Vibrating concrete with 12" to 24" thick each lift 1

[LewisLiew]

I will use mobile crane to drop concrete to 2.6 m deep pile cap. My workers will vibrate each lift of 12" thick concrete with 6" inside lower lift of concrete.

My question is how many drum (0.7 cu.m/drum) should I drop before I need to start vibrate? Can I just fill out 12" thick of the pile cap or just start it from first drum? Is that any code define it?

Should I vibrate it till no more air bubble come out?

 

[Ron]

Put the first layer in. Vibrate it only slightly as the drop will consolidate the concrete if the slump is reasonable.

Put each layer in above that and vibrate as you noted; however, DO NOT vibrate until all the air bubbles come out. That will cause segregation and a loss of air content. Vibrate only about 5 to 10 seconds in each location and move the vibrator around the concrete mass, avoiding the rebar.

The American Concrete Institute and others provide guidelines on proper consolidation of concrete using a vibrator.

 

[LewisLiew]

Is that ok if I discharge first layer fully then only start vibrator?

 

[hokie66]

A contrary view to Ron's. The object of vibration is to compact the concrete, and that means removing the entrapped air. So my instructions have always included vibrating at each location as Ron said, but until the bubbles stop coming. This does not remove beneficial entrained air.

The exception to my position would be for lightweight concrete, where the light aggregate can rise.

You want to keep the vibrator immersed at each position, as vibration of the surface is what causes segregation. In my experience, it is best to err on the side of over-vibration, as the problems of vibration almost always occur on the under-vibrated side, just due to human nature.

Your question did not indicate the plan size of your pile cap. If it is not too big, and the first lift can be placed in say 10 minutes, then yes, wait until the entire lift is in before vibrating. This is better, as it eliminates issues of moving the concrete laterally. When you vibrate subsequent layers, penetrate the layer below.

 

[hokie66]

This publication gives a good description of concrete compaction.

http://www.boral.com.au/brochures/o...pdf?pdfName=DS2006-Compaction-of-Concrete.pdf