Some of the rebar (steel reinforcement rods) have pushed through (the bottom of the slab), and that's pretty typical. That happens because of the weight of the concrete.

Although GPR cannot differentiate between different types of embedded items, such as rebar post-tension cables, it is highly effective in examining concrete slabs. This makes it a crucial tool for ...

This creates a situation that engineers often refer to by the technical term "bad." Rebar helps to alleviate this issue because, unlike concrete, rebar is pretty great taking tensile stress.