3D Characterisation of microcracks in concrete

The nature of microcracks that developed in concrete is not well understood. One reason for this is the lack of suitable techniques to detect and characterise the microcracks. Conventional methods include imaging polished cross sections with scanning electron microscopy and optical microscopy. However, these techniques only provide a two-dimensional representation of a three-dimensional structure, which significantly reduces the insights from such analysis. Another reason is that the development of microcracks may be associated with various complex forms of concrete deterioration during service life, e.g. due to mechanical loading, drying, thermal effects and chemical reactions. This complicates laboratory scale experiments and inducing “realistic” microcracks in concrete samples becomes very difficult. The aim of this study is to develop new techniques for three-dimensional quantitative characterisation of microcracks and to apply these to understand the properties of microcracks in concrete. A thorough literature review was conducted to identify the causes of microcracking in concrete, mechanisms of microcrack initiation and propagation, transport properties of micro-cracked concrete and methods to characterise microcracks in two dimensions (2D) and three dimensions (3D). Materials and experimental procedures for inducing different types of microcracks, sample preparation for imaging and image analysis of microcracks are discussed. The feasibility of three-dimensional techniques such as focused ion beam nanotomography (FIB-nt), broad ion beam combines with serial sectioning (BIB), X-ray microtomography (μ-CT) and laser scanning confocal microscopy (LSCM) for imaging microcracks were investigated. A new approach that combines LSCM with serial sectioning was proposed to enhance the capability of LSCM for imaging microcracks in 3D. A major focus of this thesis was dedicated to microcracks induced by autogenous shrinkage because this has been previously neglected due to the dominant role of drying shrinkage. Nonetheless, the increasing use of high strength concretes containing low water/binder ratio, complex binder systems and multiple chemical admixtures in recent years has highlighted the problem of autogenous shrinkage in these concretes. This study presents a first attempt on direct characterisation and understanding of the microcracks caused by autogenous shrinkage in 3D. Various concrete samples were produced and sealed cured to induce autogenous shrinkage. The water/binder ratio, cement type and content, and aggregate particle size distribution were varied to vary the magnitude of autogenous shrinkage and degree of microcracking. Linear deformation measurement was performed to correlate autogenous shrinkage with degree of microcracking. Samples were imaged in 2D using laser scanning confocal microscope (LSCM) and in 3D with X-ray microtomography (μ-CT). Subsequently, 2D and 3D image analysis was employed to quantify microcracks > 1 μm in width. A major challenge was to isolate the microcracks that are inherently connected to pores and air voids. Therefore, an algorithm was developed to separate microcracks from pores, and to extract quantitative data such as crack density, orientation degree, distribution of width and length, as well as connectivity and tortuosity. The results show that use of supplementary cementitious materials and low water/binder ratio can increase linear deformation and the amount of the microcracks. The thesis discusses the effect of autogenous shrinkage on the characteristics of the induced microcracking, which is critical to understanding the transport properties and long-term durability of concretes containing supplementary cementitious materials.Open Acces

Acquisition and Mining of the Whole Mouse Brain Microstructure

Charting out the complete brain microstructure of a mammalian species is a grand challenge. Recent advances in serial sectioning microscopy such as the Knife- Edge Scanning Microscopy (KESM), a high-throughput and high-resolution physical sectioning technique, have the potential to finally address this challenge. Nevertheless, there still are several obstacles remaining to be overcome. First, many of these serial sectioning microscopy methods are still experimental and are not fully automated. Second, even when the full raw data have been obtained, morphological reconstruction, visualization/editing, statistics gathering, connectivity inference, and network analysis remain tough problems due to the unprecedented amounts of data. I designed a general data acquisition and analysis framework to overcome these challenges with a focus on data from the C57BL/6 mouse brain. Since there has been no such complete microstructure data from any mammalian species, the sheer amount of data can overwhelm researchers. To address the problems, I constructed a general software framework for automated data acquisition and computational analysis of the KESM data, and conducted two scientific case studies to discuss how the mouse brain microstructure from the KESM can be utilized. I expect the data, tools, and studies resulting from this dissertation research to greatly contribute to computational neuroanatomy and computational neuroscience

Optical In-Process Measurement Systems

Information is key, which means that measurements are key. For this reason, this book provides unique insight into state-of-the-art research works regarding optical measurement systems. Optical systems are fast and precise, and the ongoing challenge is to enable optical principles for in-process measurements. Presented within this book is a selection of promising optical measurement approaches for real-world applications

Histologie massive basée sur la microscopie à tomographie par cohérence optique

L’histologie consiste en l’étude des tissus vivants à l’échelle microscopique. Cette discipline a permis de grandes avancées, tant en biologie qu’en médecine, allant de la découverte de la cellule, jusqu’à devenir l’outil de prédilection pour le diagnostic de nombreuses maladies. L’avènement de l’histologie s’est fait en parallèle avec le développement du microscope, nécessaire pour visualiser les tissus sous grossissement. La microscopie est par nature limitée à imager une très petite région d’intérêt et ne donne donc qu’un petit aperçu de l’échantillon en entier. Récemment, des microscopes tomographiques sériels combinant la microscopie au sectionnement du tissu ont permis d’imager automatiquement de larges échantillons de tissu à l’échelle du micron. Des algorithmes spécifiquement développés pour ces appareils permettent de reconstruire dans une grande matrice tridimensionnelle l’échantillon imagé. Dans le cadre de cette thèse, un tel système a été construit avec la tomographie par cohérence optique comme modalité d’imagerie. Cette technique d’imagerie, qui est basée sur la réflectance intrinsèque des tissus, permet une acquisition de données volumétriques à haut débit en plus d’offrir une haute résolution spatiale et une bonne pénétration dans les tissus. Le système développé a permis d’imager de façon fiable et répétable un organe de souris en l’espace de quelques heures avec un voxel d’une taille de (4,88 x 4,88 x 6,5) μm. L’objectif général de ce projet était d’utiliser le système développé pour faire des études de groupe sur la souris, pour répondre à des questions spécifiques. D’abord, une validation du système d’imagerie était de mise pour vérifier que la plateforme d’imagerie donne une représentation fidèle du tissu in vivo. En imageant une population de cerveaux de souris in vivo en imagerie par résonance magnétique, puis avec la plateforme d’imagerie, les déformations entre les modalités d’imageries furent quantifiées. L’utilisation d’outils d’analyses morphométriques développés pour l’imagerie par résonance magnétique a démontré que le sectionnement et la fixation ne déforment pas de façon significative le tissu et que les algorithmes permettant la reconstruction en un volume tridimensionnel donnent une représentation fidèle du cerveau in vivo. Cette démonstration ouvre la voie à des études de groupes s’intéressant à des altérations microscopiques dans un organe entier. Considérant la répétabilité et la fiabilité prouvée de la plateforme d’imagerie, l’effet du vieillissement normal sur le coeur de la souris a été examiné. En comparant les coeurs de souris jeunes à ceux de souris âgées, il a été mis en évidence que des changements dans l’architecture du myocarde s’opèrent en vieillissant. Chez les souris âgées la paroi du ventricule gauche s’épaissit résultant en une diminution du taux de changement d’orientation des fibres musculaires dans cette même paroi. En imageant préalablement la fonction cardiaque de ces mêmes coeurs in vivo, il fut démontré que ces changements microscopiques s’accompagnent de changements fonctionnels.----------ABSTRACT Histology consists in the study of biological tissue at the microscopic scale. This discipline has led to great advances in biology, such as permitting the discovery of the cell and in medicine, where it is to this day the gold standard to detect many diseases. The advent of histology has been brought to in parallel with the development of microscopy, necessary to visualize tissues under magnification. Microscopy is limited to imaging small field of views, thus giving only a small representation of the entire sample. Recently, serial scanning microscopes, combining light microscopy and tissue sectioning have allowed to automatically image large tissue samples, expanding the imaged region to the order of the centimeter while keeping micrometer scale resolution. Post processing algorithms, specifically developed for serial scanning microscopes, are used to reconstruct in large 3D datasets the imaged sample. In this thesis, a serial scanning optical coherence tomography microscope was developed. This imaging modality, based on the intrinsic reflectance of tissue, allows high-speed acquisition of volumetric datasets at micrometer scale spatial resolution and penetrates deep in biological tissue. The developed platform allowed reliable and repeatable imaging of whole mouse organs within a time lapse of a few hours with a voxel size of (4,88 x 4,88 x 6,5) μm. The general objective of this project was to use this developed imaging platform to perform group studies on mice, to answer specific questions on tissue morphology. First, a system validation was required to verify that the imaging platform gives reliable representation of in vivo tissue. By imaging a group of in vivo mice brains with magnetic resonance imaging before serial sectioning, inter-modality deformations were quantified. The use of morphometric analysis tools developed for magnetic resonance imaging demonstrated that tissue sectioning and fixation does not significantly deform tissue and that reconstruction algorithms to obtain a large 3D dataset give a reliable representation of the in vivo brain. This proof of concept investigation opens the way to further group studies looking at microscopic alterations in an entire small animal organ. Considering the previously demonstrated repeatability and reliability of the imaging platform, the effect of normal aging on the mouse heart was examined. By comparing hearts of young and old mice, it was shown that architectural changes in the myocardium occur with aging. In old mice, there was a thickening of the left ventricle wall, which showed a decrease of muscle fiber orientation change. Prior imaging of the cardiac function in vivo revealed that these microscopic changes in morphology were accompanied by changes in the heart function

Modeling and Simulation in Engineering

This book provides an open platform to establish and share knowledge developed by scholars, scientists, and engineers from all over the world, about various applications of the modeling and simulation in the design process of products, in various engineering fields. The book consists of 12 chapters arranged in two sections (3D Modeling and Virtual Prototyping), reflecting the multidimensionality of applications related to modeling and simulation. Some of the most recent modeling and simulation techniques, as well as some of the most accurate and sophisticated software in treating complex systems, are applied. All the original contributions in this book are jointed by the basic principle of a successful modeling and simulation process: as complex as necessary, and as simple as possible. The idea is to manipulate the simplifying assumptions in a way that reduces the complexity of the model (in order to make a real-time simulation), but without altering the precision of the results

X-ray computed tomography for additive manufacturing: a review

In this review, the use of x-ray computed tomography (XCT) is examined, identifying the requirement for volumetric dimensional measurements in industrial verification of additively manufactured (AM) parts. The XCT technology and AM processes are summarised, and their historical use is documented. The use of XCT and AM as tools for medical reverse engineering is discussed, and the transition of XCT from a tool used solely for imaging to a vital metrological instrument is documented. The current states of the combined technologies are then examined in detail, separated into porosity measurements and general dimensional measurements. In the conclusions of this review, the limitation of resolution on improvement of porosity measurements and the lack of research regarding the measurement of surface texture are identified as the primary barriers to ongoing adoption of XCT in AM. The limitations of both AM and XCT regarding slow speeds and high costs, when compared to other manufacturing and measurement techniques, are also noted as general barriers to continued adoption of XCT and AM

Advanced Applications of Rapid Prototyping Technology in Modern Engineering

Rapid prototyping (RP) technology has been widely known and appreciated due to its flexible and customized manufacturing capabilities. The widely studied RP techniques include stereolithography apparatus (SLA), selective laser sintering (SLS), three-dimensional printing (3DP), fused deposition modeling (FDM), 3D plotting, solid ground curing (SGC), multiphase jet solidification (MJS), laminated object manufacturing (LOM). Different techniques are associated with different materials and/or processing principles and thus are devoted to specific applications. RP technology has no longer been only for prototype building rather has been extended for real industrial manufacturing solutions. Today, the RP technology has contributed to almost all engineering areas that include mechanical, materials, industrial, aerospace, electrical and most recently biomedical engineering. This book aims to present the advanced development of RP technologies in various engineering areas as the solutions to the real world engineering problems