Placing and Finishing Concrete. Basic Requirements for Placing Concrete (1) n Preserve concrete quality u Water-cement ratio u Slump u Air-content u Homogeneity

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


Basic Requirements for Placing Concrete (2)

Avoid excessive horizontal movement

Consolidate adequately Maintain sufficient placement

capacity Choose the right equipment for

the concrete


Preparation Before Placing Includes:

Trimming the subgrade



Moistening the subgrade



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 it


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


Depositing Concrete

Discharging into previously placed concrete

Effective use of wheelbarrows


Incorrect Placement with Conveyor Belt

Baffle

Mortar

Rock Mortar

Mortar

Rock

Shallow hopper


Placement with Conveyor Belt

Belt Scraper

No Separation

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


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


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


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


Horizontal Construction Joint


Horizontal Construction Joints


Underwater Placement Methods

Tremie Pump Bottom dump buckets Grouted preplaced

aggregate (specialized) Toggle bags Bagwork Diving bell


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


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

d

R

1½ R

Vibrator

Radius of Action


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)

9000-15,00080-150(3-6)

0.8-4(1-5)

Plastic and flowing concrete in thin

members. Also used for lab test specimens.

30-60(1¼-2½)

8500-12,500130-250(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


Systematic Vibration of Each New Lift

CORRECTCORRECTVertical penetration a few inches into previous lift (which should not yet be rigid) of systematic regular intervals will give adequate consolidationINCORRECTINCORRECTHaphazard random penetration of the vibrator at all angles and spacings without sufficient depth will not assure intimate combination of the two layers


Placing Concrete in a Sloping Lift

CORRECTCORRECTStart placing at bottom of slope so that compaction is increased by weight of newly added concrete. Vibration consolidates the concrete.INCORRECTINCORRECTWhen 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.


External Vibration

Form vibrators Vibrating tables Surface vibrators

Vibratory screeds Plate vibrators Vibratory roller screeds Vibratory hand floats or

trowels


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


Bullfloating


Darbying


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 finishing operation for interior slabs

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


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 ConcretePreparing Hardened Concrete


Bonding New to Previously Hardened Concrete

Cement-sand grout

Latex Epoxy


Isolation Joints


Contraction Joints


Spacing of Contraction Joints in Meters

Slab thickness,

mm

Maximum-size aggregate

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

MetricMetric


Spacing of Contraction Joints in Feet

Slab thickness, in.

Maximum-size aggregate less than ¾ in.


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-PoundInch-Pound


Making Contraction Joints

Dry-cut sawing concrete

Grooving tool on bull-float


Construction Joints


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


Typical Joint Layout


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


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.


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

http://www.cement.org/pdf_files/ms271.pdfhttp://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.


Videos 1/4

Placing and Consolidating Vibration


Videos 2/4

Finishing I Finishing II


Videos 3/4

Contraction Joints Jointing


Videos 4/4

Improper Finishing

Documents

Placing and Finishing Concrete. Basic Requirements for Placing Concrete (1) n Preserve concrete quality u Water-cement ratio u Slump u Air-content u Homogeneity