There was extremely little concrete left in the rubble on the ground. Even if the force of the collapse had broken it up there should have been millions of pieces of concrete strewn and piled everywhere quite apart from the percentage that had been pulverised. There should have been 100,000 tons of structural steel in and around each footprint including 5,000 floor pans that the concrete floors were poured into. Plus 110 ACRES of rebar or wire mesh reinforcing for the floors.
If you look at the attached animated gif- allow it to load and cycle a few times you get the impression of how little rubble there WAS on the ground after the collapse.Concrete, steel, wire mesh or anything else. Even more tellingly, reverse the view in your mind and watch the Two biggest Towers in the world grow and reassemble hemselves from the paltry few sticks and stones we can see on the ground. Always remembering that the inside of the buildng was full of structure too, including 110 one-acre 4'' thick concrete floors.
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http://www.acebaker.com/9-11/HTR/web...RTitleAnim.gif animated gif
http://www.engr.psu.edu/ae/WTC/wtc-photo.jpg Huge photo (slow loading,zoomable)
(F11 may toggle fullscreen on/off on yur computer)