It was preconstructed and installed in one piece last Saturday. It seems they were making adjustments to the tensioning when it collapsed.
From the video, it would seem then that they over tightened and a cable snapped and the rest followed.
If so I think the contractors are screwed.
(Looks like MCM Construction ?)
Traffic under and across should have been stoped, detoured, whatever during any positioning or adjusting until the final support and cables were in place
Just my 2 cents
Is there anything known yet about the actual quality of the concrete itself?
The Romans knew better to wash the sand they used to purge the salt content out of the sand.
That's why to this day there are many Roman built concrete and cement structures still standing.