Survey of Materials for Nanoskiving and Influence of the Cutting Process on the Nanostructures Produced

This paper examines the factors that influence the quality of nanostructures fabricated by sectioning thin films with an ultramicrotome (“nanoskiving”). It surveys different materials (metals, ceramics, semiconductors, and conjugated polymers), deposition techniques (evaporation, sputter deposition, electroless deposition, chemical-vapor deposition, solution-phase synthesis, and spin-coating), and geometries (nanowires or two-dimensional arrays of rings and crescents). It then correlates the extent of fragmentation of the nanostructures with the composition of the thin films, the methods used to deposit them, and the parameters used for sectioning. There are four major conclusions. (i) Films of soft and compliant metals (those that have bulk values of hardness less than or equal to those of palladium, or ≤500 MPa) tend to remain intact upon sectioning, whereas hard and stiff metals (those that have values of hardness greater than or equal to those of platinum, or ≥500 MPa) tend to fragment. (ii) All conjugated polymers tested form intact nanostructures. (iii) The extent of fragmentation is lowest when the direction of cutting is perpendicular to the exposed edge of the embedded film. (iv) The speed of cutting−from 0.1 to 8 mm/s−has no effect on the frequency of defects. Defects generated during sectioning include scoring from defects in the knife, delamination of the film from the matrix, and compression of the matrix. The materials tested were: aluminum, titanium, nickel, copper, palladium, silver, platinum, gold, lead, bismuth, germanium, silicon dioxide ($\textrm{SiO}_2$), alumina ($\textrm{Al}_2\textrm{O}_3$), tin-doped indium oxide (ITO), lead sulfide nanocrystals, the semiconducting polymers poly(2-methoxy-5-(2′-ethyl-hexyloxy)-1,4-phenylene vinylene) (MEH-PPV), poly(3-hexylthiophene) (P3HT), and poly(benzimidazobenzophenanthroline ladder) (BBL), and the conductive polymer poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS).Chemistry and Chemical Biolog

Fracture characterization of multi-layer wire mesh rubberized ferrocement composite slabs by means of acoustic emission

This study investigated the fracture behaviour of multi-layer ferrocement composite slabs with partial replacement of tire rubber powder as filler utilizing acoustic emission (AE) technique for characterization. Ferrocement slab specimens prepared using normal-compact cement mortar, self-compact cement mortar, fly ash, and rubberized self-compact cement mortar –with varying steel mesh reinforcement layers– were statically loaded to failure. The inclusion of 10% rubber powder (by weight) was found capable of altering the failure mode of composite slabs from brittle to ductile with a slight reduction in the ultimate flexural strength. Fracture development of the specimens was closely monitored using AE for enhanced characterization. It is seemingly evident that the measured AE parameters could be effectively processed to distinguish different modes of fracture. The collected AE data was utilized to quantify stiffness reduction in the specimens due to progressive damage.No Full Tex

CONSOLIDATION AND RESTORATION OF HISTORICAL HERITAGE: THE FLAVIAN AMPHITHEATER IN ROME

Abstract. The recovery and retrofitting techniques adopted for historical structures and archaeological sites face an apparent dichotomy between conservation of constructions and the safety of users. Literatures show several examples where the current day structural safety of historical constructions, gets defined by the nature of past interventions, the compatibility of materials and elements used in retrofitting. The adopted interventions were, in their time, considered innovative, but over the years their compatibility and reversibility leave the historic constructions structurally vulnerable. For these reasons, a careful understanding of the structural systems is fundamental for the implementation of appropriate retrofitting solutions. Especially for monuments and Archaeological sites the objective to be achieved has to be clear, avoiding destructive investigation tests. In this work the instabilities caused by a consolidation intervention on some travertine columns in a sector of the Flavian Amphitheatre, better known as "Colosseum" in Rome, are critically analysed. The current consolidation operations are compared to the previous one. The restoration activity involves in-depth diagnosis process: the historical analysis of the failures and restorations of that area of the Colosseum, a survey of the crack pattern and an indirect investigation on the travertine of the columns. Subsequently the various data coming from the knowledge phase are elaborated, in order to have a correct interpretation of the causes triggering the failure and guide the choice of the most correct retrofitting techniques

Crack detection in "as-cast" steel using laser triangulation and machine learning

We describe a high-accuracy inspection system designed to automatically detect cracks in "as-cast" steel slabs. Real-time slab inspection requires instrumentation capable of withstanding high temperatures above the steel surface as well as coping with the dirty and dusty environment present in a steel mill. Crack detection is also challenging due to the presence of oxidation scale on the slab surface. A bespoke laser triangulation system has been developed, providing images at 250 fps with a calibrated surface resolution of 97 μm from a 1m standoff distance. Cracks are detected using a combination of morphological detection and SVM classifier. Results are reported from laboratory testing and from extended trials at a production steel mill

A review of the effects of chemical and phase segregation on the mechanical behaviour of multi-phase steels

In the drive towards higher strength alloys, a diverse range of alloying elements is employed to enhance their strength and ductility. Limited solid solubility of these elements in steel leads to segregation during casting which affects the entire down-stream processing and eventually the mechanical properties of the finished product. Although it is thought that the presence of continuous bands lead to premature failure, it has not been possible to verify this link. This poses as increasingly greater risk for higher alloyed, higher strength steels which are prone to centre-line segregation: it is thus vital to be able to predict the mechanical behaviour of multi-phase (MP) steels under loading. This review covers the microstructure and properties of galvanised advanced high strength steels with particular emphasis to their use in automotive applications. In order to understand the origins of banding, the origins of segregation of alloying elements during casting and partitioning in the solid state will be discussed along with the effects on the mechanical behaviour and damage evolution under (tensile) loading. Attention will also be paid to the application of microstructural models in tailoring the production process to enable suppression of the effects of segregation upon banding. Finally, the theory and application of the experimental techniques used in this work to elucidate the structure and properties will be examined.Comment: 53pages, 34 figures, 4 table

Characterization and performance of eco and crack-free high-performance concrete for sustainable infrastructure

The main objective of this study is to develop, characterize, and validate the performance of a new class of environmentally friendly, economical, and crack-free high-performance concrete referred to as Eco and crack-free HPC that is proportioned with high content of recycle materials. Two classes of Eco-HPC are designed for: (I) pavement (Eco-Pave-Crete); and (II) bridge infrastructure (Eco-Bridge-Crete). Eco-HPC mixtures were designed to have relatively low binder content up to 350 kg/m3 and develop high resistance to shrinkage and superior durability. A stepwise mixture design methodology was proposed to: (i) optimize binder system and aggregate skeleton to optimize packing density and flow characteristics; (ii) evaluate synergy between shrinkage mitigating materials, fibers, and moist curing duration to reduce shrinkage and enhance cracking resistance; and (iii) validate performance of Eco HPCs. The composition-reaction-property correlations were developed to link the hydration kinetics of various binder systems to material performance in fresh state (rheological properties) and hardened state (strength gain and shrinkage cracking tendency). Results indicate that it is possible to design Eco-HPC with drying shrinkage lower than 300 µstrain after 250 days and no restrained shrinkage cracking even after 55 days. Reinforced concrete beams made with Eco-Bridge-Crete containing up to 60% replacement of cement with supplementary cementitious materials and recycled steel fibers developed significantly higher flexural toughness compared to the reference concrete used for bridge applications. In parallel, autogenous crack healing capability of concrete equivalent mortar mixtures was monitored using microwave reflectometry nondestructive testing technique. Research is in progress towards analyzing life cycle assessment of Eco-HPCs under field condition --Abstract, page iii

Développement des bétons nano-modifiés aux performances améliorées

In light of the well-established multi-scale nature of flaws in concrete, it follows that existing diverse attempts in fiber-reinforced concrete (FRC) technology-intended to mitigate the inherent tendency of concrete to cracking-remain relatively inefficient. This is majorly attributed to the fact that the large inter-fiber spacing in conventionally used macrofibers does not promote an effective bridging of multiscale cracks. As a result, increasing research and development are currently being invested to develop concretes incorporating nanoscale particles. Thus, nanoscale fibers emerged as a promising tool for manipulating concrete nanostructure towards a controlled macrobehavior necessary for enhanced overall performance. In this context, while carbon nanostructure (CNS) such as carbon nanofibers (CNF) and carbon nanotubes (CNT) have gained a relative popularity, it should be noted that eco-efficiency incentives would favor the currently emerging nanocellulose materials (NCM) extracted from cellulose-based systems, the most abundant and renewable resource on the planet. NCM have been demonstrated as a means to engineer superior composite properties necessary for versatile applications including optics, biomedical applications, and transparent electronics. The current study is aimed at disclosing the possibilities of re-engineering concrete properties using a new type of NCM, namely, cellulose filaments (CF) in order to achieve superior concrete performance necessary for specific applications. CF are cellulosic fibrils with a nanometric diameter (30–400 nm) and micrometric length (100–2000 µm), thereby exhibiting the highest aspect ratio (100–1000) among all currently available NCM. The study focuses on the influence of CF as a tool for nano-tailoring the properties of concrete in its three major states (fresh, hardening, and hardened). As a result, three applications in relation to the above concrete states were identified through intensive experimentation: (i) enhancing the properties of fresh concrete by using CF as a viscosity modifying admixture (VMA), (ii) enhancing the properties of hardening concrete by using CF as a shrinkage reducing admixture (SRA), and (iii) improving the performance of concrete at the hardened state by using CF as a nanoscale reinforcement. The study further aims at leveraging those different enhancements in concrete properties obtained with CF towards developing a new concrete formulation that optimizes the advantages of CF. The enhancement of concrete properties at fresh state was undertaken in the context of valorizing the hydrophilic and flexible nanoscale CF to function as a VMA in self-consolidating concrete (SCC) whereby the design of flowable (yet stable and robust) mixtures requires a delicate balance between flowability and stability. For this, CF were incorporated at concentrations ranging from 0.05 to 0.30% per weight of binder in cement pastes and SCC. CF were demonstrated as a valuable tool not only for rheology modification, but also to impart collateral positive effects on mechanical performance (strength enhancement of 12–26% in compression, splitting-tension, and flexure) when compared to commercially available VMA of Welan Gum type. CF were found to serve as a VMA due to the buildup of flexible nanoscale networks as demonstrated by a geometry-based percolation model as well as by microstructure investigations. Interestingly, this effect was found to be accompanied by a shear thinning effect attributable to the streamlining of flexible nanocellulose fibrils in the direction of flow under increasing shear rates, thereby potentially enhancing pumpability. The potential of CF to enhance the properties of hardening concrete was attempted in the context of exploiting the hydrophilic and hygroscopic characters of CF to mitigate autogenous shrinkage (AS) in ultra-high-performance concrete (UHPC). While s such, when UHPC formulation was adjusted to accommodate CF at rates of 0-0.30% per cement mass, and silica fume content was varied (from 15 to 25%), CF were found to be more beneficial in reducing AS at early-age with a reduction of up to 45% during the first 24 hours and 35% at 7 days. On the other hand, adjusting SF content from 25 to 15% had a negligible effect on AS at early-age (0–4% reduction at 1 day) but a higher effect at later-age (28% reduction at 7 days) attributable to the time-dependent pozzolanicity of silica fume. However, this alternative was found to have adverse effects on mechanical performance (32% lower flexural capacity). Finally, the potential of CF as a nanoscale reinforcement was investigated on cement pastes and on concrete. In the former, strength enhancement in engineering properties (compressive strength, flexural capacity, and elastic modulus) of up to 25% were achieved. In the latter, strength improvements of up to 16% (in compression), 34% (in splitting tension), 22% (in flexure), and 96% (in energy absorption) were obtained. To disclose the mechanisms underpinning the effect of CF on strength of cement systems, the above findings were supplemented by microstructure investigations, namely, degree of hydration and micromechanical properties (indentation modulus M, hardness H, and contact creep modulus C) of major microstructure phases using nanoindentation coupled with quantitative energy-dispersive spectroscopy (NI-QEDS). As a result, the improved macromechanical performance was found to sprout from a twofold microstructure change, i.e.: an increased degree of hydration and higher micromechanical properties of C-S-H gel matrix (~12–25%). To leverage the above different advantages offered by CF on cement and concrete composites, particularly the nanoreinforcing effect and the potential synergy between the nanoscale CF and macrofibers, a novel multi-scale fiber-reinforced strain-hardening cementitious composite (SHCC) was developed. The design of this SHCC followed a new approach that couples packing density optimization with micromechanical tailoring. Thus, high-volume ground-glass pozzolans (HVGP) were incorporated under the guidance of particle pacing optimization to replace fly ash (FA) commonly used in SHCC such that composite strength can be increased. The newly formulated SHCC was further improved in terms of ductility and strain-hardening capacity by the incorporation of CF whereby the latter was a useful tool to nanomodify SHCC matrix and interface properties towards enhanced strain-hardening behavior. In outcome, HVGP-SHCC formulations with GP replacement of fly ash of up to 100% were developed. The resulting formulations have self-consolidation ability (mini-slump dimeter in the range of 250 mm) and exhibited (at 28 days) 60-75 MPa compressive strength, 9-15 MPa flexural capacity, 3-6 MPa tensile strength, 2-5% tensile strain capacity, and a significantly increased electrical resistivity (up to 60% enhancement). Thus, the mechanical properties of the newly developed HVGP-SHCC exceed those reported in the commonly used high-volume fly ash (HVFA)-SHCC. Nevertheless, while the strength enhancement obtained with GP does not jeopardize composite ductility up to 40% GP content, a reduced ductility was noticed at GP>40%. As a result, CF were used to impart a nanoreinforcing effect to HVGP-SHCC as well as to nanomodify the interface properties of PVA fibers. In outcome, a twofold effect was obtained by nanomodifying SHCC with CF: (i) CF imparted higher elastic modulus to the bulk cementitious matrix (Em) thereby contributed to attenuating the crack tip toughness (J_tip=K_m^2/E_m) with Km being matrix fracture toughness, (ii) CF led to attenuating the excessive frictional bond encountered at higher GP content (densifying the matrix and increasing its strength, but limiting strain-hardening behavior) and imparted a characteristic slip-hardening effect (β) which contributed towards improving composite strain-hardening capacity and ductility. Thus, enhancement in ultimate strain-capacity above 200% as compared to systems without CF were obtained. Therefore, with the incorporation of CF, it was possible to produce SHCC with up to 100%GP replacement of FA while exhibiting higher strength and ductility. To scale-up the enhanced mechanical performance (particularly the high strength and ductility) demonstrated by the new SHCC, the latter was used as a topping to develop a novel type of composite deck slabs at full-scale (dimensions of up to 2400 × 900 mm). The composite deck slabs thus constructed are intended to benefit from the improved strength and ductility of nanomodified HVGP-SHCC topping such that better compatibility between the steel deck and its concrete topping can be obtained. This has the potential to increase the performance of composite deck slabs under shear bond failure, a major failure mode in composite deck slabs. Results indicated that, compared to composite deck slabs with a high-strength concrete topping having similar compressive strength as the nanomodified HVGP-SHCC, the slabs constructed with the SHCC exhibited up to 35 and 42% enhancement in ultimate load-carrying capacity and ductility, respectively. Furthermore, composite deck slabs with nanomodified HVGP-SHCC exhibited higher shear bond capacity. Considering theses results, it is perceivable that the newly developed SHCC (implemented from the material level at the nanoscale to the structural level at the macroscale) has benefited from a twofold ecoefficiency perspective. The first concerns the valorization of post-consumer recycled glass into the development of high-performance concrete, thereby contributing to relieve a significant socio-economical burden created by landfilling post-consumer glass. The second concerns exploiting the power of cellulose, the most abundant naturally occurring polymer on the planet, towards a biomimetic design of high-performance multiscale-reinforced cement composites necessary for sustainable and resilient concrete infrastructure systems.Compte tenu de la nature multi-échelle des défauts dans le béton, il s'ensuit que les diverses tentatives existantes en technologie de béton fibré (BF)-visant à atténuer la tendance intrinsèque du béton à la fissuration-demeurent toujours relativement inefficaces. Ceci est attribué non seulement au fait que le grand espacement interfibrillaire des macro-fibres (dans un BF) ne favorise pas un pontage efficace des fissures multi-échelles, mais aussi au fait que le phénomène de fissuration commence tout d’abord à l’échelle nanométrique. En conséquence, des travaux de recherche et de développement considérables ont été investis au cours de la dernière décennie pour développer des bétons incorporant des particules nanométriques. Ainsi, les nanofibres ont émergé comme un outil efficace permettant la manipulation du béton au niveau de sa nanostructure tel que celle-ci soit conçue de manière à contrôler le comportement du béton à l’échelle macroscopique pour obtenir des bétons à performances améliorées. Dans ce contexte, bien que les nanomatériaux à base de carbone tels que les nanofibres de carbone et les nanotubes de carbone ont acquis une popularité relative, certaines préoccupations reliées à leur coût actuel ainsi qu’à la santé humaine et environnementale favoriseraient plutôt les matériaux nano-cellulosiques. Ces derniers ont apparu récemment comme un enjeu permettant de conférer des propriétés composites améliorées nécessaires pour des applications aussi variées telles que les adhésifs, les nano-composites, et les électroniques transparentes. La présente étude vise à explorer les possibilités d’améliorer les propriétés du béton à l'aide d'un nouveau type de matériaux nano-cellulosiques, notamment, les filaments de cellulose (FC), afin d'obtenir des performances améliorées nécessaires pour des applications ciblées. Les FC sont des fibrilles cellulosiques de diamètre nanométrique (30 à 400 nm) et de longueur micrométrique (100 à 2000 µm), présentant ainsi le ratio d’aspect le plus élevé (100 à 1000) parmi tous les matériaux nano-cellulosiques actuellement disponibles. L'étude se concentre sur l'impact de FC comme un outil permettant d’améliorer les propriétés du béton dans ses trois principaux états (frais, durcissant et durci). En conséquence, trois applications en relation avec ces états du béton ont été identifiées grâce à un programme expérimental compréhensive: (i) amélioration des propriétés du béton frais en utilisant le FC comme agent modificateur de viscosité (VMA), (ii) amélioration des propriétés du béton durcissant en utilisant le FC comme un agent réducteur de retrait (iii) amélioration de la performance du béton à l'état durci en utilisant le FC comme un renforcement nanométrique pour conférer un pontage de fissures à l'échelle des hydrates. L'étude vise, en outre, à mettre en vigueur ces différentes améliorations (en propriétés du béton) apportées par l’utilisation de FC pour développer une nouvelle formulation de béton, ainsi optimisant les apports de FC. L’amélioration des propriétés du béton à l’état frais a été entamée dans le cadre de valoriser l’aspect hydrophile des FC, leur taille nanométrique et leur flexibilité afin de conférer un effet VMA dans les bétons autoplaçants (BAP) dont la formulation nécessite un équilibre délicat entre la fluidité et la stabilité. Dans ce contexte, les FC ont été incorporés à des concentrations de 0,05-0,30% en masse de liants dans des pâtes de ciment et des BAP. Les résultats démontrent que les FC peuvent servir d’un adjuvent VMA permettant non seulement d’améliorer la rhéologie, mais aussi de conférer des effets positifs collatéraux aux performances mécaniques (amélioration de 12–26% de la résistance en compression, traction brésilienne et flexion) par rapport aux bétons contenant de VMA conventionnels de type Welan Gum. L’effet VMA des FC est attribué à la formation des réseaux de fibrilles de FC nanométriques et flexibles permettant de percoler les particules cimentaires et accroitre la stabilité des mélanges tel que démontré à travers un modèle de percolation géométrique ainsi que par les études de la microstructure. A ce propos, Il est à noter que l’effet de VMA conféré par les FC est également accompagné d’un effet rhéofluidifiant attribuable à la tendance des FC flexibles à s’aligner dans la direction de l’écoulement du mélange sous un cisaillement croissant. La potentialité des FC d’améliorer les propriétés des bétons durcissant a été évaluée dans le contexte d’exploiter les caractères hydrophiles et hygroscopiques des FC pour atténuer le retrait endogène dans les bétons fibrés à ultra hautes performances (BFUP). Ainsi, alors que les BFUP peuvent contenir jusqu’à 25% de fumée de silice (pour accroitre la compacité et maximiser la résistance mécanique), cette teneur élevée en fumée de silice rend la matrice vulnérable au retrait endogène. Cependant, la réduction de la teneur de la fumée de silice jusqu’à 15% résulte à une matrice moins vulnérable au retrait endogène, néanmoins présentant une faible résistance mécanique. Dans ce sens, l’incorporation des FC à des taux de 0-0,30% par masse de liant a permis produire des BFUP ayant 25% de fumée de silice et présentant une réduction en retrait endogène allant jusqu'à 45% et 35% au cours des premières 24 heures et 7 jours, respectivement. Enfin, la potentialité des FC en tant que renforcement nanométrique a été étudiée sur des pâtes de ciment et sur des bétons. Dans le premier cas, des propriétés mécaniques améliorées (résistance à la compression, résistance à la flexion et module d'élasticité) allant jusqu'à 25% ont été obtenues. Dans le deuxième cas, des améliorations de résistance allant jusqu'à 16% (en compression), 34% (en traction brésilienne), 22% (en flexion) et 96% (en ténacité) ont été obtenues. Pour identifier les mécanismes sous-jacents à l'effet des FC sur la résistance mécanique des composite cimentaires, les observations ci-dessus ont été supplémentées par des études de la microstructure, notamment le degré d'hydratation et les propriétés micromécaniques (dureté, module d'indentation, et le fluage par contact) de phases de microstructure en utilisant la méthode de Nanoindentation coupled with quantitative energy-dispersive spectroscopy (NI-QEDS). Ainsi, il a été constaté que les performances macro-mécaniques améliorées découlaient d’un double effet des FC sur la microstructure, à savoir : un degré d’hydratation augmenté (15%) et des propriétés micromécaniques supérieures dans la matrice de C-S-H (~ 12-25%). Pour une mise en valeur des différents apports de la nano-modification des composites cimentaires par l’incorporation des FC, en particulier l’effet nano-renforçant et la synergie entre les FC à l’échelle nanométrique et les macro-fibres, une nouvelle formulation d’un béton de haute performance de type béton écrouissant (Strain-hardening cementitious composites) a été développée. La conception de ce nouveau béton a suivi une nouvelle approche articulant l’optimisation de la compacité granulaire avec les modèles micromécaniques. Ainsi, la poudre de verre (PV) provenant du concassage des bouteilles de verre a été incorporée en remplacement de la cendre volante (CV) – souvent utilisée dans cette application – de manier à optimiser la compacité de la matrice pour améliorer la résistance mécanique. Pa la suite, les FC ont été introduits comme un renforcement nanométrique permettant d’obtenir un béton renforcé à multi-échelle. Les résultats démontrent que les FC ont permis de nano-renforcer la matrice ainsi que d’améliorer les propriétés d'interface entre la matrice et les macro-fibres d'alcool polyvinylique (PVA), permettant ainsi d'améliorer le comportement d'écrouissage. Ainsi, des bétons écrouissant contenant jusqu’à 100% de PV en remplacement de CV ont été développés. Les formulations obtenues ont un caractère autoplaçant (≈250 mm d’étalement) et présentent (à 28 jours) une résistance à la compression de 60-75 MPa, une capacité de flexion de 9-15 MPa, une résistance à la traction de 3-6 MPa, une capacité de contrainte en traction de 2-5% et une résistivité électrique améliorée. Les bétons formulés présentent, alors, des performances mécaniques supérieures à celles des bétons écrouissants contenant la CV. Néanmoins, bien que l’amélioration en résistance mécanique obtenue avec la PV ne compromette pas la ductilité du composite jusqu’à une teneur de 40% de PV, une ductilité réduite a été observée quand la teneur en PV dépasse 40%. Pour ce, le FC a été utilisé pour conférer un effet nano-renforçant ainsi que pour améliorer les propriétés d'interface entre la matrice et les macro-fibres. L’incorporation des FC a démontré un double effet sur le comportement des bétons écrouissants : (i) le module d'élasticité de la matrice plaine des bétons écrouissant est très important en présence des FC. Ceci a contribué à réduire la ténacité de la fissuration, (ii) les FC ont atténué la friction excessive – entre les macro-fibres et la matrice – rencontrée à des teneurs élevées en PV (limitant la ductilité du béton). Les FC ont aussi conféré un effet écrouissant à l’arrachement des macro-fibres de PVA permettant ainsi d’accroitre la capacité de contrainte en traction. Une amélioration en capacité de déformation et en ductilité au-delà de 200% par rapport aux bétons écrouissants sans FC a été obtenue. Ainsi, avec l’incorporation de FC, il était possible de produire des bétons écrouissant contenant jusqu’à 100% de PV en remplacement de CV tout en présentant des résistances mécaniques et ductilités plus importantes. Pour une mise à l’échelle des performances mécaniques améliorées (particulièrement la ductilité importante) démontées par la nouvelle formulation de béton écrouissant, cette dernière a était utilisée comme un surbéton pour développer un nouveau type de dalles composites à échelle réelle (allant jusqu’à 2400 × 900 mm). La nouvelle dalle composite est envisagée de bénéficier de la ductilité améliorée de son surbéton écrouissant de manière à accroitre la compatibilité structurale entre le tablier métallique et son surbéton. Ceci a pour but d’améliorer la résistance à la détérioration de l’adhésion d’interface tablier-béton, un des principaux types de ruptures des dalles composites. Les résultats indiquent que, comparément à des dalles composites construites de béton à haute performance ayant la même résistance en compression que le nouveau béton écrouissant, les dalles composites au béton écrouissant ont démontré une amélioration de 35 et 42% en capacité maximum de chargement et en ductilité, respectivement. De même, les dalles composites au béton écrouissant ont démontré une résistance plus élevée à la détérioration de l’adhésion d’interface tablier-béton, autrement dit, une amélioration à la capacité cisaillement-adhésion connue par shear-bond capacity. À cet égard, la nouvelle formulation du béton écrouissant développée dans le cadre cette étude (et implémentée de l’échelle nano/micro jusqu’à l’échelle structurale réelle) s’est vue bénéficiée de deux aspects liés à l’éco-efficacité. Le premier concerne la valorisation du verre recyclé dans un béton à haute performance, contribuant ainsi à alléger le fardeau socio-économique important créé par l’enfouissement de verre de post-consommation. Le deuxième concerne la mise en exergue de la cellulose-le polymère naturel le plus abondant et le plus renouvelable sur la planète-vers le développement de bétons à haute performance (renforcés à multi-échelle) nécessaires pour des infrastructures en béton plus performantes

Characterization of concrete materials using non-destructive wave-propagation testing techniques

Non-destructive testing (NDT) of concrete members has been widely used for characterisation of material and assessment of functional structures without impairing their functions and performances. This thesis focuses on addressing critical challenges related to the practical implementation of NDT techniques based on wave-propagation approaches for characterisation of concrete members used in civil infrastructures. Specially, this research aims to achieve three interdependent objectives related to developing NDT techniques with piezoceramic-based transducers: monitoring of very early-age concrete hydration process, detection, and monitoring of cracking in concrete members of different complexity under loading. The concept of piezoceramic-based Smart Aggregate (SA) transducers is central to this research. Embedded SA transducers with an active sensing method have shown great potential for characterisation of construction materials such as concrete and concrete-steel composites. Based on the developed SA based approaches, an active sensing approach with appropriate arrangement of SAs in and on concrete members, and analysis of the received signal using the power spectral density, total received power and damage indexes is developed and applied in this thesis. To confirm its applicability for characterisation of very early-age concrete, a systematic investigation is performed into concrete specimens with different values of water-to-cement ratio due to slightly different initial water amounts, and different separation distances between the embedded SAs. For the detection and monitoring of cracking in concrete members under loading the mounted SA based approach is proposed and applied. It is shown that NDT systems, based on this approach, provide detection and monitoring of cracking in a variety of concrete members under loading, including relatively simple concrete beams and reinforced concrete beams under bending, and reinforced concrete slab as a part of a complex composite member under cyclic loading. Comparisons are provided between the proposed system and conventional load cell and strain gauge systems with each tested member