Kitchens – Removing burnt plastic residue from gas cooktop cap

There are lots of concrete cleaning products on the market, but I have had good luck with a 1 gallon solution of 1/4 bleach, 1 cup TSP and 3/4 water. Assuming you are talking about a driveway or garage floor, I would pressure wash the area first to get off the surface crud, then lay on some of the solution and let it set 5 mins or so. Scrub it down with a stiff broom and power wash again. Repeat this as necessary.
As a last resort, you can also use some muriatic acid, but test a small area first to be sure it doesn't effect the color too much.

Orange oil (limonene) based cleaners dissolve sticker residue as well or better than acetone. Put some on, let it sit a bit, scrub a little with nylon,and wash off. There are zillions of different brands of the stuff.