Placing and Finishing Concrete

ByProf. Adel El Kordi

&Dr. Meheddene Machaka

Structural EngineeringDepartment

Faculty of EngineeringBeirut Arab University

CVLE 321

Basic Requirements for Placing Concrete (1)

Preserve concrete quality Water-cement ratio Slump Air-content Homogeneity

Avoid separation ofaggregate and mortar

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Basic Requirements for Placing Concrete (2)

Avoid excessive horizontalmovement

Consolidate adequately Maintain sufficient placement

capacity Choose the right equipment for

the concrete

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Preparation Before Placing Includes: Moistening the subgrade

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Preparation Before Placing Includes: 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

Discharging into previouslyplaced concrete

Effective use ofwheelbarrows

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Incorrect Placement with Conveyor Belt

Baffle

Mortar Rock Mortar

MortarRock

Shallowhopper

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Placement with Conveyor Belt

Belt Scraper

NoSeparation

Provide at least 0.6 m(24 in.) headroom fordownpipe, elephanttrunk or equivalent

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Depositing Concrete

Pavement Slab

Concrete deposited infront of slip form paverby dump trucks

Concrete spreadevenly across thesubgrade by the paverbefore consolidationand finishing

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Curb/Curb and Gutter

Depositing Concrete

Concrete depositedinto hopper of slipform curb and guttermachine which thenextrudes the concreteinto the desiredshape

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Depositing Concrete

Deposit in horizontal layers ofuniform thickness Reinforced — 150 mm to 500 mm Mass — 375 mm to 500 mm

Consolidate each layer beforenext is placed

Timely placement & consolidationprevents flow lines and cold joints

Walls

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Horizontal Construction Joint

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Horizontal Construction Joints

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Underwater Placement Methods

Tremie Pump Bottom dump buckets Grouted preplaced

aggregate (specialized) Toggle bags Bagwork Diving bell

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Placing Concrete Under Water

Water velocity 3 m (10 ft) / min. Water temperature 5°C

(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 ConcreteUnderwater

Used: Tremie

Advantages: Can be used tofunnel concrete down throughthe water into the structure.

Watch for: Discharge endalways has to be buried in freshconcrete to ensure sealbetween water and concretemass.

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ConsolidatingConcrete

Internal Vibration

External Vibration

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Internal Vibration

d

1½ R

Vibrator

Radius of Action19

Systematic Vibration of Each New Lift

CORRECTVertical penetration a few inches intoprevious lift (which should not yet berigid) of systematic regular intervalswill give adequate consolidation

INCORRECTHaphazard random penetration of thevibrator at all angles and spacingswithout sufficient depth will not assureintimate combination of the two layers

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Placing Concrete in a Sloping LiftCORRECTStart placing at bottom of slope sothat compaction is increased byweight of newly added concrete.Vibration consolidates the concrete.

INCORRECTWhen placing is begun at top of slopethe upper concrete tends to pullapart especially when vibrated belowas this starts flow and removes fromconcrete above. 21

External Vibration

Form vibrators Vibrating tables Surface vibrators

Vibratory screeds Plate vibrators Vibratory roller screeds Vibratory hand floats or

trowels

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Consolidating Concrete

Inadequate consolidationcan result in: Honeycomb Excessive amount of entrapped

air voids (bugholes) Sand streaks Cold joints Placement lines Settlement cracking

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Nuclear Gauges to Determine Subbase Compaction

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Screeding (Strikeoff)The process of cutting off excessconcrete to bring the top surface of aslab to proper grade

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VibratoryScreeds

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Flooring

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Flooring

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Edging

Required along all edge forms,isolation and construction jointsin floors and exterior slabs

Cut concrete away from formsto a depth of 25 mm with apointed mason or margin trowel

Edging may be required aftereach subsequent finishingoperation for interior slabs

Edging densifies and compacts concretenext to forms where floating is less effective

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Highway Straightedges

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Floating (Power or Hand)

To embed aggregateparticles just beneath thesurface

To remove slightimperfections, humps, andvoids

To compact the mortar atthe surface in preparationfor additional finishingoperations.

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Toweling Creates smooth, hard,

dense surface Exterior concrete should

not be toweled because: it can lead to a loss of

entrained air caused byoverworking the surface

toweled surfaces can beslippery when wet.

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Curing and Protection

Cure for 7 days33

Placing on Hardened ConcretePreparing Hardened Concrete

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Bonding New to Previously Hardened Concrete

Cement-sandgrout

Latex Epoxy

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1- Isolation Joints

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2- Contraction Joints

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Spacing of Contraction Joints in MetersSlab

thickness,mm

Maximum-sizeaggregate

less than 19 mm

Maximum-sizeaggregate

19 mm and larger100 2.4 3.0125 3.0 3.75150 3.75 4.5175 4.25 5.25200 5.0 6.0225 5.5 6.75250 6.0 7.5

Metric38

Making Contraction Joints

Dry-cut sawing concrete

Grooving toolon bull-float

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3- ConstructionJoints

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Typical Joint Layout

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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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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 time Edging Jointing (optional if hand tooled) Floating

Lapse of time Texturing (brooming/swirl float finish) Curing

Sidewalks, Driveways etc.

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Patching

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Curing Patches

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Cleaning Concrete Surfaces

Cleaning methods:

Water

Chemical

Mechanical

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Special Surface Finishes

Pattern and Textures

Exposed Aggregate Concrete

Colored Finishes

Stains, Paints and Clear

Coatings

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Placing andFinishing Concrete

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Videos 1/4

Placing and Consolidating Vibration

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Videos 2/4

Finishing I Finishing II

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Videos 3/4

Contraction Joints Jointing

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Videos 4/4

Improper Finishing

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