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Re: Structural Concrete subject to sub zero temp. conditions

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Dear Mr. Harold, 
 
Thanks a lot for the information.  You are right,  the pump foundation is not subject to cyclic temparature effect.  As this is a harded concrete subject to ice cover,  we felt, there should not be any structural deteroiration.  Hence  we planned to inspect the fundation top surface for any cracks at the next opportunity.  I think your suggestion of hammer test, using a brass hammer, would give us confidence on the condition of the concrete. 
 
Best Regards
Lakshmana RK Nukala
 
 
On Fri, Mar 21, 2008 at 7:07 PM, Harold Sprague <spraguehope(--nospam--at)hotmail.com> wrote:
The problem with freezing concrete that was cured prior to exposure is freeze thaw cycling as opposed to a steady state freeze.  Any concrete that is cycling freezing and thawing can exhibit problems if it is not air entrained.  What you are describing does not appear to be cycling.  It is only unfrozen on rare occassions that the pump is out of service. 

The integrity can be routinely checked by whacking the surface with a hammer.  Sound concrete will have a definite ring.  Freeze damaged concrete will be a thud.  It is very distinctive.  You can get an NDT test using impulse response.  That will tell you if you have consistant concrete.  Freeze damaged concrete will have a different response than sound concrete.  But I would elect to just whack it with a hammer.  If that shows damage then get the NDT.
http://olsonengineering.com
 
Concrete that is subject to freeze thaw cycling should be air entrained.  You may have some level of air entrainment allready.  It is often used to aid pumping.  If you are unsure or want to be more definitive, a petrographic examination can determine the level of air entrainment. 

Regards,
Harold Sprague



Date: Mon, 17 Mar 2008 22:20:52 +0300
From: lakshmana.nukala(--nospam--at)gmail.com
To: seaint(--nospam--at)seaint.org
Subject: Re: Structural Concrete subject to sub zero temp. conditions


Jerry & Daryl,
 
Thanks alot for responding to my mail, and for the offered info. 
 
The foundation was cast and cured as per spec,(QC confirm the 28day strength),  after commissioning of the plant,  the Ice formation has started.  Actually It was hhardened concrete.  foundation foot print is about 1.5mX 0.8mX1.0mdeep, it supports a critical pump in LNG process plant. Hence the integrity of the foundation is big concern.  This fdn is subject to ice formation about 2 years ago, and was continuously under same condition, expect for plant down time.
 
I have following questions, 
1.   As this is a hardened concrete, and due to smaller size, can I ignore the effect of freezing of entrapped moisture?
2.  we have to leave it same condition due to operational aspect,  how would i ensure the integrity of the foundation?
 
Any suggestion and references would be highly appreciated. 
 
Best Regards
Lakshmana RK Nukala
 
 

 
On Mon, Mar 17, 2008 at 3:14 PM, Jerry Coombs <JCoombs(--nospam--at)carollo.com> wrote:
When was it frozen?  Did the uncured fndn freeze and at what point?   How big (all directions) is the footing?  How critical is said footing?  You can't place fresh concrete on a surface below freezing temp.  Has to be thawed, warmed and thermally protected afterward.


>>> On 3/16/2008 at 1:24 PM, "Lakshmana Nukala" <lakshmana.nukala(--nospam--at)gmail.com> wrote:
Dear All,
 
We are facing a situation, where the top 3 to 4 inch depth of top surface of a concrete foundation for pump is covered with ice formation. 
Original design had never anticipated this situation, hence normal M35 grade concrete is used for this foundation.  Surface temp of the concrete fdn found to be above -20 Degree C,
 
Any input or reference to to handle this situation would be great help for me.
 
 
Best Regards
Lakshmana RK Nukala
 




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