Outdoor carpet glue does a great job of adhering to concrete; even when you no longer want it to. It can be so unsightly once the outdoor carpet is removed that one may begin to wonder if covering it back up is a good idea. Outdoor carpet glue may be stubborn, but it isn't impervious to everything. There are several known ways to get rid of stubborn concrete glue.
Heat the glue with a heat gun until it is soft and pliable and scrape it away with a scraper.
Using a scraper, scrape away as much of the glue as will come up. Use a sander with 40 grit paper and remove the residual. Sweep the area free of dust.
Place a metal tray with a ½-pound to ¼-pound of dry ice directly on the adhesive for several minutes. Remove the tray and place it on the next spot. The glue will now be brittle enough to scrape away. Sweep the area to remove any residual.
Make a paste by mixing laundry detergent and warm water. Use a soft bristled brush and soapy water to scrub as much of the glue away as possible. For any remaining adhesive, use a pressure washer with hot water. Allow the concrete to air dry.