Concrete in conduit
Ran into this years ago on a new Building addition. We hoped that it was a small plug of Concreted. It wasn't. We purchased one of the inexpensive Hand Held Drain Snakes. The type that is a Coiled Steel cable like an old Choke Cable. We cut the large end off the Drain Snake and kept trying to poke through the Conduit like there was a snag during a wire pull. After a couple of hours, the Concreted Plug cracked and broke. We used a Shop Vac to pull the chips out of the pipe then kept ramming until all of it came out.
I like the idea of Muriatic Acid, it is used to clean Concrete so it may work or help. The only caution other than PPE type protection is that the Fumes or Vapor from the Acid is Corrosive and you could cause unwanted Rust / Corrosion within several feet of it's use inside a Building. Once you get the Concrete out, dilute the Acid with plenty of water. At that point, the Conduit can be treated like a flooded Construction issue.
Good luck, nothing like tearing up a new Slab to re-run a Conduit.
JimO
