construction practises
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1DEPARTMENT OF CIVIL ENGINEERING, IIT DELHI
CEL 774 CONSTRUCTION PRACTISES
Concrete: Production(Compaction )
B. Bhattacharjee
CIVIL ENGINEERING DEPARTMENT
IIT DELHI
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Compaction by vibrationCompaction by vibration
B. Bhattacharjee
DEPARTMENT OF CIVIL ENGINEERING, IIT DELHI
Placed concrete contains air voids (30%) .Placed concrete contains air voids (30%) .
Seldom confirms intimately to the shape ofSeldom confirms intimately to the shape ofthe form.the form.
Compaction is required to drive entrappedCompaction is required to drive entrappedair outair out to densify concrete.to densify concrete. Increase homogeneity and uniformity areIncrease homogeneity and uniformity are
the other benefits.the other benefits. This compaction is achieved throughThis compaction is achieved through
vibration.vibration. Self compacting concrete does not needSelf compacting concrete does not need
vibration.vibration.
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Concrete vibrationConcrete vibration
B. Bhattacharjee
DEPARTMENT OF CIVIL ENGINEERING, IIT DELHI
Energy for compaction is supplied throughEnergy for compaction is supplied throughoscillatory motion of vibration (nearly SHM).oscillatory motion of vibration (nearly SHM).
Vibration is usually generated by means ofVibration is usually generated by means ofrotating eccentric having a frequency androtating eccentric having a frequency andamplitude of vibrationamplitude of vibration ..
Although the frequency can be easily Although the frequency can be easilymeasured in air, it is difficult to measuremeasured in air, it is difficult to measurewithin concrete although that is morewithin concrete although that is morerelevant..relevant..
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Types of VibratorsTypes of Vibrators
B. Bhattacharjee
DEPARTMENT OF CIVIL ENGINEERING, IIT DELHI
Internal vibrators.Internal vibrators. Flexible shaft type. Electric motor in hand type. Air vibrators.
Form vibratorsForm vibrators .. Vibrating table.Vibrating table. Surface vibrators.Surface vibrators.
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Types of VibratorsTypes of Vibrators
B. Bhattacharjee
DEPARTMENT OF CIVIL ENGINEERING, IIT DELHI
Immersion/
Submersible/Poker/ spudtype
Flexible shaftVibrator &
Motor in head
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Types of VibratorsTypes of Vibrators
B. Bhattacharjee
DEPARTMENT OF CIVIL ENGINEERING, IIT DELHI
Air Vibrator
1. Casing2. Plunger
3. Distribution box
Compressed air
Moves the plunger To one or other side25mm to 150mm
diameter
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Types of VibratorsTypes of Vibrators
B. Bhattacharjee
DEPARTMENT OF CIVIL ENGINEERING, IIT DELHI
Flexible shaft type most common (fig a &b)Flexible shaft type most common (fig a &b)ranges from a diameter of 20 to 180 mm.ranges from a diameter of 20 to 180 mm.
Vibration is usually generated by means ofVibration is usually generated by means ofrotating eccentric having a frequency androtating eccentric having a frequency andamplitude of vibrationamplitude of vibration ..
Although the frequency can be easily Although the frequency can be easilymeasured in air, it is difficult to measuremeasured in air, it is difficult to measurewithin concrete although that is morewithin concrete although that is morerelevant. (given in table).relevant. (given in table).
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Immersion VibratorsImmersion Vibrators
B. Bhattacharjee
DEPARTMENT OF CIVIL ENGINEERING, IIT DELHI
P is plastic concrete, M is Mass concrete, T isthin member, C stands for congested, S standsfor slump, St stands for structure & O stands foropen forms
[ ])R R (5.02
112
12eR R aa
=
a 2 is the amplitude of vibration at a distance R 2From center line of vibrator. is coeff. Of damping
a 1 is the amplitude of vibration at the surfaceof the vibrator having a radius equal to R 1
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Immersion VibratorsImmersion Vibrators
B. Bhattacharjee
DEPARTMENT OF CIVIL ENGINEERING, IIT DELHI
Head dia(mm) Reco f (kcyl/min) Average Amp (mm) Radi actn.(cm) Comp.rate cm./h Applic-n
20-40 10-15 0.4-0.8 8-15 0.8-4 P, t, C
30-60 9-13.5 0.5-1.0 13-25 2.3-8 P, wall,col, beam
50-90 8-12 0.6-1.3 18-36 4.6-15 S
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Form VibratorsForm Vibrators
B. Bhattacharjee
DEPARTMENT OF CIVIL ENGINEERING, IIT DELHI
Form vibrator are external vibrators,Form vibrator are external vibrators,transmits impulses both in plane andtransmits impulses both in plane andperpendicular to the form.perpendicular to the form.
Form is vibrated and the vibration isForm is vibrated and the vibration istransmitted from the form to concretetransmitted from the form to concrete ..
Acceleration is 1g Acceleration is 1g --3g for adequate3g for adequateamplitude.amplitude.
Both rotary and reciprocating types areBoth rotary and reciprocating types areused and can either be electricallyused and can either be electrically(3000(3000 --6000rpm)6000rpm) pneumatically (6000pneumatically (6000 --12000 cycle/min) driven12000 cycle/min) driven
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Form VibratorsForm Vibrators
B. Bhattacharjee
DEPARTMENT OF CIVIL ENGINEERING, IIT DELHI
Reciprocating type accelerates in aReciprocating type accelerates in agiven direction and imparts impactgiven direction and imparts impactcausing vibration.causing vibration.
Reciprocating vibrators are usuallyReciprocating vibrators are usuallypneumatically driven.pneumatically driven.
Frequencies are in the range of 1000Frequencies are in the range of 1000 --5000 cycles/minute.5000 cycles/minute.
The impulses are mostly perpendicularThe impulses are mostly perpendicularto the formto the form
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VibratorsVibrators
B. Bhattacharjee
DEPARTMENT OF CIVIL ENGINEERING, IIT DELHI
Vibrating table are usually used forVibrating table are usually used forprepre --cast elements, frequency
0.12mm.0.12mm. Surface vibrators exerts their effects atSurface vibrators exerts their effects at
top surface and include:top surface and include:
Vibrating screed, pan type vibrator,Vibrating screed, pan type vibrator,Vibrating roller screed, vibrating plateVibrating roller screed, vibrating plateand vibratory roller for pavementand vibratory roller for pavementconcrete.concrete.
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VibratorsVibrators
B. Bhattacharjee
DEPARTMENT OF CIVIL ENGINEERING, IIT DELHI
Form vibrators are used where it isForm vibrators are used where it isimpractical to use internal vibrators.impractical to use internal vibrators.
Vibrating screed are used in thin slabs.Vibrating screed are used in thin slabs.
High frequency and low amplitudeHigh frequency and low amplitudevibrations generally results in morevibrations generally results in more
efficient compaction .efficient compaction .
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Fresh concrete under VibrationFresh concrete under Vibration
B. Bhattacharjee
DEPARTMENT OF CIVIL ENGINEERING, IIT DELHI
Prior to compaction concrete is a massPrior to compaction concrete is a massof separate particles coated withof separate particles coated withmortar held in a pile by arching actionmortar held in a pile by arching action
of coarser particle.of coarser particle. The arching is result of frictionThe arching is result of friction
between aggregate particles, surfacebetween aggregate particles, surface
tension & cohesive forces of thetension & cohesive forces of thecement paste.cement paste.
The voids caused by arching are filledThe voids caused by arching are filledwith air up to about 30%.with air up to about 30%.
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Fresh concrete under VibrationFresh concrete under Vibration
B. Bhattacharjee
DEPARTMENT OF CIVIL ENGINEERING, IIT DELHI
Vibratory impulse liquefy the mortarVibratory impulse liquefy the mortarportion of concrete and thus reduceportion of concrete and thus reducethe internal friction resulting inthe internal friction resulting in
consolidation by force of gravity . Inconsolidation by force of gravity . Invibrated concrete friction isvibrated concrete friction isreestablished cohesion is restored andreestablished cohesion is restored and
strength increases.strength increases. The velocity of compression wavesThe velocity of compression waves
generated is 45m/sec in the beginninggenerated is 45m/sec in the beginning
of vibration and increases to240 m/secof vibration and increases to240 m/secat the end.at the end.
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Fresh concrete under VibrationFresh concrete under Vibration
B. Bhattacharjee
DEPARTMENT OF CIVIL ENGINEERING, IIT DELHI
For 200 Hz these velocities correspondFor 200 Hz these velocities correspondto 0.2 m and 1.2 m wavelength.to 0.2 m and 1.2 m wavelength.
The waves moves water more than theThe waves moves water more than thesolids and generates hydraulicsolids and generates hydraulicpressure within interstitial water filledpressure within interstitial water filled
space .space . The pressure is maximum in mostThe pressure is maximum in most
constricted space and causes reducedconstricted space and causes reducedinternal friction giving the pasteinternal friction giving the pastetemporary fluidity.temporary fluidity.
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Fresh concrete under VibrationFresh concrete under Vibration
B. Bhattacharjee
DEPARTMENT OF CIVIL ENGINEERING, IIT DELHI
Process of liquefaction is easilyProcess of liquefaction is easilyunderstood through box shear test results.understood through box shear test results.
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Fresh concrete under VibrationFresh concrete under Vibration
B. Bhattacharjee
DEPARTMENT OF CIVIL ENGINEERING, IIT DELHI
Shear Stress-strain relationship during vibration
F h d Vib iF h d Vib i
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Fresh concrete under VibrationFresh concrete under Vibration
B. Bhattacharjee
DEPARTMENT OF CIVIL ENGINEERING, IIT DELHI
y
Normal stress
S h e a r
S t r e
n g
t h
y
D represent a called agitation pressure
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Fresh concrete under VibrationFresh concrete under Vibration
B. Bhattacharjee
DEPARTMENT OF CIVIL ENGINEERING, IIT DELHI
Consolidation of concrete takes place in twoConsolidation of concrete takes place in twostages.stages.
In the first stage vertical settlement of coarseIn the first stage vertical settlement of coarseaggregate takes place in a manner similar toaggregate takes place in a manner similar topacking of granular material and shape ofpacking of granular material and shape ofthe aggregate plays a major role, air voids upthe aggregate plays a major role, air voids upto 5% remains after this stage.to 5% remains after this stage.
In the second stage concrete behaves likeIn the second stage concrete behaves likedense liquid and air voids are removed fromdense liquid and air voids are removed fromthe surface forcing mortar to appear at thethe surface forcing mortar to appear at thesurface .surface .
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Measurement of compactionMeasurement of compaction
B. Bhattacharjee
DEPARTMENT OF CIVIL ENGINEERING, IIT DELHI
Unit weight can be a measure of compactionVarious density gauges can be used
Time of vibration
U n
i t w e i g
h t
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Measurement of compactionMeasurement of compaction
B. Bhattacharjee
DEPARTMENT OF CIVIL ENGINEERING, IIT DELHI
Settlementh=h f +(h 0-h f ) e -b( a /g)ty
Is angular frequencyb experimental factor a amplitude
g acceleration due to gravityy depends on mix consistency
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Execution of vibrationExecution of vibration
B. Bhattacharjee
DEPARTMENT OF CIVIL ENGINEERING, IIT DELHI
Vibration shall be completed when is in dormantperiod; penetration resistance 35 kg/sq.cm
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26B. Bhattacharjee
DEPARTMENT OF CIVIL ENGINEERING, IIT DELHI
Dos & DonDos & Don tstsin concretein concretevibrationvibration
Concrete shallConcrete shallnot be movednot be movedusing internalusing internal
Vibrator, resultsVibrator, resultsIn segregationIn segregation
Execution of VibrationExecution of Vibration
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Execution of VibrationExecution of Vibration
B. Bhattacharjee
DEPARTMENT OF CIVIL ENGINEERING, IIT DELHI
Penetrate vertically to sufficiently embed inPenetrate vertically to sufficiently embed inconcrete, held stationary and removedconcrete, held stationary and removedslowly (7.5 cm/sec) .slowly (7.5 cm/sec) .
At regular spacing to ensure compaction of At regular spacing to ensure compaction ofall portions if required with adequateall portions if required with adequateoverlap.overlap.
A minimum of 10 A minimum of 10 secssecs is necessary foris necessary forcomplete compaction . Vibration time neededcomplete compaction . Vibration time neededis given by:is given by:
( )( )f 0f
2 hhhhln
ay bgt =
EQUATIONS FOR TIME NEEDED FOR VIBRATIONEQUATIONS FOR TIME NEEDED FOR VIBRATION
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28B. Bhattacharjee
DEPARTMENT OF CIVIL ENGINEERING, IIT DELHI
EQUATIONS FOR TIME NEEDED FOR VIBRATIONEQUATIONS FOR TIME NEEDED FOR VIBRATION
t =total needed vibration time (s) for V liters concrete = diameter of the needle vibrator in mm. S= Slump of the concrete in cm A = Coefficient representing shape of aggregate. For
rounded aggregate A=1 for crushed aggregate A=5 F=Coefficient representing denseness of steel; F=1.5
for very dense and F= 1 for no reinforcement
VFA5S
10025t ++= For V < 25 liters
For V > 25 liters
( )5.2V1.0FA5S10025
t +
++=
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Vibrator SpacingVibrator Spacing
B. Bhattacharjee
DEPARTMENT OF CIVIL ENGINEERING, IIT DELHI
Cover All locations within the member
D is spacing R radius of
action E is sectionthickness
VibrationVibration
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30B. Bhattacharjee
DEPARTMENT OF CIVIL ENGINEERING, IIT DELHI
VibrationVibration
1
2
ttsuR 7200q
+=
q = volume of compacted concrete cu.m/hr u= utilization factor. R= radius of action
s= thickness of the layer in m t= time of vibration in one place t1= time of moving the vibrator from one place to
another
Execution of VibrationExecution of Vibration
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Execution of VibrationExecution of Vibration
B. Bhattacharjee
DEPARTMENT OF CIVIL ENGINEERING, IIT DELHI
For form vibrators fastening with the form isFor form vibrators fastening with the form isimportant, vibration time is 2 minutes to 30important, vibration time is 2 minutes to 30minutes depending upon concrete andminutes depending upon concrete andvibrator .vibrator .
Vibrating screed need s two passes.Vibrating screed need s two passes.
Degree of vibration achieved by surfaceDegree of vibration achieved by surface
vibrator is shown in fig.vibrator is shown in fig.
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Execution of VibrationExecution of Vibration
B. Bhattacharjee
DEPARTMENT OF CIVIL ENGINEERING, IIT DELHI
Imperfection in VibratorsImperfection in Vibrators
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pe ect o V b ato sp
B. Bhattacharjee
DEPARTMENT OF CIVIL ENGINEERING, IIT DELHI
Name Descript-ion
Design Form &Cond
Concrete& Place
Compact-ion
Honecom-b
Stony, Airvoids
Narrowsection
Grout losstemp
Free falllow slump
Poorvibration
Blow/ bugholes
Smallholes
Excessform oil
Lean, lowslump
Inadequate
Subsidenc
e cracking
Short
cracks
Plastic
settlement
High
water c
In-
adequateFormoffset
Irregularsurface
Weakform
Nonuniform D
ColdJoints
discontinuity
Poorplanning
Delayedplacing
Inadequate lower L
Special VibrationSpecial Vibration
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Special VibrationSpecial Vibration
B. Bhattacharjee
DEPARTMENT OF CIVIL ENGINEERING, IIT DELHI
ReRe --vibration can be done as long as thevibration can be done as long as therunning internal vibrator sink in the concreterunning internal vibrator sink in the concreteby its own weight. This corresponds to aby its own weight. This corresponds to a
penetration resistance of 3.5 MPa. Canpenetration resistance of 3.5 MPa. Canincrease strength, bond, impermeability,increase strength, bond, impermeability,reduced shrinkage and creep.reduced shrinkage and creep.
-- Vacuum Vibration is accomplished byVacuum Vibration is accomplished byapplying vacuum to surface of freshapplying vacuum to surface of freshconcrete. Cement paste is densified byconcrete. Cement paste is densified by
removal of air from the surface and waterremoval of air from the surface and waterfrom certain depth.from certain depth.
Special VibrationsSpecial Vibrations
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Special VibrationsSpecial Vibrations
B. Bhattacharjee
DEPARTMENT OF CIVIL ENGINEERING, IIT DELHI
Vacuum Vibration allows placing of concrete withVacuum Vibration allows placing of concrete with
higher water content by extracting extra water. Thushigher water content by extracting extra water. Thusan enhancement in strength is observed. Commonlyan enhancement in strength is observed. Commonlyused for slabs, walls etc. Vacuum between 30used for slabs, walls etc. Vacuum between 30 --50 cm50 cm
of Mercury is applied by means of special for liners orof Mercury is applied by means of special for liners ormat. Shall be applied as early as possible. Penetrationmat. Shall be applied as early as possible. Penetrationof vacuum is up to 30 cm. Is less efficient in airof vacuum is up to 30 cm. Is less efficient in airentrained concrete.entrained concrete.
Fresh mix subjected to high frequency vibrationFresh mix subjected to high frequency vibration>100Hz u>100Hz u \\is calledis called vibrovibro --activation increases theactivation increases the
strength by intensifying hydration, generally does notstrength by intensifying hydration, generally does nothave any thing to do with compactionhave any thing to do with compaction
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36DEPARTMENT OF CIVIL ENGINEERING, IIT DELHI
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