This thesis evaluates a particular ultrasonic nondestructive testing (NDT) system in order to determine its capabilities and limitations in locating defects in concrete structures; specifically tunnel linings, bridge decks, and pavements. The device, a phased-array ultrasonic tomography (UST) system that utilizes shear waves, is a significant advancement in NDT systems. Consequently, there is a need in structural engineering to verify new technologies by assessing their flaw-detecting capabilities in a variety of structural applications. The UST technique does not currently have a testing methodology that is field-ready. In order to develop a methodology, the system was evaluated based on its ability to detect simulated defects, then taken to the field to evaluate natural structural defects on public tunnels, pavements, and airport runways. Types of concrete defects the system is used to detect and localize include air- and water-filled voids, vertical cracks, horizontal delaminations, and abnormalities such as clay lumps. The device is also used to determine reinforcement depth and spacing as well as concrete thickness measurements. This research concludes that the UST system is exceptional at locating horizontal delaminations ranging from 0.05-2.0 mm (0.002-0.079 in.), and is able to differentiate between fully debonded and partially-bonded areas. Vertical cracks could only be detected once they begin to form parallel to the testing surface; however, omission of surface details was found to be a strong indicator of crack presence. Backwall surfaces up to a depth of 762 mm (30 in.) were successfully and accurately determined. Air- and water-filled voids as well as reinforcement details such as layout and depth were also successfully determined and located. With the exception of some medium-sized clay lumps (with a diameter of approximately 102 mm, or 4 in.) surrounding reinforcement, all clay lumps tested were also highly successful.

The underlying opportunity for this study is that process materials may show considerable change in their electrical properties in response to an injected signal over a wide frequency range. The use of this concept to demonstrate the construction of tomographic images for a range of frequency bands is described. These can then provide a deeper understanding and interpretation of a process under investigation. The thesis presents an in-depth review of the characteristics of the various wideband signals that could be used for simultaneous spectral measurements. This includes an objective selection process that demonstrates that a Chirp signal form offers key advantages. It then addresses the details of the developed method and algorithms for WElT systems that deploy a Chirp wideband excitation signal and a further aspect of the method, based on the time-frequency analysis, particularly wavelet transform, which is used to reveal spectral data sets. The method has been verified by simulation studies which are described. To provide measurements over a required frequency range a linear chirp is deployed as the excitation signal and corresponding peripheral measurements are synthesised using a 2D model. The measurements are then analysed using a wavelet transform algorithm to reveal spectral datasets which are exemplified in the thesis. The thesis then examines the feasibility of the presented method through various experimental trials; an overview of the implementation of the electronic system is included. This provides a single-channel EIT chirp excitation implementation, in essence simulating a real-time parallel data collection system. through the use of pseudo-static tests on foodstuff materials. The experimental data were then analysed and tomographic images reconstructed using the frequency banded data. These included results illustrate the promise of this composite approach in exploiting sensitivity to variations over a wide frequency range. They indicate that the described method can augment an EIT sensing procedure to support spectroscopic analysis of the process materials.

Cette étude expérimentale traite la localisation des déformations sur un grès poreux: le grès de Vosges. Un nombre des essais triaxiaux sont effectués sous des pressions de confinement (i.e., 20 MPa - 190 MPa) et des déformations axiales différentes pour mieux comprendre la réponse mécanique de ce grès. La localisation des déformations a été étudiée dans des différentes échelles en appliquant une variation de mesures de champs (full-field methods) comme la Tomographie Ultrasonore (en 2D), les Emissions Acoustiques (en 3D), les Rayons X (en 3D), et la Corrélation des Images (en 3D). Les méthodes expérimentales ont été appliquées avant, pendant et après les essais triaxiaux. Des coupes fine ont été observées sous le microscope optique et électronique (SEM). La combinaison des multiples techniques expérimentales, qui ont des différentes sensitivités et résolutions, a décrit la procédure de la formation et l’évolution des bands de déformation observées sur le grès de Vosges. Des bandes de cisaillement ont été formées sous des pressions intermédiaires et des bandes de compaction sous des pressions élevées. Des bandes de compactions pure n’ont pas été observées.Les bandes de déformations observées se sont caractérisées comme des zones de déformation de cisaillement localisée et/ou de compaction. En plus, elles se sont caractérisées comme des structures de fable vitesse ultrasonore, des places d’origine des fissures inter- ou intra- granulaires, et des places des densités de matériel élevées.Deux mécanismes principales ont été observées au niveau de grain dans les bandes de cisaillement et de bandes de compaction (shear-enhanced compaction bands): d’un cote c’est la fissuration des grains (endommagement) et de l’autre cote c’est la réduction de porosité (sur la forme de compaction). Les deux mécanismes i présent différences sur leurs proportions et leur ordre d’occurrence dans le temps. / This PhD thesis presents a laboratory study aiming at a better understanding of the stress-strain response of the Vosges sandstone (porous rock) tested at a range of confining pressures (i.e., 20-190 MPa) and different axial strain levels. Localised deformation was captured at different scales by a combination of full-field experimental methods, including Ultrasonic Tomography (2D), Acoustic Emissions (3D), X-ray Tomography (3D), and 3D volumetric Digital Image Correlation, plus thin section and Scanning Electron Microscope observations (2D). These experimental methods were performed before, during and after a number of triaxial compression tests. The combined use of the experimental techniques, which have different sensitivity and resolution, described the processes of shear band and shear-enhanced compaction band generation, which formed at low to intermediate and relatively high confining pressures, respectively. Pure compaction bands were not identified. The deformation bands were characterised as zones of localised shear and/or volumetric strain and were captured by the experimental methods as features of low ultrasonic velocities, places of inter- and intra-granular cracking and structures of higher density material. The two main grain-scale mechanisms: grain breakage (damage) and porosity reduction (compaction) were identified in both shear band and shear-enhanced compaction band formation, which presented differences in the proportions of the mechanism and their order of occurrence in time.

[ES] Hoy en día, los materiales cementicios están presentes en la gran mayoría de las infraestructuras de nuestro entorno, como pueden ser el hormigón y el mortero, debido a su bajo coste y sus características mecánicas estructurales y de durabilidad. Pese a todo, estas se ven degradadas por factores externos e internos, reduciendo la viabilidad de estos con el paso del tiempo. Para inspeccionar estos materiales se han creado múltiples ensayos destructivos (ED) y ensayos no destructivos (END) que indican mediante ciertos parámetros el estado de los materiales de construcción. Dentro de los no destructivos, encontramos los ultrasonidos cuya propagación en estos materiales otorga información sobre su estado y estructura interna. Entre los múltiples ensayos ultrasónicos se encuentra la tomografía ultrasónica cuya base nace gracias a las Tomografías Computarizadas (TC): se ilumina un objeto mediante una fuente y se reciben las señales mediante los receptores. Se rota entorno al objeto bajo estudio combinando las señales mediante los algoritmos tomográficos y obteniendo una reconstrucción del objeto interno sin producirle ningún tipo de daño. No obstante, aunque para determinadas longitudes de onda podemos asumir una trayectoria de rayo recto, los ultrasonidos son ondas dispersivas que se difractan y se reflejan alejándose de esta condición de idoneidad afectando negativamente a las reconstrucciones. En esta tesis se estudia la tomografía de ultrasonidos aplicada a probetas de mortero. Para ello, previamente se realiza un estudio de los algoritmos de reconstrucción tomográfica donde se hace un recorrido por los principales algoritmos convencionales. Los transformados (FBP y DFT) cuyos resultados son excelentes en caso de que tengamos un nivel elevado de rayos y direcciones que conforman las proyecciones. Los algoritmos de redes neuronales (BPE y RBF) y métodos algebraicos (ART, CART, SART y SIRT) presentan buenos resultados en aquellas situaciones donde se tenga un bajo número de rayos y direcciones o alta presencia de ruido. Se comparan entre ellos mediante proyecciones obtenidas con señales simuladas y se obtienen los mejores resultados para el algoritmo FBP, con lo que las siguientes reconstrucciones reales se llevan a cabo con este método. La aplicación en la que se centra este trabajo consiste en la detección del frente de carbonatación en probetas cementicias. Es por ello que se diseñan diferentes casos de probetas con daño y sin daño para validar el funcionamiento de un sistema tomográfico. Se diseña y se construye el sistema hardware capaz de la toma automatizada de medidas empleando una configuración de rayos paralelos o de rayos en abanico. Además, se ha adaptado para que sea capaz de inspeccionar tanto con transductores acoplados por aire como inspeccionar el objeto en inmersión (acoplamiento por agua). Se concluye que la tomografía por inmersión ofrece una solución de compromiso entre transferencia de energía y proceso de automatización. Además se implementan dos modelos de redes neuronales entrenados mediante sinogramas simulados para posteriormente reconstruir casos reales. Todos los algoritmos y casos son evaluados tanto en calidad de reconstrucción como en prestaciones. / [CA] Avui dia, els materials cimentants són presents a la majoria de les infraestructures del nostre entorn com poden ser el formigó i el morter, donat el seu baix cost i les seues característiques mecànic estructurals i la seua durabilitat. Malgrat tot, aquestes es veuen degradades per factors externs i interns, reduint la seua viabilitat amb el pas del temps. Per inspeccionar dits materials s'han creat múltiples assajos destructius (AD) i assajos no destructius (AND) que indiquen mitjançant certs paràmetres l'estat dels materials de construcció. Dins del no destructius trobem els ultrasons, la propagació dels quals per aquests materials ens aporta informació sobre el seu estat i estructura interna. Entre els múltiples assajos ultrasònics, es troba la tomografia ultrasònica, la base de la qual neix gràcies a les Tomografies Computeritzades (TC): s'il·lumina un objecte per mitjà d'una font i es reben les senyals a través dels receptors. Es rota entorn l'objecte en estudi combinant les senyals mitjançant els algoritmes tomogràfics i obtenint una reconstrucció de l'objecte intern sense produir-li cap tipus de dany. No obstant això, i encara que per a determinades longituds d'ona podem assumir una trajectòria recta del raig, els ultrasons són ones dispersives que es difracten i reflecteixen, allunyant-se d'aquesta condició d'idoneïtat i afectant negativament les reconstruccions. En aquesta tesi s'estudia la tomografia d'ultrasons aplicada a provetes de morter. Amb aquesta finalitat, prèviament es realitza un estudi dels algoritmes de reconstrucció tomogràfica on es fa un recorregut pels principals algoritmes convencionals. Els transformats (FDB i DFT) els resultats dels quals son excel·lents en cas que tinguem un nivell elevat de raigs i direccions que conformen les projeccions. Els algoritmes de xarxes neuronals (BPE i RBF) i mètodes algebraics (ART, CART, SART i SIRT) presenten bons resultats en aquelles situacions on es tingui un baix número de raigs i direccions o una alta presència de soroll. Es comparen entre ells per mitjà de projeccions obtingudes amb senyals simulades i s'obtenen els millors resultats per a l'algoritme FBP, duent-se a terme les següents reconstruccions amb aquest mètode. L'aplicació en la que es centra aquest treball consisteix en la detecció del front de carbonatació en provetes cimentants. És per això que es dissenyen diferents casos de provetes amb desperfectes i sense desperfectes per validar el funcionament d'un sistema tomogràfic. Es dissenya i es construeix el sistema hardware capaç de la presa automatitzada de mesures emprant una configuració de raigs paral·lels o de raigs en ventall. A més, s'ha adaptat per a que sigui capaç d'inspeccionar tant amb transductors acoblats per aire com inspeccionar l'objecte en immersió (acoblament per aigua). Es conclou que la tomografia per immersió ofereix una solució de compromís entre la transferència d'energia i el procés d'automatització. A més s'implenten dos models de xarxes neuronals entrenats per mitjà de sinogrames simulats per a posteriorment reconstruir casos reals. Tots els algoritmes i casos són avaluats tant en qualitat de reconstrucció com en prestacions. / [EN] Nowadays, cementitious materials are present in the great majority of our surrounding infrastructures such as concrete and mortar, due to its low cost mechanic-structural features and its lasting. Nevertheless, this characteristics are degraded because of external and internal factors, reducing its viability over time. In order to inspect this materials, multiple destructive testing (DT) and non-destructive testing (NDT) have been created. This trials show construction materials conditions with certain parameters. In the non-destructive group, we found ultrasounds whose spreading in this materials gives us information about their condition and internal structure. Among the multiple ultrasonic tests, we can find the ultrasonic tomography which is based in the Computed Tomography Scans (CT) basis: an object is illuminated by a source and signals are received through receivers. Rotation is made around the object under study combining the signals using tomographic algorithms for the purpose of obtaining an internal object reconstruction without damaging it. However we can assume a straight beam path for certain wavelengths, ultrasound are dispersive waves that diffract and reflect, making them less suitable because they worsen the quality of reconstructions. In this thesis, the ultrasonic tomography applied to mortar specimens is studied. For that, a study of tomographic reconstruction algorithms is carried out and the main conventional algorithms are reviewed. The transforms (FBD and DFT) whose results are excellent in case we have a high level of beams and directions that make up the projections. The neuronal network algorithms (BPE and RBF) and the ones for algebraic methods (ART, CART, SART and SIRT) have good results in situations where a low number of beams and directions or high noise presence are found. A comparation between them is made using projections obtained with simulated signals and the best FBP algorithm results are extracted. The following real reconstructions are carried out with this method. The application on which this work focuses consists of the detection of the carbonation front in cementitious specimens. That is why different types of specimens with damage and without damage are designed to validate a tomographic system function. A hardware system capable of taking automated measures using a configuration of parallel beams or fan beams is designed and built. Moreover, it has been adapted to be able to inspect both with air-coupled transducers and to inspect the object while submerged (water coupled). It is concluded that immersion tomography offers a compromise solution between energy transfer and automation process. Two models of neuronal networks trained through simulated sinograms are also implemented to reconstruct real cases afterwards. All the algorithms and cases are evaluated both in reconstruction quality and in features. / Gallardo Llopis, C. (2023). Tomografía ultrasónica para la evaluación de daño por gradiente en materiales cementantes [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/194552