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

    THANK YOU FORHEARING