I have some cracks in driveway that I need to fill. I have seen, in
commercial driveways and sidewalks, a gray filler that appears to be
non-hardening. Does anyone know what this crack-filler is called and where
I might get some.

I don't think Lowes/HD carry this stuff. It might be for commercial use.

hd has that in a caulking tube thats called concrete repair. i used
it and it works well .about the color of concrete..good for cracks,
lucas

http://www.minibite.com/america/malone.htm

I think the really good stuff is sold by concrete mixing outlets and
pool maintenance stores. It is very expensive, but will stretch more
and last longer than the cheap stuff at the big box store.

http://www.quikrete.com/catalog/cata...cksealers.html

I've used this product...and am extremely dis-satisfied with it's
performance. It seems like it's too brittle and with the Freeze/Thaw,
it busted up and dis-located.

I would use a polyurathane culking Lowe's has one brand Vulkem, that
comes in a variety of colors. It's similar to what the industrial
folks use on concrete connections.

Good luck,

Darwin