I purchased a 1970s condo, which I am rennovating. The large concrete patio is covered in green outdoor carpet and I want to remove it and just have bare concrete. The patio is covered but not enclosed, and faces North. This ugly carpet gets wet from snow and rain and takes ages to dry, so moss grows on it.

I would rather a neutral surface that can be hosed off and swept.

I don't know what adhesive was used and haven't tried to pull it up because I am affraid of the condition od the slab. It could just peel off since it's so old, or I could be left with a mess. If the adhesive doesn't come up, how can I clean the slab?

1) First try any household cleaner like Mr Clean or whatever you have, and a long handled scrub brush with stiff bristles.
If that doesn't work, buy a metal bristle scrub brush and try 2 then 3 below. 3 is dangerous.
2) phosphoric acid masonry cleaner
3) Muriatic acidhttp://www.naturalhandyman.com/iip/infxtra/infmur.html