Jul
17
Written by:
Blog Editor
7/17/2008 9:38 AM
Internal mechanical vibration is the most consistent and effective method of consolidating concrete for Insulated Concrete Form (ICF) applications and therefore will be the focus of this entry.
Equipment
Low modulation (small movement) and high frequency (many times per minute) is the best method to vibrate within Insulated Concrete Forms (ICF). The most effective vibrator to achieve this result is an immersion type concrete vibrator with a 12’ (3.7m) flex shaft. The specific requirements differ slightly for different concrete core sizes. The following chart provides the recommended specifications for concrete vibrators used with ICF:
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Requirement
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4” & 6”
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8” & 10”
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Maximum Vibrator Head Diameter
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1” (25mm)
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1.25” (38mm)
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Frequency (vibrations/min)
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10000
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9000
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Minimum Radius of Action (overlap)
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4” (100mm)
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6” (152mm)
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Insertion on Center Spacing
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6” (152mm)
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9” (228mm)
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Centrifugal Force
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220lbs (100kg)
2-4 yds3/hr
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500lbs (225kg)
2-5 yds3/hr
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Compaction Rate
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1.5-3m3/hr
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1.5-3.8m3/hr
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Technique
The most important part of consolidation is proper technique. To vibrate properly, plunge the vibrator head to the bottom of the 4’ (1.2m) lift of concrete as quickly as possible and retract it slowly (approximately 3” (76mm) per second). Remove the vibrator head and re-insert it at a distance 1.5 times the radius of action. This will create an overlap with the previously vibrated area ensuring proper consolidation. When working on subsequent lifts, repeat the above method, but also penetrate into the top 6” (152mm) of the previous lift. This will fuse the lifts together, eliminating any pour seams or cold joints.
Keys to Success
For effective concrete consolidation, follow these three guidelines to ensure success:
1. Use a concrete mix with a slump of at least 6” (152mm).
2. Brace corners and lintels very well and vibrate them thoroughly.
3. Hire an experienced trained operator.
Copyright ©2008 Amvic Inc.
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4 comments so far...
Re: Proper Concrete Consolidation for Insulated Concrete Forms (ICF)
What is your opinion of the external vibrators on the market today. Do they do a proper job or are they inferior to internal vibration??
By Bob Scardina on
7/25/2008 1:16 PM
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Re: Proper Concrete Consolidation for Insulated Concrete Forms (ICF)
Currently we do not recommend any exterior vibration methods. We always advise using internal vibration.
By Amr on
7/25/2008 1:25 PM
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Re: Proper Concrete Consolidation for Insulated Concrete Forms (ICF)
Here is my opinion; the most effective method of ensuring proper concrete consolidation is to vibrate the concrete internally as this method comes in direct contact with the concrete, reducing the likelihood of air pockets and voids. External vibration is not as effective with air pockets and voids as you are reducing the vibration impact by having an extra 2.5” of foam insulation to deal with along with not being in direct contact with the concrete. Can you mix pancake batter better with a spoon in the bowl or by smacking it on the outside with a bat?
By GB on
7/25/2008 2:15 PM
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Re: Proper Concrete Consolidation for Insulated Concrete Forms (ICF)
Depends on what type of external vibration you are looking at. There are a few ICF specific plate vibrators available that can do a good job providing that they are used properly. One drawback is the weight of the tool and the body positioning required to use it. They can be effective when used on ground level, but once onto a scaffolding deck there is not sufficient room to work the tool safely, as your body must be positioned directly behind the tool and most platforms only give you at the most two feet of space.
As to effectiveness of the plate vibrators, as long as they are used properly then they can do a good job. You may want to look at combining this method with using the new rebar vibrators or internal vibration for the upper part of the wall. You can also look at changing your mix design and letting the concrete do the work you.
Whether you internally or externally vibrate the key is to perform this job function properly.
Final note on external plate vibrators, they have been used in Japan successfully for many years where they are advanced in concrete forming. They use this method on conventional forms there partly due to the amount of rebar required for the seismic zone that they build in.
By John on
7/28/2008 8:29 AM
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