You might try removing the black crud with a wire brush, then polishing with emery cloth (the auto body kind) and waxing it.

You might also consider spraying some different kinds of solvent on it to see if it loosens the "black stuff", WD-40 or PB blaster. If that don't work, gasoline melts asphalt as will Berrymans B-12.
If you can get that off, there are numerous options to sand, shine and /or polish. You might even try putting some of the sticky back sandpaper on a pad to let the kids slide down the slide on, cleanin and sanding while having fun. Just kinda thinking out loud, here! Consider all aspects, use reasonable care and caution with whatever you choose to try. Good luck and let us know how it turns out. Post some pictures if you got em.
Bill P.

Thank you both for your ideas. We won't be closing on the house until November 1st. So I'm just thinking ahead. If I get a chance to take a picture before then, I will! Otherwise, you'll hear back from me after November 1st with results. Thanks again!

Just coat it with epoxy paint...