Most likely was the sand, rather than the aggregate used in the concrete. Sand taken from saltwater prone areas tends to be high in calcites. When mixed with cement and water, it tends to form CaCO3 over the years and expands within the concrete mix, causing concrete spalling and strength reduction.
Aggregate with expansive minerals is not too uncommon. It is always ruled out for ready-mix. However, poor design standards and mix testing lets crap like this slip through. Salt water calcium chloride contamination of sand can be bad in the gulf, I don’t know about this area in question.
Sounds like the quarry pulled a lot of wool over peoples eyes to get them to look the other way.
I knew some guys that built a runway with oversized aggregate that had internal contamination like this situation. The runway had to be shut for over a year prior to resurfacing or replacement. I was second bidder so I had no sadness for the Owner or the contractor with the bad design/build problem.