Systems and methods for inspecting reinforced concrete structures

1. An inspection system for a metal-reinforced concrete structure, comprising:

(a) a radio frequency (RF) system configured to be movable with respect to a surface of the concrete structure in a scan direction, transmit radio signals into the interior of the structure at a plurality of scan locations, and receive reflected radio signals; and

(b) a processor configured to process the reflected radio signals by:

normalizing each waveform of the reflected radio signals for unity amplitude,

performing a principal component analysis to remove a first reflection from a first interface of the radio signals to the metal-reinforced concrete structure,

obtaining a first principal component representative of the transmitted radio signals and using the first principal component to filter each waveform,

correcting attenuation of the radio signals in the metal-reinforced, concrete structure,

creating an analytical signal for each waveform,

generating a sub-surface 2D image of the metal-reinforced concrete structure using the magnitude of the waveforms,

projecting the 2D image to the scan direction by estimating a maximum value at each scan location to estimate reflection amplitude,

for each identified peak location, plotting a phase for each waveform, and

estimating a slope of the phase prior to and after a metal-reinforcement, wherein the slope corresponds to the physical condition of the metal-reinforcement.

2. The inspection system of claim 1 , wherein the RF system includes at least one antenna configured to transmit the radio signals and receive the reflected radio signals.

3. The inspection system of claim 1 , wherein the RF system is a frequency-modulated continuous wave radar system.

4. The inspection system of claim 3 , wherein a frequency bandwidth of the continuous wave radar system is in the range of about 1.7 gigahertz (GHz) to about 2.1 gigahertz (GHz).

5. The inspection system of claim 1 , wherein at least the RF system is provided on a platform that can be controllably moved in the scan direction, on or adjacent to the surface of the concrete structure.

6. The inspection system of claim 5 , wherein the platform is provided on a track system.

7. The inspection system of claim 5 , wherein the processor is further configured to control movement of the platform in the scan direction.

8. The inspection system of claim 1 , wherein estimating a maximum value at each scan location to estimate reflection amplitude comprises using a spatial resolution; and wherein the processor comprises a synthetic-aperture radar (SAR) sub-system configured to enhance the spatial resolution.

9. The inspection system of claim 1 , wherein the RF system is a frequency-modulated pulsed wave radar system.

10. The inspection system of claim 1 , wherein correcting attenuation of the radio signals comprises increasing amplitudes of the radio signals based on propagation delay.

11. The inspection system of claim 1 , wherein creating an analytical signal for each waveform comprises performing a Hilbert transform on each waveform.

12. The inspection system of claim 1 , wherein the first reflection corresponds to a surface reflection from an air/concrete interface.

13. A method for determining the condition of a metal-reinforced concrete structure, comprising:

(a) transmitting radio signals into the interior of the metal-reinforced concrete structure at a plurality of scan locations with a radio frequency (RF) system while moving the RE system in a scan direction with respect to a surface of the metal-reinforced concrete structure; and receiving reflected radio signals; and

(b) processing the reflected radio signals by

normalizing each waveform of the reflected radio signals for unity amplitude,

performing a principal component analysis to remove a first reflection from a first interface of the radio signals to the metal-reinforced, concrete structure,

obtaining a first principal component representative of the transmitted radio signals and using the first principal component to filter each waveform,

correcting attenuation of the radio signals in the metal-reinforced concrete structure,

creating an analytical signal for each waveform,

generating a sub-surface 2D image of the metal-reinforced concrete structure using the magnitude of the waveforms,

projecting the 2D image to the scan direction by estimating a maximum value at each scan location to estimate reflection amplitude,

for each identified peak location, plotting a phase for each waveform, and estimating a slope of the phase prior to and after a metal-reinforcement, wherein the slope corresponds to the physical condition of the reinforcement.

14. The method of claim 13 ;

the first reflection corresponds to a surface reflection from an air/concrete interface.

15. The method of claim 13 , wherein transmitting radio signals comprises continuously transmitting radio signals.

16. The method of claim 15 , wherein a frequency bandwidth of the continuous transmitted radio signals is in the range of about 1.7 gigahertz (GHz) to about 2.1 gigahertz (GHz).

17. The method of claim 13 , wherein transmitting radio signals comprises transmitting pulsed radio signals.

18. The method of claim 13 , wherein estimating a maximum value at each scan location to estimate reflection amplitude comprises using a spatial resolution technique.