The pictures you show only serve what I say. Right in there, at the base of it, it's dust, gravel and strangely rounded pieces of larger 'stones' which look smooth ...but where are the pictures of the surrounding streets and buildings covered with thick dust? - where are the at least partially intact floors? It's obvious - it went up in a pyroclastic dust cloud.
Up? Up where?
Regarding "strangely rounded pieces of larger 'stones' which look smooth" - what do you expect? That's what happens to RC when it breaks up. Have a look at this considerably less energetic example. Of course there's vastly more of it as the building is made of concrete, but the nature of the concrete here is not dissimilar to the WTC examples above. Not as much dust as it has been watered down.