NATIONAL INSTITUTE OF TECHNOLOGY AGARTALA
Presented By:- RAVI GUPTA (10UCE111) Department Of Civil Engineering NIT Agartala
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
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
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
Underwater Placement Methods
TremiePumpBottom dump bucketsGrouted preplaced aggregate (specialized)Bagwork
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 0.45Cementing materials content
390 kg/m3 (600 lb/yd3)Slump range 150 to 225 mm (6
to 10 in.)
Basic Recommendations
Placing and Finishing Concrete
Placing Concrete Underwatern Used: Tremie
n Advantages: Can be used to funnel concrete down through the water into the structure.
n 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
R
1½ R
Vibrator
Radius of Action
Placing and Finishing Concrete
Internal VibratorsDiameterof 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)
8000-12,000180-360(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
CORRECTVertical penetration a few inches into previous lift (which should not yet be rigid) of systematic regular intervals will give adequate consolidationINCORRECTHaphazard 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
Consolidating ConcreteInadequate 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
Darbying
Placing and Finishing Concrete
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
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
LatexEpoxy
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
Making Contraction Joints
Dry-cut sawing concrete
Grooving tool on bull-float
Placing and Finishing Concrete
Construction Joints
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 ConcreteProtect:
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.