Concrete – How to Shorten a Concrete Pipe Sticking from the Ground: Complete Guide

The standard approach used by electricians routing large conduits through concrete floors is using a diamond edged hole saw cutting 3 or 4 inch holes. Several of these holes overlapping could do it. Or several holes near each other might suit your purpose. These drills need to be water cooled while drilling. You may be able to rent one.

Alternatively a smaller grinder could score the cutout on both sides, a drill could then break through the webbing left under the scoring and a chisel to finish it off.

You're not going to like the answer, but the way to properly fix this for good is to break up the concrete, cut out and replace the damaged section of pipe.

There are a variety of ways you could break this up. A sledge hammer, a hammer and chisel, a SDS drill with a chisel bit, or a larger chisel like a Brute. If you have a ton of time on your hands, you could use a standard hammer drill and drill tons of little holes around the area to remove and then break it up with a smaller hammer and chisel. The concrete should not crack outside of the immediate area you are working on. As for the pipe, yes you might damage it further but you need to replace a section anyways.

Once repaired you would add new concrete and replace the finish (hard to tell from the pic).

Any other fix is unlikely to be permanent or without compromise.