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Re: Freezer Slab

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Jim,

        Since you're essentially rebuilding the freezer sub floor your objective should be to ensure that there is NO frozen material below the insulation regardless of the frost susceptibility of your gravel.  Essentially, this is a heat flow problem and, if you are not comfortable in solving it yourself (which I would certainly not be comfortable in doing) you should get one of your mechanical colleagues who does this for a living to do it for you.

        As I see it, there are (at least) three possible solutions you should consider.  These are
1.)  Provide thick enough insulation that the equilibrium thermal gradient established by heat flow [from groundwater (or other subsurface scorch) plus heat flow from the surrounding floor areas] maintains the 32 degree F  isotherm within the insulation.
2.)  Provide a grid work of refrigeration system lines BELOW the insulation and divert some of the waste heat from the refrigeration process into this area.
3.)  Provide (a rat slab?? whatever that is) hollow core masonry units on their sides or by some other means provide for ventilation below the slab.  Either forced or convection airflow would do.

        All three options that I have suggested require some heat flow analysis in order to ensure that they will work properly.

        Hope this is of some assistance.

Regards,

H. Daryl Richardson

Jim Persing wrote:

 Jim K,All of the test pits had very fine sandy silt to about 6 to 8 feet deep.  The building is a supermarket and the freezer is only about 12' x 20'.  I guess what bothers me most is that this is such a usual configuration but such an unusual occurrence.I had planned on putting 24" of granular fill below the new slab consisting of 2" of sand over a 10 mil vapor barrier over 4" of crushed gravel over 18" of non frost susceptible gravel.  Maybe the vapor barrier should go below the non frost susceptible gravel?  The slab will be the normal 4" concrete, 4" insulation and a 4" concrete "rat" slab for a total of 12". Jim
-----Original Message-----
From: Kestner, James W. [mailto:jkestner(--nospam--at)somervilleinc.com]
Sent: Tuesday, July 29, 2003 12:54 PM
To: seaint(--nospam--at)seaint.org
Subject: RE: Freezer Slab
 
Jim:I read a report one time that said that it has been observed that some silty soil can draw water up thru capillary action as far as 20 feet away. A freezer building or an ice skating rink that has been in continual operation for a long period of time can have large ice lenses form and heave the floor slab. Ground water can, of course, fluctuate so the fact that there was no ground water in the test pit may or may not have any bearing. It could have been taken during a dry year or a dry season.What kind of soil do you have? What kind of gradation does it have? How much material passes a number 200 sieve?One possible solution is to dig out the ice lense and replace it with non-frost susceptible fill material, insulation and slab. What solution were you thinking of?Jim K.
[Kestner, Jim] -----Original Message-----
From: Jim Persing [mailto:jpersing(--nospam--at)fhoarch.com]
Sent: Monday, July 28, 2003 12:51 PM
To: seaint(--nospam--at)seaint.org
Subject: Freezer Slab
 
I have been asked to make a recommendation for repair of a freezer slab that has risen about 6" from the edge to the middle - 10' +/-.The freezer is kept at about -10 degrees F and has a floor consisting of 4" concrete over 3" rigid insulation over 4" of concrete.  The building is in a mild climate in the Pacific Northwest and is about 10 years old and the original soil report shows no ground water to the bottom of the test pits.  Somewhere water has intruded - broken water line?As far as I can tell (and also from a core through the floor) the cause is from frost heaving.  I have done a little bit of work in Alaska and dealt with frost heaving but this is in reverse.  I think I know what to do but just wondered if anybody has dealt with this problem before and has recommendations on how to fix it.Jim Persing, PE