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Development of an advanced, high-frequency GPR technique for the assessment of concrete structures: from modeling predictions to experimental results
Smart Materials and Nondestructive Evaluation for Energy Systems 2016
E. Cheilakou, T. E. Matikas, University of Ioannina (Greece)

Abstract

The main objective of this paper is to develop a portable, advanced and high operating frequency GPR prototype system, which will be able to provide an increased sensitivity and resolution in terms of defects detectability at a penetration depth range up to 40-50 cm in concrete. For this purpose, the theoretical assessment of multiple GPR antenna-frequency approaches was initially performed using electromagnetic wave simulation tools for the propagation of radar waves within concrete, aiming to predict the required antenna frequency and characteristics that are most effective in detecting internal concrete elements and defects of interest found in realistic structures. Form the modeling results obtained, which are described in this paper, a portable, advanced, single-channel GPR system was developed, which uses a high frequency shielded dipole antenna in monostatic arrangement and operates at a central operating frequency of 2600 MHz. Finally, the evaluation of the performance of the developed GPR technology was carried out under laboratory conditions, where concrete samples of varying dimensions and with different embedded structural features of known characteristics were tested. The validation results produced from this study indicated the high potential and efficiency of the developed GPR device to accurately detect internal concrete features with superior resolution and with sufficient penetration for concrete to be adequately resolved in depths up to 40 cm. © (2016) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.


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Comparison study on migration methods of GPR scanning images for concrete inspection
8th European Workshop On Structural Health Monitoring (EWSHM 2016)
Haitao Zheng [1], Tat-Hean Gan [1], Cem Selcuk [1] & Eleni Cheilakou [2]
[1] Brunel University
[2] University of Ioannina

Abstract
Large infrastructures like dams, power stations, cooling towers and bridges use concrete as the main building material. Concrete structures that offer critical services require routine inspection to prevent the occurrences of catastrophic failure. Ground Penetrating Radar (GPR) is a nondestructive technique particularly well adapted to the inspection of concrete structures and widely adopted for sub-surface imaging to assess the structural condition and to locate inner defects. However, in the B-scan GPR image, the subsurface scatterers (reinforcing bars, inner defects etc.) shows up as a hyperbola distortion. A standard migration is therefore needed in order to migrate the unfocused B-scan image and to identify the scatterer’s correct placement and dimension. Three image migration techniques: F-K, SAR and Kirchhoff methods were evaluated for GPR B-scan image processing in this study. The developed GPR system operating at central frequency of 1600 MHz has been applied for the inspection of a variety of concrete samples with known internal structural features, such as reinforcing bars, plastic ducts and fabricated air-filled voids. 2D radar data were acquired along single parallel profile lines of all samples in order to locate the position and depth of the embedded elements and defects. All the objects in the concrete samples can be focused by three methods. By comparison, the Kirchhoff method focused the image slightly better than the other two algorithms with higher resolution in terms of sizes and locations of the objects.

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Non Destructive Testing Technique for NPP Containment Concrete Structure Inspection

11th International Conference of the Croatian Nuclear Society
Mateljak, P. [1], Zheng, H. [2], Cheilakou, E. [3], Garcia, A. [4], Papadimitriou, V. [5]
[1] INETEC
[2] Brunel University
[3] University of Ioannina
[4] InnoTec UK
[5] INNORA

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Vortex Robot for Rapid Low Cost Scanning and Improved Non-Destructive Testing of Large Concrete Structures

24th International Conference Nuclear Energy for New Europe
Mateljak, P. [1}, Artigao, E. [2], Cheilakou, E. [3], Kappatos, V. [2], Garcia A. [4], Budimir M. [1]
[1] INETEC
[2] Brunel University
[3] University of Ioannina
[4] InnoTecUK

Abstract
Large  public  infrastructure  facilities  around  the  world  like  dams,  cooling  towers  and bridges  use  concrete  as  the  main  building  material.  Although made from a durable material many of these large assets have begun to age and are in need of periodic inspection to ensure their integrity. Current inspection routine involves setting up scaffolds that have to be moved around for personnel to reach the whole surface.

The  VortexScan  project  has  developed  a vortex  robot  that  is  used  to  autonomously  navigate  the  vertical  surfaces  of  such  structures while deploying a combination of non-destructive inspection techniques. Air suction through a nozzle of a specific geometry creates a vortex and initiates a force that attaches the robot to a vertical surface while its wheels move it around.  Novel phased array Ground Penetrating Radar (GPR) technique is one of the two NDT equipment carried by the robot. Low frequency ultrasonic technique is also developed and an innovative fusion of data from the two techniques is performed. The data fusion is used to diminish the drawbacks of each technique and create an accurate representation of the underlying material and its defects.  VortexScan project  goal  is  to  create  a  system  that  can  rapidly  and  economically inspect  large  vertical concrete   structures   saving   huge   amounts   currently   spent   during the   manual   periodic inspections. The system will be used on EUs electrical power industry structures such nuclear reactor containment, dams and cooling towers as  a large number of these infrastructure types are beginning to age; some of them having been built nearly a century ago.