3D Microwave Camera for Concrete Delamination and Steel Corrosion Detection (SN-4)

University: Missouri University of Science and Technology (Missouri S&T)

Principal Investigator: Dr. Reza Zoughi, Missouri S&T

PI Contact Information: Phone: (573) 341-4656  |  Email: zoughi@mst.edu

Co-Principal Investigators: Dr. Mohammed Tayeb Ghasr, Missouri S&T
                                                        Dr. Genda Chen, Missouri S&T

Funding Source(s) and Amounts Provided:
Missouri S&T: $160,716
INSPIRE UTC: $215,992

Total Project Cost: $376,708

Match Agencies ID or Contract Number: Missouri S&T: In-Kind Match   |  INSPIRE UTC: 00059220

INSPIRE Grant Award Number: 69A3551747126

Start Date: March 1, 2017
End Date: June 30, 2020

Brief Description of Research Project:

Corrosion of embedded steel reinforcement in concrete leads to concrete cracking and delamination, followed by increased salt and moisture permeation and further damage. Invisibility of the embedded rebar in combination with physical inaccessibility in elevated bridges presents a challenge in the assessment of RC bridge elements. Wideband (3D) microwave synthetic aperture radar (SAR) imaging techniques that can be integrated into a robot or UAV offer a potential practical solution to overcome this challenge.

Microwave SAR imaging acquires wideband data over a 2D spatial grid by raster (or electronic) scanning a reflectometer - real-time images. Our recently-developed microwave camera can produce 3D SAR images at 30 image frames per second (see https://youtu.be/mK_zU-GHxRA). This 45-N microwave camera operates at a frequency range of 20-30 GHz and has an aperture size of 130 x 165 mm. Similar but lighter systems can be designed with aperture size and frequency range optimized for imaging of concrete in bridges and pavements. When mounted on a robot or UAV, microwave cameras can cover a wide area of infrastructure as SAR imaging has been for terrain mapping and remote sensing.  However, the position tracking accuracy requirement must be more stringent for SAR imaging in NDE applications. The higher accuracy can be achieved in multiple ways (e.g. a more precise positioning device (laser) and a small optical camera). A recent study of concrete specimens with relatively high moisture and high chloride levels indicated great potential of 3D imaging to detect corrosion of the embedded steel bars in concrete. The 2D slice of a 3D image showed two corroded steel bars, embedded at 25 mm deep. 

Approach and Methodology: Microwave signals can propagate through concrete and be reflected by steel reinforcing bars, delamination and voids. They are attenuated by moisture, ionic solution, and corrosion by-products. The principle of microwave SAR imaging in NDE applications has been well-documented . A wideband antenna is used to scan a bridge element surface following a 2D grid of certain step (sub-Nyquist sampling rate for reduced measurement time). Using a uniquely-designed and patented reflectometer, the collected reflected data (reference to aperture of the antenna) is then fed to a custom 3D SAR imaging algorithm. The resulting image resolution depends upon the overall scanned area dimension, the wavelength inside materials, and the standoff distance. Higher frequencies (or shorter wavelength) render images with higher 3D resolution depending on the operation frequency, bandwidth and the permittivity of the material.

Overall Objectives: This project aims to develop and optimize a 3D microwave camera for bridge inspection on a robot or UAV platform, quantify its performance for steel corrosion evaluation and concrete delamination detection in RC bridge elements, and build a microwave camera prototype that can be installed on a UAV for field applications.

Scope of Work in Year 1: (1) Prepare concrete specimens with embedded reinforcing bars, (2) Evaluate corrosion rate or mass loss of rebar in 3.5wt.% NaCl solution with EIS tests over time, (3) Periodically take the specimens out of the solution and scan them (for processing 3D images) at various relative humidity levels (measured) to quantify the effect of moisture on delamination, and (4) Optimize critical design parameters of 3D microwave cameras for high fidelity and spatial resolution.

Scope of Work in Year 2: (1) Use laboratory-designed imaging probes and especially-prepared concrete specimens (with delamination and cyclically-corroded rebar) to determine optimal operating frequency, bandwidth, scanning approach (i.e., uniform vs. non-uniform and mono-static vs. bi-static) for each type of damage in order to optimize these critical design parameters for producing images with high fidelity and spatial resolution, (2) Perform numerical full-wave electromagnetic simulations to corroborate and further optimize findings in the previous task, (3) Evaluate and investigate the trade-off between a UAV and a climbing robot platform for microwave imaging system installation, and (4) Investigate commercially-available systems for providing critical geometrical information for the imaging system needed for proper SAR image production.

Scope of Work in Year 3: (1) Perform experimental laboratory optimization for determining optimal frequency, bandwidth and scanning configuration and the influence of these parameters on such an imaging system characteristics for concrete delamination detection and steel rebar corrosion evaluation in reinforced concrete (RC), (2) Perform limited and pertinent numerical electromagnetic simulations by which to also electromagnetically-optimize those measurement parameters for corroborating and further enhancement of the measurement parameters determined in (1), (3) Design and build a suitable antenna with operational frequency bandwidth that spans from several hundred MHz to a few GHz (e.g., 250 MHz – 4 GHz) since the conflicting penetration depth and resolution criteria must be optimized, (4) Design a transceiver system for the imaging system to incorporate the antenna into it (as a single antenna or a linear array fashion), (5) Investigate issues related to a mobile platform movement and its effects on SAR image data collection and determine methods by which to account for, reduce or remove any such unwanted effects, and (6) Begin performing in-field measurements of some bridges.

Describe Implementation of Research Outcomes:
Research outcomes and implementation plan will be described towards the end of this project.

Impacts/Benefits of Implementation:
Impact/Benefits of Implementation will be summarized at the end of this project.

Project Website: https://inspire-utc.mst.edu/researchprojects/completedprojects/sn-4/
Progress Reports: