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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    Placing and

    Finishing Concrete

    Videos 3/4

    Contraction Joints Jointing

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    Placing and

    Videos 4/4

    Improper Finishing