Thing is though, for stuff like concrete slabs where the detail is mostly high frequency and pretty small, you can't really justify the time to sculpt this stuff, when you can get pretty close to whatever reference by generating normal from photos.
Let's not be rude. I'm not suggesting you don't know what you're talking about, because you certainly do, I just think the point is debatable, and not simply method A is correct, method B is obsolete. Even in the great art dumps from people working on really big-budget titles that you find on this forum you'll frequently…
Well, one possibility would be taking textures from a site like http://cgtextures.com/ (also take a look at their texturing tutorials!). If you want to take your own photos, you don't have to find EXACTLY what you want your result to look like. The best start would be a simple concrete texture, and a metal texture, i guess…