You can get a concrete grinder from the rental store. Or if you know someone that is into concrete they may be able to turn you on to one. It uses different stones to grind down the concrete and eventually polish it. Kind of puts you in mind of a floor sander. I would like to see some pics though. 23 yds. is a hell of a lot to have messed up!!! If you do pour over it, use a bonding agent between the two.
Kevin