properties of fresh concrete presentation

7/25/2019 Properties of Fresh Concrete Presentation

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FRESH CONCRETE

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Properties OF Fresh

ConcreteIntroductionThe potential strength and durability of concrete of agiven i! proportion is very dependent on the degree ofits copaction"

#t is vital$ therefore$ that the consistency of the i! be

such that the concrete can be transported$ placed$ and%nished su&ciently early enough to attain the e!pectedstrength and durability"

Signifcance

The %rst '( hours are very iportant for theperforance of the concrete structure"

#t controls the long)ter behavior$ in*uence f+c ,ultiate

strength-$ Ec ,elastic odulus-$ creep$ and durability" .


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/ain Prop" OF Fresh Concrete

Consistency

Slup Test Flo0 Test PenetrationTest

or2ability

CopactingFactor Test

3e4e TieTest

Segregation

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4leeding

4leedingater Test

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Concrete or2ability

DefnitionThe property of fresh concrete 0hich is indicated by the

aount of useful internal 0or2 re6uired to fully copact theconcrete 0ithout bleeding or segregation in the %nishedproduct"

Workabilityis one of the physical paraeters of concrete0hich a7ects the strength and durabilityas 0ell as the costof labor and appearance of the %nished product

Concrete is said to be workable when it is easilyplaced and compacted homogeneously i.e withoutbleeding or Segregation" 8n0or2able concrete needsore 0or2 or e7ort to be copacted in place$ alsohoneycobs 9:or poc2ets ay also be visible in %nished

concrete" '


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Concrete or2ability

Factors aecting workabilityater content in the concrete i!

;ount of ceent 9 its Properties

;ggregate istribution-

Nature of ;ggregate Particles ,Shape$ SurfaceTe!ture$ Porosity etc"-

Teperature of the concrete i!

Huidity of the environent

/ode of copaction

/ethod of placeent of concrete

/ethod of transission of concrete ?


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Concrete or2ability

How o impro!e the workability o"concreteincrease 0ater:ceent ratio

increase si=e of aggregate

use 0ell)rounded and sooth aggregate instead ofirregular shape

increase the i!ing tie

increase the i!ing teperature

use non)porous and saturated aggregate0ith addition of air)entraining i!tures

;n on site siple test for deterining 0or2ability is theS@8/P TEST"

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Factors

/i! ProportionsB;ggregate :Ceent ratio is an iportant

factor"

High aggregate :ceent ratio ) @eanConcrete

Here 6uantity of ceent paste is less forproviding lubrication and obility of aggregate isrestrained"

@o0er aggregate :ceent ratio RichConcrete

Here 6uantity of ceent paste is ore to a2ei! fatty and better 0or2ability"

Si=e of aggregateB D


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Shape of ;ggregateB;ngular$ elongated and *a2yaggregate a2es

concrete harsh copared to rounded aggregate"

Surface Te!tureBRough te!tured aggregate 0ill sho0 poor

0or2ability"


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/easureent of 0or2ability

Slup Test

Copacting Factor test

Flo0 Test elly 4all Test

3ee 4ee Consistoeter Test


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Slup Test

Defnition

; slup test is a ethod used to deterine the consistencyof concrete" The consistency$ or sti7ness$ indicates ho0uch 0ater has been used in the i!" The sti7ness of theconcrete i! should be atched to the re6uireents for the%nished product 6uality

Slup is a easureent of concreteGs 0or2ability$ or*uidity"

#tGs an indirect easureent of concrete consistency orsti7ness"

#rinciple

The slup test result is a easure of the behavior of acopacted inverted cone of concrete under the action ofgravity" #t easures the consistency or the 0etness ofconcrete"

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Slup Test

$pparatusSlup cone B frustu of a cone$ 5 ,1.in- of height" The base is . ,(in- indiaeter and it has a saller opening at thetop of 1

Scale for easureent$

Teping rod,steel- 1? diaeter$ Aclength"

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Slup Test

ypes %" Slump

The sluped concrete ta2es various shapes$and according to the pro%le of sluped concrete$

the slup is tered asICollapse Slup

Shear Slup

True Slup

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Slup TestDegree o"

workability Slump &mm'

Compacting

Factor

(se "or which

concrete is suitable

3ery lo0 ) .? "D(3ery dry i!esI used in roada2ing" Roads vibrated bypo0er operated achines

@o0 .? ) ? "(?

@o0 0or2ability i!esI used

for foundations 0ith lightreinforceent" Roadsvibrated by hand operated/achines

/ediu ? ) 1 ".

/ediu 0or2ability i!esIanually copacted *atslabs using crushedaggregates" Noralreinforced concrete anually

copacted and heavilyreinforced sections 0ithvibrations

High 1 ) 1D? "?

High 0or2ability concreteIfor sections 0ith congestedreinforceent" Notnorally suitable forvibration

JTable B or2ability$ Slup and Copacting Factor of concrete 0ith 1 or 5( ,5:' or 1 1:.

in- a!iu si=e of

aggregate" 15


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Copacting Factor Test

$pparatusTro0els

Hand Scoop ,1?". c long-

Rod of steel or other suitable aterial,1"A c diaeter$ A1 c long rounded

at one end -"

4alance"

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Copacting Factor Test

or2ability Slup ,- C"F 8ses

3ery @o0 ) .? "D( Roads ) Paveents

@o0 .? ) ? "(?Foundations

Concrete

/ediu .? ) 1 ". Reinforced Concrete

High 1 ) 1D? "?Reinforced Concrete

,HighReinforceent-

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Flo0 Table TestDefnition

The )ow table testor )ow testis a ethod todeterine the consistence of fresh concrete"

;pplication hen fresh concrete is delivered toa site by a truc2 i!er it is soeties

necessary to chec2 its consistence beforepouring it into for0or2"

#f the consistence is not correct$ the concrete0ill not have the desired 6ualities once it has

set$ particularly the desired strength" #f theconcrete is too pasty$ it ay result in cavities0ithin the concrete0hich leads to corrosion ofthe rebar$ eventually leading to the foration of

crac2s ,as the rebar e!pands as it corrodes-0hich 0ill accelerate the 0hole process$ rather1A


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Flo0 Table Test

*+uipment

Flo0 table 0ith a grip and a hinge$ D c ! Dc"

;bras cone$ open at the top and at thebotto ) 5 c high$ 1D c top diaeter$ .?

c base diaeterater buc2et and broo for 0etting the *o0

table"

Taping rod$ A c height

Scale for easureent

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Flo0 Table Test

ConductingThe *o0 table is 0etted"

The cone is placed on the *o0 table and %lled

0ith fresh concrete in t0o layers$ each layer .?ties tap 0ith taping rod"

The cone is lifted$ allo0ing the concrete to *o0"

The *o0 table is then lifted up several

centieters and then dropped$ causing theconcrete *o0 a little bit further"

;fter this the diaeter of the concrete iseasured in a A di7erent direction and ta2e theaverage"

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Flo0 Table Test

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Flo0 Table Test

Percent ofFlo0

. L . A L A 1 L1 1.

L1. 1?

L

Consistenc

y >ry Sti7 Plastic et Sloppy

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4all Penetration Test ,elly 4all-

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Defnition

;nother ethod used in the %eld andlaboratory to easure the consistency ofconcrete is the ball penetration test ,;ST/ C5A-0hich is also 2no0n as the ,elly ball testM"

#rocedure

#t is perfored by easuring the penetration$in inches$ of a A)in" diaeter steel cylinder 0itha hei spherically shaped botto $ 0eighing15"A2g ,5 lbs-"

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;dvantagesB

One of the advantages of the ball penetration

test can be perfored on the concrete in ahopper$ buggy$ 0heelbarro0$ or other suitablecontainer"

;nother advantage of this ethod is its

siplicity and the rapidity 0ith 0hich theconsistency of the concrete can be deterined"

#t is also not dependent on a procedure of %llingand rodding a container li2e the slup test"

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3e4e Consistoeter Test

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3ee)4ee Consistoeter TestDefnition

#t is based on easuring the tie ,Called 3EE)4EE tie-needed to transfer the shape of a concrete i! fro afrustu cone to a cylinder ,these shapes are standardi=ed bythe apparatus of this test-$ by vibrating and copacting thei!" The ore 3E4E tie needed the less 0or2able the i!is" This ethod is very useful for sti7 i!es"

$pparatusCylindrical container 0ith diaeter .' $ and height

.

/oldB the sae old used in the slup test"

>isc B ; transparent hori=ontal disc attached to a rod 0hichslides vertically

3ibrating Table B 5(M.A $ supported by four rubbershoc2 absorbers

Taping Rod

Stop 0atch .?

3 4 C i t t T t


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3ee)4ee Consistoeter Test#rocedure

1- Slup test as described earlier is perfored$placing the slup cone inside the sheet etalcylindrical pot of the consist eter"

.- The glass disc attached to the s0ivel ar is turnand place on the top of the concrete in the pot"

5- The electrical vibrator is then s0itched on andsiultaneously a stop 0atch started"

'- The vibration is continued till such tie as theconical shape of the concrete disappears and theconcrete assue a cylindrical shape"

?- This can be udge by observing the glass disc frothe top disappearance of transparency"

A- #ediately 0hen the concrete fully assue acylindrical shape$ the stop 0atch is s0itched o7"

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3ee)4ee Consistoeter Test

D- The tie re6uired for the shape of concrete tochange fro slup cone shape to cylindricalshape in second is 2no0n as 3ibe >egree"

(- This ethod is very suitable for very dry

concrete 0hose slup value cannot beeasure by slup test$ but the vibration is toovigorous for concrete 0ith slup greater thanabout ?"

The test failsif 3ee)4ee Tie is less than ?seconds "" ;nd the test ust be created 0hen nocollapse or shears slup in concrete

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Concrete Segregation

DefnitionSegregation can be de%ned as separation of

constituent aterials of concrete"

Segregation is 0hen the coarse and %ne aggregate$and ceent paste$ become separated"

Segregation ay happen 0hen the concrete isi!ed$ transported$ placed or copacted

Segregation a2es the concreteE;ER$

@ESS >8R;4@E$

and 0ill leave ; POOR S8RF;CE F#N#SH QM

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Concrete Segregation-asic types o" segregation

Coarse segregationB Occurs 0hen gradation is shiftedto include too uch coarse aggregate and not enough %neaggregate" Coarse segregation is characteri=ed by lo0asphalt content$ lo0 density$ high air voids$ rough surfacete!ture$ and accelerated rutting and fatigue failure,illias et" al"$ 1Ab-" Typically$ coarse segregation is

considered the ost prevalent and daaging type ofsegregationI thus segregation research has typicallyfocused on coarse segregation" The ter segregationby itself is usually ta2en to ean coarse segregation"

Fine segregationB Occurs 0hen gradation is shifted to

include too uch %ne aggregate and not enough courseaggregate" High asphalt content$ lo0 density$ soothsurface te!ture$ accelerated rutting$ and better fatigueperforance characteri=e %ne segregation ,illias$>uncan and hite$ 1A-"

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Concrete Segregation


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Concrete Segregationo $!oid SegregationChec2 the concrete is not +too 0et+ or +too dry+"

/a2e sure the concrete is properly i!ed" #t isiportant that the concrete is i!ed at thecorrect speed in a transit i!er for at least t0oinutes iediately prior to discharge"

The concrete should be placed as soon aspossible"

hen transporting the i!$ load carefully"

;l0ays pour ne0 concrete into the face of

concrete already in place"hen copacting 0ith a po2er vibrator be sure

to use it carefully

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Concrete Segregationo $!oid Segregation

#f placing concrete straight fro a truc2$ pourvertically and never let the concrete fall orethan one)and)a)half eters"

3ibration should be done coparatively for dry

i! " E!cessive vibration leads to segregationof concrete" Hence should be done foroptiu period only"

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Concrete 4leeding

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Concrete 4leeding

IntroductionThis refers to the appearance of 0ater along 0ithceent particles on the surface of the freshly laidconcrete" This happens 0hen there is e!cessive6uantity of 0ater in the i! or due to e!cessive

copaction" 4leeding causes the foration of poresand renders the concrete 0ea2" 4leeding can beavoided by suitably controlling the 6uantity of 0ater inthe concrete and using %ner grading of aggregates"

; thorough 2no0ledge of 0hy concrete bleeds and ho0i! proportions a7ect it$ is re6uired to preventing theharful e7ects of bleeding" ;doption of right %nishingethods also helps to ensure that the bleedingprobles 0on+t ruin a slab surface"

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Concrete 4leeding-leeding #rocess

;lost all freshly placed concrete bleeds" ;s aggregate and ceent

particles settle$ they force e!cess i!ing 0ater up0ard" Theprocess continues until settleent stops$ either because of solidsbridging or because the concrete has set"

The total aount of bleeding or settleent depends on i!properties$ priarily 0ater content and aount of %nes ,ceent$ *yash$ %ne sand-" #ncreasing 0ater content increases bleeding$ and

increasing the aount of %nes reduces bleeding" ;ount ofbleeding is also proportional to the depth of concrete placed" /orebleed 0ater rises in deep sections than in thin ones"

4leeding usually occurs gradually by unifor seepage over the0hole surface$ but soeties vertical channels for" ater *o0sfast enough in these channels to carry %ne particles of ceent andsand$ leaving 0orholes in the interior or sand strea2s at thefor face" Channels are ore li2ely to for 0hen concrete bleedse!cessively"

Channels that reach the surface are open paths for deicingsolutions to penetrate the concrete" This leads to free=ing and

tha0ing daage and rebar corrosion" 5'


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Concrete 4leeding

*ects %" *cessi!e bleeding in Deep Section

Soeties bleed 0ater can+t entirely evaporatebecause it has been trapped near the top surfaceby setting" This raises the 0ater)ceent ratio$increases pereability$ and lo0ers strength"

E!cessive bleeding also causes soe otherprobles in deep sectionsB bond loss at aggregateand rebar surfacesI and unsightly sand strea2s"

-leeding #roblems in Flatwork

Never *oat or tro0el concrete 0hile there+s bleed0ater on the surface" That+s the cardinal rule of%nishing" Finishing before bleed0ater hasevaporated can cause dusting$ cra=e crac2ing$

scaling$ and lo0 0ear resistance" or2ing bleed)5?

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Concrete 4leeding

How to control bleedingE!cessive bleeding can be avoided" >on+t add

too uch 0ater to the concrete" /ost of the0ater added to a2e placing easier bleeds out of

the concrete" ;ny tie saved during placeent0ill be lost 0hile 0aiting for the bleed0ater toevaporate" Place concrete at the lo0est possibleslup" #f you need a higher slup to speed

placeent$ consider using a super plastici=er";dd additional concrete %nes to reduce bleeding

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Concrete 4leeding


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Concrete 4leeding

The %nes ay coe fro a nuber of sourcesB8se a ore %nely ground ceent" Concretes ade 0ith

high early strength ,Type ###- ceent bleed less becausethe ceent is ground %ner than noral ,Type #- ceent"

8se ore ceent" ;t the sae 0ater content$ rich i!esbleed less than lean i!es"

8se *y ash or other po==olansin the concrete"

#f concrete sands don+t have uch aterial passing theNo" ? and 1 sieves$ blend in a %ne blo0 sand at thebatch plant"

For air) entrained concrete$ use the a!iu allo0ableaount of entrained air" Consider using an air) entrainingagent 0henever e!cessive bleeding is a proble"Entrained air bubbles act as additional %nes" ;irentrainent also lo0ers the aount of 0ater needed to

reach a desired slup" 5D


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Than2 Uou

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properties of fresh concrete presentation

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