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RE: Concrete mix for placement in water

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Paul,

In general, underwater concrete mixes contain 10 to 15% more cement.  The
real trick is in the placement, which is usually done through a tremie or
pump.  The bottom of the discharge is to be kept buried in plastic concrete.

For your particular application.  Use your normal caisson mix if the holes
can be pumped out, and they remain with no standing water while the concrete
is placed.  The plastic concrete will keep the water from flowing into the
pier once the concrete is in place.

Use a chute and elephant trunk if there is no water in the hole.  This will
drop the concrete down the center of the hole.  You can displace a few
inches of water without a problem.  If you have a foot or 2 of water, I
would suggest a tremie.  The problem with a tremie is that you have to have
a hydro crane to raise the tremie as you place concrete.  The other option
is to pump.  Pumping will require an adjustment to the mix to allow pumping.

Regards,
Harold Sprague


> -----Original Message-----
> From:	Paul Feather [SMTP:pfeather(--nospam--at)san.rr.com]
> Sent:	Tuesday, September 12, 2000 11:18 AM
> To:	SEAOC List
> Subject:	Concrete mix for placement in water
> 
> We have a project with 24" dia. drilled caisson foundation.  The soils
> report did not indicate a water table problem, yet we are finding water in
> many of the caisson locations.  The water is seeping slowly in the last
> five feet.
>  
> The borings are in a clay layer, and hole integrity is not being adversely
> affected.  The contractor intends to pump the hole prior to placing
> concrete.  There will still be a wet condition, and some of the water will
> be displaced by the concrete during placing.
>  
> Are there any special precautions or mix changes that should be
> implemented?
>  
> How is the mix design different when placing concrete under water? (not
> exactly my problem, but I find the question interesting)
>  
> All input is appreciated,
>  
> Paul Feather

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