Pea gravel mix for drilled piers?

[dwduqu]

Hi Everyone!

I have a design which calls for 18" dia drilled piers of fc'=2500psi with a 4" slump, 1 1/2 aggragate, and a .45 wc ratio. The contractor wants to use a "7 sack" pea gravel mix design for workability. It has been a while since I've taken my mix design class (I'm 55)but I seem to remember that a 3/8" aggragate will have more surface area and thus strenght, cracking and shrinage could be a problem. Any one familiar with this application?

Thanks for your help ... and Blessings,

David

 

[Swizzle]

A 7 sack mix (658lbs. of cement) is closer to a 4000 psi mix. A w/c ratio of .45 may be difficult to place. In this application , I would add a high range water reducer
to increase the workability, decrease the shrinkage, and keep your strengths up.

 

[lkjh345]

dwdugu:

Are these piers placed by pumping the concrete through the auger stem? (I typically call these 'auger cast piles', and use them a lot).

If so, I think the contractor is proposing a fairly typical mix for such piles. 1 1/2" aggregate is difficult to pump down the auger stem. 3/8" aggregate mixes, in the 4,000 psi range are fairly typical mix designs.

Agree that a high range water reducer or fluidizer admixture is required for pumpability.

 

[dwduqu]

Thanks to all as it your input was very helpful! And yes, the piers are placed via pumping. My old "Design and Control of Concrete Mixtures" - pca from the class I took many many years ago helped as well but didn't get much into the pea gravel mix. Do you have any recommendations for ref material that is a little more updated on this topic? You guys are great and thanks again!

Blessings,

David

 

[lkjh345]

My best source of information about concrete mixes is my local Readi-Mix supplier. Very knowledgable and helpful people who know far more about concrete mixes than I'll ever know.

 

[dwduqu]

Thxs ... I will give them a call!!!

 

[minorchord2000]

dwduqu: There is a great treatment of cast-in-place drilled shafts methodologies in the free CALTRANS downsload pages. I do not have the exact site address with me but they have a decent search engine.

 

[dwduqu]

Hey thanks ... that is a great idea! I've down loaded stuff from the before so I'll take another look ...

Blessings,

David

 

[Qshake]

Think before using pea gravel.

If your shafts require coring and you wish to core at first chance, your pea gravel mix could wind up helping the core bit wobble out the hole and push the gravel through the washout giving the impression that you've a void in the drilled shaft.

And on the other side of the coin, if you wait too long to core, the pea gravel mix is a much, much harder product to core.

Lot's of folks use the pea gravel and pumping since it doesn't absorb as much water as say limestone. But if you're coring look out.

good luck.

Regards,
Qshake

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