Can this be done in a circle like around a fire pit?

Yes. You can do either option, build on the paved or build on the ground. The paved option would probably be safer. There are videos and instructions on-line that show how to do curves.

Building the fire pit on the ground, including a structure to contain it, is recommended. Reference: http://www.lowes.com/projects/gardening-and-outdoor/build-a-fire-pit/project or https://www.quikrete.com/athome/video-concrete-fire-pit.asp for instructions for building a fire pit. Once you have constructed the fire pit, you may use the QUIKRETE® Walk Maker® to build a concrete patio surrounding it. Reference: https://www.quikrete.com/pdfs/projects/patioswalkwaysandsteppingstones.pdf for instructions, including how to make curves using the QUIKRETE® Walk Maker®. If a fire pit is built on an existing paved patio, it will cause the concrete to be stained, and may ultimately cause it to crack and degrade as Portland cement, the base material out of which concrete is made, can degrade in temperatures as low as 200 degrees F. Please call the QUIKRETE® Technical Center directly at 1-800-282-5828 if you have any further questions.