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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.

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Presentation on theme: "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."— Presentation transcript:

1 Placing and Finishing Concrete

2 Basic Requirements for Placing Concrete (1) n Preserve concrete quality u Water-cement ratio u Slump u Air-content u Homogeneity n Avoid separation of aggregate and mortar

3 Placing and Finishing Concrete Basic Requirements for Placing Concrete (2) n Avoid excessive horizontal movement n Consolidate adequately n Maintain sufficient placement capacity n Choose the right equipment for the concrete

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

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

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

7 Placing and Finishing Concrete Depositing Concrete n DO NOT (a)disturb saturated subgrades so bearing capacity is maintained (b)deposit on frozen subgrade n Deposit continuously and as near as possible to its final position n Rate of placement should be such that previously placed concrete has not set when the next layer is placed upon it

8 Placing and Finishing Concrete Depositing Concrete n Start placing along perimeter at one end with each batch discharged against previously placed concrete n 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

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

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

11 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

12 Placing and Finishing Concrete Depositing Concrete Pavement Slab n Concrete deposited in front of slip form paver by dump trucks n Concrete spread evenly across the subgrade by the paver before consolidation and finishing

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

14 Placing and Finishing Concrete Depositing Concrete n Deposit in horizontal layers of uniform thickness u Reinforced 150 mm to 500 mm u Mass 375 mm to 500 mm n Consolidate each layer before next is placed n Timely placement & consolidation prevents flow lines and cold joints Walls

15 Placing and Finishing Concrete Horizontal Construction Joint

16 Placing and Finishing Concrete Horizontal Construction Joints

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

18 Placing and Finishing Concrete Placing Concrete Under Water n Water velocity 3 m (10 ft) / min. n Water temperature 5°C (if below test for strength gain) n w/c 0.45 n Cementing materials content 390 kg/m 3 (600 lb/yd 3 ) n Slump range 150 to 225 mm (6 to 10 in.) Basic Recommendations

19 Placing and Finishing Concrete Placing Concrete Underwater n 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.

20 Placing and Finishing Concrete Consolidating Concrete n Internal Vibration n External Vibration

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

22 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 (3/4-1½) , (3-6) (1-5) Plastic and flowing concrete in thin members. Also used for lab test specimens (1¼-2½) , (5-10) (3-10) Plastic concrete in thin walls, columns, beams, precast piles, thin slabs, and along construction joints (2-3½) , (7-14) (6-20) Stiff plastic concrete (less than 80-mm [3- in.] slump) in general construction. Adapted from ACI 309

23 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

24 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.

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

26 Placing and Finishing Concrete Consolidating Concrete Inadequate consolidation can result in: u Honeycomb u Excessive amount of entrapped air voids (bugholes) u Sand streaks u Cold joints u Placement lines u Subsidence cracking

27 Placing and Finishing Concrete Nuclear Gauges to Determine Subbase Compaction

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

29 Placing and Finishing Concrete Vibratory Screeds

30 Placing and Finishing Concrete Bullfloating

31 Placing and Finishing Concrete Darbying

32 Placing and Finishing Concrete Edging n Required along all edge forms, isolation and construction joints in floors and exterior slabs n Cut concrete away from forms to a depth of 25 mm with a pointed mason or margin trowel n 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

33 Placing and Finishing Concrete Highway Straightedges

34 Placing and Finishing Concrete Floating (Power or Hand) n To embed aggregate particles just beneath the surface n To remove slight imperfections, humps, and voids n To compact the mortar at the surface in preparation for additional finishing operations.

35 Placing and Finishing Concrete Troweling n Creates smooth, hard,dense surface n Exterior concrete should not be troweled because: u it can lead to a loss of entrained air caused by overworking the surface u troweled surfaces can be slippery when wet.

36 Placing and Finishing Concrete Brooming

37 Placing and Finishing Concrete Tining

38 Placing and Finishing Concrete Curing and Protection n Cure for 7 days

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

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

41 Placing and Finishing Concrete Isolation Joints

42 Placing and Finishing Concrete Contraction Joints

43 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 Metric

44 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 Inch-Pound

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

46 Placing and Finishing Concrete Construction Joints

47 Placing and Finishing Concrete Joint Layout for Slabs n Panels created by contraction joints should be approximately square n Panel aspect ratio max. 1½ to 1 n Contraction (control) joints should only terminate at a free edge or at an isolation joint n When joint spacing exceeds 4.5 m (15 ft), load transfer by aggregate interlock decreases significantly Basic Factors to Remember

48 Placing and Finishing Concrete Typical Joint Layout

49 Placing and Finishing Concrete Finishing Operations n Consolidation n Strike-off n Edging n Darbying or Bull Floating Lapse of Time n Edging n Grooving (if desired) n Floating (power or hand) n Troweling (power or hand) Lapse of Time n Second Troweling (power or hand) n Final Troweling (hand) n Curing Single Course Floors

50 Placing and Finishing Concrete Finishing Operations - Exterior Slabs n Consolidation n Strike-off n Depress aggregate with metal/wood strip at joint location if hand tooled n Darbying or Bull floating Lapse of time n Edging n Jointing (optional if hand tooled) n Floating Lapse of time n Texturing (brooming/swirl float finish) n Curing Sidewalks, Driveways etc.

51 Placing and Finishing Concrete Patching

52 Placing and Finishing Concrete Curing Patches

53 Placing and Finishing Concrete Cleaning Concrete Surfaces n Cleaning methods: u Water u Chemical u Mechanical

54 Placing and Finishing Concrete Finishing Formed Surfaces n Rough-form finishes n Smooth off-the-form finish n Smooth, rubbed finish n Sand-floated finish n Grout cleandown (sack-rubbed finish)

55 Placing and Finishing Concrete Special Surface Finishes n Pattern and Textures n Exposed Aggregate Concrete n Colored Finishes n Stains, Paints and Clear Coatings

56 Placing and Finishing Concrete

57 Working Safely with Concrete Protect: n Your Eyes n Your Back n Your Skin

58 Placing and Finishing Concrete Precautions 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.

59 Placing and Finishing Concrete Videos 1/4 Placing and Consolidating Vibration

60 Placing and Finishing Concrete Videos 2/4 Finishing I Finishing II

61 Placing and Finishing Concrete Videos 3/4 Contraction Joints Jointing

62 Placing and Finishing Concrete Videos 4/4 Improper Finishing


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