You are correct, it is a cast section of the dome.
Here are a few interesting tidbits about the latest photographs:
- The thickness is the same as the arch brick.
- The form's custom nature took over 43 hours of professional design effort. Not counting the manufacturing time.
- Each section takes a day or more to set up properly.
- There is only one form in the world so we are only able to pour one section at a time.
- The dome has eleven total pieces so the process will take nearly two weeks, at a minimum.
- The entire process has to be repeated exactly the same for all sections; disassembly of the form, removal of the dome section, re-assembly of the form, gathering of the right stuff (forklift, mixer, air-compressor, vibrator, scale, materials, etc), mixing, pouring, vibrating, then general cleanup.
Painstakingly complex and slow but worth it to get exactly what I want.