Is it suitable for outside use, on a path?

I'll explain better: running along the back of my house is a strip of
concrete, about 25' long by 5' wide, which is evenly flat but quite badly
cracked. Rather than digging the whole lot out and re-laying more concrete I
wondered if there's something available which would give a nice "new"
surface but be no more than about 15mm-20mm thick?

It can't be too thick because there's a rainwater drain in the corner and a
big square metal access lid to the sewer right in the middle of it. What I'd
like is something which could be poured on and left to level itself. Yeah
right

Any ideas?

Si