The message
from John Rumm contains these words:

I would expect if you laid out a grid of rebar and wired it together
before pouring the screed it would be plenty strong enough. It is not
really carrying the load of the cars - it just needs to spread it a
little before it is transferred to the jablite (or whatever you use). A
quarter of a tonne (each wheel) over say 1m^2 ought not make a
noticeable impact on the insulation.

After all, that's only the same as two of me standing close together.

--
Skipweasel
Pay no attention to the man behind the curtain.