Collapsed Concrete is a unique material that is created by terrain-crumbling effects such as Earthquake, Earthquake Shot, and Giga Black Hole. It is a very soft material, roughly on par in terms of explosion resistance as the Grey Rock found throughout the Coal Pits.
Unlike most materials, Collapsed Concrete does not have a particular look of its own. Instead, it takes its appearance from the terrain type(s) it was originally composed of. When initially created, chunks of Collapsed Concrete behave like rigid-body objects, able to be flung around, kicked, picked up with Telekinetic Kick, and so on.
Collapsed Concrete rigid-body chunks are unusually dangerous, being both much more damaging than normal rigid-body objects, as well as being able to bypass any immunity to normal physics damage; physics-immune enemies, including bosses, ghosts, and even the player themselves will be very rapidly killed if hit with chunks of Collapsed Concrete.
After the Collapsed Concrete chunks have fallen and settled, within a short period of time they will cease to be rigid-body entities and become static terrain objects, although they will retain their material composition of Collapsed Concrete.
When Collapsed Concrete is damaged or destroyed, it has a small chance to create tiny Concrete powder fragments, which are a soft powdery material. They behave somewhat similarly to the normal Collapsed Concrete, but are notably different to the normal kinds of Concrete you can get from the Cement spell.