[GranTorino]

That concrete was probably filled with a foam core.
Anyone know where the missing fertilizer went?
Those flames sure look like ammonium nitrate burning.
Isn’t that odd?

[GingisK]

Concrete bridge sections are hollow, filled with air. Ammonium nitrate does not itself burn, but will provide oxygen for something else. On the other hand, ammonium nitrate will explode if detonated by another explosive. It is very clear that this did not happen.

Concrete disintegrates when it gets hot. It decomposes into the raw materials used when the concrete was made when water is driven from the molecular bonds. The concrete itself doesn't not burn, it reverts to cement powder.

This happened in Atlanta a few years ago. Construction materials were stored under the bridge and vagrants set it on fire. It takes about four months to rebuild what was destroyed in Atlanta.