Literatura académica sobre el tema "Amorphous metallic fiber"

This paper investigates the strength, drying shrinkage, and carbonation characteristic of amorphous metallic fiber-reinforced mortar with natural and artificial lightweight aggregates. The use of artificial lightweight aggregates has the advantage of reducing the unit weight of the mortar or concrete, but there is a concern that mechanical properties of concrete such as compressive strength and tensile strength may deteriorate due to the porous properties of lightweight aggregates. In order to improve the mechanical properties of lightweight aggregate mortar, we added 0, 10, 20, and 30 kg/m3 of amorphous metallic fibers to the samples with lightweight aggregate; the same amount of fiber was applied to the samples with natural aggregate for comparison. According to this investigation, the flow of mortar decreased as the amount of amorphous metallic fiber increased, regardless of the aggregate type. The compressive strength of lightweight aggregate mortar with 10 kg/m3 amorphous metallic fiber was similar to that of the LAF0 sample without amorphous metallic fiber after 14 days. In addition, the flexural strength of the samples increased as the amount of amorphous metallic fiber increased. The highest 28-d flexural strength was obtained as approximately 9.28 MPa in the LAF3 sample, which contained 30 kg/m3 amorphous metallic fiber. The drying shrinkage of the samples with amorphous metallic fiber was smaller than that of the sample without amorphous metallic fiber.

In this study, high-strength concrete containing hooked-end steel or amorphous metallic fibers was fabricated, and the electrical conductivity and electromagnetic shielding effectiveness were evaluated after 28 and 208 days based on considerations of the influences of the moisture content. Amorphous metallic fibers, which have the same length and length/equivalent diameter ratio as hooked-end steel fibers, were favored for the formation of a conductive network because they can be added in large quantities owing to their low densities. These fibers have a large specific surface area as thin plates. The electromagnetic shielding effectiveness clearly improved as the electrical conductivity increased, and it can be expected that the shielding effectiveness will approach the saturation level when the fiber volume fraction of amorphous metallic fibers exceeds 0.5 vol.%. Meanwhile, it is necessary to reduce the amount of moisture to conservatively evaluate the electromagnetic shielding performance. In particular, when 0.5 vol.% of amorphous metallic fibers was added, a shielding effectiveness of >80 dB (based on a thickness of 300 mm) was achieved at a low moisture content after 208 days. Similar to the electrical conductivity, excellent shielding effectiveness can be expected from amorphous metallic fibers at low contents compared to that provided by hooked-end steel fibers.

The aim of this research work is to develop a corrosion resistant fiber-reinforced concrete for radioactive waste disposal structures. In the case of precast concrete, the use of fibers is a solution to reduce the amount of steel reinforcement while maintaining high mechanical performance and durability. Concrete has a low strain capacity and a limited tensile strength. Generally, reinforcing bars are used to ensure tensile strength. A fiber reinforcement can also help to overcome such a mechanical weakness. For this purpose, an amorphous metallic fiber (AMF), corrosion-resistant and suitable for application in severe environment conditions are used. The fresh and hardened properties of the self-compacting fiber reinforced concrete (SCFRC) are studied with volume fractions of AMF of 0% and 0.28% and with three different aspect ratios (82, 114 and 123). Flexural tensile tests according to European standard EN 14651 are conducted to quantify the contribution of the fiber reinforcement on the residual flexural tensile strength. Since these fibers are electrically conductive, they are also tested to design a smart concrete. For this purpose, electrical resistance of specimens submitted to cyclic flexural loadings are monitored using a Wheatstone bridge.

To improve the flexural behavior of thin bonded cement-based overlays, this study was carried out on the use of repair material incorporating amorphous metallic fibers (AMFs) in combination with the rubber aggregates obtained from grinding of worn-out tires. For this study, sixteen mortar mix compositions were prepared to contain AMFs and/or rubber aggregates to be used as overlay material while the substrate used was plain cement mortar. Rubber aggregates were incorporated at three different replacement ratios (i.e., 10%, 20% and 30%) by an equivalent volume of sand, and AMFs were added in three different dosages (i.e., 10 kg/m3, 20 kg/m3 and 30 kg/m3). In this study, composite beams (500 × 100 × 140 mm) comprising substrate (500 × 100 × 100 mm) and repair layer (500 × 100 × 40 mm) were prepared and investigated under flexural loading. Experimental results showed that the increase in rubber content resulted in a decrease compressive strength, flexural strength and modulus of elasticity. Rubberized fiber-reinforced cementitious composites (30R30F) exhibited higher flexural toughness and the flexural toughness improved up to 400%. Toughness and maximum deflection of composite beams enhanced significantly due to synergetic effect of AMF and rubber aggregates. It was observed that before peak load, rubber plays its role by delaying the micro-crack propagation. Results also revealed that the steel fibers reinforcement plays an important role in restraining the crack openings under flexure loading. In the post-peak region, steel fibers control the cracks from propagating further by bridging action and provide higher post-peak residual strength.

Cette thèse résulte d'un appel à projet de l'Agence Nationale pour la gestion des Déchets Radioactifs (Andra), responsable des centres de stockage de déchets radioactifs en France depuis 1991. Outre les centres en activité, l'Andra supervise aussi le projet Cigéo, visant à stocker en profondeur les déchets radioactifs représentant le plus de risque. Le projet de Cigéo comporte des galeries souterraines à 500 m de profondeur, destinées à stocker ces déchets pendant des milliers d'années. Il se divise en deux étapes principales : d'abord la phase d'acheminement des colis dans les galeries, puis la phase de stockage, scellant le projet et rendant impossible les éventuelles interventions humaines. La thèse vise à répondre aux défis de durabilité, stabilité et surveillance des ouvrages. Le béton armé habituellement utilisé présente des problèmes de corrosion, générant du dihydrogène dans l'environnement anoxique des galeries, provoquant à terme un risque de surpression. Afin de diminuer ce risque, l'Andra examine d'autres options que celui du béton armé conventionnel, parmi lesquelles l'intégration de fibres non corrosives dans le but de réduire le taux d'armature. Deux types de fibres ont été sélectionnées : les premières, les fibres FIBRAFLEX (FF) de l'entreprise Saint-Gobain SEVA, sont des fibres métalliques amorphes caractérisées par un grand élancement, une résistance à la corrosion et une conductivité électrique élevée. Les secondes, des fibres de carbone (FC) provenant de Toray Carbon et conditionnées par Apply Carbon, sont caractérisées par une résistance à la traction et un module élastique très élevés et par un diamètre très faible. Le manuscrit se divise en quatre grandes parties. Outre l'étude bibliographique, la deuxième partie s'est concentrée sur la caractérisation et la mise au point des formulations. Différentes configurations de renforcement par des fibres ont été testées, avec des dosages de 0,27 % et 0,41 % en volume pour les FF. En ce qui concerne les FC, un dosage de 0,27 % a été testé, avec des fibres ensimées et non ensimées. Les essais de compression et de module d'élasticité n'ont pas montré d'impact majeur des fibres sur ces propriétés. En revanche, en traction par flexion, les FF ont apporté une amélioration de la ductilité du béton et une maîtrise des fissures dès leur apparition en apportant une résistance résiduelle post-pic. Quant à elles, les FC n'ont pas apporté d'améliorations significatives. La troisième partie s'est penchée sur l'impact des fibres sur la résistivité électrique des bétons et le potentiel de détection d'endommagement qui en découle. Les essais de traction par flexion ont montré qu'il existe un lien entre la résistance électrique et l'évolution de l'ouverture des fissures. En particulier pour les formulations avec les FC, où cette technique montre une sensibilité avant même l'initiation de la fissure. Par ailleurs, les formulations avec les FF ont, elles aussi, permis d'obtenir des résultats fiables, mais nécessitent une fissure déjà initiée pour observer un changement significatif de la résistance électrique. Enfin, la dernière campagne expérimentale a étudié le comportement mécanique des éléments structuraux en béton armés et fibrés. Les essais se sont portés sur des poutres en flexion 4 points, avec différentes configurations de renforcement par des aciers et des fibres. Il a été montré que les FF ont limité l'ouverture des fissures dans la phase élastique fissurée des poutres, tout en améliorant légèrement les résistances. En parallèle, différents systèmes d'acquisition ont été utilisés pour suivre l'endommagement des poutres, notamment des fibres optiques, la vidéo-corrélation, des mesures de résistance électrique et d'émission acoustique. Ces techniques de mesures indirectes ont permis de détecter précisément l'endommagement des poutres, et l'ajout de fibres a amélioré la fiabilité de ces mesures
This thesis is a part of a research project initiated by the French National Agency for Radioactive Waste Management (Andra), which has been responsible for radioactive waste storage facilities in France since 1991. In addition to active storage sites, Andra oversees the Cigéo project that aims to dispose high-risk radioactive waste at a deep geological disposal. The Cigéo project includes underground galleries located 500 meters below the surface, designed for the long-term storage of radioactive waste. It is divided into two main phases: the first involves the transportation of radioactive waste packages into the galleries, while the second phase encompasses the storage itself, sealing the project and rendering it infeasible to any human intervention. This thesis addresses the challenges of sustainability, stability, and health monitoring of the structures. Conventional reinforced concrete is susceptible to corrosion, generating dihydrogen in the anoxic environment of the galleries. Thus, leading to a long-term risk of overpressure. To mitigate this risk, Andra is exploring alternatives to conventional reinforced concrete; one of which is the incorporation of non-corrosive fibers to reduce the rate of reinforcement. Two types of fibers have been selected: the firsts, FIBRAFLEX fibers (FF) provided by Saint-Gobain SEVA are amorphous metallic fibers. They are characterized by high aspect ratio, corrosion resistance, and high electrical conductivity. The second type, carbon fibers (CF), provided by Toray Carbon and processed by Apply Carbon, are known for their high tensile strength, high elastic modulus, and small diameter. The manuscript is divided into four main sections. In addition to the literature review, the second part focused on the mechanical characterization and formulation development. Various fiber reinforcement configurations were tested, with dosages of 0.27% and 0.41% by volume for FF. For CF, two sets were tested: with sizing and without sizing at a dosage of 0.27%. Compression and elastic modulus tests showed no significant impact of the fibers on these properties. However, in flexural tensile tests, FF fibers improved the ductility of the concrete and crack control upon their initiation by increasing the residual tensile strength after the peak. The CF, on the other hand, did not yield significant improvements. The third section studied the impact of fibers on the electrical resistivity of concrete and its potentiality for damage detection. Flexural tests revealed a correlation between electrical resistivity and crack opening; particularly in batches with CF, which exhibited sensitivity even before crack initiation. Batches with FF fibers also provided reliable results, but they required a crack initiation to observe a significant change in electrical resistivity. Lastly, the final experimental campaign focused on the mechanical behavior of steel reinforced and fiber-reinforced concrete structural elements. The tests involved four-point bending on real-scale beams with different combinations of steel and fiber reinforcements. It was demonstrated that FF limited crack openings in the elastic-cracking phase of the beams while slightly enhancing their strengths. In parallel, various data acquisition systems, including optical fibers, digital image correlation, electrical resistance measurements, and acoustic emission analysis, were used to monitor beam damage. These indirect measurement techniques precisely detected damage in the beams, and the addition of fibers improved the reliability of these measurements