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Mixing, Placing andCuring Concrete
CIVL 3137 2
Concrete Start to Finish
1. Batch2. Mix3. Transport4. Place5. Consolidate6. Finish7. Cure
CIVL 3137 3
Concrete Start to Finish
1. Batch2. Mix3. Transport4. Place5. Consolidate6. Finish7. Cure
ReadyMixed
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Ready-Mixed Concrete
Ready-MixedConcrete
CentralMixing
TransitMixing
ShrinkMixing
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Central Mixing
• Approximately 20% of all plants in US• Concrete is completely mixed using a
stationary mixer (drum, paddle, pan)• High production volumes (4000 yd3/day)• Rapid mixing (30 to 120 seconds)• Improved quality control• Can use ordinary dump trucks for transit
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Concrete Wet Mix Plant
https://www.easymixconcrete.com/news/the-ready-mix-concrete-process/
Cement andFly Ash Silos
Aggregate Bins
Mixer
Control Room
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Concrete Wet Mix Plant
Concrete Slipform Paving
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https://www.gomaco.com/Resources/gp2400.html
Concrete Slipform Paving
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https://www.gomaco.com/Resources/gp2400.html
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Shrink Mixing
• Concrete is partially mixed using a stationary plant mixer to reduce volume
• 1 yd3 of fully mixed concrete requires 1½ yd3 of ingredients
• Concrete finishes mixing in a transit mix truck on the way to the job site
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Transit Mix Truck
Transit Mix Truck
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https://concretetruckmixer.net/volumetric-concrete-mixer-truck/
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Transit Mix Trucks
• 9-12 yd3 mixing drums are typical• Low speed rotation (2 rpm) agitates• High speed rotation (12-15 rpm) mixes• Drum rotates one direction to mix• Drum rotates the other to discharge
Transit Mix Truck
CIVL 3137 25https://en.wikipedia.org/wiki/Concrete_mixer
OPERATIONOF A TRUCK MIXER
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Transit Mixing
• Concrete is batched dry at a central plant and placed in a transit mix truck
• Water is either added at the plant or from a tank on the truck itself
• Concrete is mixed entirely in the truck
Dry Batch Concrete Plant
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https://www.cmi-roadbuilding.com/concrete
Dry Batch Concrete Plant
CIVL 3137 29https://www.ceienterprises.com/literature/52-products/concrete-equipment/
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Transit Mixing Options
1. Mixing at the batch planta) Mix for 50 revs at 12-15 rpm at batch plantb) Agitate at 2 rpm while in transit
2. Mixing in transita) Mix for 70 revs at 8 rpm while in transitb) Agitate at 2 rpm until ready to discharge
3. Mixing at the job sitea) Agitate at 2 rpm while in transitb) Mix 50-100 revs at 12-15 rpm at job site
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Concrete Start to Finish
1. Batch2. Mix3. Transport4. Place5. Consolidate6. Finish7. Cure
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Placement Methods
WheelbarrowConveyor Belt
ChuteBucketPump
Tuckerbilt
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Chute Delivery
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Bucket Delivery
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Concrete Pumping
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Concrete Pumping
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Tuckerbilt
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Concrete Start to Finish
1. Batch2. Mix3. Transport4. Place5. Consolidate6. Finish7. Cure
Consolidation
Consolidation is the process of reducing the volume of voids, air pockets, and entrapped air in fresh concrete, usually through the input of mechanical energy (e.g., vibrating, tamping, or rodding).
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Consolidation
Consolidation is needed because freshly placed concrete is usually honeycombed with entrapped air voids that are larger than the intentionally entrained air voids.
Without consolidation, the concrete will be weak, porous, and poorly bonded to the reinforcement (and unsightly).
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Poor Vibration
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Poor Vibration
https://www.construct-ed.com/concrete-vibration/
Tamping
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https://www.concretenetwork.com/concrete/concrete_tools/tampers.htm
Internal Vibrators
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https://civilsnapshot.com/concrete-vibrators-and-its-type/
External Vibrators
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https://www.mooser.net/en/construction-references/industry-construction/bv-augustin-riederau-e.html
CIVL 3137 49
Concrete Start to Finish
1. Batch2. Mix3. Transport4. Place5. Consolidate6. Finish7. Cure
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Flatwork Finishing Methods
Screedingbringing concrete to correct height
Floatingpushing coarse aggregate below surface
Trowelingbringing bleed water to surface and sealing
Broomingproviding nonskid texture
Flatwork
Flatwork is any poured concrete whose surface is horizontal. This includes floor slabs, patios, sidewalks, driveways, and pavements.
In tilt-up construction, walls are poured flat on the ground then tilted into place, so that is also a form of flatwork.
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Screeding
Screeding removes excess concrete and brings the surface to the proper grade.
Screeding takes place immediately after the concrete is placed and must be completed before excess bleedwater appears on the surface.
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Screeding
Floating
Floating fills voids left by screeding and pushes the coarse aggregate particles slightly below the surface.
Floating leaves a thin layer of mortar at the surface to aid in finishing.
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Floating
Troweling
Troweling brings a small amount of bleed water to the surface to produce a hard, dense finish.
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CIVL 3137 57
Troweling
Brooming / Dragging
Brooming and dragging impart a rough texture to the surface of pavement slabs to provide good traction in wet weather.
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Brooming
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Burlap Dragging
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Concrete Start to Finish
1. Batch2. Mix3. Transport4. Place5. Consolidate6. Finish7. Cure
Concrete Curing
Curing is essential to developing proper strength and durability by1. Maintaining adequate moisture in the
concrete to hydrate the cement2. Maintaining a minimum temperature
in the concrete so hydration proceeds at an adequate rate
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Poor Curing
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Concrete Curing
Replacement Methods
pondingfogging
wet burlapwet straw
wet sawdust
Barrier Methods
plastic sheetscuring compoundsinsulating blankets
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Ponding
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Ponding
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Fogging
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Fogging
http://www.concretebridgeviews.com/i80/Article3.php
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Wet Burlap / Straw
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Wet Burlap and Plastic Sheeting
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Plastic Sheeting
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Insulating Blankets
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Curing Compounds
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Curing Compounds