Placing and Finishing Concrete Basic Requirements for Placing

Placing and Finishing Concrete

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

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

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

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

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

Depositing Concrete n n n Placing and Finishing 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

Depositing Concrete Slab Construction n n 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 Placing and Finishing Concrete (mortar flows ahead of coarser material)

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

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

Placement with Conveyor Belt Provide at least 0. 6 m (24 in. ) headroom for downpipe, elephant trunk or equivalent Placing and Finishing Concrete Belt Scraper No Separation

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

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

Depositing Concrete Walls n Deposit in horizontal layers of uniform thickness u u n n Placing and Finishing Concrete 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

Horizontal Construction Joint Placing and Finishing Concrete

Horizontal Construction Joints Placing and Finishing Concrete

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

Placing Concrete Under Water Basic Recommendations n n n Placing and Finishing Concrete 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/m 3 (600 lb/yd 3) Slump range 150 to 225 mm (6 to 10 in. )

Placing Concrete Underwater n n n Placing and Finishing Concrete 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.

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

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

Internal Vibrators Recommended Approximate Rate of Diameter frequency, radius of placement, of head, vibrations per action, mm m 3/h mm (in. ) minute (in. ) (yd 3/h) 20 -40 (3/4 -1½) 9000 -15, 000 80 -150 (3 -6) 0. 8 -4 (1 -5) 30 -60 (1¼-2½) 8500 -12, 500 130 -250 (5 -10) 2. 3 -8 (3 -10) 50 -90 (2 -3½) 8000 -12, 000 180 -360 (7 -14) 4. 6 -15 (6 -20) Placing and Finishing Concrete Application Plastic and flowing concrete in thin members. Also used for lab test specimens. Plastic concrete in thin walls, columns, beams, precast piles, thin slabs, and along construction joints. Stiff plastic concrete (less than 80 -mm [3 in. ] slump) in general construction. Adapted from ACI 309

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 Placing and Finishing Concrete Haphazard random penetration of the vibrator at all angles and spacings without sufficient depth will not assure intimate combination of the two layers

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 Placing and Finishing Concrete 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.

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

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

Bullfloating Placing and Finishing Concrete

Darbying Placing and Finishing Concrete

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

Highway Straightedges Placing and Finishing Concrete

Floating (Power or Hand) n n n Placing and Finishing Concrete 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.

Troweling n n 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 u troweled surfaces can be slippery when wet. u Placing and Finishing Concrete

Brooming Placing and Finishing Concrete

Tining Placing and Finishing Concrete

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

Placing on Hardened Concrete Preparing Hardened Concrete Placing and Finishing Concrete

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

Isolation Joints Placing and Finishing Concrete

Contraction Joints Placing and Finishing Concrete

Spacing of Contraction Joints in Meters Slab thickness, mm 100 Maximum-size aggregate less than 19 mm 2. 4 Maximum-size aggregate 19 mm and larger 3. 0 125 150 175 200 225 250 3. 75 4. 25 5. 0 5. 5 6. 0 3. 75 4. 5 5. 25 6. 0 6. 75 7. 5 Placing and Finishing Concrete Metric

Spacing of Contraction Joints in Feet Slab thickness, in. 4 Maximum-size aggregate less than ¾ in. 8 Maximum-size aggregate ¾ in. and larger 10 5 6 7 8 9 10 10 12 14 16 18 20 13 15 18 20 23 25 Placing and Finishing Concrete Inch-Pound

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

Construction Joints Placing and Finishing Concrete

Joint Layout for Slabs Basic Factors to Remember n n Placing and Finishing Concrete 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

Typical Joint Layout Placing and Finishing Concrete

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

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

Patching Placing and Finishing Concrete

Curing Patches Placing and Finishing Concrete

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

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

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

Placing and Finishing Concrete

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

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. Placing and Finishing Concrete http: //www. cement. org/pdf_files/ms 271. pdf