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Placing and Finishing Concrete

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Placing and Finishing Concrete Basic Requirements for Placing Concrete (1) Preserve concrete quality Water-cement ratio Slump Air-content Homogeneity Avoid separation ... – PowerPoint PPT presentation

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Title: Placing and Finishing Concrete


1
Placing and Finishing Concrete
2
Basic Requirements for Placing Concrete (1)
  • Preserve concrete quality
  • Water-cement ratio
  • Slump
  • Air-content
  • Homogeneity
  • Avoid separation of aggregate and mortar

3
Basic Requirements for Placing Concrete (2)
  • Avoid excessive horizontal movement
  • Consolidate adequately
  • Maintain sufficient placement capacity
  • Choose the right equipment for the concrete

4
Preparation Before Placing Includes
  • Trimming the subgrade

5
Preparation Before Placing Includes
  • Moistening the subgrade

6
Preparation Before Placing Includes
  • Compacting the subgrade

7
Depositing Concrete
  • DO NOT
  • (a) disturb saturated subgrades so bearing
    capacity is maintained
  • (b) deposit on frozen subgrade
  • Deposit continuously and as near as possible to
    its final position
  • Rate of placement should be such that previously
    placed concrete has not set when the next layer
    is placed upon it

8
Depositing Concrete
Slab Construction
  • Start placing along perimeter at one end with
    each batch discharged against previously placed
    concrete
  • Do not
  • (a) dump in separate piles then level and
    work together
  • (b) deposit in large piles then move
    horizontally into position
  • These practices result in segregation
  • (mortar flows ahead of coarser material)

9
Depositing Concrete
Effective use of wheelbarrows
Discharging into previously placed concrete
10
Incorrect Placement with Conveyor Belt
Baffle
Mortar
Mortar
Rock
Shallow hopper
Rock
Mortar
11
Placement with Conveyor Belt
12
Depositing Concrete
  • Pavement Slab
  • Concrete deposited in front of slip form paver by
    dump trucks
  • Concrete spread evenly across the subgrade by the
    paver before consolidation and finishing

13
Depositing Concrete
Curb/Curb and Gutter
  • Concrete deposited into hopper of slip form curb
    and gutter machine which then extrudes the
    concrete into the desired shape

14
Depositing Concrete
Walls
  • 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

15
Horizontal Construction Joint
16
Horizontal Construction Joints
17
Underwater Placement Methods
  • Tremie
  • Pump
  • Bottom dump buckets
  • Grouted preplaced aggregate (specialized)
  • Toggle bags
  • Bagwork
  • Diving bell

18
Placing Concrete Under Water
Basic Recommendations
  • 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.)

19
Placing Concrete Underwater
  • Used Tremie
  • Advantages Can be used to funnel concrete down
    through the water into the structure.
  • Watch for Discharge end always has to be buried
    in fresh concrete to ensure seal between water
    and concrete mass.

20
Consolidating Concrete
  • Internal Vibration
  • External Vibration

21
Internal Vibration
Radius of Action
22
Internal Vibrators
Diameter of head, mm (in.) Recommended frequency, vibrations per minute Approximate radius of action, mm (in.) Rate of placement,m3/h (yd3/h) Application
20-40 (3/4-1½) 9000-15,000 80-150 (3-6) 0.8-4 (1-5) Plastic and flowing concrete in thin members. Also used for lab test specimens.
30-60 (1¼-2½) 8500-12,500 130-250 (5-10) 2.3-8 (3-10) Plastic concrete in thin walls, columns, beams, precast piles, thin slabs, and along construction joints.
50-90 (2-3½) 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
23
Systematic Vibration of Each New Lift
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
24
Placing Concrete in a Sloping Lift
CORRECT 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 slope
the upper concrete tends to pull apart especially
when vibrated below as this starts flow and
removes from concrete above.
25
External Vibration
  • Form vibrators
  • Vibrating tables
  • Surface vibrators
  • Vibratory screeds
  • Plate vibrators
  • Vibratory roller screeds
  • Vibratory hand floats or trowels

26
Consolidating Concrete
  • Inadequate consolidation can result in
  • Honeycomb
  • Excessive amount of entrapped air voids
    (bugholes)
  • Sand streaks
  • Cold joints
  • Placement lines
  • Subsidence cracking

27
Nuclear Gauges to Determine Subbase Compaction
28
Screeding (Strikeoff)
  • The process of cutting off excess concrete to
    bring the top surface of a slab to proper grade

29
Vibratory Screeds
30
Bullfloating
31
Darbying
32
Edging
Edging densifies and compacts concrete next to
forms where floating is less effective
  • 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
    finishing operation for interior slabs

33
Highway Straightedges
34
Floating (Power or Hand)
  • To embed aggregate particles just beneath the
    surface
  • To remove slight imperfections, humps, and voids
  • To compact the mortar at the surface in
    preparation for additional finishing operations.

35
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.

36
Brooming
37
Tining
38
Curing and Protection
  • Cure for 7 days

39
Placing on Hardened Concrete
Preparing Hardened Concrete
40
Bonding New to Previously Hardened Concrete
  • Cement-sand grout
  • Latex
  • Epoxy

41
Isolation Joints
42
Contraction Joints
43
Spacing of Contraction Joints in Meters
Slab 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 6.0
225 5.5 6.75
250 6.0 7.5
Metric
44
Spacing of Contraction Joints in Feet
Slab thickness, in. Maximum-size aggregate less than ¾ in. Maximum-size aggregate ¾ in. and larger
4 8 10
5 10 13
6 12 15
7 14 18
8 16 20
9 18 23
10 20 25
Inch-Pound
45
Making Contraction Joints
Grooving tool on bull-float
Dry-cut sawing concrete
46
Construction Joints
47
Joint Layout for Slabs
Basic Factors to Remember
  • Panels created by contraction joints should be
    approximately square
  • Panel aspect ratio max. 1½ 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

48
Typical Joint Layout
49
Finishing Operations
Single Course Floors
  • 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

50
Finishing Operations - Exterior Slabs
Sidewalks, Driveways etc.
  • 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

51
Patching
52
Curing Patches
53
Cleaning Concrete Surfaces
  • Cleaning methods
  • Water
  • Chemical
  • Mechanical

54
Finishing Formed Surfaces
  • Rough-form finishes
  • Smooth off-the-form finish
  • Smooth, rubbed finish
  • Sand-floated finish
  • Grout cleandown
  • (sack-rubbed finish)

55
Special Surface Finishes
  • Pattern and Textures
  • Exposed Aggregate Concrete
  • Colored Finishes
  • Stains, Paints and Clear Coatings

56
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57
Working Safely with Concrete
  • Protect
  • Your Eyes
  • Your Back
  • Your Skin

58
Precautions
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,
use waterproof 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.
http//www.cement.org/pdf_files/ms271.pdf
59
Videos 1/4
Placing and Consolidating
Vibration
60
Videos 2/4
Finishing I
Finishing II
61
Videos 3/4
Contraction Joints
Jointing
62
Videos 4/4
Improper Finishing
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