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process and techniques of placing of concrete

process and techniques of placing of concrete

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    • NATIONAL INSTITUTE OF TECHNOLOGY AGARTALA Placing and Finishing Concrete Presented By:- RAVI GUPTA (10UCE111) Department Of Civil Engineering NIT Agartala
    • Basic Requirements forPlacing Concrete (1)  Preserve concrete quality ◦ Water-cement ratio ◦ Slump ◦ Air-content ◦ Homogeneity  Avoid separation of aggregate and mortar Placing and Finishing Concrete
    • Preparation Before PlacingIncludes:  Trimming the subgrade Placing and Finishing Concrete
    • Preparation Before PlacingIncludes:  Moistening the subgrade Placing and Finishing Concrete
    • Preparation Before PlacingIncludes:  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 Concrete Placing and Finishing it
    • Depositing Concrete Effective use of wheelbarrows Discharging into previously placed concrete Concrete Placing and Finishing
    • Incorrect Placement withConveyor Belt Baffle Mortar Rock Mortar Shallow hopper Rock Mortar Placing and Finishing Concrete
    • Placement with ConveyorBelt Provide at least 0.6 m Belt Scraper (24 in.) headroom for downpipe, elephant trunk or equivalent No Separation 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
    •  Tremie Underwater Placement Pump Methods Bottom dump buckets Grouted preplaced aggregate (specialized) Bagwork Placing and Finishing Concrete
    • Placing ConcreteUnder WaterBasic 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 ConcreteUnderwater 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
    • ConsolidatingConcrete Internal Vibration External Vibration Placing and Finishing Concrete
    • Internal Vibration Vibrator d 1½ R Radius of Action Placing and Finishing Concrete
    • 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 ofEach 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
    • 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 DetermineSubbase 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
    • VibratoryScreeds Placing and Finishing Concrete
    • Darbying Placing and Finishing Concrete
    • EdgingEdging densifies and compacts concretenext 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 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
    • TiningPlacing 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 PreviouslyHardened Concrete  Cement-sand grout  Latex  Epoxy Placing and Finishing Concrete
    • Contraction Joints Placing and Finishing Concrete
    • 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 7.5Placing and Finishing Concrete Metric
    • Making Contraction Joints Grooving tool on bull-float Dry-cut sawing concrete Placing and Finishing Concrete
    • Construction Joints Placing and Finishing Concrete
    • PatchingPlacing and Finishing Concrete
    • Curing Patches Placing and Finishing Concrete
    • Cleaning ConcreteSurfaces  Cleaning methods: ◦ Water ◦ Chemical ◦ Mechanical Placing and Finishing Concrete
    • Finishing FormedSurfaces  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
    • PrecautionsWARNING: Contact with wet (unhardened) concrete, mortar,cement, or cement mixtures can cause SKIN IRRITATION, SEVERECHEMICAL BURNS (THIRD-DEGREE), or SERIOUS EYEDAMAGE. Frequent exposure may be associated with irritant and/orallergic contact dermatitis. Wear water-proof gloves, a long-sleevedshirt, full-length trousers, and proper eye protection when workingwith these materials. If you have to stand in wet concrete, usewaterproof boots that are high enough to keep concrete from flowinginto them. Wash wet concrete, mortar, cement, or cement mixturesfrom your skin immediately. Flush eyes with clean water immediatelyafter contact. In-direct contact through clothing can be as serious asdirect contact, so promptly rinse out wet concrete, mortar, cement,or cement mixtures from clothing. Seek immediate medical attentionif you have persistent or severe discomfort. http://www.cement.org/pdf_files/ms271.pdf Placing and Finishing Concrete