Concrete Production, Compaction of Concrete, Reducing Porosity in Concrete, compacting concrete, concrete compaction

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CONCRETE : COMPACTION
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

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GEN OUTLINE
 What is Compaction
 Why is it required
 Compacting Efforts
Manual
Mechanical
 Certain Do’s & Don’ts
Compaction of Concrete
What is Compaction
 Process adopted for expelling the
entrapped air to achieve dense
mass
Constituent Entrapped Air
Before
Compaction
After
Compaction
Aggregates 60-75% 60-75%
Cement 25-40% 25-40%
Air 25-30% 1-2%

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Compaction of Concrete
Why is Compaction required
 To drive out entrapped air to densify
fresh concrete
 During Mixing, Transportation & Placing – air gets
entrapped
 Quantity of air entrapped inversely proportional
to workability
 Entrapped air adversely affects quality & strength
 To make fresh concrete conform
intimately to shape of form
 Increased homogeneity & uniformity
Why is Compaction Required

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Compaction of Concrete
Adverse Effects of Entrapped Air
 Low Strength & Durability
 Low resistance to abrasion
 Poor bonding with reinforcement and
low bond strength
 High Porosity
 Resulting in easy ingress of moisture,
chemicals
 Weakening of Concrete & reinforcement
CONSOLIDATING CONCRETE
Inadequate consolidation
can result in:
 Honeycomb
 Excessive amount of
entrapped air voids (bug-
holes)
 Sand streaks
 Placement lines (Cold joints)

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Consolidating Concrete
Improper Compaction
STRENGTH OF CONCRETE
 The strength of a concrete specimen
prepared, cured and tested under specified
conditions at a given
age depends on:
 w/c ratio
 Degree of
compaction

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Compaction of Concrete
How to Achieve Full Compaction
 Adequate Workability
 Mix not to be too wet – reduces strength
 For max strength – driest possible mix to
be used
 Usage of Compacting Efforts

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Compaction of Concrete
Compacting Efforts
 Manual Compaction
 Rodding
 Ramming
 Tamping
 Compaction by Vibrations
 By Vibratory rollers
 Compaction by Pressure and Jolting
 Compaction by Spinning
Compaction of Concrete
Manual Compacting Efforts
 Suitable For
 Unimportant Concrete work, small works
 Places where reinforcement is more &
does not permit use of vibrating
equipment
 Higher consistency
 Upto concrete thickness of 15 to 20 cms

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Compaction of Concrete
Manual Compacting Efforts
 Rodding
Poking concrete with 2 m long, 16 mm dia
rod to pack concrete between rft, corners
& edges
 Ramming
In foundations, unreinforced concrete on
ground
Not permitted where rft may be disturbed
or formwork may fail
Compaction of Concrete
Manual Compacting Efforts
 Tamping
Consists of beating the top fresh concrete
surface by wooden crossbeam of size 10 x
10 cm
When thickness is less
Surface is more
Not only compacts, but also levels top
surface

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Compaction of Concrete
Compaction by Vibrations
 Manual Compaction – may give
satisfactory results; iff - Adequate
Workability & Care
 Strength low because high W/C ratio
 In case of High Strength Concrete, Low
W/C ratio, thick members, larger
volumes – mechanical means of
compaction - mandatory
Compaction of Concrete
Compaction by Vibrations
 Energy for compaction is supplied
through oscillatory motion of vibrations
(nearly SHM)
 Vibrations are generated by means of
rotating eccentric masses having
 Frequency
 Amplitude

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Compaction of Concrete
Principle behind Compaction by Vibrations
 Prior to compaction, concrete is mass of
separate particles coated with mortar,
held in pile by arching action of coarser
particles.
 Arching is result of friction between
aggregate particles, surface tension &
cohesive forces of cement paste.
 Voids caused by arching – upto 30%
Compaction of Concrete
Principle behind Compaction by Vibrations
 Vibratory impulses liquefy mortar portion of
concrete, thus help reduce friction resulting in
consolidation under gravity
 After vibrations, concrete internal friction is re-
established, cohesion restores and strength
increases
 Velocity of compression waves generated is 45
m/sec in beginning of vibrations which
increases to 240 m/sec at the end

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Compaction of Concrete
Principle behind Compaction by Vibrations
 Waves move air & water more than
solids & generate hydraulic pressure
with interstitial water filled space. Excess
pressure results in pressure on pores,
causes these to break, forces water out.
 Pressure max in most constricted spaces
& causes reduction in internal friction
giving the paste temporary fluidity
Compaction of Concrete
Principle behind Compaction by Vibrations
 Consolidation takes place in two stages
 Stage – I
 Vertical settlement of coarse aggregates
takes place in a manner similar to packing
of granular material
 Shape of aggregates plays a major role, air
voids up to 5% remains at this stage

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Compaction of Concrete
Principle behind Compaction by Vibrations
 Stage – II
 Concrete behaves like dense fluid
 Internal vibrations set particles in motion,
reducing internal friction, achieving temp
liquefaction, thus enabling easy settlement
 Air voids are removed forcing mortar to
appear at the surface
 This is one of the way to assess sufficiency
achieved in of compaction by vibrations
Optimum Vibration Time
Timings of Vibrations in Seconds
Unitweight
 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

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Compaction of Concrete
Advantages : Compaction by Vibrations
 Efficient than Manual
 Concrete can be placed and compacted in
difficult sections
 Slump requirements – 4 cm with vibrations &
12 cms with manual method
 Facilitates use of less water – thus increased
strength & durability
 In essence, method of removal of entrapped
air is different
Compaction of Concrete
Type of Vibrators
 Internal
 Poker - immersed in concrete for compaction
 Poker can easily be removed & moved from
point to point
 External
 External vibrators clamp direct to the
formwork requiring strong & rigid forms.
 Examples - Formwork, Table, Platform,
Surface & Vibratory Rollers type

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 To aid in the removal of trapped air the
vibrator head should be rapidly plunged into
the mix and slowly moved up and down.
Internal Vibrators
 The actual completion
of vibration is judged by
the appearance of the
concrete surface which
must be neither rough
nor contain excess
cement paste.
 Immersion / Poker
/ Submersible /
Spud Type
 Flexible Drive
Type
 Motor in Head
Internal Vibrators

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 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 Vibrators
Internal Vibrators
d
1½ R
Vibrator
R - Radius of Action

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Characteristics&Applications
ofImmersionVibrators
Internal Vibrators
Diameter
of head,
(mm)
Recommended
frequency,
(vib./min.)
Approximate
radius of
action, (mm)
Rate of
placement,
(m3/h)
Application
20-40 9000-15,000 80-150 0.8-4
Plastic and flowing
concrete in thin
members. Also used for
lab test specimens.
30-60 8500-12,500 130-250 2.3-8
Plastic concrete in thin
walls, columns, beams,
precast piles, thin slabs,
and along construction
joints.
50-90 8000-12,000 180-360 4.6-15
Stiff plastic concrete
(less than 80-mm
slump) in general
construction .
Adaptedfrom ACI 309

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 Penetrate vertically to sufficient depth,
hold stationary and remove slowly @
7.5 m/sec
 Vibrations at regular spacing to ensure
compaction of all portions & overlap
 Minimum 10 sec are required for
complete compaction.
Execution of Vibrations

Execution of Vibrations

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Execution of Vibrations
 R is Radius of
action
 D is Spacing
 E is thickness
of section
Execution of Vibrations
CORRECT
Vertical penetration a few inches
into previous lift (which should not
yet be rigid) of systematic regular
intervals will give adequate
consolidation
INCORRECT
Haphazard random penetration of
the vibrator at all angles and
spacings without sufficient depth
will not assure intimate combination
of the two layers

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External Vibrators
 Form vibrators
 Vibrating tables (Lab)
 Surface vibrators
Vibratory screeds
Plate vibrators
Vibratory roller
screeds
Vibratory hand floats
or trowels
 External vibrators rigidly clamped to formwork so
that form & concrete are subjected to vibrations.
 Considerable work needed to vibrate forms.
 Forms must be strong and tied enough to prevent
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 Vibrators

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 Vibrating Table
 Used for small
quantities of
concrete (lab &
some precast
elements)
External Vibrators
Table Vibrators
 Larger than table vibrators.
 Used for manufacture of
 Concrete Poles
 Railway Sleepers
 Prefabricated roofing elements
 Platform vibrators may also be coupled for
jerking and shock to achieve thorough
compaction.
External : Platform Vibrators

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 Also : Screed Board Vibrators
 Suitable for
 Roof slabs
 Floor Slabs
 Roads surfaces
 Effective 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,
pavements.
 Heavy roller vibrates dry lean concrete
 Tech originated in Japan & now being
used worldwide.
 Example : Roller compacted M-10 grade
concrete used in Mathura Highway and
Pune Expressway.
External : Vibratory Rollers

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External : Surface Vibrators
External : Surface Vibrators

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 Combined action of Vibrations – Pressure
& Jolting results in very good compaction
& dense concrete
 Very effective for very dry lean mixes
 Gen used for compacting hollow blocks,
cavity blocks, solid concrete blocks,
railway sleepers etc.
Compaction of Concrete
Vibrations with Pressure & Jolting
 Efficient
 High frequency & Low amplitude
results in efficient compaction
Compaction by Vibrations

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 Used for compacting concrete pipes.
 Recent technology
 Plastic concrete when spun at a very high
speed, gets well compacted by centrifugal
force.
 Used for concrete spun pipes, hume pipes
etc.
Compaction of Concrete
External : Spinning
 Vibrators are powered by
 Electric motor either driving the vibrator
through flexible shaft or by motor situated in
head of vibrator
 IC engines driving the vibrator needle
through flexible shaft.
 Compressed air motor situated near the
head of vibrator
Compaction of Concrete
Guidelines for use of Vibrators

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 Electricity driven or electric motor
driven – most reliable & efficient
 Light & Compact
 Consistent
 Ease of Handling
Compaction of Concrete
Guidelines for use of Vibrators
 Care should be taken for
 Vibrating head – not to come in
contact with hard objects – Impact
may damage bearings.
 No sharp bends in flexible shaft drive
 Vibrators to conform to IS 2505 – 1963
Compaction of Concrete
Guidelines for use of Vibrators

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 Vibrators to be selected on
appreciation of quantum & type of
concreting
 Concrete to be compacted must be
stiff of high compaction factor of 0.75
to 0.85
 Good and strong formwork
Compaction of Concrete
Guidelines for use of Vibrators
 Size of vibrating needle, Timings of
vibration & time of introduction &
removal of needle must be taken care
of.
 Joints of formwork to be tight to
prevent squeezing out of grout and
sucking in of air during vibrations.
Compaction of Concrete
Guidelines for use of Vibrators

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 Absence of precautions may lead to
honeycombing.
 Needles must be inserted vertical and
at regular intervals.
 Careful application of mould releasing
agents.
 Ensure bonding between layers.
Compaction of Concrete
Guidelines for use of Vibrators
 Internal vibrator not to be used to
spread concrete.
 Deposit concrete in advance and then
vibrate.
 No vibrations recommended near free
end of concrete, usually not within
120 cms of it.
Compaction of Concrete
Guidelines for use of Vibrators

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 Restrict concrete layers upto 60 cms
to ensure proper vibrations and
removal of trapped air. Concrete upto
1m thick may require very powerful
vibrators.
 Depth of vibrations must facilitate
bonding between layers.
Compaction of Concrete
Guidelines for use of Vibrators
 Ensure careful spacing and overlap
for full compaction at all places.
 Vibrations to be completed within an
hour - initial setting time.
 Grouping of reinforcement may be
resorted to enable vibrations.
 Over vibrations result in segregation.
Compaction of Concrete
Guidelines for use of Vibrators

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Imperfections in Concrete
Guidelines 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