrete

200. Mixing
Handmixing
•Pourthecementonthetopofit,andmixthemdrybyshovel,turning
themixtureoverandoveragainuntiluniformityofcolourisachieved.
•Wateristakeninawater-canfittedwitharose-headandsprinkledover
themixtureandsimultaneouslyturnedover.
•Thisoperationiscontinuedtillsuchtimeagooduniform,
homogeneousconcreteisobtained.
Fresh Concrete

201. Mixing
MachineMixing
•Mixingofconcreteisalmostinvariablycarriedoutbymachine,forreinforcedconcrete
workandformediumorlargescalemassconcretework.
•Machinemixingisnotonlyefficient,butalsoeconomical,whenthequantityofconcreteto
beproducedislarge.
•Theycanbeclassifiedasbatch-mixersandcontinuousmixers.
•Batchmixersproduceconcrete,batchbybatchwithtimeinterval,whereascontinuous
mixersproduceconcretecontinuouslywithoutstoppagetillsuchtimetheplantisworking.
Fresh Concrete

202. Mixing
MachineMixing
•Innormalconcretework,itisthebatchmixersthatareused.Batchmixermaybeofpantypeordrumtype.
•Thedrumtypemaybefurtherclassifiedastilting,non-tilting,reversingorforcedactiontype.
•AsperI.S.1791–1985,concretemixersaredesignatedbyanumberrepresentingitsnominalmixedbatchcapacityinlitres.
Thefollowingarethestandardizedsizesofthreetypes:
a.Tilting:85T,100T,140T,200T
b.Non-Tilting:200NT,280NT,375NT,500NT,1000NT
c.Reversing:200R,280R,375R,500Rand1000R
Fresh Concrete

203. Mixing
How do we mix concrete in a mixer?
•Firstly about half the quantity of coarse aggregate is placed into the mixer.
•Over this about half quantity of fine aggregate is poured.
•On this mixture, 1 bag of cement is poured and over this remaining half quantity of coarse and fine aggregates is placed. This
prevents the blowing away of cement in windy weather.
•Before the loading skip is placed into the drum, about 25% of water is added to the drum in order to avoid the sticking of cement to
the surface / deposition at the bottom. After loading skip is placed, remaining 75% of water is added. If the mixer is havingan
independent feeding of water, it is desirable that remaining 75% of water is added simultaneously along with the loading skip.
Fresh Concrete

204. •MixingTime:
•Concretemixersaregenerallydesignedtorunataspeedof15to20revolutionsper
minute.
•Forpropermixing,itisseenthatabout25to30revolutionsarerequiredinawell
designedmixer.
•Inthesite,thenormaltendencyistospeeduptheoutturnofconcretebyreducingthe
mixingtime.Thisresultsinpoorqualityofconcrete.
•Ontheotherhand,iftheconcreteismixedforacomparativelylongertime,itis
uneconomicalfromthepointofviewofrateofproductionofconcreteandfuel
consumption.
•Therefore,itisofimportancetomixtheconcreteforsuchadurationwhichwillaccrue
optimumbenefit.
Fresh Concrete

205. TransportingofConcrete:
•Concretecanbetransportedbyavarietyofmethodsandequipment's.Theprecautiontobetakenwhiletransportingconcreteisthat
thehomogeneityobtainedatthetimeofmixingshouldbemaintainedwhilebeingtransportedtothefinalplaceofdeposition.
Mortar Pan
Wheel Barrow, Hand Cart,
Crane, Bucket and Rope way ,
Truck Mixer and Dumpers,
Chute,
Skip and Hoist ,
TansitMixer,
Pump and Pipe Line,
Helicoptor
Fresh Concrete

206. TransportingofConcrete:
MortarPan
•Useofmortarpanfortransportationofconcreteisoneofthecommonmethodsadoptedinthiscountry.
•Inthiscase,concreteiscarriedinsmallquantities.
•Whilethismethodnullifiesthesegregationtosomeextent,particularlyinthickmembersGreaterlossofwater,
particularly,inhotweatherconcreting
Fresh Concrete

207. TransportingofConcrete:
WheelBarrows
•Wheelbarrowsarenormallyusedfortransportingconcretetobeplacedatground
level.
•Thismethodisemployedforhaulingconcreteforcomparativelylongerdistanceas
inthecaseofconcreteroadconstruction.
•Ifconcreteisconveyedbywheelbarrowoveralongdistance,onroughground,itis
likelythattheconcretegetssegregatedduetovibration
Fresh Concrete

208. TransportingofConcrete:
Crane,BucketandRopeway
•Acraneandbucketisoneoftherightequipmentfortransportingconcrete
abovegroundlevel.
•Cranecanhandleconcreteinhighriseconstructionprojectsandare
becomingafamiliarsitesinbigcities.
•Cranesarefastandversatiletomoveconcretehorizontallyaswellas
verticallyalongtheboomandallowstheplacementofconcreteatthe
exactpoint.
•Cranescarryskipsorbucketscontainingconcrete.Skipshavedischarge
dooratthebottom,whereasbucketsaretiltedforemptying.
•Foramediumscalejobthebucketcapacitymaybe0.5m
3
.
Fresh Concrete

209. TransportingofConcrete:
TruckMixerandDumpers
•Forlargeconcreteworksparticularlyforconcretetobeplacedatground
level,trucksanddumpersorordinaryopensteel-bodytippinglorriescan
beused.
•Astheycantraveltoanypartofthework,theyhavemuchadvantage
overthejubileewagons,whichrequirerailtracks.
•Dumpersareofusually2to3cubicmetrecapacity,whereasthecapacity
oftruckmaybe4cubicmetreormore
Fresh Concrete

210. TransportingofConcrete:
BeltConveyors
•Beltconveyorshaveverylimitedapplicationsinconcreteconstruction.
•Theprincipalobjectionisthetendencyoftheconcretetosegregateon
steepinclines,attransferpointsorchangeofdirection,andatthepoints
wherethebeltpassesovertherollers.
•Conveyorscanplacelargevolumesofconcretequicklywhereaccessis
limited
Fresh Concrete

211. TransportingofConcrete:
Chute
•Chutesaregenerallyprovidedfortransportingconcretefromgroundlevel
toalowerlevel.
•Thesectionsofchuteshouldbemadeoforlinedwithmetalandallruns
shallhaveapproximatelythesameslope,notflatterthan1verticalto2
1/2horizontal.
•Thelay-outismadeinsuchawaythattheconcretewillslideevenlyina
compactmasswithoutanyseparationorsegregation
Fresh Concrete

212. TransportingofConcrete:
TransitMixer
•Transitmixerisoneofthemostpopularequipment'sfortransportingconcrete
overalongdistanceparticularlyinReadyMixedConcreteplant(RMC).
•InIndia,today(2000AD)thereareabout35RMCplantsandanumberof
centralbatchingplantsareworking.Theyaretruckmountedhavingacapacity
of4to7m3.
•Inone,mixedconcreteistransportedtothesitebykeepingitagitatedall
alongataspeedvaryingbetween2to6revolutionsperminute.
•Intheothercategory,theconcreteisbatchedatthecentralbatchingplantand
mixingisdoneinthetruckmixereitherintransitorimmediatelypriorto
dischargingtheconcreteatsite.
Fresh Concrete

213. TransportingofConcrete:
Pipelines&coupling
•Generallyalmostallpumpedconcreteisconveyed125mmpipeline.
•Generalruleisthatthepipediametershouldbebetween3to4timesthe
largestsizeofaggregate.
•Concretehasbeenpumpedtoaheight400mandtoadistanceof2000m
Fresh Concrete

214. PumpableConcrete
•Aconcretewhichcanbepushedthroughapipelineiscalledapumpable
concrete.
•Itismadeinsuchamannerthatitsfrictionattheinnerwallofthepipeline
doesnotbecomeveryhighandthatitdoesnotwedgewhileflowing
throughthepipeline.
•Pumpableconcreteemergingfromapipelineflowsintheformofaplug
whichisseparatedfromthepipewallbyathinlubricatinglayerconsisting
ofcementpaste.
•Forcontinuousplugmovement,thepressuregeneratedbytheflow
resistancemustnotbegreaterthanthepumppressurerating.
Fresh Concrete

215. PlacingofConcrete
•Itisnotenoughthattheconcreteisproperlymixed,correctlybatchedandtransported,butalsoithastobeplacedina
sequentialmannertoobtainbetterresults.
•Placingconcretewithinearthmould(examplefoundationconcreteforwalloracolumn)
•Placingconcretewithinlargeearthmouldortimberplankformwork(example:RoadslabandAirfieldslab).
•Placingconcreteinlayerswithintimberorsteelshutters(example:Massconcreteindamconstructionorconstructionof
concreteabutmentorpier).
•Placingconcretewithinusualfromwork.(example:Columns,beamsandfloors).
•Placingconcreteunderwater.
Fresh Concrete

216. Placingconcretewithinearthmould(examplefoundationconcreteforwallora
column)
•Concreteisinvariablylaidasfoundationbedbelowthewallsorcolumns.
•Beforeplacingtheconcreteinthefoundation,allthelooseearthmustbe
removedfromthebed.
•Anyrootoftreespassingthroughthefoundationmustbecutandburnt
effectivelytopreventitsfurthergrowthandpiercingtheconcreteatalater
date.
•Thesurfaceoftheearth,ifdry,mustbejustmadedampsothattheearthdoes
notabsorbwaterfromconcrete.
•Ifthereisanyseepageofwatertakingplaceintothefoundationtrench,
effectivemethodfordivertingtheflowofwatermustbeadoptedbefore
concreteisplacedinthetrenchorpit.
Fresh Concrete

217. Placingconcretewithinlargeearthmouldortimberplankformwork:
•Fortheconstructionofroadslabs,airfieldslabsandgroundfloorslabsinbuildings,
concreteisplacedinbays.
•Thegroundsurfaceonwhichtheconcreteisplacedmustbefreefromlooseearth,
poolofwaterandotherorganicmatterslikegrass,roots,leavesetc.
•Theearthmustbeproperlycompactedandmadesufficientlydamptopreventthe
absorptionofwaterfromconcrete.
•Ifthisisnotdone,bottomportionofconcretebecomesweak.
•Sometimes,inordertopreventtheabsorptionofmoisturefromconcrete,a
polyethylenefilmisplacedbetweenconcreteandgroundsurfacegivesenough
scopefortheconcretetoundergosufficientshrinkage.
Fresh Concrete

218. Placingconcreteinlayerswithintimberorsteelshutters:
•Whenconcreteislaidingreatthickness,asinthecaseofconcreteraftforahighrise
buildingorintheconstructionofconcretepierorabutmentorintheconstructionofmass
concretedam,concreteisplacedinlayers.
•Thethicknessoflayersdependsuponthemodeofcompaction.
•Inreinforcedconcrete,itisagoodpracticetoplaceconcreteinlayersofabout15to30cm
thickandinmassconcrete,thethicknessoflayermayvaryanythingbetween35to45cm.
•Beforeplacingtheconcrete,thesurfaceofthepreviousliftiscleanedthoroughlywith
waterjetandscrubbingbywirebrush.
•Sometimescementslurryoraverythinlayerofrichmortarisplacedontheoldsurface
andthenthefreshconcreteislaid.
•Thisisdoneinordertoavoidformationofcoldjoints.Soitisbettertoleavethetop
surfaceasrough,whichgivesbetterbindingbetweenthetwolayers.
Fresh Concrete

219. Placingofconcretewithinusualfromwork.(example:Columns,beamsand
floors):
Formwork:
•Formworkshallbedesignedandconstructedsoastoremainsufficientlyrigid
duringplacingandcompactionofconcrete.
•Thejointsarepluggedtopreventthelossofslurryfromconcrete.
•Reinforcementshouldbecleanedandfreefromoils.Whenreinforcementis
placedincongestion,concretemustbeplacedverycarefully.Whilecasting
columns,droppingofconcretefromgreaterheightcausessegregation.Inorder
toavoidthis,concreteisplacedwithtremie,dropchuteorbyanyothermeans
withinthereinforcementandties.
•Whentheformworkisnarrow,asmallopeningismadeonthesidesofthe
formworkandconcreteisplaced.
Fresh Concrete

220. StrippingTime:
Formworkshouldnotberemoveduntiltheconcretehas
developedstrengthofatleasttwicethestresstowhich
concretemaybesubjectedatthetimeofremovalof
formwork.
Fresh Concrete

221. Placingconcreteunderwater:
•Insuchcases,useofbottomdumpbucketortremiepipeismadeuseof.
•Inthebottomdumpbucketconcreteistakenthroughthewaterinawater-
tightboxorbucketandonreachingthefinalplaceofdepositionthebottom
ismadetoopenbysomemechanismandthewholeconcreteisdumped
slowly.
•Atremiepipeisapipehavingadiameterofabout20cmcapableofeasy
couplingforincreaseordecreaseoflength.
•Afunnelisfittedtothetopendtofacilitatepouringofconcrete.
•Thebottomendisclosedwithaplugorthickpolyethylenesheetorsuch
othermaterialandtakenbelowthewaterandmadetorestatthepoint
wheretheconcreteisgoingtobeplaced.
Fresh Concrete

222. Placingconcreteunderwater:
•Sincetheendisblocked,nowaterwillenterfromthebottomofthepipe.
•Theconcretehavingaveryhighslumpofabout15to20cmispouredintothe
funnel.Whenthewholelengthofpipeisfilledupwiththeconcrete,thetremie
pipeisliftedupandaslightjerkisgivenbyawinchandpulleyarrangement.
•Whenthepipeisraisedandgivenajerk,duetotheweightofconcrete,the
bottomplugfallsandtheconcretegetsdischarged.
•Particularcaremustbetakenatthisstagetoseethattheendofthetremiepipe
remainsinsidetheconcrete,sothatnowaterentersintothepipefromthe
bottom.
•Inthisway,concreteworkisprogressedwithoutstoppingtilltheconcretelevel
comesabovethewaterlevel.
Fresh Concrete

223. CompactionofConcrete
•Compactionofconcreteistheprocessadoptedforexpellingtheentrappedairfromtheconcrete.
•Intheprocessofmixing,transportingandplacingofconcreteairislikelytogetentrappedintheconcrete.
•Inotherwords,stiffconcretemixhashighpercentageofentrappedairand,thereforewouldneedhigher
compactingeffortsthanhighworkablemixes.
•Inordertoachievefullcompactionandmaximumdensity,withreasonablecompactingeffortsavailableatsite,
itisnecessarytouseamixwithadequateworkability.
Fresh Concrete

224. Fresh Concrete

225. HandCompaction
•Handcompactionofconcreteisadoptedincaseofunimportantconcreteworkofsmall
magnitude.
•Roddingisdonecontinuouslyoverthecompleteareatoeffectivelypacktheconcreteand
driveawayentrappedair.
•Lightrammingcanbepermittedinunreinforcedfoundationconcreteoringroundfloor
construction.
•Tampingisoneoftheusualmethodsadoptedincompactingrooforfloorslaborroad
pavementswherethethicknessofconcreteiscomparativelylessandthesurfacetobe
finishedsmoothandlevel.
•Tampingconsistsofbeatingthetopsurfacebywoodencrossbeam
Fresh Concrete

226. CompactionbyVibration:
•Itispointedoutthatthecompactionbyhand,ifproperlycarriedoutonconcretewithsufficientworkability,gives
satisfactoryresults,butthestrengthofthehandcompactedconcretewillbenecessarilylowbecauseofhigherwatercement
ratiorequiredforfullcompaction.
•Wherehighstrengthisrequired,itisnecessarythatstiffconcrete,withlowwater/cementratiobeused.
•Tocompactsuchconcrete,mechanicallyoperatedvibratoryequipment,mustbeused.
•Thevibratedconcretewithlowwater/cementratiowillhavemanyadvantagesoverthehandcompactedconcretewith
higherwater/cementratio.
Fresh Concrete

227. CompactionbyVibration:
Internalvibrator(Needlevibrator):
•Theinternalvibratorismostcommonlyused.
•Thisisalsocalled,“NeedleVibrator”,“ImmersionVibrator”.
•Thisessentiallyconsistsofapowerunit,aflexibleshaftandaneedle.
•Thepowerunitmaybeelectricallydrivenoroperatedbypetrolengine
oraircompressor.
•Thevibrationsarecausedbyeccentricweightsattachedtotheshaftor
themotorortotherotorofavibratingelement.
•Thefrequencyofvibrationvariesupto12,000cyclesofvibrationper
minute.
•Theneedlediametervariesfrom20mmto75mmanditslengthvaries
from25cmto90cm.
•Thebiggerneedleisusedintheconstructionofmassconcretedam.
Fresh Concrete

228. CompactionbyVibration:
•Formworkvibrator(Externalvibrator):
•Formworkvibratorsareusedforconcretingcolumns,thinwallsorinthe
castingofprecastunits.
•Themachineisclampedontotheexternalwallsurfaceoftheformwork.
•Thevibrationisgiventotheformworksothattheconcreteinthevicinityofthe
shuttergetsvibrated.
•Thismethodofvibratingconcreteisparticularlyusefulandadoptedwhere
reinforcement,lateraltiesandspacersinterferetoomuchwiththeinternal
vibrator.
•Useofformworkvibratorwillproduceagoodfinishtotheconcretesurface.
Fresh Concrete

229. CompactionbyVibration:
Tablevibrator:
•Thisisthespecialcaseofformworkvibrator,wherethevibratoris
clampedtothetable.ortableismountedonspringswhicharevibrated
transferringthevibrationtothetable.
•Theyarecommonlyusedforvibratingconcretecubes.
Fresh Concrete

230. CompactionbyVibration:
Platformvibrator:
•Platformvibratorisnothingbutatablevibrator,butitislargerinsize.
•Thisisusedinthemanufactureoflargeprefabricatedconcreteelements
suchaselectricpoles,railwaysleepers,prefabricatedroofingelements
etc.
•Sometimes,theplatformvibratorisalsocoupledwithjerkingorshock
givingarrangementssuchthatathroughcompactionisgiventothe
concrete.
Fresh Concrete

231. CompactionbyVibration:
Surfacevibrator(Screedvibrator):
•Surfacevibratorsaresometimesknowsas,“ScreedBoardVibrators”.
•AsmallvibratorplacedontheScreedboardgivesaneffectivemethodof
compactingandLevelingofthinconcretemembers,suchasfloorslabs,roof
slabsandroadsurface.
•Mostly,floorslabsandroofslabsaresothinthatinternalvibratororanyother
typeofvibratorcannotbeeasilyemployed.
•Insuchcases,thesurfacevibratorcanbeeffectivelyused.Ingeneral,surface
vibratorsarenoteffectivebeyondabout15cm.
Fresh Concrete

232. CompactionbyVibration:
CompactionbyPressureandJolting:
•Thisisoneoftheeffectivemethodsofcompactingverydryconcrete.
•Thismethodisoftenusedforcompactinghollowblocks,cavityblocksand
solidconcreteblocks.
•Thestiffconcreteisvibrated,pressedandalsogivenjolts.
•Withthecombinedactionofthejoltsvibrationsandpressure,thestiffconcrete
getscompactedtoadenseformtogivegoodstrengthandvolumestability
Fresh Concrete

233. CompactionbyVibration:
CompactionbySpinning:
•Spinningisoneoftherecentmethodsofcompactionofconcrete.
•Thismethodofcompactionisadoptedforthefabricationofconcretepipes.
•Theplasticconcretewhenspinnedataveryhighspeedgetswellcompacted
becauseofcentrifugalforce.
Fresh Concrete

234. CompactionbyVibration:
VibratoryRoller:
•Oneoftherecentdevelopmentsofcompactingverydryandleanconcreteisthe
useofVibratoryRoller.
•SuchconcreteisknownasRollerCompactedConcrete
Fresh Concrete

235. CuringofConcrete
•Concretederivesitsstrengthbythehydrationofcementparticles.
•Thehydrationofcementisnotamomentaryactionbutaprocesscontinuingforlongtime.
•Thequantityoftheproductofhydrationandconsequentlytheamountofgelformeddependsupontheextentofhydration.
•Cementrequiresawater/cementratioabout0.23forhydrationandawater/cementratioof0.15forfillingthevoidsinthe
gelpores.
•Inotherwords,awater/cementratioofabout0.38wouldberequiredtohydratealltheparticlesofcementandalsoto
occupythespaceinthegelpores.
Fresh Concrete

236. CuringofConcrete
•Curingistheprocessofcontrollingtherateandextentofmoisturelossfromconcreteduringcementhydration
•Curingcanalsobedescribedaskeepingtheconcretemoist,sothatthehydrationofcementcancontinue.
•Curingmethodsmaybedividedbroadlyintofourcategories:
(a)Watercuring
(b)Membranecuring
(c)Applicationofheat
(d)Miscellaneous
Fresh Concrete

237. Purposeofcuring:
•Inthefieldthoughenoughwaterisusedformixingtheconcrete,somepartofwatergets
evaporatedandthewateravailableforhydrationprocessbecomesinsufficient.
•Ifthehydrationhastobeprogressed,thenextrawaterisaddedwhichreplenishesthelossof
waterduetoevaporation.
•Hydrationprocessmustcontinuetoattainthedesirablepropertiesofconcrete.
Fresh Concrete

238. Watercuring:
•Thisisthebestmethodofcuringasitsatisfiesalltherequirementsofcuring,namely,
promotionofhydration,eliminationofshrinkageandabsorptionoftheheatofhydration.
•Watercuringcanbedoneinthefollowingways:
Immersion
Ponding
SprayingorFogging
Wetcovering
Fresh Concrete

239. •Theprecastconcreteitemsarenormallyimmersedincuringtanksfora
certainduration.
•Pavementslabs,roofslabetc.arecoveredunderwaterbymakingsmall
ponds.
•Verticalretainingwallorplasteredsurfacesorconcretecolumnsetc.are
curedbysprayingwater.
•Insomecases,wetcoveringssuchaswetgunnybags,hessiancloth,
etc.,arewrappedtoverticalsurfaceforkeepingtheconcretewet.
•Forhorizontalsurfacessawdust,earthorsandareusedaswetcovering
tokeeptheconcreteinwetconditionforalongertimesothatthe
concreteisnotundulydriedtopreventhydration.
Fresh Concrete

240. Membrane curing:
It is adopted in the following conditions
•When there is scarcity of water for curing
•When the building is located in remote areas
•When the curing of concrete cannot be properly supervised
•When the workman does not understand the importance of curing
Fresh Concrete

241. •Curinghastobedonetopromotehydrationofconcretebynotallowingthewater
presentintheconcretetogetevaporated.
•Thiscanbedonebyprovidingamembraneorsealantonthesurfaceofconcrete.
•Thisideaofsealingistoobtainacontinuouscovertothetopsurfaceofconcreteby
meansofimperviousfilmtopreventtheescapeofmoisturecontentduetoevaporation
andatthesametimeitisplacedinbetweenthegroundandconcretetoavoidthe
absorptionofmoisturefromtheconcrete.
•Forthispurposebituminouscompoundslikepolyethyleneorpolyester,waterproofing
paperandrubbercompoundsareused.
Fresh Concrete

242. Applicationofheat
•Thedevelopmentofstrengthisafunctionofnotonlytimealsothatoftemperature.
•Whenconcreteissubjectedtohighertemperature,itacceleratesthehydrationprocessresultinginfasterdevelopmentof
strength.
•Concretecannotbesubjectedtodryheattoacceleratethehydrationprocessasthepresenceofmoistureisalsoessential.
•Hencesubjectingtheconcretetohighertemperatureandmaintainingtherequiredmoisturecanbeachievedbystream
curing.
Fresh Concrete

243. Advantagesoffasterattainmentofstrength
•Concretemembercanbehandledveryquickly
•Lessspacewillbesufficientduringcasting
•Asmallcuringtankwillbesufficient
•Thepre-stressingbedcanbereleasedearlyforfurthercasting
Fresh Concrete

244. Theexposureofconcretetohighertemperatureisdonebyfollowingways:
•Steamcuringatordinarypressure
•Steamcuringathigherpressure
•Curingbyinfraredradiation
•Electricalcuring
Fresh Concrete

245. •Steamcuringatordinarypressure
Thismethodofcuringisadoptedforprefabricatedconcreteelements.
Steamcuring@ordinarypressureisappliedonaprefabricatedelementsstoredinachamber.
Thechambershouldbebigenoughtoholdaday’sproduction.
Thedoorofthechamberisclosedandthensteamisapplied.
Thesteammaybeappliedeithercontinuouslyorintermittently.
Anacceleratedhydrationtakesplaceatthishightemperatureandconcreteproductsattainthe28daysstrength
ofnormalconcreteinabout3days.
Fresh Concrete

246. •Steam curing at high pressure
•This is similar to the above method but the only difference is that high pressure and temperature is applied on the
concrete. This process is also called as Autoclaving.
Following are the advantages of this method
•High pressure steam cured concrete develops in one day, or less the strength as much as the 28days strength of
normally cured concrete.
Fresh Concrete

247. •Steam curing at high pressure
•High pressure steam cured concrete exhibits higher resistance to sulphate attack, freezing and thawing action. It also
shows less efflorescence.
•High pressure steam cured concrete exhibits lesser shrinkage and less moisture movement
•Improvement in durability is more for the concrete made with higher water-cement ratio than for concrete made with
low water-cement ratio.
Fresh Concrete

248. •Curing by infrared radiation
This method is practiced in very cold climate region. This system is adopted for curing of hallow concrete blocks.
The normal operative temperature is around 90ºC.
Fresh Concrete

249. •Electriccuring
Thismethodisappliedtoverycoldclimateregions.
Concretecanbecuredelectricallybypassingalternativecurrentthroughtheconcretebetweentheelectrodes
eitherburreidinconcreteorappliedtothesurfaceofconcrete.
Caremustbetakentopreventthemoisturetoevaporateswhichmakestheconcretecompletelydry.
Fresh Concrete

250. •AcceleratedCuring
Byadoptingthismethod,concreteachieveshighearlystrength.
Adoptedforprefabricatedconcreteelements.
Formworkcanberemovedwithin24hrs.
Itreducesthetimeintervalbetweensuccessivecasting
Costsavingbenefits.
Commonlyusedmethodsaresteamcuring,warmwatercuring,boilingwatercuringandautoclavemethod.
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251. •Selfcuringorinternalcuring
TheACI-308Codestatesthat“internalcuringreferstotheprocessbywhichthehydrationofcementoccurs
becauseoftheavailabilityofadditionalinternalwaterthatisnotpartofthemixingWater.”
Conventionally,curingconcretemeanscreatingconditionssuchthatwaterisnotlostfromthesurfacei.e.,
curingistakentohappen‘fromtheoutsidetoinside’.
Incontrast,‘internalcuring’isallowingforcuring‘fromtheinsidetooutside’throughtheinternalreservoirs
(intheformofsaturatedlightweightfineaggregates,superabsorbentpolymers,orsaturatedwoodfibers)
‘Internalcuring’isoftenalsoreferredas‘Self–curing’.
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252. •NeedforSelf–curing
Whenthemineraladmixturesreactcompletelyinablendedcementsystem,theirdemandforcuringwater
(externalorinternal)canbemuchgreaterthanthatinaconventionalordinaryPortlandcementconcrete.
Whenthiswaterisnotreadilyavailable,duetode-percolationofthecapillaryporosity,forexample,significant
autogenousdeformationand(early-age)crackingmayresult.
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253. •PotentialMaterialsforIC
LightweightAggregate(naturalandsynthetic,expandedshale),
LWSSand(Waterabsorption=17%)
LWA19mmCoarse(Waterabsorption=20%)
Super-absorbentPolymers(SAP)(60-300mmsize)
SRA(ShrinkageReducingAdmixture)(propyleneglycoltypei.e.polyethylene-glycol)
Woodpowder
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254. •MiscellaneousMethods:
Calciumchlorideisusedeitherasasurfacecoatingoranadmixture.
Ithasbeenusedsatisfactoryascuringmedium.
Boththesemethodsarebasedonthefactthatcalciumchloridebeingasalt,showsaffinityformoisture.
Thesaltnotonlyabsorbsmoisturefromatmospherebutalsoretainsitatthesurface.
Thismoistureheldatthesurfacepreventsthemixingwaterfromevaporationandtherebykeepstheconcrete
wetforalongtimetopromotehydration.
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255. •MiscellaneousMethods:
Formworkpreventsescapingofmoisturefromtheconcrete,particularlyinthecaseofbeamsandcolumns.
Keepingtheformworkintactandsealingthejointwithwaxoranyothersealingcompoundpreventsthe
evaporationofmoisturefromtheconcrete.
Thisprocedureofpromotinghydrationcanbeconsideredasoneofthemiscellaneousmethodsofcuring.
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256. •Finishing
Finishingoperationisthelastoperationinmakingconcrete.
Finishinginrealsensedoesnotapplytoallconcreteoperations.
Forabeamconcreting,finishingmaynotbeapplicable,whereasfortheconcreteroadpavement,airfield
pavementorfortheflooringofadomesticbuilding,carefulfinishingisofgreatimportance.
Particularly,manytypesofprefabricatedconcretepanelsusedasfloorslaborwallunitaremadeinsuchaway
astogiveveryattractivearchitecturalaffect.
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257. •Finishing
FormworkFinishes
Concreteobeystheshapeofformwork.
Byjudiciouslyassemblingtheformworkeitherinplanesurfaceorinundulatedfashionorhaving,apleasing
surfacefinishcanbegiventoconcrete.
Apre-fabricatedwallunitcastbetweensteelformworkhavingverysmoothsurfaceusingrightproportioningof
materialscangivesuchanicesurfacewhichcanneverbeobtainedbythebestmasons.
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258. •Finishing
Surfacetreatment
Thisisoneofthewidelyusedmethodsforsurfacefinishing.
Theconcretepavementslabisrequiredtobeplanebutroughtoexhibitskidresistance,soistheair-field
pavementsandroadslabs.
Concretehavingbeenbroughttotheplanelevelsurface,israkedlightlyorbroomedortexturedorscratchedto
makethesurfacerough.
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259. •Finishing
Appliedfinish
Thetermappliedfinishisusedtodenotetheapplicationofrenderingtotheexteriorsofconcretestructures.
Theconcretesurfaceiscleanedandroughenedandkeptwetforsufficientlylongtime.
Overthisamortarofproportionofabout1:3isapplied.
Thismortarrenderingcanbegivenbyanyrequiredpleasantfinish,suchascementstipplingeitherfineor
coarse,keying,renderingsetc.
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260. •SpecialSurfaceFinishes
PatternandTextures
ExposedAggregateConcrete
ColoredFinishes
Rough-formfinishes
Smoothoff-the-formfinish
Sand-floatedfinish
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261. •GoodandBadPractices
Concreteisacomplexconstructionmaterialconsistingofdifferentingredients,whichhavedifferentfunctions.
Thepropertiesofconcretedependontheparticularmixtureofconstituents.
Thebasicconstituentsusedtomakeconcretearecement,lime,water,aggregates,andadmixtures.
Yourconcretingworkcanbesuccessfulifitinvolvesagoodplanningandrightpractices.
Mostoftherepairandmaintenanceproblemsmayoccurinthebuildingduetobadpracticesinconcrete
construction.
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262. •Do’s
DohireanexperiencedConcretecontractorforsuccessfulconcretingoperation.
Also,seethatthemain/generalcontractorhiregoodskilledsub/labourcontractorforconcreting.
Seethatconcretingisdoneunderskilledsupervision.Neverleaveittolabouronsite.
AlwayswearsuitablePPE(PersonalProtectiveEquipment)beforecastingconcrete.
Startplacementofconcretewithadequatemanpower,properequipmentandtools.
Alwayschooserightcementfortheparticularjob.
If you have confusion, ask the technical person.
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263. •Do’s
Alwayspourtheconcretewhentheweatherconditionsarefavourable.
Suitablemixdesignshouldbeusedforparticularspecifications(i.e.M25,M30etc.).
Chooserightconcretemixasperspecifications.
Firstmixthedryconcreteuniformlyi.e.cement,coarseaggregates,fineaggregates(eithermanuallyorin
transitmixture)asperpredeterminedquantity(i.e.batchingofconcretematerials).
A good concrete contractor will always mix the dry concrete first.
Add water as per predetermined quantity only.
Always measure the water with measuring container before adding in concrete.
Mix the wet concrete thoroughly for around 2 minutes to get the consistent concrete.
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264. •Do’s
Doslump testbefore placing the concrete.
Concrete must be placed within 15 to 20 minutes of pouring water. If delayed add fresh cement or concern the
consultant.
Do the proper compaction to the concrete with avibratoror wooden tamp to remove air from the concrete.
If compaction is not well, it will create voids/honeycomb in concrete resulting in leakages from the concrete
structure, thereby causing corrosion and also reducing the strength. This also affects the life of the structure.
Pour the concrete throughout in an even thickness.
Always keep on checking the stability of props/ supports of formwork below.
See that the covers insert doesn’t get displaced.
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265. •Do’s
Do proper finishing at joints during concrete construction.
Give attention towards thebleedingin concrete. Water should not evaporate rapidly.
Calculate the number of cement bags concreted per hour. If more than 25 to 30 bags are used per
hour, then mixing time allowed is less and it should not be permitted (For 1 bag mixture machine).
See that no one walks on the concrete surface till the concrete gets hardened.
Do propercuringwhen the concrete has hardened initially.
Start curing after 6 to 10 hours.
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266. •Don'ts
Don’t use damaged formwork. It affects the concrete resulting in the honeycomb.
Don’t use unwashed aggregates in concrete; it may result in a weak concrete and substantial cost of
maintenance.
Don’t start concreting before casting of a concrete cube. The Strength of the concrete should be as
per predetermined mix design.
Don’t go for volumetric batching. Never allow the use of gamellas.
Don’t use high concrete slump, excessively high air content, or excessive fines.
Don’t runconcrete mixermore than two minutes resulting in segregation of concrete constituents.
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267. •Don'ts
Don’t add more water for ease of placement during the making of concrete.
Don’t use semi-dry concrete in pouring. There will be chances of honeycomb inside the concrete.
Don’t drop concrete form greater height as this will causesegregation.
Don’t allow heaping of concrete at one place during pouring.
Don’t vibrate the concrete after the initial setting has taken place. (i.e. after 30 minutes)
Don’t finish the concrete whilebleedingis present on the surface of the concrete.
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268. •Don'ts
Unless must and unavoidable, never do concreting at night.
The lighting arrangements are never adequate at all work places and hence some errors can always
happen somewhere.
Don’t remove formwork until the concrete has gained sufficient strength.
When finishing of the concrete is carried out, never throw or sprinkle the water on to the concrete surface.
Don’t try to finish the dried concrete.
Don’t do concreting if it is raining heavily
Never allow child labouron site. You will land in jail for violence of law.
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269. •EffectofHeatofhydrationincaseofmassconcretingworks
Mass concrete is defined by ACI “Any volume of concrete with dimensions large enough to require that measures be taken
to cope with generation of heat from hydration of the cement and attendant volume change to minimize cracking.
Mass concrete is defined by some agencies as “any concrete element having a least dimension greater than 3 ft(0.9 m).
Examples:
Dam
RaftFoundation
PileCap.
ThickWall.
Thickcolumn.
DeepSlap.
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270. Fresh Concrete
Cement Composition “Type I -OPC”

271. Fresh Concrete
Main Chemical Cement Reactions with Water

272. Fresh Concrete
HOH generated from cement main ingredients

273. Fresh Concrete
% of HOH generated from cement main ingredients

274. Whyistemperaturecontrolnecessary?
•Concreteisthermallyverypoorconductor.
•Heattransfer(heatofhydration)resultsinunequalthermalexpansion
•Tensilestressatthefreesurfaceduetoexpansionofcoreexceedsthetensilestrength
•Thensurfacecrackingwilldevelop
•Temp.differencebetweeninterior&outersurfaceofmorethan20
0
Ccausecracks.
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275. Cracksmaycause
•Cracksgeneratedduetothermalgradientsmaycause
•lossofstructuralintegrity
•lossinmonolithicaction
•excessiveshrinkage
•lossindurability
•aestheticallyobjectionable
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276. Methodsoftemperaturecontrol
•Methodsofcontrollingmassconcretetemperaturesrangefromrelativelysimpletocomplex,andfrominexpensiveto
costly.
•Dependingonaparticularsituation,itmaybeadvantageoustouseoneormoremethodsoveranother.
•Low-heatmaterial-GGBFS,Flyash,Silicafume,largesizeaggregates
•Precoolingofconcrete–Usechilledmixwater,Liquidnitrogen
•Post-coolingofconcrete
•Surfaceinsulation–Insulatingformwork
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