cartagena colombia, floating concrete, honeycomb and shell structures, concept testing, it is clear that giant industrial floating structurs can be built in concrete - oil/gas industry has widley tested and implemented that concept already.
The interesting question is, how small can you actually go for building a modular floating concrete structure in honeycomb and shell design.
The outcome : if you do it right you can start very small and have modular structures that can be expanded to unlimited size while floating on the watersurface.