9-11 Debunker, Steven Dutch (Natural and Applied Sciences, of the University of Wisconsin), has this to say
If the World Trade Center was hot enough to melt steel, where's all the molten concrete? Iron melts around 1500o C but so do many of the silicate minerals in concrete, and a mixture of silicate minerals would melt at a temperature lower than any of the individual minerals (I'm a geologist - I get paid to know about stuff like that). The fine particle size of the concrete dust would facilitate melting. So why wasn't there a huge puddle of molten concrete at Ground Zero? (There was some, but about what you'd expect from a large fire; certainly not what you'd expect from something hot enough to melt large amounts of steel.)
- Does concrete melt?