Consolidation Consolidation does not mean vibration. Vibration can be a method to consolidate www.concrete-pipe.org

Consolidation What is Consolidation as related to concrete? 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. Consolidation does not mean vibration. Vibration can be a method to consolidate www.concrete-pipe.org

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

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 1) Philosophical (depends on the type of mixer – high speed vs.. ribbon) 2) Explain entrained vs. entrapped here (We want entrained to stay, entrapped out) Big drops and transporting by Tuckers 3) Ultimate goal

Proper Vibration Should Eliminate voids and honeycombs Release entrapped air Fully encase reinforcement, embedded items, and block outs with fresh concrete Vibration will accomplish these goals IF proper amplitude and frequency are applied.

THE THEORY MASS FREQUENCY AMPLITUDE ACCELERATION FORCE RESONANCE Mass…the total off balance in the vibrator that creates the vibration Amplitude….the distance that the vibrator will influence the concrete Frequency….how fast the vibrator spins. RPM or VPM Force….the pounds of impact that the vibrator puts into the load Resonance…when all of the materials vibrate together www.concrete-pipe.org

MASS=WEIGHTS COUGAR D-SERIES ISKCO HKM75LFS OLI 5100 OLI 3550

It is how many RPM or VPM that the vibrator shaft rotates. 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

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

Determine the FREQUENCY Which affects the AMPLITUDE 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 But you have another factor to account for when describing an object in simple harmonic motion: its acceleration at any particular point. When an object is going around in a circle, the acceleration is the centripetal acceleration

Amplitude & Frequency of Vibration Effects heavier mass Moves the aggregate Determines the radius of action Frequency Effects lighter mass Moves the paste Governs liquefaction We mount the vibrator so it doesn’t move, we are trying to get the skin on the form to move.

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

In order to match the vibrator you would have to hit the board 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!!

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

Methods of Vibration INTERNAL – Stingers (flexible shaft or immersion) EXTERNAL – Mounted on forms both jacket and core. Vibrating tables Internal is not putting the vibrator in the core

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

Stinger Vibrators Rule of Thumb The Head Diameter should be approximately Wall Thickness 4 It is important to assess your common cage configurations Hydraulic most common, but also most expensive Stick diameter – more rule of thumb…..what will fit, what type of clearance do you have

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Stinger vibrators are usually 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 Important to have regulators

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. Flowability note – if it leaves a hole when removed, it was too fast

Overlapping Field of Action

No vibration www.concrete-pipe.org

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 Duct tape on housing for level indicators Avoid touching form work – critical with architectural, more of a maintenance issue with our industry

Effects of not overlapping fields of action Reduced strength and durability because of: voids honeycombing entrapped air Reinforcement not covered If vibration is not overlapped, may find voids as shown above – but this also depends on the flowability of the mix. There may not be a need to vibrate each are if the mix is flowable (trials)

External Vibration Hangs on forms Vibrating table

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

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

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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H I G F R E Q U N C Y O L PNEUMAT I C CONVEYOR PRODUCTS / WAM CORPORATION CR-5500 20 PSI 40 PSI 60PSI 80 PSI VPM LBS CFM 5,800 1350 34 8,500 2750 46 12,300 6000 54 16,000 11,000 60   MARTIN ENGINEERING COMPANY CCR-5500 6,600 1560 32 10,000 3582 42 12,500 5596 55 14,000 7,020 58 PNEUMAT I C www.concrete-pipe.org

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

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

DO YOU TORQUE THE MOUNTING BOLTS?

Check vibrator weight settings

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

WHICH WAY DO THE VIBRATORS ROTATE? X

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 Work with supplier

This type of vibrator needs air to cool itself Use of mud flap

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

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 “walking” is when there is only 1 vibrator going in 1 direction walking the concrete down the form. Suggest at least 2 rotating in opposite directions.

Unidirectional Vibration This vibration is all vertical

Clamping is critical!!! Notice rubber cushions to dampen the vibration to be put into the concrete, not the floor

Box form for Betodan Equipment (Notice the struts and point out no vibrator mounts are available, table only system)

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

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.

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

Understand what fill rate means to the product!! The amount of concrete put in per pass is critical to consolidation and that rate MUST be controlled if you are to achieve good, watertight concrete. www.concrete-pipe.org

Effects of Over-Vibration Segregation Form deflection and Damage Sand streaks Water bleed areas (Usually near a vibrator)

Form Deflection Prevention

Important Note Dry-cast vibration is very different from wet-cast vibration Dry-cast forms are designed for specific vibration system Don’t mix & match dry and wet-cast systems! Looking for different results

Keep this in mind……. It is the form vibrating that consolidates the concrete. If the form remains rigid, the concrete has a very difficult time moving and it will require a larger vibrator to get the required results. www.concrete-pipe.org

The concept of consolidation is to get the concrete to compact by removing trapped air and forcing the aggregate, sand, and cement to spread uniformly throughout the form while forming a water and air tight matrix that will meet the designed compressive strength requirements. www.concrete-pipe.org

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