1. Ground Penetrating Radar Gonzalo Gallo CEE 498KM

2. Outline • Introduction • Principle • Instrumentation • Data Analysis • Advantages and Limitations • Manufacturers and costs

3. Introduction • RADAR → Radio Detection and Ranging • Detect target in free space • Determine the range • Civil engineering applications • Probing into soil to detect pipelines and tanks • Cavities • Thickness determination • Locating reinforcement • Identifying deterioration

4. Principle • An EM pulse is sent through an antenna, penetrating into the surveyed material • A portion of the energy is reflected back to the antenna when an interface between materials of dissimilar dielectric constants is encountered http://www.cait.rutgers.edu/finalreports/GPR-RU4474.pdf

5. The reflected signal has information on: how quickly the signal traveled how much was attenuated These quantities depend on spatial configuration and materials The thickness of a layer is given by: where diis the thickness of layer i, ti the total travel time through that layer, C is the speed of light and εr,i the dielectric constant of the layer Principle

6. Principle • The amount of reflected energy at an interface is governed by: where ρ1,2 is the reflection coefficient and εr1 and εr2 are the dielectric constants Typical Dielectric Constants

7. Instrumentation • The typical instrumentation for GPR includes the following: • Antenna • Air-couple • Ground-coupled • Control Unit • Display device • Storage device

8. Instrumentation http://www.cait.rutgers.edu/finalreports/GPR-RU4474.pdf http://georadar.ids-spa.it/images/new/gpr_products/antennas.gif

9. Instrumentation • Another configuration is a portable arrangement • Small, hand-held dipole antenna • Used for locating rebar, embedments, voids, and other abnormalities • 2.4lbs – 10” penetration http://www.ndtjames.com/catalog/rebarLocators/datascanMKII.html

10. Data Analysis • Before using calibrate • Copper plate → Complete reflection • Air → Complete transmission • Establish dielectric constant of test surface with reflected energy equation

11. Data Analysis • Techniques for analysis • Cluster analysis • Topographic plotting • Quantitative peak tracking • Peak plotting http://www.cait.rutgers.edu/finalreports/GPR-RU4474.pdf

12. Advantages Fast speed scanning with non-contact antennas Very sensitive to presence of embedded metal objects Sensitive to the presence of moisture In general, fast scanning and saves money Limitations Rebar reflects as arch patterns – if dense, individual bars are no longer discerned Limitations if dielectric properties are similar Dielectric properties unknown Material “loss” Difficult in thin layers Extensive data Operator dependant Advantages and Limitations

13. Manufacturers and costs • Hand-held • Datascan MKII • James Instruments ND • $12.000 • IRIS systems • Penetradar • GSSI handy-scan • $6.500 b&w • $10.000 color http://ndtdirect.com/shop/products.asp?viewall=1&stritem=CN-JA-RB1,CN-JA-RB2,CN-JA-RB3&keyword=Concrete&id1=44&id2=136 http://www.penetradar.com/GPR_Vehicles.htm

14. Manufacturers and costs • Antennas • Air-coupled • Ground-coupled Penetradar Corporation http://www.penetradar.com/GPR_Vehicles.htm

15. Manufacturers and costs • Vehicular GPR’s • Single antenna • Multiple antennas • Custom configurations Penetradar Corporation GSSI (GeographicalSurvey Systems, Inc.) $48.000 (includes vehicle, antenna, software and training) http://www.penetradar.com/GPR_Vehicles.htm

16. Links and References • http://www.geophysical.com/ • http://www.penetradar.com/ • http://ndtdirect.com/ • http://www.ndtjames.com/ • http://www.cait.rutgers.edu/finalreports/GPR-RU4474.pdf • Al-Qadi, I.L. and Lahouar (2005). “Measuring layer thickness with GPR –Theory to practice”. Construction and Building Materials, 19, 763-772 • ACI Committee 228, (2003). “In-place methods to estimate concrete strength (ACI 228.1R-03).” Farmington Hills: American Concrete Institute.