polysteryne compressiv strength? Cast on top

[lolobau]

I would need it to build up an platform of 800mm height difference
And cast a slab on top.

And I was wondering if I can just use the normal polysteryne sheets
build it 700mm up and cast the 100mm slab on top (reinforced with mesh)

would it work? Or could it sattel or spring?

 

[lolobau]

this is my sketch

 

[TehMightyEngineer]

Couldn't download the second file. Sounds like you're looking for something like geofoam.

Maine EIT, Civil/Structural.

 

[SlideRuleEra]

Suggest that you do not use the inexpensive polystyrene foam shown in your photo. It will compress without much load.

However, polystyrene foam is made for the use you describe. It is typically used for insulation around and under concrete slabs. There are several strengths of the foam available. Here is a link to one rated for 25 PSI:

http://commercial.owenscorning.com/products/foam/foamular-250/

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[TLHS]

I wouldn't use a significant depth of foam along with a non-structural slab without looking at it carefully. Your foam *will* compress to some degree. The deeper it is, the more it's going to compress. If it's in the range of depth you'd get for normal insulation you're probably okay, but when you start talking about a couple of feet I'd worry about cracking. I'd either put something stiffer down there or I'd treat the area like a void and design the slab as self-supporting to span over the void area. If you really want to do the legwork you could call up the vendor and ask for a strain curve of whatever materials you're looking at and determine whether it's actually a problem. You may also need to know if it can rebound if you'll see variation in load.

Why can't you throw in some gravel, or just pour the slab deeper?

Alternately, you could look at something like geofoam, which is intended to be used as a fill material. I haven't personally used it, but it's getting more common.

 

[haynewp]

XPS foams are rated to support a compressive load with an associated deformation (ex., 10% deformation at 15 or 25 psi). After a certain pressure, they can continue to compress without added weight. You can get higher strength types but I would not use XPS.

 

[SlideRuleEra]

TLHS and haynewp are right, I did not pay attention to the large 700 mm thickness for the foam.

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