PEE Paragraph "Rebirth of Lower Manhattan"

They are wanting to make this World Trade Center more safe than the old Twin Towers. They are using special state of the art concrete that must be used within 90 minutes of mixing.  The concrete must be pretty thick for them to have to use it so soon after mixing it. In the "Rebirth of Manhattan" that the walls were going to be 3 feet thick, that is pretty safe.