Arch segments allow the construction of arches, vaults and circular rooms. Special arch sizes require special segment angles.
A possible design is a curved version of the ten-hole-cuboid. The curved sides lack holes.
Another possibility is to use interlocking segments with post-tensioned rods. This is already in use to create liners for tunnels on Earth.
Thick arch segments can serve in the construction of pressure vessels with non circular walls. Allowing for variety in construction with little mass penalty.