Many early adopters of ground penetrating radar (GPR) technology found concrete scanning to be the effective application. Those anchoring, saw cutting, or core drilling concrete would hire a contractor to scan the area before cutting to avoid accidentally hitting an object.
For this reason, construction firms have come around to the notion that concrete scanning is vital to job site safety and efficiency. Toledo, Ohio-based Ground Penetrating Radar Systems (GPRS) was one of the first companies in the country to focus on concrete scanning using ground penetrating radar (GPR) technology. They determined that GPR was preferable to other non-destructive subsurface survey technologies, including X-ray.
While a concrete X-ray remains a valid technique to locate reinforcing steel in certain applications, GPRS found it lacked the flexibility to meet the demands of many projects. The method must be done in conditions in which radioactivity can be safely introduced; it also requires access to the underside of the concrete to be scanned and the job site to be closed.
GPR is used without any radioactive element, instead emitting a pulse of energy into the concrete that bounces off any objects in the slab. When some of that energy returns to the antenna, it creates a signature which clearly shows where and at what depth items within the slab are located. GPRS opted for this more versatile technology, which can be used for both elevated concrete slabs and slab-on-grade applications.
GPRS found that GPR equipment helps contractors safely avoid obstacles in concrete, reducing costly delays and potential injuries. For example, during a recent project to revitalize the upper deck at New York’s Yankee Stadium, the general contractor had to penetrate the concrete floor to work on the ballpark’s protective railings and expected the presence of post-tension cables. If accidentally severed, these high-tension steel strands can snap with enough force to break through the concrete and possibly injure the contractor. Due to the severity of the potential risk and the popularity of Yankee Stadium, the use of X-ray was impossible for this job.
The contractor turned to GPRS, which scanned the area with the GSSI StructureScan Mini XT. The compact tool, combined with a GSSI Palm XT antenna, gives operators the ability to cross-polarize for an enhanced level of horizontal and vertical positioning accuracy. Since GPR is entirely safe to use around people, no section of the stadium was closed to other workers, avoiding any major work disruption.
“We would never do a concrete job without GPR,” says Jason Schaff, vice president of sales and marketing at GPRS. He explains, “You never really know what’s beneath the surface. GPR lets us provide quantitative data and relevant information to our customers so that they’re able to do their jobs more safely.”
The GPRS team was also hired by a structural engineering firm to determine the structural reinforcement of a building in Boston, Massachusetts, that was originally used to manufacture cannons and as an armory. The building featured an 8-inch slab with a 1.5-inch topping slab. Scanning the slab and topping with the SIR 4000 and Palm Antenna, the technicians uncovered a complex circumferential reinforcement design. GPRS provided a mark-out of the location and depth of targets as well as a 3D camera report with a virtual tour to the structural engineering client.
When paired with GPR equipment, GPRS also complements other tools. A reference point locater gives operators an added certainty that the area they scan on one side of a thick slab corresponds exactly to the same scan on the other side, and an electromagnetic tool hooks onto a conduit that will passively look for something drawing power. To meet the need to locate live power in conduits, GPRS also began providing utility detection services.
Branching Into Different Markets
In recent years, GPRS has moved into using GPR for utility location, diversifying its business from 95 percent concrete scanning in the early 2000’s to now performing 40 percent concrete scanning and 60 percent utility scanning. Utility projects range from mapping out an entire facility’s utility plan and providing a detailed AutoCAD file to examining a small area before installing even a single light pole.
Just like combining GPR with other techniques for concrete scanning, GPR is an integral part of the utility locator’s toolbox. Rodders are used to send traceable lines through pipes to then put a tone on the tracer to assist location. A radio detection tool actively locates pipes under the surface, putting a tone on a tracer and tracing metallic pipes. Magnetometers measure magnetic fields and provide a useful backup to confirm the location of a cleanout. Other electromagnetic induction equipment serves a similar purpose. GPRS also uses closed-circuit video (CCTV) robots that navigate pipes internally to produce an inside-out visual pipe inspection.
GPR can determine the location of a PVC pipe that does not have a tracer wire, which would have evaded radio detection or discovery by an electromagnetic tool. According to GPRS’s Schaff, “GPR technology really allows us to hone in, be more precise, and sets us apart from other service companies that don’t have it.”
Utility locating also came into play at the Yankee Stadium project, where GPRS had to locate utilities under the sidewalk in front of the stadium before the contractor dug a 125 square foot trench. For the utility locating portion of the job, GPRS used GSSI’s SIR 4000, with a 400 MHz Antenna. The SIR 4000’s modular design enabled the team to easily configure the system for utility location.
Ground penetrating radar allows GPRS to scale both halves of business nationwide. “Because our business has two different verticals with concrete scanning and utility location, we want to use an equipment company that has the ability to cross over and do both,” Schaff says. In 2019 alone, GPRS completed 70,000 individual projects in nearly 60 markets with an overall accuracy rate of 99.5 percent. “We use GSSI GPR for every one of those markets and every one of those jobs.”