Thor, or should that be Zeus?

[Chaz]

The ribs won't add any strength without rebar. the mix for small cross sectional beams/lintles ect is 3parts aggregate(10mm) 2 parts sharp sand 1 poart cement. but you still need the rebar.
i feel really bad about this as i should have mentioned it earlier.
But you seem to have gone into it in detail as you have with the rest of the build.
Mike

No problem. Lets see how it holds out.