Elon Musk's original pitch for the underground hyperloop system / boring company included the claim that the dug out dirt would be repurposed as super building bricks, and that this would keep the projects at or under budget.

https://finance.yahoo.com/news/almost-7-years-ago-elon-145526694.html?guccounter=1

He literally did this, sold reformed, shitty dirt and called it a miraculous building material.