I am going to pour an uninsulated slab for a carport/simple uninsulated garage, this is an extension so just one long side and the short sides. Initially, I was thinking of pouring an uninsulated slab on the ground without an edge beam. But since the ground is quite high, I would like to have the foundation 10cm deeper under the slab mainly for aesthetic reasons. I would like to pour the entire slab in one go. I was thinking of making the form with regular boards.
The question is how can I most easily get the concrete to go 10cm deeper as an "edge beam" along the outer edges mainly for aesthetic reasons?
Some suggestions for solutions are in the image. In suggestion 1, is there a simple way to prevent the gravel from moving back against the form on the inside? Sheet metal? Plank?
In my opinion, Option 1 is still the way to do it.
Macadam is not so loose that it flows; instead, you have to dig out for your foundation/edge beam and then gravel with a slope down towards the excavation bottom.
So if you want 5cm at the bottom, it will be maybe 35cm at the top.
And once you've started, it will work out for you.
Edit: and of course, you fill the edge beam first when you cast.
Thank you for the quick response. Is 1 an established way to do it? I'm thinking of also trying to reinforce there with 2 pieces of 12mm rebar. (Of course, reinforcement mesh on the slab as well)
For the edge beam, I would recommend villa stirrups and 4 pieces of 10/12 mm iron.
This is where the greatest force ends up when walls, roofs, and snow press on it. Under the posts, extra thickness and reinforcement may also be needed.
Considering now perhaps using L-elements after all. It's between the two options in the image below. Is it easy for the foam plastic to float up if done according to option 1? I imagine the risk is lower with option 2 since the foam plastic is held together with plastic spikes. Is there any way to anchor a single layer of foam plastic in the gravel otherwise? I'm digging today so a bit hurried to get someone's opinion Will be casting with S4 semi-fluid concrete.
Will be casting with S4 semi-fluid concrete. 
