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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. Basic Requirements for Placing Concrete (2). Avoid excessive horizontal movement

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Placing and Finishing Concrete

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  1. Placing and Finishing Concrete

  2. 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

  3. 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

  4. Preparation Before Placing Includes: • Trimming the subgrade Placing and Finishing Concrete

  5. Preparation Before Placing Includes: • Moistening the subgrade Placing and Finishing Concrete

  6. Preparation Before Placing Includes: • Compacting the subgrade Placing and Finishing Concrete

  7. 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

  8. Depositing Concrete Slab Construction • 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) Placing and Finishing Concrete

  9. Depositing Concrete Effective use of wheelbarrows Discharging into previously placed concrete Placing and Finishing Concrete

  10. Incorrect Placement with Conveyor Belt Baffle Mortar Mortar Rock Shallow hopper Rock Mortar Placing and Finishing Concrete

  11. Belt Scraper Provide at least 0.6 m (24 in.) headroom for downpipe, elephant trunk or equivalent No Separation Placement with Conveyor Belt Placing and Finishing Concrete

  12. Depositing Concrete PavementSlab • 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

  13. Depositing Concrete • Concrete deposited into hopper of slip form curb and gutter machine which then extrudes the concrete into the desired shape Curb/Curb and Gutter Placing and Finishing Concrete

  14. Depositing Concrete Walls • 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 Placing and Finishing Concrete

  15. Horizontal Construction Joint Placing and Finishing Concrete

  16. Horizontal Construction Joints Placing and Finishing Concrete

  17. Underwater Placement Methods • Tremie • Pump • Bottom dump buckets • Grouted preplaced aggregate (specialized) • Toggle bags • Bagwork • Diving bell Placing and Finishing Concrete

  18. 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

  19. 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

  20. Consolidating Concrete • Internal Vibration • External Vibration Placing and Finishing Concrete

  21. Vibrator d R 1½ R Internal Vibration Radius of Action Placing and Finishing Concrete

  22. Internal Vibrators Placing and Finishing Concrete Adapted from ACI 309

  23. 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

  24. 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

  25. External Vibration • Form vibrators • Vibrating tables • Surface vibrators • Vibratory screeds • Plate vibrators • Vibratory roller screeds • Vibratory hand floats or trowels Placing and Finishing Concrete

  26. 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

  27. Nuclear Gauges to Determine Subbase Compaction Placing and Finishing Concrete

  28. Screeding (Strikeoff) The process of cutting off excess concrete to bring the top surface of a slab to proper grade Placing and Finishing Concrete

  29. Vibratory Screeds Placing and Finishing Concrete

  30. Bullfloating Placing and Finishing Concrete

  31. Darbying Placing and Finishing Concrete

  32. Edging Edging densifies and compacts concrete next to forms where floating is less effective • 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 Placing and Finishing Concrete

  33. Highway Straightedges Placing and Finishing Concrete

  34. 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

  35. 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

  36. Brooming Placing and Finishing Concrete

  37. Tining Placing and Finishing Concrete

  38. Curing and Protection • Cure for 7 days Placing and Finishing Concrete

  39. Placing on Hardened Concrete Preparing Hardened Concrete Placing and Finishing Concrete

  40. Bonding New to Previously Hardened Concrete • Cement-sand grout • Latex • Epoxy Placing and Finishing Concrete

  41. Isolation Joints Placing and Finishing Concrete

  42. Contraction Joints Placing and Finishing Concrete

  43. Spacing of Contraction Joints in Meters Placing and Finishing Concrete Metric

  44. Spacing of Contraction Joints in Feet Placing and Finishing Concrete Inch-Pound

  45. Making Contraction Joints Grooving tool on bull-float Placing and Finishing Concrete Dry-cut sawing concrete

  46. Construction Joints Placing and Finishing Concrete

  47. Joint Layout for Slabs Basic Factors to Remember • 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 Placing and Finishing Concrete

  48. Typical Joint Layout Placing and Finishing Concrete

  49. Finishing Operations Single Course Floors • 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 Placing and Finishing Concrete

  50. Finishing Operations - Exterior Slabs Sidewalks, Driveways etc. • 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 Placing and Finishing Concrete

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