Ppt

NATIONAL INSTITUTE OF TECHNOLOGY AGARTALA

Placing and Finishing
Concrete

Presented By:- RAVI GUPTA (10UCE111)
Department Of Civil Engineering
NIT Agartala

Basic Requirements for
Placing Concrete (1)

 Preserve concrete
quality
◦ Water-cement ratio
◦ Slump
◦ Air-content
◦ Homogeneity
 Avoid separation of
aggregate and mortar
Placing and Finishing Concrete

Preparation Before Placing
Includes:
 Trimming the subgrade


Includes:
 Moistening the subgrade


Includes:
 Compacting the subgrade


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 Concrete
it

Depositing Concrete
Effective use of
wheelbarrows

Discharging into previously
placed concrete Concrete

Incorrect Placement with
Conveyor Belt

Baffle

Mortar Rock Mortar

Shallow
hopper

Rock Mortar

Placement with Conveyor
Belt

Provide at least 0.6 m Belt Scraper
(24 in.) headroom for
downpipe, elephant
trunk or equivalent
No
Separation


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


 Tremie Underwater Placement
 Pump Methods
 Bottom dump buckets
 Grouted preplaced aggregate (specialized)
 Bagwork


Placing Concrete
Under Water
Basic Recommendations
 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.) Placing and Finishing Concrete

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.

Consolidating
Concrete

 Internal Vibration

 External Vibration


Internal Vibration

Vibrator

d

1½ R

Radius of Action

Internal Vibrators
Recommended Approximate Rate of
Diameter frequency, radius of placement,
of head, vibrations per action, mm m3/h
mm (in.) minute (in.) (yd3/h) Application
Plastic and flowing
20-40 80-150 0.8-4 concrete in thin
9000-15,000 members. Also used
(3/4-1½) (3-6) (1-5) for lab test
specimens.
Plastic concrete in
30-60 130-250 2.3-8 thin walls, columns,
8500-12,500 beams, precast piles,
(1¼-2½) (5-10) (3-10) thin slabs, and along
construction joints.
Stiff plastic concrete
50-90 180-360 4.6-15 (less than 80-mm [3-
8000-12,000 in.] slump) in general
(2-3½) (7-14) (6-20)
construction .

Placing and Finishing Concrete Adapted from ACI 309

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

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


Nuclear Gauges to Determine
Subbase Compaction


Screeding (Strikeoff)
The process of cutting off excess
concrete to bring the top surface
of a slab to proper grade


Vibratory
Screeds


Darbying


Edging
Edging densifies and compacts concrete
next to forms where floating is less effective

 Required along all edge forms,
isolation and construction
joints
in 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

Highway Straightedges


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.

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.


Brooming


Tining


Curing and Protection

 Cure for 7 days

Placing on Hardened Concrete
Preparing Hardened Concrete


Bonding New to Previously
Hardened Concrete

 Cement-sand
grout
 Latex
 Epoxy


Contraction Joints


Spacing of Contraction
Joints in Meters
Slab Maximum-size Maximum-size
thickness, aggregate aggregate
mm less than 19 mm 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

Placing and Finishing Concrete Metric

Making Contraction Joints

Grooving tool
on bull-float

Dry-cut sawing concrete

Construction
Joints


Patching


Curing Patches


Cleaning Concrete
Surfaces

 Cleaning

methods:
◦ Water
◦ Chemical
◦ Mechanical

Finishing Formed
Surfaces

 Rough-form finishes
 Smooth off-the-form finish
 Smooth, rubbed finish
 Sand-floated finish
 Grout cleandown
(sack-rubbed finish)

Special Surface Finishes

 Pattern and Textures
 Exposed Aggregate
Concrete
 Colored Finishes
 Stains, Paints and Clear
Coatings


Working Safely with Concrete
Protect:

 Your Eyes

 Your Back

 Your Skin


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

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