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Consolidation

Consolidation. What is Consolidation as related to concrete?. Consolidation. The even distribution of all ingredients in the concrete mix but……. does not necessarily reduce the size or volume.

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Consolidation

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  1. Consolidation www.concrete-pipe.org

  2. What is Consolidation as related to concrete? Consolidation • The even distribution of all ingredients in the concrete mix but……. does not necessarily reduce the size or volume. • When good consolidation is achieved it allows for better COMPACTION which is the process of reducing the size or volume. In this case it is very dense concrete that we are looking for. • It is the packing of the concrete by the • removal of air. www.concrete-pipe.org

  3. How does Vibration Assist in Consolidation? • Pressure waves from the vibration separate the aggregate particles thereby reducing friction. • It also drives out the air which reduces the volume www.concrete-pipe.org

  4. Why Vibrate? Freshly placed concrete can contain as much as 20% entrapped air Proper vibration increases density by driving out entrapped air (vs.. entrained) Results in: Optimum strength Durability Quality appearance Water tightness

  5. Proper Vibration Should Eliminate voids and honeycombs Release entrapped air Fully encase reinforcement, embedded items, and block outs with fresh concrete

  6. THE THEORY MASS FREQUENCY AMPLITUDE ACCELERATION FORCE RESONANCE www.concrete-pipe.org

  7. MASS=WEIGHTS COUGARD-SERIES ISKCO HKM75LFS OLI 5100 OLI 3550

  8. Frequency It is how many RPM or VPM that the vibrator shaft rotates. 3450 3600 6000 7200 10,000 17,000 www.concrete-pipe.org

  9. Amplitude It is affected by frequency…. The higher the frequency the lower the amplitude. Which means the lower the frequency the higher the amplitude. www.concrete-pipe.org

  10. Take the MASS Determine the FREQUENCY Which affects the AMPLITUDE Which is also affected by the ACCELERATION (CENTRIPETAL) And you come up with the FORCE FORCE IS WHAT IS ACTUALLY DOING THE WORK OF CONSOLIDATION

  11. Amplitude & Frequencyof Vibration Frequency Effects lighter mass Moves the paste Governs liquefaction Amplitude Effects heavier mass Moves the aggregate Determines the radius of action

  12. Amplitude and Frequency Example HOW MUCH FORCE CAN YOU APPLY WHEN YOU SWING THE HAMMER?

  13. Hit the board as hard as you can with one blow Now hit the board 10 times as fast as you can In order to match the vibrator you would have to hit the board 60 TIMES PER SECOND!!

  14. What changed in the way the hammer was used? AMPLITUDE FREQUENCY AND FORCE www.concrete-pipe.org

  15. Methods of Vibration INTERNAL – Stingers (flexible shaft or immersion) EXTERNAL – Mounted on forms both jacket and core. Vibrating tables

  16. Internal Vibration Stingers - commonly used for smaller wet cast items and flat work

  17. Stinger Vibrators Rule of Thumb The Head Diameter should be approximately Wall Thickness 4 It is important to assess your common cage configurations

  18. www.concrete-pipe.org

  19. Vibration Frequency Stinger vibrators are usually VERY HIGH Vibrations per minute 10,000-17,000 VPM (however they typically loose 20% when inserted in the concrete unless the motor is in the head of the stinger) Be careful when using an air entrainment additive as it may significantly reduce the air if over vibrated

  20. Stinger Vibration Procedure Drop vertically under own weight (~1sec/ft.) Let gravity do its job Withdraw slightly slower than inserted (~3sec/ft) Flowability is the key Place stick into each area only once overlapping the vibrating radius.

  21. Overlapping Field of Action

  22. No vibration www.concrete-pipe.org

  23. Stinger Vibration Procedure When layering concrete, place stick ~4” into previous layer Vibrate until surface is shiny and level, and no more large breaking bubbles Avoid touching formwork

  24. Effects of not overlapping fields of action Reduced strength and durability because of: • voids • honeycombing • entrapped air • Reinforcement • not covered

  25. External Vibration Hangs on forms Vibrating table

  26. Electric 3600 RPM Electric 7200 RPM Pneumatic 6600 RPM www.concrete-pipe.org

  27. Form Vibration Electric Pneumatic Hydraulic Faster filling than stinger vibration but forms must be stronger

  28. What size goes on which form? THE CONCEPT IS QUITE SIMPLE…. ENOUGH VIBRATION TO CONSOLIDATE THE CONCRETE WITHOUT DESTROYING THE FORM!!!! • Rule of thumb: Use vibrator with an impact force that is 1.5 to 2 times larger than the weight of the concrete plus the weight of the form www.concrete-pipe.org

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  30. H I G H F R E Q U E N C Y R O L L E R PNEUMAT I C www.concrete-pipe.org

  31. Form Vibration Mounting brackets should be welded onto the stiffener. Don’t fasten vibrator directly onto the skin.

  32. www.concrete-pipe.org

  33. Torque Vibrator bolts must be properly torqued to manufacturers recommendations!!!

  34. DO YOU TORQUE THE MOUNTING BOLTS?

  35. Check vibrator weight settings

  36. Check with supplier for orientation and location of vibrators on forms. They can also recommend the number of vibrators to use.

  37. WHICH WAY DO THE VIBRATORS ROTATE? X

  38. Form Vibration Sizing The harsher the mix = more power The stiffer the form = more power More flowability = less power *Take away: it all varies by plant, forms size and raw materials. Work with your suppliers on sizing

  39. Form Vibration Procedure • Ideally start when concrete is 6” above vibrator (Not always the case) • Stop when concrete is level, glossy surface, and no more large breaking bubbles • Air bubbles go to vibrating surface

  40. Table Vibration Rotary or linear vibrators Shaker tables - eccentric shaft With rotary vibrators, vibration must be unidirectional to avoid “walking” the concrete Sizing Use vibrator with an impact force that is 1.5 to 2 times larger than the weight of the concrete plus the weight of the form

  41. Unidirectional Vibration

  42. Effects of Under-Vibration Can have serious detrimental effects Inadequate Concrete Strength & Durability Excessive entrapped air Unbonded Reinforcement Honeycombing Poor Appearance Honeycombing Sand streaks Bug holes

  43. Effects of Dry Concrete This can have serious detrimental effects You can vibrate all you want but if the concrete can’t flow it will be very difficult to make it compact or consolidate. This adds critical minutes to vibrating time that adversely affects production time and often results in a rejected piece of product.

  44. Test Your Concrete !!!! The Dry Cast Slump Test will give you a benchmark that can be used to determine the correct range of moisture that will make the fill time much more consistent

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