I have a rule on the sand: If it hurts my feet to stand on it, it's hurting hers as well and I think that is a good rule for doggies and hot ground is concerned.
I've seen several documentary regarding heat and dogs and they say the same. If you can stand on the asphalt bare feet, then it's safe for dogs (and cats too I suppose). Otherwise it's not safe for them.
RE: Nadi hanging out with her human friends and a few dogs she tolerates