What I am talking about is a concrete based foam, with small fiber reinforcement. Basically a bullet catch, that uses space to slow things down, rather than the harder job of stopping it outright. The 45cm number is if one uses a very low density mixture, since it’d be best used when space isn’t a concern.
So it’s actually somewhat comparable to styrofoam, but doesn’t burn.
That said, there is a wide range of potential mixtures, ranging anywhere from straight concrete to pure foam, so one can increase the density, and make it more compact, but it’s about what you are optimizing for. So that yes the actual capabilities of whatever is being referenced will be a bit confusing unless density is explicitly mentioned.
A big prefabricated slab of what I am considering is human movable, and everything needed for on site application fits in a pickup truck. Not quite suitable for frontline application, but would be a great option for those in defensive positions farther back.
Something as simple a spraying a few to several inches some over a tarp would offer huge overhead protection from things like drone grenades or suicide drones in a trench, were implementing wood and sandbags isn’t as widely viable as just dropping a slab that supports it’s own weight.