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RE: Concrete floor overlay using rigid foam to save weight

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Eric,

This is one of the methods used in "Filigree" concrete.  They use it to
create composite concrete where the precast concrete serves as a form and to
contain the positive moment rebar.  Polystyrene slabs are placed, the
negative rebar is placed, and then the topping concrete is placed.  The
polystyrene serves to create voids.

Their web site is http://www.filigreeinc.com/  Click on the Filigree Flat
Plate for an illustration.

Regards,
Harold O. Sprague

> -----Original Message-----
> From:	Eric Green [SMTP:EGreen(--nospam--at)walterpmoore.com]
> Sent:	Tuesday, October 01, 2002 9:11 AM
> To:	seaint(--nospam--at)seaint.org
> Subject:	Concrete floor overlay using rigid foam to save weight
> 
> 	I have an existing elevated concrete floor slab that needs elevated
> 9 inches. Because the floor is only rated to 100 psf LL, I cannot add 9
> inches of concrete. Therefore, I am going to use 6 inches of rigid foam
> insulation with a 3 inch reinforced concrete slab poured over the
> insulation (The architect & owner understand this will drop the allowable
> LL and are ok with this). I have see this done several times before,
> although I have never been involved in the design of such a system.
> 
> 	 
> 
> 	My question is this. Dow has rigid insulation rated for 25 psi
> compressive strength, where compressive strength is defined at 10%
> deflection under load. However, they also sell a material called high
> load, which has a compressive strength of 40/60/100 psi (there are 3
> varieties) at 5% deflection under load. Dow technical services cannot
> provide me with any information regarding what the allowable load should
> be when used under a concrete floor slab. Has anyone here ever dealt with
> this issue?
> 
> 	 
> 
> 	It seems the 25 psi material should work as this provides a FS of
> about 18 under DL+LL (100 psf), even using the 5% deflection criteria
> (i.e. compressive stress of 12.5 psi rather than 25 psi).
> 
> 	 
> 
> 	 
> 
> 	Eric Green, PE
> 
> 	 
> 
> 	 
> 

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