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

University : Missouri University of Science and Technology

Principal Investigator : Dr. Reza Zoughi, Missouri University of Science and Technology

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: $66,278
INSPIRE UTC: $86,369

Total Project Cost : $152,647

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 :  July 31, 2018

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 UAV offer a 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 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 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: The focus of the first year will be to: (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.

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: http://inspire-utc.mst.edu/researchprojects/sn-4/
Progress reports: