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Placing and Finishing Concrete

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Presentation on theme: "Placing and Finishing Concrete"— Presentation transcript:

1 Placing and Finishing Concrete
EB001 –Design and Control of Concrete Mixtures—14th Edition, 2002, Chapter 11, pages 191 to 217.

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 Fig A base course foundation for concrete pavement is shaped by an auto-trimmer to design grades, cross section and alignment by automatic sensors that follow string lines. (69935) Placing and Finishing Concrete

5 Preparation Before Placing Includes:
Moistening the subgrade Fig Water trucks with spray-bars are used to moisten subgrades and base course layers to achieve adequate compaction and to reduce the amount of water drawn out of concrete as it’s placed. (69931) Placing and Finishing Concrete

6 Preparation Before Placing Includes:
Compacting the subgrade Fig (left) Adequate compaction of a base course foundation for concrete pavement can be achieved by using a vibratory roller. (right) Vibratory plate compactors are also used to prepare subgrades under slabs. (69934, 69930) 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
Fig Wheelbarrows are used to place concrete in areas that are not easily accessed by other placement methods. (69929) Note placing slab how concrete is discharged into the previously placed concrete Fig Concrete should be placed as near as possible to its final position. (70009) Discharging into previously placed concrete Placing and Finishing Concrete

10 Incorrect Placement with Conveyor Belt
Baffle Mortar Rock Mortar Shallow hopper Fig The swing arm on a conveyor belt allows fresh concrete to be placed fairly evenly across a deck. (70002) Rock Mortar Placing and Finishing Concrete

11 Placement with Conveyor Belt
Belt Scraper No Separation Provide at least 0.6 m (24 in.) headroom for downpipe, elephant trunk or equivalent Fig The swing arm on a conveyor belt allows fresh concrete to be placed fairly evenly across a deck. (70002) Placing and Finishing Concrete

12 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 Fig Dump trucks deposit concrete ahead of a slip-form paver that places the entire width of a street in one pass. Epoxy coated dowels on metal chairs are positioned at a joint and spiked down to the base course just ahead of the paver. (69936) Placing and Finishing Concrete

13 Depositing Concrete Curb/Curb and Gutter
Concrete deposited into hopper of slip form curb and gutter machine which then extrudes the concrete into the desired shape Fig Curb machines continuously extrude low-slump concrete into a shape that immediately stands without support of formwork. (69937) 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 Placement lines Placing and Finishing Concrete

15 Horizontal Construction Joint
Fig A straight, horizontal construction joint can be built using this detail. Placing and Finishing Concrete

16 Horizontal Construction Joints
Fig Horizontal construction joints in walls with V-shaped (a) and beveled (b) rustication strips. 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. IX 56—Tremie placement for a bridge. Placing and Finishing Concrete

20 Consolidating Concrete
Internal Vibration External Vibration Fig Proper vibration makes possible the placement of stiff concrete mixtures, even in heavily-reinforced concrete members. (55806) Placing and Finishing Concrete

21 Internal Vibration Radius of Action Vibrator
Fig Internal vibrators are commonly used to consolidate concrete in walls, columns, beams, and slabs. (69970) Schematic: Radius of action ( R) of a vibrator is about three to five times the vibrator diameter (d). A Vibrator should be inserted about 1 ½ times the radius of action to consolidate concrete properly. The operator will be able to see the radius of action in the concrete. Radius of Action Placing and Finishing Concrete

22 Internal Vibrators Placing and Finishing Concrete 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) ,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) ,500 (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) ,000 (7-14) 4.6-15 (6-20) Stiff plastic concrete (less than 80-mm [3-in.] slump) in general construction . Table Range of Characteristics, Performance, and Applications of Internal Vibrators. Generally, extremely dry or very stiff concrete does not respond well to internal vibrators. While vibrator is operating in concrete. Distance over which concrete is fully consolidated. Assumes the insertion spacing is 11¼2 times the radius of action, and that vibrator operates two-thirds of time concrete is being placed. These ranges reflect not only the capability of the vibrator but also differences in workability of the mix, degree of deaeration desired, and other conditions experienced in construction. 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 129-18 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 Fig Honeycomb and rock pockets are the results of inadequate consolidation. (50207) Bottom: Sand streaks Placing and Finishing Concrete

27 Nuclear Gauges to Determine Subbase Compaction
Fig Nuclear gauges containing radioactive sources used to measure soil density and moisture can determine if a subbase has been adequately compacted. (69932) 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 Is the process of cutting off excess concrete to bring the top surface of a slab to proper grade. (Left) Hand strikeoff (screeding) by the use a a straightedge. The straightedge is moved across the slab from side to side in a saw like fashion advancing forward with each movement. (Right) Strikeoff with a vibratory screed which consolidates the concrete as the strikeoff is being done. Vibratory screeds are used for consolidating nonreinforced or lightly reinforced slabs up to 250 mm in thickness. Fig Vibratory screeds such as this truss-type unit reduce the work of strikeoff while consolidating the concrete. (55801) Placing and Finishing Concrete

29 Vibratory Screeds Placing and Finishing Concrete
Fig Where floor tolerances are not critical, an experienced operator using this vibratory screed does not need screed poles supported by chairs to guide the screed. Instead, he visually matches elevations to forms or previous passes. The process is called wet screeding. (69938) Fig A laser level stimulating the sensors on this screed guides the operator as he strikes off the concrete. Screed poles and chairs are not needed and fewer workers are required to place concrete. Laser screeds interfaced with total station surveying equipment can also strike off sloped concrete surfaces. (69939) Placing and Finishing Concrete

30 Bullfloating Placing and Finishing Concrete
Fig Bullfloating must be completed before any bleed water accumulates on the surface. (69940, 70011) Placing and Finishing Concrete

31 Darbying Placing and Finishing Concrete
Fig Darbying brings the surface to the specified level and is done in tight places where a bullfloat cannot reach. (70010) 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 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

33 Highway Straightedges
Fig Highway straightedges are used on highway pavement and floor construction where very flat surfaces are desired. (69941) 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. Fig Power floating using walk-behind and ride-on equipment. Footprints indicate proper timing. When the bleedwater sheen has evaporated and the concrete will sustain foot pressure with only slight indentation, the surface is ready for floating and final finishing operations. (69942) 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. Fig Hand floating (right hand) the surface with a hand float held flat on the concrete surface and moved in a sweeping arc with a slight sawing motion. Troweling (left hand) with blade tilted is performed before moving the kneeboards. (69933) Placing and Finishing Concrete

36 Brooming Placing and Finishing Concrete
Fig Brooming provides a slip-resistant surface mainly used on exterior concrete. (69943) Placing and Finishing Concrete

37 Tining Placing and Finishing Concrete
Fig (top) This machine is tining the surface of fresh concrete. (bottom) Tining of pavements improves tire traction and reduces hydroplaning. (69944, 69945) Placing and Finishing Concrete

38 Curing and Protection Cure for 7 days Placing and Finishing Concrete
Fig An excellent method of wet curing is to completely cover the surface with wet burlap and keep it continuously wet during the curing period. (69946) Placing and Finishing Concrete Cure for 7 days

39 Placing on Hardened Concrete
Preparing Hardened Concrete Fig Sandblasting can clean any size or shape surface – horizontal, vertical or overhead. Consult local environmental regulations regarding sandblasting. (55805) Placing and Finishing Concrete

40 Bonding New to Previously Hardened Concrete
Cement-sand grout Latex Epoxy Fig Application of a bonding grout just ahead of the overlay concrete. The grout must not dry out before the concrete is placed. (51995) Placing and Finishing Concrete

41 Isolation Joints Placing and Finishing Concrete
Fig Isolation joints permit horizontal and vertical movements between abutting faces of a slab and fixed parts of a structure. Placing and Finishing Concrete

42 Contraction Joints Placing and Finishing Concrete
Fig Contraction joints provide for horizontal movement in the plane of a slab or wall and induce controlled cracking caused by drying and thermal shrinkage. Fig Sawing a continuous cut in the top of a slab is one of the most economical methods for making a contraction joint. (69947) Placing and Finishing Concrete

43 Spacing of Contraction Joints in Meters
Slab thickness, mm Maximum-size aggregate less than 19 mm Maximum-size aggregate mm and larger 100 2.4 3.0 125 3.75 150 4.5 175 4.25 5.25 200 5.0 6.0 225 5.5 6.75 250 7.5 Table 11-2 (Metric). Spacing of Contraction Joints in Meters* *Spacings are appropriate for slumps between 100 mm and 150 mm. If concrete cools at an early age, shorter spacings may be needed to control random cracking. (A temperature difference of only 6°C may be critical.) For slumps less than 100 mm, joint spacing can be increased by 20%. When spacings exceed 4.5 m, load transfer by aggregate interlock decreases markedly. Placing and Finishing Concrete Metric

44 Spacing of Contraction Joints in Feet
Slab thickness, in. Maximum-size aggregate less than ¾ in. Maximum-size aggregate ¾ in. and larger 4 8 10 5 13 6 12 15 7 14 18 16 20 9 23 25 Table 11-2 (Inch-Pound Units). Spacing of Contraction Joints in Feet* *Spacings are appropriate for slumps between 4 in. and 6 in. If concrete cools at an early age, shorter spacings may be needed to control random cracking. (A temperature difference of only 10°F may be critical.) For slumps less than 4 in., joint spacing can be increased by 20%. When spacings exceed 15 ft, load transfer by aggregate interlock decreases markedly. Placing and Finishing Concrete Inch-Pound

45 Making Contraction Joints
Grooving tool on bull-float 110-13 136-19 Placing and Finishing Concrete Dry-cut sawing concrete

46 Construction Joints Placing and Finishing Concrete
Fig Construction joints are stopping places in the process of construction. Construction-joint types (a) and (b) are also used as contraction 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
100-mm to 150-mm (4-in. to 6-in.) slump 19-mm (3/4-in.) aggregate 150-mm (6-in.) thick slab Fig Typical joint layout for a 150-mm (6-in.) thick concrete floor on ground. Placing and Finishing Concrete

49 Finishing Operations Single Course Floors Consolidation Strike-off
Edging Darbying or Bull Floating Lapse of Time Grooving (if desired) Floating (power or hand) Troweling (power or hand) Second Troweling (power or hand) Final Troweling (hand) Curing If necessary, tooled edges and joints should be rerun after troweling to maintain uniformity and true lines. 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 Texturing (brooming/swirl float finish) Curing Note: no troweling of exterior slabs----knocks out air at surface where you need it for durability and smooth troweled surfaces are very slippery when wet Placing and Finishing Concrete

51 Patching Placing and Finishing Concrete
Fig Concrete prepared for patch installation. (69972) Fig Patch installation. Placing and Finishing Concrete

52 Curing Patches Placing and Finishing Concrete
Fig Good curing is essential to successful patching. This patch is covered with polyethylene sheeting plus rigid insulation to retain moisture and heat for rapid hydration and strength gain. (40434) Placing and Finishing Concrete

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

54 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

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

56 Placing and Finishing Concrete
Fig Patterned, textured, and colored concretes are very attractive. (59031, 53598, 59003, 47835, 44898) Placing and Finishing Concrete

57 Working Safely with Concrete
Protect: Your Eyes Your Back Your Skin Placing and Finishing Concrete

58 Precautions Placing and Finishing Concrete
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. Placing and Finishing Concrete

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

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

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

62 Videos 4/4 Improper Finishing Placing and Finishing Concrete

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