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7/30/2019 Placing Concrete
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Placing and FinishingConcrete
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Placing andFinishing Concrete
Basic Requirements forPlacing Concrete (1)
Preserve concrete quality
Water-cement ratio Slump
Air-content
Homogeneity
Avoid separation of
aggregate and mortar
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Placing andFinishing Concrete
Basic Requirements forPlacing Concrete (2)
Avoid excessive horizontal
movement
Consolidate adequately
Maintain sufficient placement
capacity Choose the right equipment for
the concrete
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Placing andFinishing Concrete
Preparation Before PlacingIncludes: Trimming the subgrade
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Placing andFinishing Concrete
Preparation Before PlacingIncludes: Moistening the subgrade
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Placing andFinishing Concrete
Preparation Before PlacingIncludes: Compacting the subgrade
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Depositing Concrete DO NOT
(a) disturb saturated subgrades sobearing capacity is maintained
(b) deposit on frozen subgrade
Deposit continuously and as near aspossible to its final position
Rate of placement should be suchthat previously placed concrete hasnot set when the next layer is placedupon it
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Depositing Concrete Start placing along perimeter at one
end with each batch discharged againstpreviously placed concrete
Do not
(a) dump in separate piles & thenlevel and work together
(b) deposit in large piles & thenmove horizontally into position
These practices result in segregation(mortar flows ahead of coarser material)
Slab Construction
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Depositing Concrete
Discharging into previously
placed concrete
Effective use of
wheelbarrows
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Incorrect Placement withConveyor BeltBaffle
Mortar Rock Mortar
MortarRock
Shallowhopper
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Placement with ConveyorBelt
Belt Scraper
No
Separation
Provide at least 0.6 m
(24 in.) headroom for
downpipe, elephant
trunk or equivalent
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Placing andFinishing Concrete
Depositing ConcretePavementSlab Concrete deposited in
front of slip form paver
by dump trucks
Concrete spread
evenly across the
subgrade by the paverbefore consolidation
and finishing
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Placing andFinishing Concrete
Curb/Curb and Gutter
Depositing Concrete Concrete deposited
into hopper of slip
form curb and gutter
machine which then
extrudes the concreteinto the desired
shape
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Placing andFinishing Concrete
Depositing Concrete Deposit in horizontal layers of
uniform thickness
Reinforced 150 mm to 500 mm
Mass 375 mm to 500 mm
Consolidate each layer before
next is placed
Timely placement & consolidation
prevents flow lines and cold joints
Walls
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Placing andFinishing Concrete
Horizontal Construction Joint
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Placing and
Finishing Concrete
Horizontal Construction Joints
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Placing and
Finishing Concrete
Underwater PlacementMethods Tremie
Pump
Bottom dump buckets Grouted preplaced
aggregate (specialized)
Toggle bags Bagwork
Diving bell
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Placing and
Finishing Concrete
Placing ConcreteUnder Water Water velocity 3 m (10 ft) / min.
Water temperature 5C(if below test for strength gain)
w/c 0.45
Cementing materials content
390 kg/m3 (600 lb/yd3)
Slump range 150 to 225 mm (6 to
10 in.)
Basic Recommendations
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Placing and
Finishing Concrete
Placing ConcreteUnderwater Used: Tremie
Advantages: Can be used to
funnel concrete down throughthe water into the structure.
Watch for: Discharge end
always has to be buried in freshconcrete to ensure seal
between water and concrete
mass.
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Placing and
Finishing Concrete
ConsolidatingConcrete Internal Vibration
External Vibration
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Placing and
Finishing Concrete
Internal Vibration
d
1 R
Vibrator
Radius of Action
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Placing and
Finishing Concrete
Internal VibratorsDiameter
of head,
mm (in.)
Recommendedfrequency,
vibrations per
minute
Approximateradius of
action, mm
(in.)
Rate ofplacement,
m3/h
(yd3/h) Application
20-40(3/4-1) 9000-15,000 80-150(3-6) 0.8-4(1-5)
Plastic and flowingconcrete in thin
members. Also usedfor lab testspecimens.
30-60
(1-2)
8500-12,500130-250
(5-10)
2.3-8
(3-10)
Plastic concrete inthin walls, columns,
beams, precast piles,
thin slabs, and alongconstruction joints.
50-90
(2-3)8000-12,000
180-360
(7-14)
4.6-15
(6-20)
Stiff plastic concrete(less than 80-mm [3-in.] slump) in general
construction .
Adapted from ACI 309
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Placing and
Finishing Concrete
Systematic Vibration ofEach New LiftCORRECT
Vertical penetration a few inches into
previous lift (which should not yet be
rigid) of systematic regular intervalswill give adequate consolidation
INCORRECT
Haphazard random penetration of thevibrator at all angles and spacings
without sufficient depth will not assure
intimate combination of the two layers
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Placing and
Finishing Concrete
Placing Concrete in aSloping LiftCORRECT
Start placing at bottom of slope so
that compaction is increased by
weight of newly added concrete.Vibration consolidates the concrete.
INCORRECT
When placing is begun at top of slopethe upper concrete tends to pull
apart especially when vibrated below
as this starts flow and removes from
concrete above.
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Placing and
Finishing Concrete
External Vibration Form vibrators
Vibrating tables
Surface vibrators
Vibratory screeds
Plate vibrators
Vibratory roller screeds
Vibratory hand floats ortrowels
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Placing and
Finishing Concrete
Consolidating ConcreteInadequate consolidationcan result in:
Honeycomb
Excessive amount of entrappedair voids (bugholes)
Sand streaks
Cold joints
Placement lines Subsidence cracking
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Placing and
Finishing Concrete
Nuclear Gauges to DetermineSubbase Compaction
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Placing and
Finishing Concrete
Screeding (Strikeoff)The process of cutting off excessconcrete to bring the top surface of aslab to proper grade
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Placing and
Finishing Concrete
VibratoryScreeds
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Placing and
Finishing Concrete
Bullfloating
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Placing and
Finishing Concrete
Darbying
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Placing and
Finishing Concrete
Edging
Required along all edge forms,
isolation and construction jointsin floors and exterior slabs
Cut concrete away from forms
to a depth of 25 mm with a
pointed mason or margin trowel
Edging may be required after
each subsequent finishing
operation for interior slabs
Edging densifies and compacts concretenext to forms where floating is less effective
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Placing and
Finishing Concrete
Highway Straightedges
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Placing and
Finishing Concrete
Floating (Power or Hand) To embed aggregate
particles just beneath thesurface
To remove slightimperfections, humps, andvoids
To compact the mortar atthe surface in preparationfor additional finishingoperations.
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Placing and
Finishing Concrete
Troweling Creates smooth,
hard,dense surface
Exterior concrete should
not be troweled because: it can lead to a loss of
entrained air caused by
overworking the surface
troweled surfaces can
be slippery when wet.
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Placing and
Finishing Concrete
Brooming
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Placing and
Finishing Concrete
Tining
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Placing and
Finishing Concrete
Curing and Protection
Cure for 7 days
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Placing and
Finishing Concrete
Placing on Hardened ConcretePreparing Hardened Concrete
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Placing and
Finishing Concrete
Bonding New to PreviouslyHardened Concrete Cement-sand
grout
Latex
Epoxy
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Placing and
Finishing Concrete
Isolation Joints
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Placing and
Finishing Concrete
Contraction Joints
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Placing and
Finishing Concrete
Spacing of ContractionJoints in MetersSlab
thickness,
mm
Maximum-size
aggregate
less than 19 mm
Maximum-size
aggregate
19 mm and larger
100 2.4 3.0
125 3.0 3.75
150 3.75 4.5
175 4.25 5.25
200 5.0 6.0225 5.5 6.75
250 6.0 7.5
Metric
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Placing and
Finishing Concrete
Spacing of ContractionJoints in FeetSlab
thickness, in.
Maximum-sizeaggregate
less than in.
Maximum-sizeaggregate
in. and larger
4 8 10
5 10 13
6 12 15
7 14 18
8 16 209 18 23
10 20 25
Inch-Pound
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Placing and
Finishing Concrete
Making Contraction Joints
Dry-cut sawing concrete
Grooving tool
on bull-float
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Placing and
Finishing Concrete
ConstructionJoints
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Placing and
Finishing Concrete
Joint Layout for Slabs Panels created by contraction
joints should be approximately
square
Panel aspect ratio max. 1 to 1
Contraction (control) joints should
only terminate at a free edge or at
an isolation joint When joint spacing exceeds 4.5 m
(15 ft), load transfer by aggregate
interlock decreases significantly
Basic Factors to Remember
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Placing and
Finishing Concrete
Typical Joint Layout
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Placing and
Finishing Concrete
Finishing Operations Consolidation Strike-off
Edging
Darbying or Bull Floating
Lapse of Time
Edging
Grooving (if desired)
Floating (power or hand)
Troweling (power or hand)Lapse of Time
Second Troweling (power or hand)
Final Troweling (hand)
Curing
Single Course Floors
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Placing and
Finishing Concrete
Finishing Operations - Exterior Slabs Consolidation
Strike-off
Depress aggregate with metal/wood strip
at joint location if hand tooled
Darbying or Bull floating
Lapse of t ime
Edging
Jointing (optional if hand tooled)
Floating
Lapse of t ime
Texturing (brooming/swirl float finish)
Curing
Sidewalks, Driveways etc.
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Placing and
Finishing Concrete
Patching
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Placing and
Finishing Concrete
Curing Patches
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Placing and
Finishing Concrete
Cleaning ConcreteSurfaces Cleaning methods:
Water
Chemical
Mechanical
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Placing and
Finishing Concrete
Finishing FormedSurfaces Rough-form finishes
Smooth off-the-form finish
Smooth, rubbed finish
Sand-floated finish Grout cleandown
(sack-rubbed finish)
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Placing and
Finishing Concrete
Special Surface Finishes Pattern and Textures
Exposed Aggregate Concrete
Colored Finishes
Stains, Paints and Clear
Coatings
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Finishing Concrete
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Placing and
Finishing Concrete
Working Safely with ConcreteProtect:
Your Eyes
Your Back
Your Skin
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Placing and
Finishing Concrete
Precautions
http://www.cement.org/pdf_files/ms271.pdf
WARNING: Contact with wet (unhardened) concrete, mortar,
cement, or cement mixtures can cause SKIN IRRITATION, SEVERE
CHEMICAL BURNS (THIRD-DEGREE), or SERIOUS EYE
DAMAGE. Frequent exposure may be associated with irritant and/or
allergic contact dermatitis. Wear water-proof gloves, a long-sleeved
shirt, full-length trousers, and proper eye protection when working
with these materials. If you have to stand in wet concrete, usewaterproof boots that are high enough to keep concrete from flowing
into them. Wash wet concrete, mortar, cement, or cement mixtures
from your skin immediately. Flush eyes with clean water immediately
after contact. In-direct contact through clothing can be as serious as
direct contact, so promptly rinse out wet concrete, mortar, cement,or cement mixtures from clothing. Seek immediate medical attention
if you have persistent or severe discomfort.
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Placing and
Finishing Concrete
Videos 1/4
Placing and Consolidating Vibration
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Placing and
Finishing Concrete
Videos 2/4
Finishing I Finishing II
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Finishing Concrete
Videos 3/4
Contraction Joints Jointing
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Placing and
Videos 4/4
Improper Finishing