LIke boy boy said - you could try cutting it out with an angle grinder. If the slab is thick enough, it might hold together - but at 2 x 3 feet, it'll be rather heavy, probably too heavy to lift it on your own. Just had a look - a common paving slab over here, 50x50x5 cm (roughly 1.6 x 1.6 feet, 2 inches thick), comes in at just under 30 kilos.
As for copying it: If you can do it in smaller segments, that would be very good - you won't need to handle extremely heavy slabs and fiddle around with reinforcements, and you might be able to use e.g. plaster of paris instead of concrete for the molding.
In this case, what I'd do:
- prepare a frame (or several) that are just big enough to cover one set of prints (less than 1 ft square in any case, maybe 2-3 inches high. The frames should fit flat on the concrete around the prints - if theat slab isn't plane, you'll have to improvise.
- fit that frame around the prints you want to copy
- cover the inside of the frame and the concrete with a thin seperating layer. Never done it from concrete - on human body parts, we used ordinary hand cream, vaseline should also work
- prepare plaster of paris - stir well and shake a bit, to get all the air bubbles out (unless you got a vacuum pump and jar, then you can use that.
- fill the frame with the plaster mix, let it solidify
- carefully lift the cast from the concrete
If everything went well, you'll now have a negative cast of your concrete slab. Let the plaster cure completely (may take a couple of days), then repeat from the negative cast to get a positive.
If you want to save some weight (and spend some more money), you could also use plaster dressing to make a thin shelled cast of your imprints. Easier to handle, but rather expensive: https://www.amazon.com/s/ref=nb_sb_ss_i_4_8?url=search-alias%3Daps&field-keywords=plaster+bandages&sprefix=plaster+%2Caps%2C290&crid=33WQTR7L2TNRY