How to use a Vibrator - for Cement Placement : )

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How to use a Vibrator - for Cement Placement : )

Postby developer3d » Wed Jun 16, 2010 10:30 am

How to use a Vibrator

A while ago I posted about the importance of using a vibrator when placing structural concrete, I thought that this post about how to use an internal vibrator might be useful.

Vibrators consolidate concrete by pushing the coarse aggregate downward, away from the point of vibration.

Internal vibrators are called "internal" or "insertion " vibrators because the vibrating element is inserted into the concrete.

When using an internal vibrator, insert it at approximately 18-inch intervals into air-entrained concrete for 5 to 10 seconds and into nonair-entrained concrete for 10 to 15 seconds. The exact period of time that you should leave a vibrator
in the concrete depends on its slump. Overlap the vibrated areas somewhat at each insertion. Whenever possible, lower the vibrator into the concrete vertically and allow it to descend by gravity. The vibrator should not only pass through the layer just placed, but penetrate several inches into the layer underneath to ensure a good bond between the layers.

Vibration does not normally damage the lower layers, as long as the concrete disturbed in these lower layers becomes plastic under the vibrating action. You know that you have consolidated the concrete properly when a thin line of mortar appears along the form near the vibrator, the coarse aggregate disappears into the concrete, or the paste begins to appear near the vibrator head. Then, withdraw the vibrator vertically at about the same gravity rate that it descended.

Some hand spading or puddling should accompany all vibration. To avoid the possibility of segregation, do not vibrate mixes that you can consolidate easily by spading. Also, don’t vibrate concrete that has a slump of 5 inches or more. Finally, do not use vibrators to move concrete in the form.

I read a good tip from jazzman on another thread that you can lower a small handheld vibrator on a rope into a column form if the extension is not long enough.
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Re: How to use a Vibrator - for Cement Placement : )

Postby dozer » Wed Jun 16, 2010 2:33 pm

An excellent and necessary topic related to quality structural concrete, without it you will end up excessive voids (caused by air pockets) in the concrete which reduces strength.

Here are a couple of shots of a vibrator in action.

One comment is that I have found when vibrating columns if using metal form work it can take more vibration. Sometimes the wood formwork may bow or have other problems related to vibration. The metal forms clip in place for a strong seal where the word forms are nailed together, if not sufficiently attached problems can ensue during the vibration phase.
Attachments
IMG_1742a.jpg
using a vibrator with metal formwork
IMG_1529a.jpg
using vibrator with ground beam
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Re: How to use a Vibrator - for Cement Placement : )

Postby ningnong » Sat Jun 19, 2010 2:29 am

Another very helpful post, thanks developer3d.

developer3d wrote:
When using an internal vibrator, insert it at approximately 18-inch intervals into air-entrained concrete for 5 to 10 seconds and into nonair-entrained concrete for 10 to 15 seconds.


Sorry to show my ignorance but for a complete novice can you please explain the terms "air-entrained" and "nonair-entrained"?

Thanks
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Re: How to use a Vibrator - for Cement Placement : )

Postby geordie » Sat Jun 19, 2010 4:19 am

air entrained is lightweight concrete a special mix using foam i believe to trap air in the mix
not as strong structurally but having many uses


non air entrained not as complicated as you think although in the mixing proces air becomes trapped in the concrete mixture so at some point in life i would guess you have seen concrete badly done when the formwork is removed there are loads of tiny pockets caused by trapped air
so its either not vibrated or done badly and they missed a bit but its a warning that the concrete is not at full strength /badly done
using a vibrator allows the air to escape and compacts the concrete as the vibrator shakes the mix the stones rattle themselves together and this gives the concrete a greater strength however there is a need for caution as over use can cause problems
one is that the shuttering is indestructable the stone will fall through the mix and the air and sand cement will make their way to the surface leaving you with a poor quality concrete this can in some cases be picked up as a change in coulour
you will note the use of the words indestructable shuttering it will have to be because problem two is that overvibrating can blow the shuttering open as the stone drops down it will expand sidways as well either deforming or destroying the shuttering even steel will deform given enough vibration
my comments may be wrong but never deliberately
If it aint broke, dont fix it
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Re: How to use a Vibrator - for Cement Placement : )

Postby BKKBILL » Sat Jun 19, 2010 11:31 am

There is a very good article in the Concrete Vibration Handbook @

http://www.scribd.com/doc/27239582/Conc ... 3-Handbook

A short read and should answer some if not all of the questions.
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Re: How to use a Vibrator - for Cement Placement : )

Postby ningnong » Sun Jun 20, 2010 3:50 am

BKKBILL wrote:There is a very good article in the Concrete Vibration Handbook @

http://www.scribd.com/doc/27239582/Conc ... 3-Handbook

A short read and should answer some if not all of the questions.


Great link, just pitched at the right level for me, so far :) As you correctly suggested it answers many questions. I have added it to the growing list of bookmarks from this site, thanks bkkbill
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