concrete compaction
DESCRIPTION
Compaction of Concrete, concrete, removing air from fresh concrete, shape of concrete, Production of Concrete, Increasing strength of Concrete, Concrete CompactionTRANSCRIPT
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%
Compaction of ConcreteCompaction of ConcretePrinciple behind Compaction by
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
Compaction of ConcreteCompaction of ConcretePrinciple behind Compaction by
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
Compaction of ConcreteCompaction of ConcretePrinciple behind Compaction by
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
Compaction of ConcreteCompaction of ConcretePrinciple behind Compaction by
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
Internal VibratorsInternal Vibrators
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
Internal VibratorsInternal Vibrators
Internal VibratorsInternal Vibrators
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
Execution of VibrationsExecution of Vibrations
Execution of VibrationsExecution of Vibrations
R is Radius of action
D is Spacing
E is thickness of section
Execution of VibrationsExecution of Vibrations
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
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
Compaction of ConcreteGuidelines for use of Vibrators
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
Compaction of ConcreteGuidelines for use of Vibrators
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
Compaction of ConcreteGuidelines for use of Vibrators
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.
Compaction of ConcreteGuidelines for use of Vibrators
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.
Compaction of ConcreteGuidelines for use of Vibrators
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.
Compaction of ConcreteGuidelines for use of Vibrators
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.
Compaction of ConcreteGuidelines for use of Vibrators
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.
Compaction of ConcreteGuidelines for use of Vibrators
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
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