concrete and dust

[riddles]

the steel was taken away in trucks to be famously melted down. the dust was taken away by wind and rain and clean up operations. where did the remaining chunks of concrete go? it must be known where it went. If the chunks were weighed and deducted from the initial mass of concrete in the towers, you would have a figure for the amount turned to finer dust. If you then calculated the energy required to turn that quantity of material into dust and it is greater than the potential energy initially available...then you know for sure it wasnt a natural gravity driven collapse.....i appreciate you might not be able to accurately account for all the remaining macro chunks so its a meaningless proposal....just thinking aloud