Placing and Finishing Concrete

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25 Νοε 2013 (πριν από 3 χρόνια και 6 μήνες)

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Placing and Finishing
Concrete

Placing and
Finishing Concrete

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

Basic Requirements for
Placing Concrete (2)


Avoid excessive horizontal
movement


Consolidate adequately


Maintain sufficient placement
capacity


Choose the right equipment for
the concrete

Placing and
Finishing Concrete

Preparation Before Placing
Includes:


Trimming the subgrade

Placing and
Finishing Concrete

Preparation Before Placing
Includes:


Moistening the subgrade

Placing and
Finishing Concrete

Preparation Before Placing
Includes:


Compacting the subgrade

Placing and
Finishing Concrete

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

Placing and
Finishing Concrete

Depositing Concrete


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)

Slab Construction

Placing and
Finishing Concrete

Depositing Concrete

Discharging into previously
placed concrete

Effective use of
wheelbarrows

Placing and
Finishing Concrete

Incorrect Placement with
Conveyor Belt

Baffle

Mortar

Rock

Mortar

Mortar

Rock

Shallow
hopper

Placing and
Finishing Concrete

Placement with Conveyor
Belt

Belt Scraper

No
Separation

Provide at least 0.6 m
(24 in.) headroom for
downpipe, elephant
trunk or equivalent

Placing and
Finishing Concrete

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

Placing and
Finishing Concrete

Curb/Curb and Gutter

Depositing Concrete


Concrete deposited
into hopper of slip
form curb and gutter
machine which then
extrudes the concrete
into the desired
shape

Placing and
Finishing 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

Placing and
Finishing Concrete

Horizontal Construction Joint

Placing and
Finishing Concrete

Horizontal Construction Joints

Placing and
Finishing Concrete

Underwater Placement
Methods


Tremie


Pump


Bottom dump buckets


Grouted preplaced
aggregate (specialized)


Toggle bags


Bagwork


Diving bell

Placing and
Finishing Concrete

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/m
3
(600 lb/yd
3
)


Slump range 150 to 225 mm (6 to
10 in.)


Basic Recommendations

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.

Placing and
Finishing Concrete

Consolidating
Concrete


Internal Vibration



External Vibration

Placing and
Finishing Concrete

Internal Vibration

d

1
½ R

Vibrator

Radius of Action

Placing and
Finishing Concrete

Internal Vibrators

Diameter

of head,

mm (in.)

Recommended
frequency,
vibrations per
minute

Approximate
radius of
action, mm
(in.)

Rate of
placement,
m
3
/h
(yd
3
/h)

Application

20
-
40

(3/4
-
1
½
)

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

(1
¼
-
2
½
)

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
-
3
½
)

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

Placing and
Finishing Concrete

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

Placing and
Finishing Concrete

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.

Placing and
Finishing Concrete

External Vibration


Form vibrators


Vibrating tables


Surface vibrators


Vibratory screeds


Plate vibrators


Vibratory roller screeds


Vibratory hand floats or
trowels

Placing and
Finishing Concrete

Consolidating Concrete


Inadequate consolidation
can result in:


Honeycomb


Excessive amount of entrapped
air voids (bugholes)


Sand streaks


Cold joints


Placement lines


Subsidence cracking

Placing and
Finishing Concrete

Nuclear Gauges to Determine
Subbase Compaction

Placing and
Finishing Concrete

Screeding (Strikeoff)

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

Placing and
Finishing Concrete

Vibratory
Screeds

Placing and
Finishing Concrete

Bullfloating

Placing and
Finishing Concrete

Darbying

Placing and
Finishing Concrete

Edging


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


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

Placing and
Finishing Concrete

Highway Straightedges

Placing and
Finishing Concrete

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.

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.

Placing and
Finishing Concrete

Brooming

Placing and
Finishing Concrete

Tining

Placing and
Finishing Concrete

Curing and Protection


Cure for 7 days

Placing and
Finishing Concrete

Placing on Hardened Concrete

Preparing Hardened Concrete

Placing and
Finishing Concrete

Bonding New to Previously
Hardened Concrete


Cement
-
sand
grout


Latex


Epoxy

Placing and
Finishing Concrete

Isolation Joints

Placing and
Finishing Concrete

Contraction Joints

Placing and
Finishing Concrete

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

Placing and
Finishing Concrete

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

Placing and
Finishing Concrete

Making Contraction Joints

Dry
-
cut sawing concrete

Grooving tool
on bull
-
float

Placing and
Finishing Concrete

Construction
Joints

Placing and
Finishing Concrete

Joint Layout for Slabs


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

Basic Factors to Remember

Placing and
Finishing Concrete

Typical Joint Layout

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

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 time


Edging


Jointing (optional if hand tooled)


Floating


Lapse of time


Texturing (brooming/swirl float finish)


Curing


Sidewalks, Driveways etc.

Placing and
Finishing Concrete

Patching

Placing and
Finishing Concrete

Curing Patches

Placing and
Finishing Concrete

Cleaning Concrete
Surfaces


Cleaning methods:


Water


Chemical


Mechanical

Placing and
Finishing Concrete

Finishing Formed
Surfaces


Rough
-
form finishes


Smooth off
-
the
-
form finish


Smooth, rubbed finish


Sand
-
floated finish


Grout cleandown


(sack
-
rubbed finish)

Placing and
Finishing Concrete

Special Surface Finishes


Pattern and Textures


Exposed Aggregate Concrete


Colored Finishes


Stains, Paints and Clear
Coatings

Placing and
Finishing Concrete

Placing and
Finishing Concrete

Working Safely with Concrete

Protect:



Your Eyes



Your Back




Your Skin

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, 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.

Placing and
Finishing Concrete

Videos 1/4

Placing and Consolidating

Vibration

Placing and
Finishing Concrete

Videos 2/4

Finishing I

Finishing II

Placing and
Finishing Concrete

Videos 3/4

Contraction Joints

Jointing

Placing and
Finishing Concrete

Videos 4/4

Improper Finishing