Does anybody have any thoughts about using straw bales as a "void
form" for a concrete garage pad?

Typical garage pads in my area are made on top of a gravel base that
is deeper around the edge. This gives a one-piece concrete pad that
is "thickened" around the edge for strength. These pads are pretty
good, but they are only "thickened" around the edge and can still
crack.

I want to dispense with the gravel completely, and use hay bales as a
"void" form as follows:

Place bales in a series of solid 8ft x 8ft squares on the ground.
Between each set of 8ft squares would be an 8 inch gap. If you can
imagine, the concrete is poured over the while thing. The concrete
would go down into the 8" gaps, giving an integral concrete "beam"
every 8 feet. So instead of a "thickened" edge beam only, this pad
would have a matrix of beams every 8 feet. Of course there would be
rebar also.

The hay bales are basically there to "save money" on concrete (instead
of pouring a 2 foot thick floor). I think this floor would be so
strong that you could lift one corner and the whole thing would stay
together (no cracking due to frost etc).

I am wondering about these hay bales though. I really don't care if
they rot after the concrete sets. Does anybody see any problems? I
would probably put plastic on top of the bales to seperate them from
the concrete. Do you think I should also put plastic underneath them
so they stay dry forever?

I think the cost would be less also. Typically, you need 2 feet of
gravel under the floor to raise the grade of the garage floor. With
the bales, I automatically get a 2 foot raise in the grade, as well as
the extra strength from the beams.

Also, if you really want to go nuts, the beams can be made deeper (or
the grade can be raised) with very little cost by stacking bales on
top of each other. If you were to stack 2 bales (instead of one), the
beams are deeper and it would not take much extra concrete.

I also like the fact that the beams (both in the middle and around the
edge) are nice and "square". The "thickened edge" garage pad has a
beam around the edge that is formed by the sloping gravel beneath it,
giving a "not so pretty" beam.

Thanks.