Bare copper pipes under slab with no sleeves? Bad idea. A neighbor of mine had a noticeable hot water leak under his basement slab, and called out the leak-detection/repair guys to triangulate its location, nailing it within a small dinner plate radius. It turned out to be a pin hole in the buried copper pipe caused by a small piece of aggregate that had made its way into close contact with the pipe through a torn protection sleeve. However, over time with the daily heat/cool, aka expand/contract cycles, the copper work-hardened and eventually failed, as theorized by the repair crew. He sold and moved away before he had to pay to find where his next leak would be found!