Improvement and application of ground penetrating radar non-destructive technique for the concrete brigde inspection

Tese de doutoramento em Engenharia Civil - Área de Conhecimento de Estruturas.In the last decades the number of bridges increased considerably due to the significant expansion of the roadway and railway networks. Nowadays some of those structures evidence a varied range of defects. To ensure the continuous safety and functionality of those bridges, condition and safety assessments, followed by adequate maintenance and rehabilitation actions, which requires gathering an extensive amount of data related with the bridge characteristics and condition, must be carried out frequently. In this context, Non-Destructive Testing (NDT) techniques are becoming increasingly popular and indispensable to collect reliable and valuable information without damaging the structure. In the particular case of concrete bridges, which is addressed in this thesis, the location of the tendon ducts and ordinary reinforcement is fundamental in rehabilitation design. In addition, the verification of the quality of work during the execution of the works and initial life is fundamental in order to prevent the occurrence of early deterioration, such as reinforcement corrosion. Ground penetrating radar (GPR) is one of the leading techniques that are specially prepared for these purposes. The thesis aims to give answers to the real problems raised by design offices and bridge owners concerning verification of the structural geometry of reinforced and prestressed concrete elements and verification of the structural integrity of concrete bridges. The innovations in non-destructive testing technology include application and combination of 2D and 3D radar investigations with new and cost-effective methods for regular and accurate acquisitions with software for 3D reconstruction for the verification of structural geometry and integrity of concrete bridges In addition, improvement, validation and application of radar tomography technique for the verification of structural geometry and integrity of concrete bridges is presented. The intention of the author is to focus the attention of civil engineering society that non-destructive testing is not only used as a tool itself, but can be an integral part of structural assessment process.Nas últimas décadas o número de pontes aumentou consideravelmente devido à significativa expansão das redes rodoviárias e ferroviárias. Actualmente algumas dessas estruturas evidenciam diversas anomalias. Para assegurar a segurança e funcionalidade dessas pontes, é imprescindível avaliar periodicamente o estado de conservação e aplicar acções de conservação e reabilitação, o que requer a aquisição de um vasto conjunto de dados relacionados com as características e com o estado de conservação da ponte. Neste contexto, as técnicas de ensaio não destrutivas (NDT), têm-se tornado, gradualmente, mais populares e indispensáveis para conseguir dados fiáveis, sem ter de danificar a estrutura. No caso particular de pontes de betão, que são objecto desta tese, a localização das bainhas de pré-esforço e da armadura passiva é fundamental para o projecto de reabilitação. Adicionalmente, a aferição da qualidade do betão é fundamental para prevenir a deterioração precoce, como por exemplo a devida à corrosão das armaduras. O radar de prospecção geotécnica (GPR) é uma das técnicas especialmente vocacionadas para estes propósitos. Esta tese tem por objectivo dar uma resposta a alguns dos problemas reais sentidos pela administração, construtores e projectistas, relacionados com a verificação da geometria de alguns elementos estruturais de pontes de betão armado e pré-esforçado, bem como com a aferição da integridade dessas estruturas. O contributo desta investigação, inclui a aplicação desta técnica de ensaio não destrutiva e a combinação de análises 2D e 3D com novos, económicos e precisos métodos de reconstrução de imagem, para além de se centrar na melhoria, validação e aplicação da técnica de tomografia à resolução dos problemas em epígrafe. A principal intenção do autor com este trabalho foi tornar evidente que esta técnica de ensaio não destrutiva é mais do que uma mera ferramenta, mas que pode e deve ser uma parte integrante do processo de diagnóstico.“Sustainable Bridges” European Project - FP6-PLT-01653

Verifying design plans and detecting deficiencies in concrete bridge using GPR

During the construction of concrete structures such as bridges, many deficiencies may occur due to an incorrect application or changes in the original design plans and construction errors. Frequently, areas with very poorly vibrated concrete, insufficiently grouted tendon ducts and incorrectly positioned reinforcement bars appear. Thus, the detection of these construction deficiencies is essential to prevent further damage to the bridge. Subsequently, a concrete specimen was prepared aimed at simulating some of the problems that can occur during the construction. The specimen was then mapped using a GPR system to check the effectiveness of this tool to provide information about those deficiencies. The acquisition was carried out in reflection mode and the results were further processed using 3D reconstruction software in order to obtain a more realistic and comprehensible image. These measurements showed rather good results. The 3D image provided much more detailed information about the elements placed inside the specimen relatively to 2D radargrams, which are generally used for primary target identification.Fundação para a Ciência e a Tecnologia (FCT) - POCTI SFRH/BD/6409/2001.Sustainable Bridges” European project FP6-PLT-0165

Utilização do radar de prospecção geotécnica na localização das bainhas de pré-esforço nas pontes da Barra e Lanheses

Algumas pontes de betão armado, em serviço há mais de 30 anos, apresentam, actualmente, elevados índices de deterioração, que têm levado as entidades a proceder à sua beneficiação e reforço estrutural. Neste artigo, o georadar é utilizado para localizar elementos estruturais fundamentais à segurança de duas pontes de betão armado, que doutra maneira, poderiam ser danificadas e, assim, por em causa a segurança das mesmas.União Europeia (UE) - Projecto “Sustainable Bridges” - FP6-PLT-01653

Application of radar techniques to the verification of design plans and the detection of defects in concrete bridges

Non-destructive tests (NDT) are an essential tool used in special inspections to gather detailed information about the condition of a bridge. The inspection of bridge decks is a critical task, and, currently, can be successfully carried out using a wide range of NDT techniques. Nevertheless, some of these techniques are excessively expensive and time consuming. One of these techniques, the ground penetrating radar (GPR), has been used for some decades in the non-destructive inspection and diagnosis of concrete bridges. GPR is useful to find general information about the true position of reinforcement and tendon ducts, and check the quality of the construction and materials. A significant number of reinforced and prestressed concrete bridges are deteriorating at a rapid rate and need to be repaired and strengthened. During these rehabilitation processes, designers are often faced with a lack of original design plans and unawareness of the real position of reinforcement and tendon ducts. In this paper, three case studies of the use of GPR techniques for the inspection of concrete bridges are presented and analysed. The main aim of this research is to show the strong need and usefulness of these techniques, which can provide non-visible information about structural geometry and integrity required for strengthening and rehabilitation purposes.L. T. would like to acknowledge the support from the 'Sustainable Bridges' European project, grant number FP6-PLT-01653 (www.sustainablebridges.net). F. M. F. acknowledges the partial funding of this work by the FCT through the scholarship POCTI SFRH/BPD/26706/2005

Radar investigation on civil structures using 3D data reconstruction and transmission tomography

Non-destructive investigation using Ground Penetrating Radar is becoming more popular during the inspection of civil structures. Currently, traditional 2D imaging is also used as a preliminary tool to find possible areas of interest for more detailed inspection, which can be accomplished by 3D image reconstruction or tomography techniques. In this paper, a general overview of the work done at University of Minho regarding these techniques is presented. Data acquisition was performed on two masonry walls and on one large concrete specimen. In case of masonry specimens traditional 2D imaging was supplemented by the use of transmission tomography. Data acquisition on the concrete specimen was done in reflection mode and results were further processed using 3D reconstruction software. Results from these specimens are very promising. Radar tomography and 3D image reconstruction techniques provided much more detailed information about structural integrity and shapes and location of the voids placed inside the tested specimens relatively to 2D imaging originally used for potential target identification.Portuguese Foundation for the Science and Technology (FCT) - “Sustainable Bridges” European project by the grant number FP6-PLT-01653, grant number POCTI SFRH/BD/6409/200

Practical implications of GPR investigation using 3D data reconstruction and transmission tomography

Non-destructive investigation using ground penetrating radar is becoming more popular in the inspection of civil structures. Currently, traditional 2D imaging is used as a preliminary tool to fi nd possible areas of interest for more detailed inspection, which can be accomplished by more advanced techniques like 3D image reconstruction or tomography. In this paper, a general overview of the work done at University of Minho regarding these techniques is presented, together with their limitations and advantages over typical radargrams, with implications for civil engineering applications. For this purpose, data acquisition on two large masonry walls and one large concrete specimen have been carried out, using refl ection mode, 3D reconstruction and transmission tomography. The specimens have been specially built for non-destructive inspection techniques testing, incorporating different materials and internal voids. Radar tomography and 3D image reconstruction techniques provided much more detailed information about structural integrity and shapes and location of the voids, when compared to 2D imaging originally used for potential target identification.Fundação para a Ciência e a Tecnologia (FCT) - POCTI SFRH/BD/6409/2001"Sustainable Bridges" European project - FP6-PLT-0165

Radar Tomography : Sustainable Bridges Background document SB3.8

Among different ways of radar data acquisition, tomography has so far not been fully investigated yet. In some cases, traditional B-Scan imaging does not give the operator a full idea of the integrity of civil structures, so tomographic imaging of radar data can provide more detailed information. However, it is much more time consuming than the traditional reflection mode and thus should be used on selected areas only. It requires skilled operators to perform data acquisition and analysis. In addition, radar equipment required to perform a measurement is more sophisticated and expensive. Thus, a guideline for radar operators containing detailed procedures for transmission measurements is presented. Conclusions for UMinho experiments - Attenuation tomography was successfully used to compare results from a velocity tomography - Positions of antennas close to concrete (masonry) edges should be avoided - In case of pillars or walls with an access to more than 2 sides it is advised to perform transmission measurements with full ray coverage (measurements from all sides) in order to increase information needed to detect for example air layers inside concrete or masonry structures. - Areas for testing should be chosen due to antenna penetration possibilities. Each of aradargrams obtained during a measurements should have a strong signal at the receiverantennaEC Sixth Framework ProgramSustainable Bridges – Assessment for Future Traffic Demands and Longer LivesTIP3-CT-2003-001653</p

Radar Tomography : Sustainable Bridges Background document SB3.8

Among different ways of radar data acquisition, tomography has so far not been fully investigated yet. In some cases, traditional B-Scan imaging does not give the operator a full idea of the integrity of civil structures, so tomographic imaging of radar data can provide more detailed information. However, it is much more time consuming than the traditional reflection mode and thus should be used on selected areas only. It requires skilled operators to perform data acquisition and analysis. In addition, radar equipment required to perform a measurement is more sophisticated and expensive. Thus, a guideline for radar operators containing detailed procedures for transmission measurements is presented. Conclusions for UMinho experiments - Attenuation tomography was successfully used to compare results from a velocity tomography - Positions of antennas close to concrete (masonry) edges should be avoided - In case of pillars or walls with an access to more than 2 sides it is advised to perform transmission measurements with full ray coverage (measurements from all sides) in order to increase information needed to detect for example air layers inside concrete or masonry structures. - Areas for testing should be chosen due to antenna penetration possibilities. Each of aradargrams obtained during a measurements should have a strong signal at the receiverantennaEC Sixth Framework ProgramSustainable Bridges – Assessment for Future Traffic Demands and Longer LivesTIP3-CT-2003-001653</p