My Wife’s grandfather worked on the Lake Travis Mansfield dam in just outside Austin, TX.
He was very sick one day and his Wife demanded he stay home.
As it turns out, the guy who replaced him that day fell into the wet concrete as they poured it and that became his grave.
While I don’t doubt the sincerity of all involved in your story, I can assure you that no one is buried in that dam. A rotting body makes for a weak spot in the structure. Anyone who fell into it was fished out, dead or alive.
The man killed that day by the cement was named Asa Grumbles. His family has confirmed a number of times throughout the years that although Grumbles was crushed by the cement, he was quickly fished out. His body was accurately identified by his two brothers, and he was buried at Fitzhugh Cemetery.
Grumbles was killed while filling in for a co-worker who had temporarily left to take a bathroom break.
http://www.peelinc-newsletters.com/www.peelinc.com/newsletters/0802SR.pdf