Investigating Key Techniques to Leverage the Functionality of Ground/Wall Penetrating Radar

Ground penetrating radar (GPR) has been extensively utilized as a highly efficient and non-destructive testing method for infrastructure evaluation, such as highway rebar detection, bridge decks inspection, asphalt pavement monitoring, underground pipe leakage detection, railroad ballast assessment, etc. The focus of this dissertation is to investigate the key techniques to tackle with GPR signal processing from three perspectives: (1) Removing or suppressing the radar clutter signal; (2) Detecting the underground target or the region of interest (RoI) in the GPR image; (3) Imaging the underground target to eliminate or alleviate the feature distortion and reconstructing the shape of the target with good fidelity. In the first part of this dissertation, a low-rank and sparse representation based approach is designed to remove the clutter produced by rough ground surface reflection for impulse radar. In the second part, Hilbert Transform and 2-D Renyi entropy based statistical analysis is explored to improve RoI detection efficiency and to reduce the computational cost for more sophisticated data post-processing. In the third part, a back-projection imaging algorithm is designed for both ground-coupled and air-coupled multistatic GPR configurations. Since the refraction phenomenon at the air-ground interface is considered and the spatial offsets between the transceiver antennas are compensated in this algorithm, the data points collected by receiver antennas in time domain can be accurately mapped back to the spatial domain and the targets can be imaged in the scene space under testing. Experimental results validate that the proposed three-stage cascade signal processing methodologies can improve the performance of GPR system

Feature detection algorithms in computed images

The problem of sensing a medium by several sensors and retrieving interesting features is a very general one. The basic framework of the problem is generally the same for applications from MRI, tomography, Radar SAR imaging to subsurface imaging, even though the data acquisition processes, sensing geometries and sensed properties are different. In this thesis we introduced a new perspective to the problem of remote sensing and information retrieval by studying the problem of subsurface imaging using GPR and seismic sensors. We have shown that if the sensed medium is sparse in some domain then it can be imaged using many fewer measurements than required by the standard methods. This leads to much lower data acquisition times and better images representing the medium. We have used the ideas from Compressive Sensing, which show that a small number of random measurements about a signal is sufficient to completely characterize it, if the signal is sparse or compressible in some domain. Although we have applied our ideas to the subsurface imaging problem, our results are general and can be extended to other remote sensing applications. A second objective in remote sensing is information retrieval which involves searching for important features in the computed image of the medium. In this thesis we focus on detecting buried structures like pipes, and tunnels in computed GPR or seismic images. The problem of finding these structures in high clutter and noise conditions, and finding them faster than the standard shape detecting methods like the Hough transform is analyzed. One of the most important contributions of this thesis is, where the sensing and the information retrieval stages are unified in a single framework using compressive sensing. Instead of taking lots of standard measurements to compute the image of the medium and search the necessary information in the computed image, a much smaller number of measurements as random projections are taken. The data acquisition and information retrieval stages are unified by using a data model dictionary that connects the information to the sensor data.Ph.D.Committee Chair: McClellan, James H.; Committee Member: Romberg, Justin K.; Committee Member: Scott, Waymond R. Jr.; Committee Member: Vela, Patricio A.; Committee Member: Vidakovic, Bran

Combined use of GPR and Other NDTs for road pavement assessment: an overview

Roads are the main transportation system in any country and, therefore, must be maintained in good physical condition to provide a safe and seamless flow to transport people and goods. However, road pavements are subjected to various defects because of construction errors, aging, environmental conditions, changing traffic load, and poor maintenance. Regular inspections are therefore recommended to ensure serviceability and minimize maintenance costs. Ground-penetrating radar (GPR) is a non-destructive testing (NDT) technique widely used to inspect the subsurface condition of road pavements. Furthermore, the integral use of NDTs has received more attention in recent years since it provides a more comprehensive and reliable assessment of the road network. Accordingly, GPR has been integrated with complementary NDTs to extend its capabilities and to detect potential pavement surface and subsurface distresses and features. In this paper, the non-destructive methods commonly combined with GPR to monitor both flexible and rigid pavements are briefly described. In addition, published work combining GPR with other NDT methods is reviewed, emphasizing the main findings and limitations of the most practical combination methods. Further, challenges, trends, and future perspectives of the reviewed combination works are highlighted, including the use of intelligent data analysis.Xunta de Galicia | Ref. ED431F 2021/08Ministerio de Ciencia e Innovación | Ref. RYC2019–026604-

Implementation of Ground Penetrating Radar (GPR) and Complementary Non-Destructive Testing on Concrete Structures

This study analyzes the application and practicality of different non-destructive testing (NDT) methods for the inspection of reinforced concrete. There are two studies discussed in this paper. The first one is a laboratory investigation, utilizing ground penetrating radar (GPR) on concrete slabs that consisted of simulated defects to mimic those found in real concrete structures. This served as a preliminary experiment to verify the GPR data with the design of the slabs. The following study describes a field investigation on an old bridge deck, which involved multiple testing methods. The techniques used were GPR, impact echo (IE), ultrasonic pulse echo (UPE), a cover meter, and a rebound hammer. The primary method implemented was GPR for locating the embedded reinforcement steel and suspected areas of concrete deterioration caused by rebar corrosion. Core specimens were extracted for visual inspections to compare with the GPR data. Additionally, compressive tests were completed to obtain the compressive strength of the bridge deck. This data was compared to results from the rebound hammer, which provided an estimate on the in-situ compressive strength of concrete. The cover meter provided data on the rebar depth and spacing. Lastly, the IE and UPE instruments were utilized to determine the thickness of the bridge deck slab. Through data analyses, the results were compared primarily with the GPR and actual core data, in which most of the data was validated through an acceptable percentage accuracy and mean absolute error. This study displays the limitations when using NDT methods in a practical situation as opposed to laboratory settings. The uncertainty of what objects and flaws are embedded beneath an element poses some challenges; therefore, having the appropriate knowledge and background on NDT methods is necessary for structural evaluations. However, there is a promising future for NDT in civil engineering and construction project applications

Development of In-Situ Sensing Method for the Monitoring of Water-Cement (w/c) Values and the Effectiveness of Curing Concrete

As the most widely used construction material, concrete is very durable and can provide long service life without extensive maintenance. The strength and durability of concrete are primarily influenced by the initial water-cement ratio value (w/c), and the curing condition during the hardening process also influences its performance. The w/c value is defined as the total mass of free water that can be consumed by hydration divided by the total mass of cement and any additional pozzolanic material such as fly ash, slag, silica fume. Once placed, field concrete pavements are routinely cured with liquid membrane-forming compounds. For laboratory study, concrete samples are usually cured in saturated lime water or a curing room with a relative humidity (RH) value higher than 95%. Thus, the effectiveness of curing compounds for field concrete needs to be studied. In this study, the dielectric constant value of plastic concrete was measured by ground penetrating radar (GPR). The w/c value of the plastic concrete was calculated by a mathematical model from the measured dielectric constant value. The calculated w/c value was compared with the microwave oven drying measurement determined result in AASHTO T318. A modified coarse aggregate correction factor was proposed and applied in microwave oven drying measurement to determine the w/c value of plastic concrete in AASHTO T318. The effectiveness of curing compound was evaluated by field concrete slabs by GPR measurement. It was found that GPR can be a promising NDT method for In this study, the dielectric constant value of plastic concrete was measured by ground penetrating radar (GPR). The w/c value of the plastic concrete was calculated by a mathematical model from the measured dielectric constant value. The calculated w/c value was compared with the microwave oven drying measurement determined result in AASHTO T318. A modified coarse aggregate correction factor was proposed and applied in microwave oven drying measurement to determine the w/c value of plastic concrete in AASHTO T318. The effectiveness of curing compound was evaluated by field concrete slabs by GPR measurement. It was found that GPR can be a promising NDT method for w/c determination of plastic concrete and curing effectiveness evaluation method for hardened concrete

Electromagnetic Sensing Techniques for Non-Destructive Diagnosis of Civil Engineering Structures

Environmental policy & protocol