The fact the he's able to stand there is amazing. Regular concrete has a specific gravity of about 2.5. People are pretty close to water, so around 1. If you tried to stand there in regular concrete you'd pop up like a fishing bobber. I just looked it up and foam concrete (which I had never heard of before) has a specific gravity of between 0.4 and 1.6. That's pretty crazy. So this stuff can be half as heavy as water.

Also why are they building houses with 30" of wasted space at the bottom? 4" of regular concrete for the floor is perfectly fine. That's gotta cost an arm and a leg to build like that. I wonder what the reason is?