Its called rust jacking, it can literally explode cement beams. I dont know what happened here though. It would be nice if we could tell if it was a big sinkhole or just taking a look for damaged concrete beams that are still standing. When it just completely collapses like that, thats what gets me. I've seen concrete with really bad rusted rebar that was still hard as hell to break up. Clean break from the big part still standing and it looked like a clean break on the sliver part that fell right after.