You do not have to hit concrete with a sledge hammer. Just a use a claw hammer hit in the same spot same force as driving a nail., soon you see a crack form and then off it comes. Sledge can bend the pole. Concrete is funny that way. Post setting concrete i usually weak.
I had a big chert rock in the yard, about 250 lbs. Hit it with 2 lb hammer and pretty soon it split in two. Pieces were still too big to lift, so repeated until split into small enough pieces. .Took less than 15 minutes, not all sore like wailing away with a sledge hammer would have been.
Rod