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GPR for Concrete Inspection
- 2. GPR stands for ground penetrating radar. • Commercially available since 1970’s • Type of radio wave • Electromagnetic energy (in the form of radio waves) is pulsed into the substrate (ground, concrete, etc.) via an antenna at a certain frequency What is GPR? 1-844-211-5300 |https://www.penhall.com/concrete-scanning/
- 3. • The signal bounces off of material in the ground and is picked back up by the antenna. • The computer then analyzes that signal, and displays the results on the screen for the technician to interpret. • Different materials have varying levels of conductivity • Rebar is very conductive where PVC is not. • The difference in the conductivity of materials is the science behind scanning. • Water is considered the most reflective and air the least reflective. How Does GPR Work? 1-844-211-5300 |https://www.penhall.com/concrete-scanning/
- 4. How Does GPR Work? • The differences in the conductivity of materials determines what you see on the screen • GPR is not an X-ray • GPR outputs about 1/100th the energy of a cell phone and is not dangerous. 1-844-211-5300 |https://www.penhall.com/concrete-scanning/
- 5. • GPR is considered to be one of the most effective forms of non-destructive testing (NDT) to identify subsurface hazards • GPR can be used to locate rebar, tension cables, conduit, voids, and structural integrity of concrete. • GPR allows concrete cutting projects to be on time, on budget, and safe • Different concrete projects and various settings may require different pieces of equipment to be used GPR in Concrete Application 1-844-211-5300 |https://www.penhall.com/concrete-scanning/
- 6. • GPR can be as accurate as one-fourth of an inch from the center of the target and less than a half-inch in depth under ideal circumstances. • Depths and locations marked are always APPROXIMATE • Many variables that can make that maximum level of precision difficult or impossible • Age of concrete • Wire mesh • Multiple layers of rebar • Pan decking • Moisture/water • Interpreting GPR requires a highly trained professional. • Collecting the data is easy, the hard part is the analysis How Accurate is GPR? 1-844-211-5300 |https://www.penhall.com/concrete-scanning/
- 7. • The maximum depth GPR can achieve is determined greatly by the amount of embedment when dealing with concrete. • Most GPR units can achieve 18” of penetration for solid concrete and 5’ to 10’ of penetration for utilities. 1-844-211-5300 | https://www.penhall.com/concrete-scanning/. GPR Depth
- 8. • GPR is highly successful for locating objects. However, in areas that are highly congested, GPR may not be able to detect every object due to apposing reflections. • Other limitations would include penetrating through insulation, marble or granite floors, Etc. • Radar cannot transmit through water. A water table will limit depth of examination. Similarly, young (green) concrete with a high water content shows poorly with radar. 1-844-211-5300 | https://www.penhall.com/concrete-scanning/ GPR Limitations
- 9. What equipment is used to scan concrete?
- 10. GSSI StuctureScan Mini XT/HR 1-844-211-5300 | https://www.penhall.com/concrete-scanning/ Handheld, high resolution screen Mini HR – scans to 16” deep Mini XT – scans to 20” deep
- 11. GSSI 2000 MHz “Palm” Antenna 2000 MHz Palm Antenna 1-844-211-5300 | https://www.penhall.com/concrete-scanning/ Used to get into tight spaces (2” from wall) Scans up to 16” deep
- 12. GSSI SIR SIR 3000/4000 This is the brain and display screen • 600 MHz “Standard” antenna • 2000 MHz “Palm” antenna • 400 MHz antenna • 200 MHz antenna 1-844-211-5300 | https://www.penhall.com/concrete-scanning/
- 13. GSSI Utility Cart Utility Cart Used to scan large areas of concrete Used to locate utilities SIR attached at the top (item1) Carriage hold different antennas (item 3) 1-844-211-5300 | https://www.penhall.com/concrete-scanning/
- 14. GSSI 1600 MHz Concrete Antenna 1600 MHz “Standard” antenna Scans up to 16” Used with Utility Cart and SIR 1-844-211-5300 | https://www.penhall.com/concrete-scanning/
- 15. GPR Data Examples 1-844-211-5300 | https://www.penhall.com/concrete-scanning/ This is a 2D data image of an elevated concrete slab that contains wire mesh and post tension cables.
- 16. GPR Data Examples 1-844-211-5300 | https://www.penhall.com/concrete-scanning/ This is a 2D data image of an elevated slab that contains wire mesh and conduits. There are also two beams that the GPR detected that are adjacent to the bottom of the slab
- 17. GPR Data Examples 1-844-211-5300 | https://www.penhall.com/concrete-scanning/ This is an image of a scan layout that identifies Post Tension Cables and rebars.
- 18. Limitations
- 19. • Scanning near walls and columns leaves a 6” inches section of the wall/column “unscannable.” If palm antenna is available, this is reduced to 2.5 inches • Some targets may be too deep to scan. Typically, we cannot scan beyond 36” • Concrete/ground with high moisture content may reduce the depth in which we can detect hazards • Concrete over 16” inches thick should be scanned from both sides • PVC and non-metallic objects can be difficult to locate. The plastic itself doesn’t show a signal, but rather the signal can show something inside like air or water. Fisher Wire/ Tape can be used to aide in identification • Areas with strong electromagnetic interference, such as transformers or substations with high-voltage electric pylons, may interfere with the signal , affect the depth at which we can scan, and require more time to interpret the data Limitations of GPR 1-844-211-5300 | https://www.penhall.com/concrete-scanning/
- 20. For more information visit Penhall Technologies: https://www.penhall.com/concrete-scanning/ OR CALL 1-844-211-5300 Be safe. Scan First. For More Information 1-844-211-5300 | https://www.penhall.com/concrete-scanning/
Editor's Notes
- Different materials have different properties. Pillows are soft, steel is hard, titanium is strong, and copper is conductive. All materials you encounter on a daily basis have some level of conductivity. Copper is a great conductor. That’s why power lines are made of it. Glass is quite poor. Water is considered the most reflective surface a GPR scanning unit will encounter, and air the least reflective.
- Different materials have different properties. Pillows are soft, steel is hard, titanium is strong, and copper is conductive. All materials you encounter on a daily basis have some level of conductivity. Copper is a great conductor. That’s why power lines are made of it. Glass is quite poor. Water is considered the most reflective surface a GPR scanning unit will encounter, and air the least reflective.
- The differences in conductivity of underground objects is the basic principle behind GPR scanning. The hyperbolas generated in this image are a result of the different levels of conductivity between the metal pipes and tanks, and the ground. The multi-reflection in the image is basically a ghost echo and not an actual object. The GPR picks up the contrast between materials with different levels of conductivity. For instance, it can be difficult to see two distinctly different objects next to each other that happen to have similar levels of conductivity, even though the objects may look very different from each other to the human eye! I would like to point out that GPR scanning is not the same thing as x-rays. They are very different technologies with very different costs, procedures, and PPE. It would be like comparing apples to oranges. GPR gives data in real time, and usually doesn’t need access to both sides of the slab, unlike X-ray which needs the access and has to be developed like film!
- Different materials have different properties. Pillows are soft, steel is hard, titanium is strong, and copper is conductive. All materials you encounter on a daily basis have some level of conductivity. Copper is a great conductor. That’s why power lines are made of it. Glass is quite poor. Water is considered the most reflective surface a GPR scanning unit will encounter, and air the least reflective.
- GPR is very accurate when conditions are right. Up to ¼ of an inch on the x-axis and less than ½ of an inch on the y-axis under ideal circumstances. There are many reasons why we might not be able to mark with that kind of precision.
- GPR is very accurate when conditions are right. Up to ¼ of an inch on the x-axis and less than ½ of an inch on the y-axis under ideal circumstances. There are many reasons why we might not be able to mark with that kind of precision.
- GPR is very accurate when conditions are right. Up to ¼ of an inch on the x-axis and less than ½ of an inch on the y-axis under ideal circumstances. There are many reasons why we might not be able to mark with that kind of precision.
- The Mini antenna is a stand alone, monolithic unit that does not need to hook into any other components to work. This instrument does the bulk of Penhall scanning work.
- The Palm antenna is not a stand alone unit like the Mini. Like the standard 1600 MHz, the palm must connect to the SIR 3000 “brain” to work.
- SIR 3000 does all the signal processing and displaying for the 1600 MHz and 2000 MHz antennas.
- SIR 3000 does all the signal processing and displaying for the 1600 MHz and 2000 MHz antennas.
- SIR 3000 does all the signal processing and displaying for the 1600 MHz and 2000 MHz antennas.