Styrofoam-on grade to support concrete 4

[BulbTheBuilder]

We are looking at using 2" Styrofoam to support 22" thick concrete of a foundation pad. Can anyone recommend any article, journal, or publication that I can refer to for more information on the usage of Styrofoam at foundation bases or even supporting concrete? My major concern is the adequacy of the 2" thick Styrofoam, whether we'd have to increase it. Now, we have a constraint where that pad is over an existing mat (couple of feet below) so we don't want to go down to a certain level. If you also have some expertise or knowledge of its application in foundation can kindly feel free to share.

 

[jayrod12]

Rigid insulation is rated for compressive capacity based on a certain percentage of deformation (if I remember correctly it's 2%) so thicker insulation is not your friend if you're concerned about the amount of deformation. They also come in many different strengths, Dow for example has hi-40 all the way up to hi-100, meaning 40 psi bearing capacity at a specified deformation all the way up to 100 psi.

 

[BulbTheBuilder]

I am looking at issues like compressive strength and deformation. I was also just reading a product specification manual and they had 100psi which I don't see it to be adequate for a 22" thick mat.

Edit (addition): The Styrofoam will only be at the portion which extends over the existing mat feet below it. How will the deformation of the Styrofoam affect the settlement of that area? I am anticipating unbalanced settlement at that region?

 

[jayrod12]

Why not? 100 psi translates to 14,000 PSF, your concrete only weighs 275 PSF at 22" thick. I don't see the issue?

Like I said the strength is a function of deformation, so let's say the 100 psi is at 2% deformation and you're providing 2" of insulation, that's like 3/64" of deformation to get the 100 psi. I can't imagine your loads being so high to even need the 100 psi, so your total deformation at 2" thick using hi-100 would be negligible.

 

[MotorCity]

The thickness of the mat does not matter. Its the pressure on the mat. The allowable compressive strength of insulation will probably be more than the allowable bearing strength of the soil. Select an insulation with a compressive strength that exceeds your soil bearing strength and then the insulation won't be the weak link in the chain. If you are in a cold weather region and the bottom of your mat is above the frost line, you will want to extend the insulation an adequate horizontal distance beyond the mat edge to avoid frost heave.

 

[dik]

You want to use extruded polystyrene... not styrofoam... and DOW has some good technical literature on that, and different strengths of material.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[BulbTheBuilder]

Thanks Jayrod12, I am doing different calcs and mixed up numbers. Yes, 100 psi would be adequate for 22" slab since its 275lb/ft2. We have about 26 pedestals with say 51-70kips with moments around (32kip-ft/384kip-in) for each (more or less). I currently don't know all the details but the loads are that of an industrial structure and facilities. I have been tasked to get information on Styrofoam strength and assist the design (which I am not part but helping at the moment since we are little behind schedule).

 

[BulbTheBuilder]

Thank you all for comments! I am going to check out Dow's technical literatures for more information. I really appreciate it!

 

[dik]

I stand corrected... they refer to it as styrofoam... (styrofoam was equivalent to beadboard, and not suitable)

https://www.dupont.com/content/dam/...e-Building-Solutions/literature/179-02548.pdf

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[BulbTheBuilder]

Styrofoam is a registered trademark/product and the material is the extruded polystyrene (I learnt that today). Thanks a lot!

 

[dik]

Me too...

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[BigH]

They have, in Norway I believe, place bridge abutments on styrofoam.

https://vegvesen.brage.unit.no/vegv...ntern rapport 1511.pdf?sequence=1&isAllowed=y

- see page 17 - an article talking about putting an abutment on EPS (Styrofoam)

 

[BigH]

See also:

http://www.atermit.com/upload/5th_International_Conference_on_Geofoam .pdf

This is the 5th conference so there are at least 4 previous ones.

 

[BulbTheBuilder]

Thanks a lot BigH! We went with expanded polystyrene(EPS) for our design since we could get the strength and deformation wanted for less cost. I will spend my weekend reading the book! I really appreciate it.

 

[BigH]

Here is another paper on ESP from a 2012 Indian Geotechnical Conference - see attached.

 

[BulbTheBuilder]

Thank you very much for the references!