Block building, composite materials, concrete core, skin, combination, sandwich construction, concrete honeycomb shells,
You can use blocks if you put a strong tensioned skin over them. Imagine a surfboard. The core (foam) is weak, the cover (tension resistent) does not maintain form, if you COMBINE the two you get something that is tension resistant AND maintains form (stiffness) – a surfboard. Blocks allow fast build without forming they are good to build compartments if you combine the block core with a tensioned skin (basalt fibers, synthetic fibers, wire, etc) and spray cement on it you might get something useful comparable to the poor mans float in our pilot project, that you can shape without a form, what gets you a fast and economic building process – pilot projects and cost per squarmeter build tests are required to give a final answer to “is it worth it” or “are there better solutions”. This needs to be decided on a “practical level” not on the “idea level”. Given my experiences – i would not dismiss something like that out of hands from the beginning on base of a “superficial perception” that “cinderblocks are not strong”… all depends on the combinations.
The inner structure of the Rofomex Barge is pretty much “simplyfied prefab element” building as you suggest…only the scale is different and they use concrete prefab tubes instead of blocks – not a big difference.
Seasteading thread about floating concrete building with prefab blocks…
http://www.seasteading.org/forum-list/topic/cinder-block/
Materials can drasticly change their property when combined with fibers in form of a “surface film”.