Nondestructive Test Methods

Surface Penetrating Radar

Surface Penetrating Radar (SPR) is a nondestructive technique which utilizes electromagnetic energy to locate objects or interfaces within a material. The radar unit detects back scattered radiation that is reflected at the boundary between differing dielectric media. By measuring the time it takes to receive the reflected signal, the depth of the embedded object or interface may be determined.

The system utilizes a high frequency dipole antenna to transmit a train of discrete amplitude modulation (AM) radio wave pulses. A second antenna, housed next to the transmitting antenna, is used to receive the scattered pulses as they return to the surface of the material. The output is fed to sampling circuitry before being digitally processed by a computer. A realtime visual display of the material cross section is recorded as the antennae are moved along the surface.

Surface Penetrating Radar is useful for rapid detection of embedded objects in concrete, masonry, soil and other common materials used in civil engineering applications. The unit is extremely portable and permits large areas to be surveyed with minimal disruption to the area under investigation.

Typical Applications of Surface Penetrating Radar include:

  • Locating post-tensioning tendons and mild reinforcing steel in concrete slabs
  • Locating embedded conduit, pipes or other objects in concrete slabs
  • Locating footings, pipes or other objects below grade
  • Finding grouted cells and reinforcement in masonry
  • Locating voids, delaminations and honey-combing in concrete


In a recent WDP project, SPR was used to verify the concrete slab thickness and reinforcing bar layout in a parking garage slated for expansion. Using SPR, we were able to determine the total number of reinforcing bars in each layer, spacing and depth of reinforcement and location of embedded conduits. This information, coupled with exploratory openings to verify reinforcing bar size and core extraction to verify concrete strength, permitted an accurate structural analysis of the slab system to assess as-built capacity and strengthening required to accommodate the expansion of the facility.