you can sit inside, since there is no slab or roof above that walls. While this is all cool and nice, for slabs you would still need some kind of formwork and reinforcement. Not to mention in this structure with only walls, most stresses are compression and it is fine, but when you add slab you will get tension especially over the openings in walls, and with no reinforcement it could collapse. Reinforcement is not there only to take care for tension stresses, but to provide ductility in limit state (moment when structure breaks). Of course you could make prefabricated slab on site and put it on top of that structure, but then its not 3D printed. If you look that houses printed in China they are prefabricated, and have steel truss below the roof. A side from all this I really like this and hope he will post the finished job.
Only difference I heard in that video is that he is using reinforcement. But I saw only vertical reinforcement. And in that video he mentioned micro reinforcement (fibers) added to concrete mix which adds to concrete tension bearing capacity. If you watched that video you could see that formwork for slab I have mentioned, its some kind of beams, that he puts on walls and then pour concrete over it. To be honest, while I like this Idea only thing that it could be used for today is the last mentioned in that video, spherical dome like structures, he does not need reinforcement for that, most of the stresses are compression and concrete is great for that. Most critical part of it all is that your machine better not breaks when you start, since if you make big pause in pouring concrete, old and new concrete bond will not hold.
Civil Engineer here (EIT License)! You're absolutely correct!
but this is absolutely normal! Just as long as the cracks aren't too long (you measure it from the base of the crack to the longest "strand") you're fine.
So... Are we just going to wait it out or are we going to pull a deceptive move?
Helmet on, pants down. Pony battering ram, FULL SPEED AHEAD.