Download - Concrete Compaction

CONCRETECONCRETE : : COMPACTIONCOMPACTION

BY

RAJESH JINDAL

15 Sep 2013

CTM : 2013

References

MS Shetty - Concrete Technology

Neville & Brookes - Concrete Technology

IS 456

www.concrete.org

Guide for consolidation of concrete : ACI

Committee Report 2006

GEN OUTLINEGEN OUTLINE

What is CompactionWhat is Compaction

Why is it requiredWhy is it required

Compacting EffortsCompacting EffortsManualManual

MechanicalMechanical

Certain Do’s & Don’tsCertain Do’s & Don’ts

Compaction of ConcreteCompaction of ConcreteWhat is CompactionWhat is Compaction

Process adopted for expelling Process adopted for expelling

the entrapped air to achieve the entrapped air to achieve

dense massdense massConstituent Entrapped Air

Before

Compaction

After

Compaction

Aggregates 60-75% 60-75%

Cement 25-40% 25-40%

Air 25-30% 1-2%

Compaction of ConcreteCompaction of ConcreteWhy is Compaction Why is Compaction

requiredrequired

To drive out entrapped air to densify fresh concrete During Mixing, Transportation & Placing – air During Mixing, Transportation & Placing – air

gets entrappedgets entrapped Quantity of air entrapped inversely proportional Quantity of air entrapped inversely proportional

to workabilityto workability Entrapped air adversely affects quality & Entrapped air adversely affects quality &

strengthstrength

To make fresh concrete conform intimately to shape of form

Increased homogeneity & uniformity

Why is Compaction Required

Compaction of ConcreteCompaction of ConcreteAdverse Effects of Entrapped AirAdverse Effects of Entrapped Air

Low Strength & DurabilityLow Strength & Durability Low resistance to abrasionLow resistance to abrasion Poor bonding with reinforcement Poor bonding with reinforcement

and low bond strengthand low bond strength High PorosityHigh Porosity

Resulting in easy ingress of moisture, Resulting in easy ingress of moisture,

chemicalschemicals Weakening of Concrete & Weakening of Concrete &

reinforcementreinforcement

CONSOLIDATING CONSOLIDATING CONCRETECONCRETE

Inadequate Inadequate consolidation can result consolidation can result in:in: HoneycombHoneycomb Excessive amount of Excessive amount of

entrapped air voids (bug-entrapped air voids (bug-holes)holes)

Sand streaksSand streaks Placement linesPlacement lines ( (Cold Cold

jointsjoints))

Consolidating ConcreteConsolidating ConcreteImproper Compaction

STRENGTH OF STRENGTH OF CONCRETECONCRETE

The strength of a concrete specimen The strength of a concrete specimen prepared, cured and tested under prepared, cured and tested under specified conditions at a given specified conditions at a given age depends on:age depends on: w/c ratiow/c ratio Degree of Degree of

compactioncompaction

Compaction of ConcreteCompaction of ConcreteHow to Achieve Full How to Achieve Full

CompactionCompaction

Adequate WorkabilityAdequate Workability Mix not to be too wet – reduces Mix not to be too wet – reduces

strengthstrength For max strength – driest possible For max strength – driest possible

mix to be usedmix to be used Usage of Compacting EffortsUsage of Compacting Efforts

Compaction of ConcreteCompaction of ConcreteCompacting EffortsCompacting Efforts

Manual CompactionManual Compaction RoddingRodding RammingRamming TampingTamping

Compaction by VibrationsCompaction by Vibrations By Vibratory rollersBy Vibratory rollers Compaction by Pressure and JoltingCompaction by Pressure and Jolting Compaction by SpinningCompaction by Spinning

Compaction of ConcreteCompaction of ConcreteManual Manual Compacting EffortsCompacting Efforts

Suitable ForSuitable For Unimportant Concrete work, small worksUnimportant Concrete work, small works Places where reinforcement is more & Places where reinforcement is more &

does not permit use of vibrating does not permit use of vibrating

equipmentequipment Higher consistencyHigher consistency Upto concrete thickness of 15 to 20 cmsUpto concrete thickness of 15 to 20 cms

Compaction of ConcreteCompaction of ConcreteManual Manual Compacting EffortsCompacting Efforts

RoddingRoddingPoking concrete with 2 m long, 16 Poking concrete with 2 m long, 16

mm dia rod to pack concrete between mm dia rod to pack concrete between

rft, corners & edgesrft, corners & edges RammingRamming

In foundations, unreinforced concrete In foundations, unreinforced concrete

on groundon groundNot permitted where rft may be Not permitted where rft may be

disturbed or formwork may faildisturbed or formwork may fail

Compaction of ConcreteCompaction of ConcreteManual Compacting Efforts

TampingTampingConsists of beating the top fresh Consists of beating the top fresh

concrete surface by wooden concrete surface by wooden

crossbeam of size 10 x 10 cmcrossbeam of size 10 x 10 cmWhen thickness is lessWhen thickness is lessSurface is moreSurface is moreNot only compacts, but also levels Not only compacts, but also levels

top surfacetop surface

Compaction of ConcreteCompaction of ConcreteCompaction by Vibrations

Manual Compaction – may give Manual Compaction – may give

satisfactory results; iff - Adequate satisfactory results; iff - Adequate

Workability & CareWorkability & Care Strength low because high W/C ratioStrength low because high W/C ratio In case of High Strength Concrete, In case of High Strength Concrete,

Low W/C ratio, thick members, Low W/C ratio, thick members,

larger volumes – mechanical means larger volumes – mechanical means

of compaction - mandatoryof compaction - mandatory

Compaction of ConcreteCompaction of ConcreteCompaction by Vibrations

Energy for compaction is supplied Energy for compaction is supplied

through oscillatory motion of through oscillatory motion of

vibrations (nearly SHM)vibrations (nearly SHM) Vibrations are generated by means Vibrations are generated by means

of rotating eccentric masses having of rotating eccentric masses having FrequencyFrequency AmplitudeAmplitude

Compaction of ConcreteCompaction of ConcretePrinciple behind Compaction by

Vibrations

Prior to compaction, concrete is Prior to compaction, concrete is

mass of separate particles coated mass of separate particles coated

with mortar, held in pile by arching with mortar, held in pile by arching

action of coarser particles.action of coarser particles. Arching is result of friction between Arching is result of friction between

aggregate particles, surface tension aggregate particles, surface tension

& cohesive forces of cement paste.& cohesive forces of cement paste. Voids caused by arching – upto 30%Voids caused by arching – upto 30%


Vibrations

Vibratory impulses liquefy mortar portion Vibratory impulses liquefy mortar portion

of concrete, thus help reduce friction of concrete, thus help reduce friction

resulting in consolidation under gravityresulting in consolidation under gravity After vibrations, concrete internal friction After vibrations, concrete internal friction

is re-established, cohesion restores and is re-established, cohesion restores and

strength increasesstrength increases Velocity of compression waves generated Velocity of compression waves generated

is 45 m/sec in beginning of vibrations is 45 m/sec in beginning of vibrations

which increases to 240 m/sec at the endwhich increases to 240 m/sec at the end


Vibrations

Waves move air & water more than Waves move air & water more than

solids & generate hydraulic pressure solids & generate hydraulic pressure

with interstitial water filled space. Excess with interstitial water filled space. Excess

pressure results in pressure on pores, pressure results in pressure on pores,

causes these to break, forces water out.causes these to break, forces water out. Pressure max in most constricted spaces Pressure max in most constricted spaces

& causes reduction in internal friction & causes reduction in internal friction

giving the paste temporary fluiditygiving the paste temporary fluidity


Vibrations

Consolidation takes place in two Consolidation takes place in two

stagesstages Stage – IStage – I

Vertical settlement of coarse aggregates Vertical settlement of coarse aggregates

takes place in a manner similar to takes place in a manner similar to

packing of granular materialpacking of granular material Shape of aggregates plays a major role, Shape of aggregates plays a major role,

air voids up to 5% remains at this stageair voids up to 5% remains at this stage


Vibrations

Stage – IIStage – II Concrete behaves like dense fluidConcrete behaves like dense fluid Internal vibrations set particles in motion, Internal vibrations set particles in motion,

reducing internal friction, achieving temp reducing internal friction, achieving temp

liquefaction, thus enabling easy liquefaction, thus enabling easy

settlementsettlement Air voids are removed forcing mortar to Air voids are removed forcing mortar to

appear at the surfaceappear at the surface This is one of the way to assess sufficiency This is one of the way to assess sufficiency

achieved in of compaction by vibrationsachieved in of compaction by vibrations

Optimum Vibration TimeOptimum Vibration Time

Timings of Vibrations in Seconds

Optimum Time is directly proportional to Size of Vibrator

Type of concrete

Size of concrete or

member

Type of vibrations i.e.

frequency, amplitude

& acceleration

Optimum Time

Compaction of ConcreteCompaction of ConcreteAdvantages : Compaction by

Vibrations

Efficient than ManualEfficient than Manual Concrete can be placed and compacted Concrete can be placed and compacted

in difficult sectionsin difficult sections Slump requirements – 4 cm with Slump requirements – 4 cm with

vibrations & 12 cms with manual methodvibrations & 12 cms with manual method Facilitates use of less water – thus Facilitates use of less water – thus

increased strength & durabilityincreased strength & durability In essence, method of removal of In essence, method of removal of

entrapped air is differententrapped air is different

Compaction of ConcreteCompaction of ConcreteType of Vibrators

InternalInternal PPoker oker - - immersed in concrete immersed in concrete for for

compactcompactionion Poker can Poker can easily easily be be removed removed & moved & moved

from point to pointfrom point to point ExternalExternal

External vibrators clamp direct to the External vibrators clamp direct to the formwork requiring strong & rigid formsformwork requiring strong & rigid forms..

Examples -Examples - Formwork, Table, Formwork, Table, Platform, Surface & Vibratory Rollers typePlatform, Surface & Vibratory Rollers type

To aid in the removal of trapped air the To aid in the removal of trapped air the vibrator head should be rapidly plunged vibrator head should be rapidly plunged into the mix and slowly moved up and into the mix and slowly moved up and downdown..

Internal VibratorsInternal Vibrators

The actual The actual completion of completion of vibration is judged by vibration is judged by the appearance of the appearance of the concrete surface the concrete surface which must be which must be neither rough nor neither rough nor contain excess contain excess cement paste.cement paste.

Immersion / Poker / Submersible / Spud Type Flexible Drive

Type Motor in Head


Most Common Vibrations upto 12000 cps Dia of poker 20 to 175 mm Length of poker – 25 to 90 mm Needle can be replaced by flat

needle (blade) to compact congested areas

Portable



d

R

1½ R

Vibrator

R - Radius of Action

Penetrate vertically to sufficient depth, Penetrate vertically to sufficient depth,

hold stationary and remove slowly @ hold stationary and remove slowly @

7.5 m/sec7.5 m/sec Vibrations at regular spacing to ensure Vibrations at regular spacing to ensure

compaction of all portions & overlapcompaction of all portions & overlap Minimum 10 sec are required for Minimum 10 sec are required for

complete compaction. complete compaction.

Execution of VibrationsExecution of Vibrations


R is Radius of action

D is Spacing

E is thickness of section


CORRECTCORRECT

Vertical penetration a few inches into previous lift (which should not yet be rigid) of systematic regular intervals will give adequate consolidation

INCORRECTINCORRECT

Haphazard random penetration of the vibrator at all angles and spacings without sufficient depth will not assure intimate combination of the two layers

External VibratoExternal Vibratorsrs

Form vibratorsForm vibrators Vibrating tablesVibrating tables

(Lab)(Lab) Surface vibratorsSurface vibrators

Vibratory screedsVibratory screedsPlate vibratorsPlate vibratorsVibratory roller Vibratory roller

screedsscreedsVibratory hand floats Vibratory hand floats

or trowelsor trowels

External vibrators rigidly clamped to formwork so External vibrators rigidly clamped to formwork so

that form & concrete are subjected to vibrationthat form & concrete are subjected to vibrationss. . CConsiderable work needed to vibrate forms. onsiderable work needed to vibrate forms. Forms must be strong and tied enough to prevent Forms must be strong and tied enough to prevent

distortion and leakage of the grout.distortion and leakage of the grout. Suitable for thin members or Pre-Cast units Frequency range – 1000-5000 cycles per min Finish quality – Good Consumes more power – less efficient than

internal

External VibratoExternal Vibratorsrs

Vibrating TableVibrating Table UUsed for small sed for small

quantitiequantities of s of concrete (lab concrete (lab && some some precast precast elements)elements)

External VibratoExternal VibratorsrsTable Vibrators

Larger than table vibrators.Larger than table vibrators. Used for manufacture of Used for manufacture of

Concrete PolesConcrete Poles Railway SleepersRailway Sleepers Prefabricated roofing elementsPrefabricated roofing elements

Platform vibrators may also be Platform vibrators may also be

coupled for jerking and shock to coupled for jerking and shock to

achieve thorough compaction.achieve thorough compaction.

External : Platform Vibrators

Also : Screed Board VibratorsAlso : Screed Board Vibrators Suitable forSuitable for

Roof slabsRoof slabs Floor SlabsFloor Slabs Roads surfacesRoads surfaces

Effective upto 15 cm depthEffective upto 15 cm depth Types : Pan Type, Vibrating Roller

screed, Vibratory Plate, Vibratory roller for pavements

External : Surface Vibrators

Other vibrators are not suitable

Used for mass concrete : Dams, Used for mass concrete : Dams,

pavements.pavements. Heavy roller vibrates dry lean concreteHeavy roller vibrates dry lean concrete Tech originated in Japan & now being Tech originated in Japan & now being

used worldwide.used worldwide. Example : Roller compacted M-10

grade concrete used in Mathura

Highway and Pune Expressway.

External : Vibratory Rollers

External : Surface Vibrators

Combined action of Vibrations – Combined action of Vibrations –

Pressure & Jolting results in very Pressure & Jolting results in very

good compaction & dense concretegood compaction & dense concrete Very effective for very dry lean Very effective for very dry lean

mixesmixes Gen used for compacting hollow Gen used for compacting hollow

blocks, cavity blocks, solid concrete blocks, cavity blocks, solid concrete

blocks, railway sleepers etc.blocks, railway sleepers etc.

Compaction of ConcreteVibrations with Pressure & Jolting

EfficientEfficient High frequency & Low amplitude High frequency & Low amplitude

results in efficient compactionresults in efficient compaction

Compaction by Vibrations

Used for compacting concrete pipes.Used for compacting concrete pipes. Recent technologyRecent technology Plastic concrete when spun at a very Plastic concrete when spun at a very

high speed, gets well compacted by high speed, gets well compacted by

centrifugal force.centrifugal force. Used for concrete spun pipes, hume Used for concrete spun pipes, hume

pipes etc.pipes etc.

Compaction of ConcreteExternal : Spinning

Vibrators are powered byVibrators are powered by Electric motor either driving the Electric motor either driving the

vibrator through flexible shaft or by vibrator through flexible shaft or by

motor situated in head of vibratormotor situated in head of vibrator IC engines driving the vibrator needle IC engines driving the vibrator needle

through flexible shaft.through flexible shaft. Compressed air motor situated near Compressed air motor situated near

the head of vibratorthe head of vibrator

Compaction of ConcreteGuidelines for use of Vibrators

Electricity driven or electric Electricity driven or electric

motor driven – most reliable & motor driven – most reliable &

efficientefficient Light & CompactLight & Compact ConsistentConsistent Ease of HandlingEase of Handling


Care should be taken forCare should be taken for Vibrating head – not to come in Vibrating head – not to come in

contact with hard objects – Impact contact with hard objects – Impact

may damage bearings.may damage bearings. No sharp bends in flexible shaft No sharp bends in flexible shaft

drivedrive Vibrators to conform to IS 2505 – Vibrators to conform to IS 2505 –

19631963


Vibrators to be selected on Vibrators to be selected on

appreciation of quantum & type appreciation of quantum & type

of concretingof concreting Concrete to be compacted must Concrete to be compacted must

be stiff of high compaction factor be stiff of high compaction factor

of 0.75 to 0.85of 0.75 to 0.85 Good and strong formworkGood and strong formwork


Size of vibrating needle, Timings of Size of vibrating needle, Timings of

vibration & time of introduction & vibration & time of introduction &

removal of needle must be taken removal of needle must be taken

care of.care of. Joints of formwork to be tight to Joints of formwork to be tight to

prevent squeezing out of grout and prevent squeezing out of grout and

sucking in of air during vibrations.sucking in of air during vibrations.


Absence of precautions may lead Absence of precautions may lead

to honeycombing.to honeycombing. Needles must be inserted Needles must be inserted

vertical and at regular intervals. vertical and at regular intervals. Careful application of mould Careful application of mould

releasing agents.releasing agents. Ensure bonding between layers.Ensure bonding between layers.


Internal vibrator not to be used Internal vibrator not to be used

to spread concrete. to spread concrete. Deposit concrete in advance and Deposit concrete in advance and

then vibrate.then vibrate. No vibrations recommended No vibrations recommended

near free end of concrete, near free end of concrete,

usually not within 120 cms of it.usually not within 120 cms of it.


Restrict concrete layers upto 60 Restrict concrete layers upto 60

cms to ensure proper vibrations cms to ensure proper vibrations

and removal of trapped air. and removal of trapped air.

Concrete upto 1m thick may Concrete upto 1m thick may

require very powerful vibrators.require very powerful vibrators. Depth of vibrations must Depth of vibrations must

facilitate bonding between layers.facilitate bonding between layers.


Ensure careful spacing and overlap Ensure careful spacing and overlap

for full compaction at all places.for full compaction at all places. Vibrations to be completed within Vibrations to be completed within

an hour - initial setting time.an hour - initial setting time. Grouping of reinforcement may be Grouping of reinforcement may be

resorted to enable vibrations.resorted to enable vibrations. Over vibrations result in Over vibrations result in

segregation.segregation.


Imperfections in ConcreteGuidelines for use of Vibrators

Issue Appearance &

Description

Design Issues

Form & condition

Concrete & Placement

Compaction

Honey Combing

Stony, air voids

Narrow sections

Grout loss Free Fall, Low slump

Poor

Bug Holes Small Holes Excess Oil Lean, Low slump

Inadequate

Subsidence Cracking

Short cracks Plastic settlement

High W/C Inadequate

Form Offset Irregular Surface

Weak Form Non uniform

Cold Joints Discontinuity Poor Planning

Delayed Placing

Inadequate

Thank You

Download - Concrete Compaction

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