Has anyone used Boat Dock foam in place of straw bales?

I have access to a large amount of used Styrofoam. The type that is used for flotation in Boat docks. Any thoughts?

There is a highly-manufactured building material used up north that consists of wall panels constructed like an ice-cream sandwich: traditional white Styrofoam sandwiched between two layers of half-inch oriented-strand fiberboard. It's got excellent insulation properties, but I'm not sure how well the OSB stands up to weather and I don't know how the product works structurally. Of course that stuff -- bought new, anyway -- is about as far from a sustainable building material as you can get.

You're talking about recycling blocks of old used foam in place of hay bales. I don't have an opinion about how that will work structurally, but I know you'll have to protect the foam, or it will erode into those little white pellets that last forever in the environment and eventually wind up floating in the sea. My impression is that most bale construction is surfaced with some sort of stucco or cob, so that would presumably be desirable with foam blocks as well. You might have to do something to the blocks (wrap them in chicken wire?) in order to get the surfacing material to stick.

I suspect that the wall would not breathe well and moisture would accumulate around the foam leading possibly to mold.

Well, if these are otherwise waste products, then it's pretty cool to think of ways to reuse them instead. However, as wall materials to be used much as straw bales, you might want to find out about a couple of things:
1) Was this material manufactured for uses that didn't involve living spaces? So is there a risk that it might off-gas stuff that you don't want in a living space? And what if there is ever a fire? I think I remember hearing that burning styrofoam gives off some extremely nasty toxic gick.

2) If you use earthen plasters as are usually used with straw bales, the moisture issue mentioned above is sure to be a major problem. I've lived in earthen houses for a long time and have heard a lot about impermeable layers causing structural failure in earthen structures.

So if you've got the stuff for free and want to keep it out of the waste stream, you might want to try to think of ways to use it where these won't be issues.

They can make good infill for a timber frame or post wall, using a lime or concrete stucco. Offgassing is a concern, but most of it happened long ago. Fire is a problem, so don't start it on fire!

If it is super dense foam, it would make a good stem wall for bales.

It would also make awesome north wall for a greenhouse.

There are lots of uses for them to keep them out of the waste stream, make sure they aren't a big compromise for the application.

Foam is suitable under concrete slabs and against the exterior of concrete walls.

If this material where ever to catch fire, it would create a poisonous chemical stew. Even without burning, there are many chemicals given off by certain foams. You must find out if yours is a good one or not.