Locating Rebar Mat and Post Tension Cables - Screen shot and radar image of rebar mat and post tension cables in a concrete slab. Post tension cables are commonly used in large-scale concrete construction, but once buried in a concrete slab, their exact location is not apparent. These cables are under thousands of pounds of tension, accidentally cutting or drilling one can be extremely hazardous to workers and can compromise the structural integrity of the building. GPR scanning prior to any cutting or coring lets workers know exactly where these cables are located and ensures that the project can proceed efficiently and safely.