Insulated concrete pavers for raised beds?

Hello!

We've recently cleared a plot of land and are hoping to make raised garden beds. Assuming that we want to build them with walls, we're trying to find a safe, long-lasting material.

Has anyone tried insulated concrete pavers for this purpose? These are EPS foam boards that are faced with concrete and used in membrane roofing systems. Recycled 2'x4'x2" ones are readily (and inexpensively!) available locally, and I have used them in the past to insulate a root cellar.

I think they would work structurally, and they should be long-lasting. But are there toxicity concerns (is the concrete made with fly ash?), and could it be mitigated with a waterproof barrier (e.g., 3mil plastic)?

Thanks!

Is there membrane/rubber/tar on there as well?  I'd be pretty leery of using it just due to the styrofoam...

Usually, these tiles just hold down the waterproof membrane, which is EPDM. I think EPDM is fairly inert, as people use it for potable rainwater catchment.

The styrofoam in the tiles is encased in a thin (~1/8") concrete shell. My concern, mostly, is whether the concrete is a problem and whether I can mitigate it with a waterproof barrier.

I think the main concern would be the load bearing capability of those tiles, the concrete should be fairly inert as is the EPDM, but how much side force are those tiles engineered to hold?
Soil is heavy when damp and the forces it exerts on walls trying to hold it back can be fairly high.

I am using concrete blocks that are held with rebar pieces driven into the soil 1.5 feet and my walls are only 16 inches high, these are holding well since I used mortar to hold them together and the rebar pieces keep them in place.

The full-sized concrete foundation blocks sold at the local lumber/hardware type stores make great raised bed edges that can be insulation by filling them with soil, and planting in those edges.  That creates a good 6 inch insulation barrier, two blocks high.  Just make sure the top block straddles the space between the two blocks below it.   Planting annual flowers in the edges if there's any concern about them leaching something into the soil in them.

Any vegetables in the actual big raised bed will be sending their roots down, more than to the side, so there wouldn't be much contact, rootwise, with the sides of a concrete block raised bed.  And you can change your configuration anytime you want.  

There's even a great looking bench made out of these blocked, painted and sturdy enough for outside.  They are always handy blocks to have on hand.