Thought I would show some pics of a U17 and the hammer breaking and making quick work of a foot thick chunk of concrete from a utility service pad, said service panel replaced with new unit at alternate location thus must clear away any unused equipment. I could have offered no more information, but I will add this: the cement was very white which indicated a lot of water was utilized in the batch. Aggregate separated from the paste as opposed to seeing broken aggregate, this shows the paste was weak. It is a good machine and the hammer does indeed work quite well, but if this concrete was mixed with a bit less water and had some rebar, well let's just say there would be another story.
There is a huge difference in how concrete comes apart. I remove a lot of 40 year old concrete on farmsteads that has river rock and scrap iron it. I demoed a concrete stoup that had tire chains. and cable in it. Take your time and break towards an opening. Try a reasonable distance back and if it doesn't crack, move closer to the edge.