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I would not try to support much more than its own weight plus insulation unless it is banded. This means a tension ring of some sort (reinforced concrete, iron band) to take the outward force at the dome bottom.
If using reinforced concrete, this can be about 2 inches thick by about 6 inches high and can be outside of your vermiculete insulation layer. The reinforcing could be something like two layers of 6x6 WWF (welded wire fabric) which must "communicate" continuously around the circumference and pass either under or over (or both) at your door opening. See photo. I figure I could probably carry 800 to 900 lbs (static load) on my oven.