Dissertations / Theses: 'Cementitious composite'

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Farooq, Mohammed. "Development of FRP based composite fibre for fibre reinforced cementitious composites." Thesis, University of British Columbia, 2016. http://hdl.handle.net/2429/57668.

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This thesis describes a method of development of a novel fibre based on fibre reinforced polymers (FRP), for use fibre reinforcement in concrete. Thermosetting epoxy resin matrix were reinforced with E-glass, S-glass, and Carbon fibre to produce different types of composite fibres. The FRP panels were produced using the Vacuum Infusion technique, and then cut to different fibre sizes. The volume fractions of reinforcements within the FRP fibre were controlled by using woven and unidirectional fabrics. The number of layers of reinforcing fibres were also changed, to obtain the optimal thickness of the fibres. The FRP material was characterized by means of tensile tests and microscope image analysis. Four different compositions of FRP were produced with tensile strengths ranging from 195 MPa to 950 MPa. The different combinations in geometry broadened the total number of fibres investigated to 12. Single fibre pullout tests were performed to obtain the fundamental fibre-matrix interfacial bond parameters for the different FRP fibres. The FRP fibres, being hydrophilic, along with having a unique rough surface texture, showed a good bond with cement matrix. A bond strength superior to industrially available straight steel fibres and crimped polypropylene fibres has been observed. The 3 best fibres were then chosen to examine the flexural behaviour FRP fibre reinforced concrete beams. The optimized FRP fibres, one each of Glass FRP and Carbon FRP were then further investigated to study the effect of matrix maturity, temperature, fibre inclination, and loading rate on the fibre-matrix interfacial behaviour using single fibre pullout tests. Scanning Electron Microscope (SEM) analysis was carried out to identify the effect of above-mentioned factors on the surface characteristics of the fibre. An attempt was also made to optimize the fibre-matrix interface to achieve an optimized failure mechanism by coating the fibre with oil. The ability of the fibre to transfer stresses across a cracked section over extended periods has been investigated by means of fibre-relaxation tests. Finally, to assess durability, the fibres were conditioned at high pH and high temperature after which single fibre pullout, direct tension tests, & SEM analysis were conducted.
Applied Science, Faculty of
Civil Engineering, Department of
Graduate

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Mihai, Iulia. "Micromechanical constitutive models for cementitious composite materials." Thesis, Cardiff University, 2012. http://orca.cf.ac.uk/24624/.

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A micromechanical constitutive model for concrete is proposed in which microcrack initiation, in the interfacial transition zone between aggregate particles and cement matrix, is governed by an exterior-point Eshelby solution. The model assumes a two-phase elastic composite, derived from an Eshelby solution and the Mori-Tanaka homogenization method, to which circular microcracks are added. A multi-component rough crack contact model is employed to simulate normal and shear behaviour of rough microcrack surfaces. It is shown, based on numerical predictions of uniaxial, biaxial and triaxial behaviour that the model captures key characteristics of concrete behaviour. An important aspect of the approach taken in this work is the adherence to a mechanistic modelling philosophy. In this regard the model is distinctly more rigorously mechanistic than its more phenomenological predecessors. Following this philosophy, a new more comprehensive crack-plane model is described which could be applied to crack-planes in the above model. In this model the crack surface is idealised as a series of conical teeth and corresponding recesses of variable height and slope. Based on this geometrical characterization, an effective contact function is derived to relate the contact stresses on the sides of the teeth to the net crack-plane stresses. Plastic embedment and frictional sliding are simulated using a local plasticity model in which the plastic surfaces are expressed in terms of the contact surface function. Numerical simulations of several direct shear tests indicate a good performance of the model. The incorporation of this crack-plane model in the overall constitutive model is the next step in the development of the latter. Computational aspects such as contact related numerical instability and accuracy of spherical integration rules employed in the constitutive model are also discussed. A smoothed contact state function is proposed to remove spurious contact chatter behaviour at a constitutive level. Finally, an initial assessment of the performance of the micromechanical model when implemented in a finite element program is presented. This evaluation clearly demonstrates the capability of the proposed model to simulate the behaviour of plain and reinforced concrete structural elements as well as demonstrating the potential of the micromechanical approach to achieve a robust and comprehensive model for concrete.

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Hazelwood, Tobias. "Investigation of a novel self-healing cementitious composite material system." Thesis, Cardiff University, 2015. http://orca.cf.ac.uk/76766/.

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This thesis describes a portion of the ongoing development of a novel self-healing cementitious material system named LatConX originally proposed by a group of researchers at Cardiff University. The research reported was undertaken with the aim of furthering understanding of the system’s long-term behaviour, ultimately with a view to providing predictions for the performance of the system over a structure’s working life. This aim is accomplished through a combination of experimental and numerical research. An experimental series is presented which investigates the stress relaxation behaviour of polyethylene terephthalate in order to establish how the stress induced by heat-activated restrained shrinkage varies with time. Results of these experiments displayed very little stress reduction from the peak stress, with less than a 5 % loss observed over a 124 day period. The development of a new one dimensional transient thermomechanical model for viscoelastic behaviour of pre-drawn polyethylene terephthalate is then described. This model is shown to be able to reproduce the observed experimental behaviour with good accuracy. The polymer model is coupled with a number of other constitutive models for the behaviour of steel and concrete, thus forming a model for the material system as a whole. This coupling is undertaken within the framework of an idealised simply supported beam with a strong discontinuity for the simulation of a central crack hinge. The model is validated against experimental data and design code predictions. Design considerations for the LatConX system are discussed and modified design equations derived. Parametric studies are presented investigating the structural performance and material costs of beams incorporating the LatConX system compared with that of standard reinforced concrete beams. Encouraging results are reported suggesting that the LatConX system has the potential to simultaneously improve long-term durability and structural performance of reinforced concrete structures and reduce the initial material costs by replacing a percentage of the reinforcing steel with shape memory polymer.

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Wang, J., S. Dong, Ashraf F. Ashour, X. Wang, and B. Han. "Dynamic mechanical properties of cementitious composites with carbon nanotubes." Elsevier, 2019. http://hdl.handle.net/10454/17465.

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Yes
This paper studied the effect of different types of multi-walled carbon nanotubes (MWCNTs) on the dynamic mechanical properties of cementitious composites. Impact compression test was conducted on various specimens to obtain the dynamic stress-strain curves and dynamic compressive strength as well as deformation of cementitious composites. The dynamic impact toughness and impact dissipation energy were, then, estimated. Furthermore, the microscopic morphology of cementitious composites was identified by using the scanning electron microscope to show the reinforcing mechanisms of MWCNTs on cementitious composites. Experimental results show that all types of MWCNTs can increase the dynamic compressive strength and ultimate strain of the composite, but the dynamic peak strain of the composite presents deviations with the MWCNT incorporation. The composite with thick-short MWCNTs has a 100.8% increase in the impact toughness, and the composite with thin-long MWCNTs presents an increased dissipation energy up to 93.8%. MWCNTs with special structure or coating treatment have higher reinforcing effect to strength of the composite against untreated MWCNTs. The modifying mechanisms of MWCNTs on cementitious composite are mainly attributed to their nucleation and bridging effects, which prevent the micro-crack generation and delay the macro-crack propagation through increasing the energy consumption.

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Alaee, Farshid Jandaghi. "Retrofitting of concrete structures using high performance fibre reinforced cementitious composite (HPFRCC)." Thesis, Cardiff University, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.431742.

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Boonsiri, Po. "Monitorina Stress and Strain of structures by using Carbon Fibre-Reinforced Cementitious Composite." Thesis, Imperial College London, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.523739.

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Du, Yang. "Durability performance of eco-friendly ductile cementitious composite (EDCC) as a repair material." Thesis, University of British Columbia, 2016. http://hdl.handle.net/2429/58938.

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The objective of the experimental program in this thesis is to investigate the durability performance of Eco-friendly ductile cementitious composite (EDCC), a newly developed repair material for seismic retrofitting. Several aspects of the durability performance of EDCC were investigated in this work, in terms of restrained shrinkage resistance, freeze and thaw resistance and bond strength degradation before and after environmental exposure. All the tests focused on repair overlay and substrate composite assembly. Six different EDCC fiber mixes were involved in the testing to discover the best mix in terms of performance and economical aspects. The substrate of the composite assembly includes concrete, masonry blocks and clay blocks. EDCC can be applied on different substrates by hand casting and spraying. EDCC application on concrete substrates employing the hand casting process is used to explore the durability performance of EDCC. Clay and masonry substrates, along with the spray application process, are only used to compare the influence of different application methods on the bond strength based on the bond strength data obtained in Yuan Yan’s thesis. After the whole experimental program, regarding hand applied process, both 2% PVA and 1% PVA and 1% PET hybrid mix yields to the best durability performance. In spray process, clay substrate specimens give better bond strength than the specimens prepared through hand applied process, however, masonry specimens show lower bond strength than hand applied specimens. Overall 1% PVA and 1% PET will be recommended for future seismic retrofitting application due to lower cost compared to 2% PVA EDCC. It is noted that the performance of EDCC depends greatly on good material mixing for different application processes. In order to obtain a good EDCC mix, a rigorous mixing procedure should be followed. Hence, future in-situ applications should guarantee a proper mixing procedure for good quality control. The spray process was found to be very successful with very little rebound and nearly no material sloughing off. The results of the experiments done in this study indicated that the spray process increases the material application speed to further reduce potential high labor cost.
Applied Science, Faculty of
Civil Engineering, Department of
Graduate

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Sultangaliyeva, Fariza. "Formulation of fluid fire-resistant fiber-reinforced cementitious composite : Application to radioactive waste disposal." Thesis, Pau, 2020. http://www.theses.fr/2020PAUU3041.

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Le but de ce travail est de développer un béton fluide résistant au feu renforcé en fibres de polypropylène pour les colis de stockage des déchets radioactifs de moyenne activité à vie longue. Le défi de ce travail consiste à utilizer des fibres de polypropylène qui, même ajoutées en petite quantité, améliorent la résistance au feu mais diminuent de manière significative la maniabilité des bétons frais. Des essais à l’échelle du laboratoire sont effectués afin d’évaluer les comportements rhéologique et à haute température des matériaux cimentaires contenant des fibres de polypropylène. Dans la première partie, une étude du comportement rhéologique des matériaux cimentaires avec des fibres de polypropylène a été réalisée. Le but de cette étude est d’étudier l’influence de ces fibres sur le seuil d’écoulement des pâtes de ciment et des mortiers. Un modèle qui permet d’évaluer la quantité de pâte supplémentaire nécessaire pour compenser l’effet des fibres de polypropylène en fonction de la fluidité du béton frais a été développé.Ensuite, une étude expérimentale et numérique sur le comportement des matériaux cimentaires avec des fibres de polypropylène à haute température a été réalisée afin d’optimiser le choix des fibres pour améliorer la stabilité thermique d’un matériau cimentaire. Des essais de perméabilité résiduelle radiale et des essais feu sur les trois matériaux avec squelettes granulaires différents contenant des fibres de polypropylène de différentes géométries et dosages ont été réalisés dans un but de sélectionner une géométrie et un dosage optimal des fibres. Puis, des simulations thermomécaniques ont été développées à l’échelle macroscopique et mésoscopique. Le choix du diamètre, de la longueur et du dosage des fibres a été fait en fonction de la taille maximale des granulats.Finalement, une méthode de formulation du béton autoplaçant avec des fibres de polypropylène optimisé à la fois du point de vue de la rhéologie et de la résistance au feu a été présentée. Avec cette méthode, la conformité aux critères imposés sur les propriétés à l’état frais et à l’état durci du béton est vérifiée. Des éprouvettes de bétons sont testées sous chargement mécanique uniaxial et, en fonction des résultats, les formulations finales sont sélectionnées pour les futurs essais feu à l’échelle plus importante
The aim of the thesis is to design a self-compacting concrete with polypropylene fibers resistant to fire for a use in storage containers of medium activity long-lived waste. The challenge of the work is presented by the use of polypropylene fibers that enhance fire resistance but drastically diminish workability of concrete even when added at small volume fractions. Tests on laboratory scale are conducted with a purpose of evaluating rheological behavior and high temperature behavior of cementitious materials containing polypropylene fibers.In the first part, a study of rheological behavior of cement-based materials containing polypropylene fibers was done. The aim of this study is to investigate the influence of polypropylene fibers on the yield stress of cement pastes and mortars. A model is proposed to be able to evaluate the quantity of paste necessary to compensate the addition of polypropylene fibres according the fluidity of fresh concrete.Then an experimental and numerical investigation of behavior of cementitious materials with polypropylene fibers at high temperature was done so as to optimize the choice of polypropylene fibers for cementitious material to improve its thermal stability. Three different cementitious materials with three different granular skeleton containing various polypropylene fiber geometries and dosages were tested (residual radial permeability test and fire test) in order to select an optimal fiber geometry and dosage. Then thermomechanical computations was developped at maco and meso scale. Then, a choice of diameter, length and dosage of fibres is proposed according to the maximum size of gravels.Finally, a method of concrete formulation with polypropylene fibers optimized from perspectives of rheology and resistance to fire is presented. In this method, fresh and hardened state properties are verified to ensure an accordance with performance criteria specified by the project. At the end, designed mixes were tested in fire tests conducted on uniaxially compressed prisms and, based on outcomes, final mixes are selected for further fire tests on higher scale concrete

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Ducoulombier, Nicolas. "Anisotropic concrete : 3D priting of concrete reinforced by long fibers, process, characterisation et modelisation." Thesis, Paris Est, 2020. http://www.theses.fr/2020PESC2070.

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Ce travail s’intéresse au renforcement des matériaux cimentaire mis en œuvre par fabrication additive à grande échelle. Ce nouveau procédé permet une complexité géométrique importante, généralement fortement consommatrice de moyens matériels et humains. De plus, il rend théoriquement possible l’industrialisation de la fabrication d’éléments constructifs singuliers, par exemple optimisés par répondre à un chargement mécanique donné. Cependant, il n’existe à l’heure actuelle aucune méthode de renforcement standardisée permettant d’obtenir la résistance en traction et la ductilité nécessaire pour leur utilisation dans les structures des bâtiments. Ce qui limite fortement leur utilisation dans la pratique.Si de nombreuses méthodes sont envisagées dans la littérature pour le renforcement des matériaux cimentaires mis en œuvre par impression 3D, celles-ci sont généralement calquées sur les méthodes traditionnelles du renforcement : bétons fibrés, armatures passives et câble de précontraintes. Ce travail de thèse propose un procédé de renforcement alternatif, breveté au cours de ce travail de thèse, qui tire parti de la spécificité du procédé d’extrusion. De nombreux renforts continus sont en effet insérés dans la filière d’extrusion, appelé ici tête d’impression et entrainé par le débit du matériau cimentaire, ce dernier fournissant la force nécessaire aux déroulements des renforts continus. Le matériau extrudé est alors un composite unidirectionnel à matrice cimentaire renforcé par de nombreuses fibres continues alignées selon la direction du parcours d’impression.Ce travail définit alors le cahier des charges du procédé en termes de propriétés rhéologiques de la matrice cimentaire au moment du dépôt et le type de renfort à privilégier permettant l’obtention d’une bonne adhérence des renforts à la matrice cimentaire, nécessaire au développement d’un renforcement significatif en traction. Le comportement mécanique de l’interface est par ailleurs étudié précisément grâce aux développements d’essais micromécaniques dédiées et l'observation de l’endommagement par microtomographie aux rayons X. Les perspective de ce travail sont la caractérisation et la modélisation multi-échelles du comportement du composite à matrice cimentaire et la proposition de systèmes constructifs innovants
This work focuses on the reinforcement strategies for large scale additive manufacturing of cementitious materials. This new process allows an important geometrical complexity for constructive elements, generally consuming a lot of material and human resources. In addition, it makes it theoretically possible to industrialize the manufacture of singular constructive elements, for example optimized to meet a given mechanical load. However, there is currently no standardized reinforcement method for obtaining the tensile strength and ductility required for their use in building structures. This severely limits their use in practice.While many reinforcement methods are considered in the literature for the 3D-printed cementitious materials, they are a direct transcription of the traditional reinforcement methods such as fibre-reinforced concrete, passive reinforcement and post-tension method. This thesis work proposes an alternative reinforcement process, patented during this thesis work, which takes advantage of the specificity of the extrusion process. Many continuous reinforcements can be inserted before the extrusion die and driven by the flow of the cementitious material, the latter providing the force necessary for the unwinding of each individual continuous reinforcements. The extruded material is then a unidirectional cementitious matrix composite reinforced by many continuous fibers aligned in the direction of the printing path.This work then defines the specifications of the process in terms of rheological properties of the cementitious matrix at the time of deposition and the type of reinforcement to be preferred, allowing good cohesion between the reinforcements and the cementitious matrix necessary for the development of a significant tensile reinforcement. The mechanical behaviour of the interface is also precisely studied thanks to the development of dedicated micromechanical tests and the observation of the damage by X-ray microtomography. The perspectives of this work are the characterization and multi-scale modeling of the behavior of the cementitious matrix composite and the proposal of innovative constructive systems

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Morsy, Mohamed Ibrahim Nasr Verfasser], Harald [Akademischer Betreuer] [Garrecht, and Farouk [Akademischer Betreuer] Heider. "Properties of Rice Straw Cementitious Composite / Mohamed Ibrahim Nasr Morsy. Betreuer: Harald Garrecht ; Farouk Heider." Darmstadt : Universitäts- und Landesbibliothek Darmstadt, 2011. http://d-nb.info/1106113357/34.

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Morsy, Mohamed Ibrahim Nasr [Verfasser], Harald [Akademischer Betreuer] Garrecht, and Farouk [Akademischer Betreuer] Heider. "Properties of Rice Straw Cementitious Composite / Mohamed Ibrahim Nasr Morsy. Betreuer: Harald Garrecht ; Farouk Heider." Darmstadt : Universitäts- und Landesbibliothek Darmstadt, 2011. http://nbn-resolving.de/urn:nbn:de:tuda-tuprints-28473.

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Pham, Ngoc Phuong. "Rubberized cement-based composite as material for large surface applications : effect of the rubber-cementitious matrix bond." Thesis, Toulouse 3, 2018. http://www.theses.fr/2018TOU30077.

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La capacité de déformation améliorée et la résistance à la fissuration par retrait rendent les composites cimentaire caoutchoutés adaptés aux applications de grande surface telles que les chaussées et les rechargements minces adhérents à base cimentaire. Cependant, le défaut d'adhérence entre les agrégats de caoutchouc et la matrice cimentaire, bien connu, demeure nuisible aux propriétés mécaniques et de transferts de ces matériaux. De plus, en raison de la faible rigidité des granulats caoutchouc, il est universellement accepté une réduction de certaines propriétés mécaniques des composites caoutchoutés à base de ciment. Néanmoins, leurs propriétés de transfert pourraient être compétitives avec le mortier à base de granulats naturels si la liaison à l'interface caoutchouc-ciment est améliorée. Afin d'améliorer l'interface, les granulats caoutchouc ont d'abord été revêtus d'un copolymère styrène-butadiène et après densification complète de ce copolymère à la surface des agrégats caoutchouc, ils ont été incorporés au mélange cimentaire. Dans un premier temps, une analyse microstructurale utilisant la microscopie électronique à balayage (MEB), la spectrométrie de rayons X à dispersion d'énergie (EDS) et la diffraction des rayons X (DRX) a permis de préciser que la pâte de ciment adhérait fermement aux granulats caoutchouc revêtus de copolymère. Dans un second temps, les propriétés mécaniques et de transfert de ce mortier ont ensuite été comparées à celles du mortier témoin (granulats naturels) et de deux autres mortiers caoutchoutés dans lesquels l'un d'entre eux a été ajouté un désentraineur d'air pour produire un mélange caoutchouté ayant la même teneur en air que le mortier témoin. Les résultats ont démontré une interface améliorée du caoutchouc-ciment fournissant une amélioration significative des propriétés de transfert telles que la perméabilité à l'air et l'absorption capillaire d'eau. Cependant, la diminution des propriétés mécaniques (résistance à la compression et module d'élasticité) demeure en raison de la faible rigidité des granulats caoutchouc. Quant à la résistance à la traction et la résistance résiduelle post-pic témoignent d'une énergie de rupture plus élevées dans le cas de granulats revêtus du copolymère, démontrant un effet de pontage amélioré rendu possible par la liaison entre les granulats caoutchouc et la matrice de ciment. Cet effet de pontage a également contribué à améliorer la résistance des composites caoutchoutés à la fissuration par retrait empêché Afin d'étayer les effets d'une interface caoutchouc-ciment améliorée, la durabilité des mortiers caoutchoutés dans des environnements agressifs a été étudiée. En ce qui concerne l'attaque à l'acide acétique, une faible profondeur dégradée et une réduction de la perte de masse et de résistance à la compression des mortiers caoutchoutés revêtus de copolymère ont été observés par rapport au mortier témoin. Le mortier caoutchouté enduit de copolymère se comporte également mieux en empêchant la diffusion du sulfate de sodium dans le composite. La dégradation des mortiers dans des environnements agressifs a également été évaluée sur la base d'une variable d'endommagement. Il en ressort que les matériaux caoutchoutés revêtus de copolymère étaient plus durables que les matériaux non traités exposés à des environnements agressifs
Properties of improved strain capacity and high shrinkage cracking resistance make rubberized cement-based composites suitable for large surface applications such as cement-based pavements and thin bonded overlays. However, bond defect between rubber aggregates (RA) and cement matrix is well-known and detrimental to properties of rubberized cement-based materials. It is universally accepted a reduction in some mechanical properties of rubberized cement-based composites mainly due to low stiffness of RA. Nevertheless, their transfer properties could indeed be competitive with control mortar (without RA) if bond at rubber-cement matrix interface is improved. In order to enhance the interface, RA were firstly coated with styrene-butadiene copolymer and after complete densification of this copolymer on surface of RA, they were mixed with the pre-mixed cementitious mixture. Microstructural analysis using Scanning Electron Microscopy (SEM), Energy Dispersive X-ray Spectrometry (EDS), and X-Ray Diffraction (XRD) clarified that cement paste bonded firmly on copolymer-coated RA. Mechanical and transfer properties of this mortar were then compared to that of control mortar and two rubberized mortars in which one of them air-detraining admixture was added to produce rubberized mixture with the similar air content as the control mortar. Findings have demonstrated an enhanced rubber-cement matrix interface provided a significant improvement on transfer properties such as air permeability and water capillary absorption. However, a reduction in mechanical properties (compressive strength and modulus of elasticity) was still observed due to low stiffness of RA. Rubber coating appeared to limit the reduction in tensile strength and to result in a higher residual post-peak strength and fracture energy, demonstrating an improved material bridging effect made possible by the bond between RA and cement matrix. The bridging effect also contributed to improve resistance of rubberized composites to shrinkage cracking even under high restrained conditions. Based on above-mentioned characteristics, the study further investigated the durability of rubberized mortars under aggressive environments to observe the effects of RA incorporation and of an enhanced rubber-cement matrix interface. Regarding acetic acid attack, a low degraded depth and a reduction in loss of both mass and compressive strength of rubberized mortars, especially the one incorporating copolymer-coated RA, were observed compared to the ones of the control mortar. The coated rubberized mortar also behaves better in preventing sodium sulfate diffusion into the composite. The degradation of mortars under aggressive environments was also evaluated based on a damage variable, which was defined as a relative change in equivalent load-resisting area of mortar specimens between their original condition and at a given time when they were exposed to acid or sulfate solutions. From damage variable values, it can be concluded that coated rubberized mortar was more durable than the untreated one against aggressive environments. The durability of untreated and coated rubberized mortars under freeze-thaw cycles was also carried out and compared to that of control mortar. The rubberized cement- based composites were more resistant to freezing and thawing than the control one, especially in terms of dimensional expansion. The better performance can be attributed to high energy absorption of RA and to higher porosity, lower water capillary absorption and high strain capacity of rubberized mortars. Rubber coating, even reducing the permeability of rubberized cement-based composites, still remained high durability of their applications under frost environment

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Monteiro, André Oliveirinha. "Development of a multifunctional carbon black/cement composite for traffic monitoring." Doctoral thesis, Universidade de Aveiro, 2018. http://hdl.handle.net/10773/23030.

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Doutoramento em Engenharia Civil
As sociedades modernas estão fundadas em sistemas infraestruturais como redes de abastecimento de água, electricidade, comunicação e transporte. Com o aumento da procura global pela eficiência, imposto pelo século XXI, o desempenho esperado das estruturas segue inevitavelmente a mesma tendência. Esta busca de performance tem levado às infraestruturas físicas e à tecnologia digital se fundirem no conceito de “infraestruturas inteligentes”, através de vastas redes de monitorização, aliadas a subsistemas de informação. A disciplina de gestão de tráfego é talvez aquela que mais tem beneficiado destes avanços, com a implementação dos chamados Sistemas Inteligentes de Transporte (ITS). Avanços recentes na área dos materiais têm permitido o desenvolvimento de materiais de construção “inteligentes”, capazes de desempenhar tarefas autónomas. Os compósitos cimentícios piezoresistivos são um exemplo. Estes podem ser utilizados como sistemas de monitorização, graças às suas propriedades intrínsecas de sensitividade a estímulos mecânicos. A presente dissertação visa fazer a ponte entre o conceito de materiais cimentícios multifuncionais e a disciplina de monitorização de tráfego. Deste modo, um compósito piezoresistivo foi desenvolvido para aplicação em pavimentos, com base na adição de partículas de negro de fumo (CB), com o objectivo de avaliar dados de tráfego em tempo real. Numa primeira abordagem experimental foi determinada uma composição cimentícia sensitiva, concluindo que a incorporação de 7% de CB (em relação à massa de cimento) oferecia a melhor resposta resistiva a estímulos de compressão. Numa segunda campanha experimental, composição, ergonomia dos sensores cimentícios, tipologia de ensaios e sistema de aquisição foram otimizados e adequados, de acordo com a finalidade de monitorização de tráfego. Ciclos de compressão estáticos e dinâmicos demonstraram fatores de sensitividade médios (GF) de 60 e uma excelente resposta linear, não afetada por variações de temperatura, ao contrário da sensitividade piezoresistiva que registou diminuições até 30%. Em resumo, os resultados desta dissertação demonstram que a incorporação de elementos de betão sensitivo com adição de CB à superfície de pavimentos pode vir a constituir uma alternativa às soluções tradicionais de monitorização de tráfego, dado as suas vantagens como: baixo custo, simplicidade de implementação, propriedades estruturais, durabilidade e sensitividade
Today’s society is founded on infrastructure systems such as water, electricity, communication and transport networks. The global efficiency demand of the 21st century is growing rapidly and the expected performance of infrastructures follows the same trend. This pursuit for efficiency has led digital technology and physical urban infrastructures to fuse into the concept of ‘smart infrastructures’, relying on large monitoring networks coupled to information subsystems. Traffic logistics has been one of the fields which has benefited the most of such advances, with the implementation of the so-called Intelligent Transportation Systems (ITS). Over the last years, advances in materials science have enabled the development of a wide range of “smart” construction materials capable of autonomous tasks. An example of these are the piezoresistive cementitious composites, some of which may be used as monitoring systems, thanks to their self-sensing properties. The present dissertation aims to bridge the concept of multifunctional cement-based materials to the traffic monitoring discipline. Here, a stress-sensitive cementitious composite, based on the addition of carbon black (CB) particles, was developed for application in pavement surfaces with a view to perform permanent real-time evaluation of traffic data. In a first experimental approach, a sensitive CB-based cementitious composition was determined and results concluded that mixtures containing 7% of CB by mass of cement offered the most favourable piezoresistive response. In a second experimental campaign, materials, specimens design and measurement setup were reviewed, towards traffic monitoring requirements. Quasi-static and dynamic compressive load cycles showed gauge factors (GF) as high as 60 and a response linearity inaffected by temperature variations, despite registered reductions in sensitivity up to 30%. Taken together, results demonstrated that embedding conductive CB-based concrete elements in pavement surfaces may become a prospective alternative to conventional traffic monitoring solutions given their numerous advantages, including: low-cost, simplicity of implementation, structural properties, durability and good sensitivity.

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Dolores, Gonzalo Mármol de los. "Low-alkalinity matrix composites based on magnesium oxide cement reinforced with cellulose fibres." Universidade de São Paulo, 2017. http://www.teses.usp.br/teses/disponiveis/74/74133/tde-17082017-113846/.

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A lower-alkalinity cement based on MgO and SiO2 blends is analysed to develop clinker-free Fibre Reinforced Cementitious Composites (FRCC) with cellulosic fibres in order to solve the durability problems of this type of fibres when used in FRCC with Portland cement. Hydration evolution from 7 to 28 days of different MgO-SiO2 formulations is assessed. The main hydration products are Mg(OH)2 and M-S-H gels for all the formulations studied regardless of age. Hardened pastes are obtained with pH values < 11 and good mechanical properties compared to conventional Portland cement. 60% MgO-40% SiO2 system is chosen as optimal for the development FRCC since is the most mechanical resistant and is less alkaline compared with 70% MgO-30% SiO2. FRCC based on magnesium oxide and silica (MgO-SiO2) cement with cellulose fibres are produced to study the durability of lignocellulosic fibres in a lower pH environment than the ordinary Portland cement (PC). Flexural performance and physical tests (apparent porosity, bulk density and water absorption) of samples at 28 days and after 200 accelerated ageing cycles (aac) are compared. Two types of vegetable fibres are utilised: eucalyptus and pine pulps. MgO-SiO2 cement preserves cellulosic fibres integrity after ageing, so composites made out of MgO-SiO2 exhibit significant higher performance after 200 cycles of accelerated ageing than Portland cement composites. High CO2 concentration environment is evaluated as a curing treatment in order to optimise MgO- SiO2 matrices in FRCC. Samples are cured under two different conditions: 1) steam water curing at 55°C and 2) a complementary high CO2 concentration (20% by volume). In carbonated samples, Mg(OH)2 content is clearly lowered while new crystals of hydromagnesite [Mg5 (CO3)4⋅(OH) 2⋅4H2O] are produced. After carbonation, M-S-H gel content is also reduced, suggesting that this phase is also carbonated. Carbonation affects positively to the composite mechanical strength and physical properties with no deleterious effects after ageing since it increases matrix rigidity. The addition of sepiolite in FRCC is studied as a possible additive constituent of the binding matrix. Small cement replacement (1 and 2% wt.) by sepiolite is introduced and studied in hardened cement pastes and, later, in FRCC systems. When used only in cement pastes, it improves Dynamic Modulus of Elasticity over time. Bending tests prove the outcome of this additive on the mechanical performance of the composite: it improves composite homogeneity. Ageing effects are reported after embedding sisal fibres in MgO-SiO2 and PC systems and submitting them to different ageing conditions. This comparative study of fibre degradation applied in different cementitious matrices reveals the real compatibility of lignocellulosic fibres and Mg-based cements. Sisal fibres, even after accelerated ageing, do neither suffer a significant reduction in cellulose content nor in cellulose crystallinity and crystallite size, when exposed to MgO-SiO2 cement. Fibre integrity is preserved and no deposition of cement phases is produced in MgO-SiO2 environment.
Um cimento de baixa alcalinidade à base de blendas de MgO e SiO2 é analisado para o desenvolvimento de Compósitos Cimentícios Reforçados com Fibras (CCRF) celulósicas sem clínquer para resolver os problemas de durabilidade de este tipo de fibras quando são usadas em CCRF com cimento Portland. A evolução da hidratação, desde 7 aos 28 dias, das diferentes formulações é avaliada. Os principais produtos hidratados são o Mg(OH)2 e o gel M-S-H para todas as formulações independentemente da idade estudada. As pastas endurecidas apresentam valores de pH < 11 e bom desempenho mecânico comparado com o cimento Portland convencional. O sistema 60% MgO-40% SiO2 é escolhido como a formulação ótima para o desenvolvimento de CCRF já que é a mais resistente e menos alcalina comparada com 70% MgO-30% SiO2. CCRF com cimento à base de óxido de magnésio e sílica (MgO-SiO2) e fibras celulósicas são produzidos para a análise da durabilidade das fibras lignocelulósicas em ambientes com valores de pH mais baixos comparados com o cimento Portland (PC). O desempenho mecânico a flexão e os ensaios físicos (porosidade aparente, densidade aparente e absorção de água) são comparados aos 28 dias e após de 200 ciclos de envelhecimento acelerado. O cimento à base de MgO-SiO2 preserva a integridade das fibras após o envelhecimento. Os compósitos produzidos com este cimento exibem melhores propriedades após 200 ciclos de envelhecimento acelerado que os compósitos produzidos com cimento Portland. Ambientes com alta concentração de CO2 são avaliados como tratamento de cura para otimizar as matrizes MgO- SiO2 nos CCRF. As amostras são curadas sob 2 condições diferençadas: 1) cura com vapor de água a 55oC e 2) cura com alta concentração de CO2 (20% do volume). As amostras carbonatadas apresentam teores reduzidos de Mg(OH)2 enquanto é produzida uma nova fase cristalina: hidromagnesita [Mg5 (CO3)4⋅(OH) 2⋅4H2O]. Após a carbonatação, o conteúdo de gel M-S-H é reduzido também, indicando uma carbonatação desta fase. A carbonatação aumenta a rigidez da matriz o que influi positivamente no desempenho mecânico e as propriedades físicas dos compósitos sem efeitos prejudiciais ao longo prazo. A adição de sepiolita em CCRF é estudada como possível adição na composição da matriz aglomerante. Baixos teores (1 e 2% em massa) de cimento são substituídos por sepiolita para o estudo das pastas de cimento hidratado e, posteriormente, dos compósitos. O Módulo Elástico Dinâmico das pastas é incrementado com o tempo pela adição de sepiolita. Os ensaios a flexão demostram que a adição de sepiolita melhora a homogeneidade dos compósitos. Reportam-se os efeitos das fibras de sisal após da exposição a sistemas MgO-SiO2 e PC e submetidas a diferentes condições de envelhecimento. Este estudo comparativo da degradação das fibras expostas a diferentes matrizes cimentícias mostra a compatibilidade das fibras lignocelulósicas com os cimentos à base de Mg. As fibras de sisal, inclusive após o envelhecimento acelerado, não apresentam nem redução significativa no conteúdo de celulose nem na cristalinidade da celulose assim como do tamanho de cristalito, quando expostas a cimentos MgO-SiO2.

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15

Song, Gao. "Matrix manipulation to study ECC behaviour." Thesis, Stellenbosch : University of Stellenbosch, 2005. http://hdl.handle.net/10019.1/4647.

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Thesis (MScEng (Civil Engineering))--University of Stellenbosch, 2005.
192 leaves on CD format, preliminary i-xii pages and numbered pages 1-135. Includes bibliography, list of figures and tables.
ENGLISH ABSTRACT: As a fibre reinforced material, engineered cementitious composite (ECC) has tough, strain-hardening behaviour in tension despite containing low volumes of fibres. This property can be brought about by developments in fibre, matrix and interfacial properties. Poly Vinyl Alcohol (PVA) fibre has been developed in recent years for ECC, due to its high tensile strength and elasticity modulus. However, the strong interfacial bond between fibre surface and matrix is a challenge for its application. This study focuses on the tailoring of matrix and fibre/matrix interfacial properties by cement replacement with fly ash (FA) and Ground Granulated Corex Slagment (GGCS). In this study the direct tensile test, three point bending test, micro-scale analysis, such as X-Ray Fluorescence Spectrometry analysis (XRF), Scanning Electron Microscope (SEM), are employed to investigate the influence of cement replacement, aging, Water/Binder (W/B) ratio, workability on ECC behaviour. This study has successfully achieved the aim that cement replacement by FA and GGCS helps to improve the fibre/matrix interfacial properties and therefore enhances the ECC tensile behaviour. Specifically, a high volume FA-ECC has stable high tensile strain capacity at the age of 21 days. This enables a constant matrix design for the investigation of other matrix influences. The Slag-ECC has a higher tensile strength but lower tensile strain capacity. The combination of FA and GGCS, moderate tensile strength and strain capacity is achieved Both tensile tests and Micro-scale analyses infer that the high volume FA-ECC has an adhesive type fibre/matrix interfacial interaction, as opposed to the cohesive type of normal PVA fibre-ECC. The different tensile behaviour trend of steel fibre-ECC and PVA fibre-ECC with the FA content is presented and discussed in this research. The investigations of aging influence indicate that the high volume FA-ECC has a beneficial effect on the properties of the composite at an early stage. However, at a high age, it has some difficulty to undergo multiple cracking and then leads to the reduction of tensile strain capacity. The modified mix design is made with the combination of FA and GGCS, which successfully increases the interfacial bond and, thereby, improves the shear transfer to reach the matrix crack strength. Therefore, an improved high age tensile behaviour is achieved. The W/B and fresh state workability influence investigations show that the W/B can hardly affect the tensile strain at early age. However, the workability influences on composite tensile strain significantly, because of the influence on fibre dispersion. Other investigations with regard to the hybrid fibre influences, the comparison of bending behaviours between extruded plate and cast plate, the relation between bending MOR and tensile stress, and the relation between compression strength and tensile strength contribute to understand ECC behaviour.
AFRIKAANSE OPSOMMING: As ‘n veselversterkte materiaal, het ontwerpte sementbasis saamgestelde materiale, taai vervormingsverhardingseienskappe in trek, ten spyte van lae veselinhoud. Hierdie eienskap word bewerkstellig, deur ontwikkelings in vesel, matriks en tussenveselbindingseienskappe. Poli-Viniel Alkohol (PVA) vesels is ontwikkel vir ECC, as gevolg van die hoë trekkrag en hoë modulus van hierdie veseltipe. Die sterk binding tussen die PVA-veseloppervlak en die matriks is egter ‘n uitdaging vir sy toepassing. Hierdie studie fokus op die skep van gunstige matriks en vesel/matriks tussenvesel-bindingseienskappe deur sement te vervang met vlieg-as (FA) en slagment (GGCS).In hierdie navorsing is direkte trek-toetse, drie-punt-buigtoetse, mikro-skaal analise (soos die X-straal ‘Fluorescence Spectrometry’ analise (XRF) en Skanderende Elektron Mikroskoop (SEM))toegepas. Hierdie metodes is gebruik om die invloed van sementvervanging,veroudering, water/binder (W/B)-verhouding en werkbaarheid op die meganiese gedrag van ECC te ondersoek.Die resultate van hierdie navorsing toon dat sementvervanging deur FA en GGCS help om die vesel/matriks tussenveselbindingseienskappe te verbeter. Dus is die ECC-trekgedrag ook verbeter. Veral ‘n hoë volume FA-ECC het stabiele hoë trekvervormingskapasiteit op ‘n ouderdom van 21 dae. Dit bewerkstellig ‘n konstante matriksontwerp vir die navorsing van ander matriks invloede. Die Slag-ECC het ‘n hoër treksterkte, maar laer trekvervormingskapasiteit. Deur die kombinasie van FA en GGCS word hoë treksterkte, sowel as gematigde vervormbaarheid in trek verkry. Beide trektoetse en mikro-skaal analise dui aan dat die hoë volume FA-ECC ‘n adhesie-tipe vesel/matriks tussenvesel-bindingsinteraksie het, teenoor die ‘kohesie-tipe van normale PVA vesel-ECC. Die verskille in trekgedrag van staalvesel-ECC en PVA vesel-ECC ten opsigte van die FA-inhoud is ondersoek en word bespreek in die navorsing. Die navorsing toon verder dat die hoë volume FA-ECC goeie meganiese eienskappe het op ‘n vroeë ouderdom. Op hoër ouderdom word minder krake gevorm, wat ‘n verlaging in die trekvervormingskapasiteit tot gevolg het. Met die kombinasie van FA en GGCS, word die vesel-matriksverband verhoog, waardeur ‘n verbetering in die skuifoordrag tussen vesel en matriks plaasvind. Verbeterde hoë omeganiese gedrag word daardeur tot stand gebring. Navorsing ten opsigte van die invoed van die W/B en werkbaarheid dui daarop dat die W/B slegs geringe invloed het op die trekvormbaarheid, terwyl die werkbaarheid ‘n dominerende rol speel in hierdie verband.Verdere studies sluit in die invloed van verskillende vesels, die vergelyking van die buigingsgedrag van geëkstueerde plate en gegote plate, die verhouding tussen buigsterkte en treksterkte, en die verhouding tussen druksterkte en treksterkte dra by tot beter begrip van die gedrag van ECC.

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16

Cozza, Alessandro. "Bond properties of SRG anchors employed to improve the effectiveness of SRG/FRCM composites." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2019.

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Fiber reinforced cementitious matrix (FRCM) composites represent a newly-developed promising alternative to traditional materials for strengthening and retrofitting reinforced concrete and masonry structures. FRCM composites present several advantages with respect to fiber reinforced polymers (FRP) composites. However, while FRP composites have been extensively studied in the last decades and several design guidelines and analytical formulations are available, FRCM composites are still in their infancy and very few data are present in the literature. Thus, another issue that should be solved regards the stated need for the anchorage systems to improve FRP and FRCM strength in situations where debonding or lack of development length is a problem. In this study, the effectiveness of the anchorage system and the interaction with an externally bonded FRCM were studied on both concrete beams and masonry columns. The columns and beams were tested until failure condition in the Laboratory of Structural and Geotechnical Engineering (DICAM – LISG) of the University of Bologna, via del Lazzaretto 15/5, Bologna. Test parameters considered for this study are: density of steel fibers, type of anchorages and bending inclination of the fiber exerted as anchorage, respectively 45° for concrete beam and 90° for masonry column. Test results demonstrate that the introduction of additional anchorages improves the effectiveness of the FRCM composites in terms of resistance and loading capacity.

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PICANCO, MARCELO DE SOUZA. "CEMENTITIOUS COMPOSITES REINFORCED WITH CURAUÁ FIBERS." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2005. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=8936@1.

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COORDENAÇÃO DE APERFEIÇOAMENTO DO PESSOAL DE ENSINO SUPERIOR
A busca por materiais alternativos que possam substituir as fibras de amianto, compondo o fibro-cimento, tem-se tornado objeto de estudos recorrentes. As fibras vegetais surgem como opção econômica, salubre e ecologicamente adequada. O objetivo deste trabalho foi estudar o comportamento da adição da fibra de curauá em compósitos cimentícios, visando substituir o amianto. Essa fibra mineral é bastante conhecida pelos danos que provoca à saúde humana, já tendo sido banida em muitos países industrializados. Desde 1979, o Grupo de Pesquisas em Materiais não Convencionais da PUC-Rio tem desenvolvido trabalhos sobre a aplicação das fibras vegetais, disponíveis em abundância no Brasil, na fabricação de componentes para a construção civil, visando, principalmente, a produção de habitação popular. A fibra de curauá é de uso popular, na região conhecida como Baixo- Amazonas, oeste do Estado do Pará, na manufatura de cordas, cestas e tapetes, já existindo os primeiros plantios em escala comercial. Pouco conhecida nas demais regiões do país, a fibra de curauá ainda carece de estudos específicos sobre suas propriedades físicas, químicas e mecânicas, que possibilitem sua aplicação segura em compósitos para a construção civil. Nesse trabalho, foram estudadas as propriedades físicas, mecânicas e microestruturas das fibras de curauá, bem como de compósitos cimentícios que as tiveram como reforço. Buscou-se comparar o desempenho das fibras de curauá e de seus compósitos, com as fibras e compósitos de amianto e de outras fibras vegetais, tais como sisal, coco e juta. Os dados das fibras de sisal e coco, tomados para efeito de comparação, foram oriundos de trabalhos anteriores do mesmo grupo de pesquisas da PUC-Rio. Para as fibras de juta e compósitos cimentícios com reforço de juta e de sisal, foram obtidos dados através de ensaios realizados no escopo desse trabalho. Os resultados mostraram que a fibra de curauá possui características físicas e mecânicas que as habilitam à aplicação como reforço de matrizes cimentícias, principalmente quando for almejada uma maior ductilidade e capacidade de resistência após a fissuração da matriz.
In recent years, there has been an intense search worldwide for an alternative material, which can substitute the asbestos fibre, a component of the asbestos cement, which has been found to be hazardous to human and animal health and has been banned already in many countries. Since 1979 the Non- conventional Materials Research Group of PUC-Rio has carried out works on the application of vegetable fibres, available in abundance in Brazil, for the fabrication of construction components, aiming mainly at the fabrication of popular housing. The curaúa fibre has been studied as it is already of popular use in the manufacturing of ropes, baskets and carpets in the region, known as Baixo Amazonas, in the state of Para, where the first plantations have been organized on a commercial scale. In this work, the physical, mechanical and micro-structural properties of the curauá fibres, as well as their application as a cimenticious matrix reinforcement, have been studied. The performance of curauá fibres and its composites was compared with other vegetable fibres, such as sisal, coconut and jute, as a substitute for asbestos fibres and its composites. The data on sisal and coconut fibres from previous works by the same research group at PUC-Rio was considered for comparison. The behaviour of jute fibres, as well as cimenticious composites, reinforced with jute and sisal fibres, have also been studied in this work. The results have shown that the curauá fibre has good physical and mechanical characteristics that make it suitable to be used as reinforcement of cimenticious matrices, with a high ductility and post-cracking resistance capacity.

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18

Wang, Youjiang. "Mechanics of fiber reinforced cementitious composites." Thesis, Massachusetts Institute of Technology, 1989. http://hdl.handle.net/1721.1/14296.

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19

Nguyen, Thanh Hai. "Contribution à l'étude du comportement thermomécanique à très haute température des matériaux composites pour la réparation et/ou le renforcement des structures de Génie Civil." Thesis, Lyon 1, 2015. http://www.theses.fr/2015LYO10244/document.

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Dans le domaine du renforcement et/ou de la réparation des structures en béton armé par des matériaux composites à l'aide de la méthode du collage extérieur au moyen d'un adhésif époxy, une des préoccupations de la communauté scientifique est l'intégrité structurelle de ce système dans le cas d'incendie dans lequel la haute température est une caractéristique essentielle et peut atteindre jusqu'à 1200°C. Ce travail de recherche est axé sur le comportement thermomécanique à très haute température des matériaux composites [un composite à base de polymère carbone/ époxy (Carbon Fiber Reinforced Polymer- CFRP), un composite textile/ mortier cimentaire (Textile Reinforced Concrete- TRC) et un adhésif à base d'époxy]. L'évolution des propriétés mécaniques et d'autres aspects mécaniques de ces matériaux composites avec la température a été caractérisée. Une nouvelle procédure expérimentale concernant la mesure de la déformation de l'éprouvette à l'aide du capteur laser est développée et validée. Une étude numérique et expérimentale a été réalisée dans le but de déterminer principalement la température à la rupture des joints « composite/ adhésif/ composite » sous les sollicitations mécaniques et thermiques. L'efficacité de la protection thermique de deux isolants [PROMASPRAY®T (produit commercial de la société PROMAT] et Isolant A (produit développé par le LGCIE site Tusset) a aussi été étudiée dans cette thèse. Enfin, une approche numérique, à l'aide du logiciel ANSYS, est utilisée afin de déterminer, de façon préliminaire et approximative, à l'échelle matériau, les propriétés thermiques des matériaux (composite textile/ mortier cimentaire -TRC et Isolant A)
In the area of the strengthening and/or the reparation of reinforced concrete structures with composites by means of the external bonding method using an epoxy adhesive, one of the preoccupation of the scientific community is the structural integrity of this system in the event of fire in which the high temperature is the essential feature et can reach up to 1200°C. This research focuses on the thermo-mechanical behavior of composite materials [carbon/epoxy adhesive composite (or carbon fiber reinforced polymer (CFRP), textile/cementitious mortar composite (or textile reinforced concrete (TRC)] and an epoxy-based adhesive. The evolution of mechanical properties and other mechanical aspects of these materials with the temperature has been characterized. A new experimental procedure concerning the measurement of sample strain by the laser sensor is developed and validated. An experimental and numerical study has been realized in order to mainly determine the temperature at the failure of "composite/adhesive/composite" joints under thermal and mechanical loadings. The effectiveness of the thermal protection of two insulators [PROMASPRAY®T (a commercial product of the PROMAT company and the insulator A (product developed by the LGCIE site Tuset)] has also been investigated in this PhD thesis. Finally, a numerical approach, using ANSYS software, is used to determine, in the preliminary and approximate way, at material scale, thermal properties of the materials [the textile reinforced concrete (TRC) and the insulator A]

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Zhang, Jie. "Microstructure study of cementitious materials using resistivity measurement /." View abstract or full-text, 2008. http://library.ust.hk/cgi/db/thesis.pl?CIVL%202008%20ZHANG.

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Cheung, Kwok Fai. "Applications of pseudo-ductile engineered cementitious composites for construction industry /." View abstract or full-text, 2004. http://library.ust.hk/cgi/db/thesis.pl?CIVL%202004%20CHEUNGK.

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Thesis (M.Phil.)--Hong Kong University of Science and Technology, 2004.
Includes bibliographical references (leaves 314-315). Also available in electronic version. Access restricted to campus users.

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22

Ilyas, Muhammad. "Development of nano-graphene cementitious composites (NGCC)." Thesis, Brunel University, 2016. http://bura.brunel.ac.uk/handle/2438/15828.

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Ordinary Portland cement (OPC) is the main constituent of concrete works as a principal binder for aggregates and intrinsically transmits the brittleness into concrete through the formation of hydration crystals in the cement microstructure. A number of nano cementitious composites were developed in recent years to offset the brittleness with newly discovered nanomaterials and the most prevalent among those is the graphene oxide (GO). The main objective of this PhD research work is to develop nano graphene cementitious composites (NGCC) using low cost, two dimensional (2D) graphene nanoplatelets (GNPs) and one dimensional (1D) graphited carbon nanofibres (GCNFs) with unique conical surface morphology. The GNPs were sourced synthesised in an environmental friendly way via plasma exfoliation whereas, GCNFs were manufactured through catalytic vapour grown method. The project further investigated the effect of these nanomaterials in regulating the distinctive microstructure of cement matrix leading to enhance its mechanical properties. Three different types of high-performance NGCC namely NGCC-Dot, NGCC-Fnt and NGCC-CNF, are developed by activating pristine GNPs (G-Dot), functionalised GNPs (G-Fnt) and graphited nanofibers (G-CNFs) into the cement matrix respectively. It is found through various characterization and experimental techniques that both GNPs and GCNFs regulated the cement microstructure and influenced the mechanical properties of NGCC uniquely. A remarkable increase in the flexural and the tensile strength of newly developed NGCC has been achieved and that could be attributed to the formation of distinctive microstructure regulated by catalytic activation of these nanomaterials. The shape (1D, 2D) and unique morphology of these nanomaterials played a vital role in the mechanism of crystal formation to regulate the cement microstructure. Based on the observations of test results and comprehensive characterization, the possible mechanisms of crystal formation and development of distinctive microstructure of NGCC has been established which has then proceeded to the development of a physical model for NGCC development.

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23

Li, L., Q. Zheng, Z. Li, Ashraf F. Ashour, and B. Han. "Bacterial technology-enabled cementitious composites: A review." Elsevier, 2019. http://hdl.handle.net/10454/17127.

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Yes
Cementitious composites are generally brittle and develop considerable tension cracks, resulting in corrosion of steel reinforcement and compromising structural durability. With careful selection and treatment, some kinds of bacteria are able to precipitate calcium carbonate and ‘heal’ cracks in cementitious composites through their metabolism, namely bacterial activity. It is envisioned that the bacterial technology-enabled cementitious composites could have great potential for engineering applications such as surface treatment, crack repair and self-healing construction material. This paper presents the state-of-the-art development of bacterial technology-enabled cementitious composites from the following aspects: mechanisms of bacterial induced calcium carbonate precipitation; methods of applying bacteria into cementitious composites; mechanical properties, durability and their influencing factors; various applications; cost effective analysis and prospect. The paper concludes with an outline of some future opportunities and challenges in the application of bacterial technology-enabled cementitious composites in construction.
National Science Foundation of China (51578110) and the Fundamental Research Funds for the Central Universities in China (DUT18GJ203).

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24

Wiberg, Anders. "Strengthening of concrete beams using cementitious carbon fibre composites." Doctoral thesis, KTH, Civil and Architectural Engineering, 2003. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3582.

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The research described in this thesis deals with the use ofcement-based carbon fibre reinforced composites forstrengthening of existing structural concrete.

There is a large world-wide need for simple and reliablemethods to repair and strengthen aging infrastructure andbuildings. The use of cementitious fi- bre composites offersseveral advantages over the existing methods. No other work onstrengthening of structural concrete with cementitiouscomposites reinforced with continuous high strength fibres wasidentified when the present work started in 1998. At presenttime, 2003, it still is a new technique and very littleresearch has been internationally reported. This work includesa literature survey describing the state of the art of thestrengthening of structural concrete with cement based fibrereinforced composites.

Due to the novelty of this technique no specially adaptedmaterials are available and ready for use in cementitiouscomposites. In order to make many small scale tests to optimizethe composite, a new test beam has been developed. Severalparameter studies have been done in this work to determine howdifferent parameters, for example fineness of grading of thecement, additives, and fibre configuration affect thecomposite.

Large scale tests of ordinary concrete beams strengthenedwith a cementitious fibre composite are reported. The compositeused was made of a polymer modified mortar and a unidirectionalsheet of continuous carbon fibres, applied by hand. Bothflexural strengthening and shear strengthening were tested. Arelatively new method for measuring strains with digitalcameras was used on the shear strengthenings with a goodresult. It is concluded that the large scale tests have proventhat this method works and has great potential for futureuse.

Design methods for strengthenings were studied andevaluated. It is concluded that design methods formulated forstrengthening of structural concrete with carbon fibrereinforced polymers can be adapted also to cementitiouscomposites by introducing an efficiency factor.

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CAMPELLO, EDUARDO DE FIGUEIREDO. "FATIGUE BEHAVIOR OF CEMENTITIOUS COMPOSITES REINFORCED BY BAMBOO PULP." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2006. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=10091@1.

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CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO
A utilização de materiais de construção civil a base de cimento reforçado com fibras vem aumentando rapidamente nos últimos anos. No Brasil um vasto programa experimental para avaliar o comportamento mecânico desses materiais através de ensaios de flexão monotônicos e de compressão, vem sendo desenvolvidos na PUC/RIO desde 1979. Este trabalho procura dar continuidade a essa linha de pesquisa, sendo o primeiro a estudar o comportamento em fadiga de compósitos cimentícios reforçados com polpa de bambu, através de curvas de vida-fadiga S-N e da cinética de crescimento de trincas. As curvas S-N foram levantadas para compósitos entalhados e não entalhados, contendo 6% em massa de polpa em relação a massa de cimento. Essas curvas foram modeladas, com base nas propriedades mecânicas básicas levantadas nos ensaios de compressão e flexão. Com o objetivo de verificar a aplicabilidade da lei de Paris à cinética de crescimento de trincas de fadiga nesses compósitos, foi levantada a relação entre o comprimento da trinca a e o número de ciclos N durante a propagação estável da mesma, adotando-se teores de reforço de 6 e 14% em relação a massa de cimento. Finalmente as superfícies de fratura foram avaliadas por meio de microscópio eletrônico de varredura.
The use of fiber reinforced cementious composites as construction materials in civil engineering has rapidly grown in the last few years. In Brasil, a large experimental program for evaluating the mechanical behavior of these materials has been developed in PUC-RIO since 1979. The present study has the purpose of evaluating the fatigue behavior of cementitious composites by means of determining the S-N curves for notched and unnotched specimens. The fatigue curves were modeled using basic mechanical properties determined by means of compression and slow bend tests. With the purpose of verifying the applicability of Paris law to the fatigue crack growth kinetics, the crack length was determined as a function of the number of cycles N during stable crack propagation, for composites containing 6% and 14% weight percentage of bamboo pulp relative to the weight of cement. Finally, the fracture surface was analyzed by means of scanning electron microscopy.

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Chuang, Eugene (Eugene Yu) 1975. "Ductility enhancement of high performance cementitious composites and structures." Thesis, Massachusetts Institute of Technology, 2002. http://hdl.handle.net/1721.1/33272.

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Thesis (Sc. D.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 2002.
Includes bibliographical references (p. 280-287).
High performance cementitious composites (HP2C) are a new generation of fiber reinforced cementitious composites (FRCC) with substantial improvements in mechanical behavior. The most important development in these HP2C materials may be the nearly elasto-plastic ductile behavior, which allows safe exploitation of the tensile and shear capacity in structural elements. This thesis presents a comprehensive investigation into the ductility enhancement of HP2C structures. Beginning at the micromechanical level, sources of ductility are examined and micro-to-macro relations are derived from homogenization theory and fracture mechanics. These micro-to-macro relations form the basis for a novel 3-D two-phase material model, which captures macroscopically observed behavior. Currently existing models which describe the mechanical behavior of FRCC are often micromechanical in nature. However, this macroscopic approach permits one to model the mechanical behavior of HP2C in a continuous fashion, i.e. through the various states of cracking in HP2C, while capturing - through the two-phase composite structure of the model - the micromechanical sources of energy dissipation in the fiber reinforced composite.
(cont.) The 3-D model is implemented in a finite element program to simulate the behavior of two HP2C applications: a flexural girder and a shear girder, which have recently been tested by the FHWA. It is shown how the two-phase model aptly and accurately predicts the structural behavior of HP2C. Next, a sensitivity analysis of the HP2C model parameters elucidates how changes in HP2C mechanical behavior, observed at material level, manifest themselves at the structural level. By setting limits on the permanent composite matrix strain, which accounts for cracking in HP2C, one can set service limits on HP2C structures.Hence, a comprehensive (micromechanical, macroscopic, and structural) method for the assessment of the ductility enhancement of HP2C structures is presented. A significant scientific benefit of this research is the HP2C model which links micromechanical processes to macroscopic behavior and ultimately to structural behavior. This research also provides a design tool, that is the finite element application, which can be used to predict the behavior of HP2C structures and suggest improvements in HP2C structural and material design.
by Eugene Chuang.
Sc.D.

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Chin, Chee Seong Chin. "Experimental and computational analysis of fibre reinforced cementitious composites." Thesis, Swansea University, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.585523.

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A significant amount of research has been carried out on the material and structural characteristics of fibre reinforced concrete (FRC). Chapter 1 presents a literature survey of the historical background and development of FRC. New experimental data on the direct tensile, cylinder splitting, flexural, and cube crushing strengths of both plain and fibrous concretes is provided in Chapter 2. An analytical formula for predicting the direct tensile strength of FRC has also been derived. Chapter 3 comprises two tension softening models (i.e. TSM and EMIS models) for simulating the complete pre-cracking and post-cracking responses of cementitious composite. Both models have been validated using various experimental data. Chapter 4 addresses the characterization of the fiber-matrix properties where fibre pull out tests have been conducted for various types of deformed fibres. Chapter 5 covers the nonlinear finite element modelling of the deformed fibre pull out from cementitious matrix. A fibre pullout model has been developed and validated using experimental results. Chapter 6 concentrates on the simulation of the complete loaddeflection response and failure pattern of FRC flat slab at slab-column connection. Parametric studies on the slab thickness and reinforcement ratio have been conducted. Simulations of FRC flat slab and beam structures have also been performed using the EMIS model. Chapter 7 cites the details of a general analytical model for the prediction of ultimate punching shear strength of flat slab at slab-column connection. The analytical model is shown to provide reasonably good improvement when compared to several major design codes. Additionally, a unique analytical expression that provides useful information on the failure mode of flat slab has also been derived. Finally, Chapter 8 summarizes and concludes the outcomes and achievements throughout the research and possible areas for further research are suggested.

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Rajayogan, Vinod Engineering &amp Information Technology Australian Defence Force Academy UNSW. "Autogenous shrinkage in cementitious systems." Awarded by:University of New South Wales - Australian Defence Force Academy. Engineering & Information Technology, 2009. http://handle.unsw.edu.au/1959.4/44250.

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Autogenous shrinkage is of concern in high performance concrete mixtures, when specific properties like strength and durability are enhanced. Factors like low watercement ratio, low porosity and increased hydration kinetics which are associated with high performance concrete mixtures are also responsible for the development of autogenous shrinkage. With about two decades of research into autogenous shrinkage, uncertainties still exist with testing procedure, effect of supplementary cementitious materials, modelling and prediction of autogenous shrinkage. The primary focus of this study is to understand mechanisms which have been postulated to cause autogenous shrinkage like chemical shrinkage and self desiccation. In addition, this study has considered properties like porosity and internal empty voids in the analysis of the causes of bulk volume deformations of the cementitious paste systems with and without mineral admixtures. The study begins with an experimental investigation of chemical shrinkage in hydrating cementitious paste systems with the addition of fly ash, slag and silica fume using the test method recently accepted by the ASTM. This was followed by the experimental investigation of autogenous shrinkage in cementitious paste. The autogenous shrinkage in paste mixtures is studied from an early age (~1.5 hours after addition of water) for cementitious systems at a water-cementitious ratio of 0.32 (w/c 0.25 for limited mixture proportions). A non-contact measurement method using eddy current sensors were adopted. The hydration mechanism of the cementitious paste systems was then modelled using CEMHYD3D, which is a 3 dimensional numerical modelling method successfully used to study, simulate and present the hydration developments in cementitious systems. Properties like chemical shrinkage, degree of hydration, total porosity and free water content; all of which have been obtained from the CEMHYD3D simulation have been cross correlated with the experimental results in order to more comprehensively understand the mechanism contributing to bulk volume change under sealed conditions. The experimental investigations are extended to study the development in concrete with and without mineral admixtures (i.e., silica fume, fly ash and slag). Self desiccation driving the development of autogenous shrinkage has been used extensively across literature but as an alternative the author has proposed using internal drying factor in modelling autogenous shrinkage. The "internal drying factor" is described as the ratio of the empty voids (due to chemical shrinkage) to the total porosity at any point of time of hydration. Independent of the mixture proportions, a linear trend was observed between the autogenous shrinkage strain and increase in internal drying factor. Thus the internal drying factor could be incorporated into semiempirical models while attempting to predict autogenous shrinkage. An increase in the compressive strength of matured concrete at 1 year had a strong correlation to the observed autogenous shrinkage strains irrespective of the cementitious system. It is believed this could be because of the increase in gel-space ratio which is intern linked to the degree of hydration and porosity of the microstructure. The author has obtained strong evidence that the micro-structural changes associated with high strength and durable concrete have a direct impact on the autogenous shrinkage of concrete. Hence, the author suggests that autogenous shrinkage should be investigated and allowable values be stipulated as design criterion in structures that use high strength-high performance concrete.

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Koutný, Ondřej. "Balisticky odolné betony." Doctoral thesis, Vysoké učení technické v Brně. Fakulta chemická, 2019. http://www.nusl.cz/ntk/nusl-408058.

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Doctoral thesis „Ballistic-proof concretes“ deals with description, design and development of material based on ultra-high performance fibre reinforced cementitious composite with increased ballistic resistance i.e. increased resistance against high-strain rate dynamic loading induced by interaction of high-velocity moving objects. High mechanical properties, essential for such a material, are reached especially by maximal reduction of water-to-binder coefficient using high-range water reducing agents, high-strength aggregates and dense structure by precise selection and dosage of raw materials in the recipe. The main goal is to prepare a methodology for design of such a materials, observation of material behaviour on ballistic loading and quantitative description of material response for protective structures design. Properties of designed materials within this thesis are comparing with properties of commercially available and commonly used cementitious composites in order to create a concept for material limits in the field of ballistic protection. This concept enables to estimate ballistic protection of present or newly-designed materials and structures.

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Vieira, Mylene de Melo. "Assessment of chloride corrosion in steel fibre reinforced cementitious composites." Doctoral thesis, Universitat Politècnica de Catalunya, 2018. http://hdl.handle.net/10803/663458.

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High performance steel fibre reinforced cementitious composites (HPSFRCCs) show enhanced structural performance and durability. The improved properties favour its use in agressive conditions (such as marine environment) prone to corrosion. Despite the remarkable advances in the knowledge about corrosion of conventional reinforced concrete structures, questions still remain about its effects on the durability of HPSFRCC. The governing mechanisms of corrosion, the presence of cracks, the high steel fibre content, and the long-term chloride exposure still need to be properly evaluated. Given the increased application of HPSFRCC with structural responsibility and the high steel fibre content commonly used in the mixes, it is of great importance to understand the main mechanisms governing the chloride corrosion and its effects on the durability of the real-scale structures constructed with the material. To overcome these barriers and the uncertainty mentioned, this doctoral thesis adresses the following key issues: the effect of chlorides in uncracked HPSFRCCs under constant conditions; the influence of chloride corrosion in uncracked HPSFRCCs under wet-dry cycles with chlorides; the effect of corrosion in pre-cracked HPSFRCCs subjected to the same cycles and the proposal of a simplified model to consider the structural effects of corrosion. The first subject concerns the assessment of chloride corrosion on the aesthetic aspect and on the mechanical behaviour of HPSFRCCs by means of an accelerated test. For that, HPSFRCCs specimens with and without chlorides added to the mixes and with different fibre contents were tested. The preliminary experimental programme shows that, in general, the chlorides produce a level of surface corrosion with aesthetic consequences but have small influence on the mechanical performance. In the second subject, the influence of cycles was assessed in accelerated tests with uncracked HPSFRCCs prisms. The results reveal that, for uncracked HPSFRCCs elements, the corrosion affects the surface aspect but has no influence on the post-cracking response. The third subject focuses on the analysis of pre-cracked HPSFRCCs prisms under cyclic chloride exposure, considering different pre-crack widths and fibre contents. The study shows that the corrosion affects significantly the mechanical behaviour of the fibres for all specimens. The last subject covers a proposal of a simplified model to consider the effect of corrosion in the ULS design of HPSFRCC elements under cyclic chloride exposure. The model proposed was capable of reproducing the influence of the corrosion process over the cycles, being compatible with the current philosophy proposed in codes for the design of HPSFRCC structures.
Los compuestos cementicios de alta resistencia reforzados con fibra de acero (CCARRFA) muestran un mayor rendimiento estructural y durabilidad. Las mejoras en las propiedades del CCARRFA debido a la inclusión de fibras de acero favorecen su uso en condiciones agresivas (tales como el ambiente marino) propensas a la corrosión. A pesar de los notables avances en el estudio de la corrosión de estructuras de hormigón armado, aún quedan cuestiones sin resolver respecto a sus efectos en la durabilidad del CCARRFA. En relación a ello, los mecanismos que gobiernan la corrosión, la presencia de fisuras, el alto contenido de fibra de acero y la exposición prolongada a los cloruros deben ser evaluados adecuadamente. Dado el aumento de la utilización de CCARRFA con responsabilidad estructural y el alto contenido de fibra de acero comúnmente utilizado en las mezclas, resulta de gran importancia comprender los principales mecanismos que gobiernan la corrosión, así como sus efectos en la durabilidad de estructuras a escala real construidas con este material. Para superar estas barreras y las incertidumbres mencionadas, esta tesis doctoral tratará los siguientes aspectos clave: el efecto de los cloruros en CCARRFA no fisurado en condiciones constantes; la influencia de la corrosión por cloruros en CCARRFA no fisurado sometido a ciclos de mojado y secado con cloruros; el efecto de la corrosión en CCARRFA fisurados sometidos a los mismos ciclos y una propuesta de modelo simplificado para considerar los efectos estructurales de la corrosión. El primer aspecto aborda la evaluación de la corrosión por cloruros desde un punto de vista estético y del comportamiento mecánico del CCARRFA mediante un ensayo acelerado. Para ellos, se han ensayado probetas de CCARRFA con y sin cloruros añadidos a las mezclas con diferentes contenidos de fibra. La campaña experimental preliminar mostró que, en general, los cloruros producen un nivel de corrosión superficial con consecuencias estéticas, pero con poca influencia en el comportamiento mecánico. En el segundo aspecto, se evaluó la influencia de los ciclos en ensayos acelerados en probetas de CCARRFA no fisuradas. Los resultados revelaron que en los elementos de CCARRFA no fisurados la corrosión afecta al aspecto superficial pero no influye en la respuesta post-fisuración. El tercer aspecto trata el análisis de probetas de CCARRFA fisuradas con diferentes anchos de fisura y contenidos de fibra sometidas a una exposición cíclica de cloruros. El estudio muestra que la corrosión afecta significativamente al comportamiento mecánico de las fibras de todas las probetas. El último aspecto se centra en la propuesta de uno modelo simplificado que considera el efecto de la corrosión en el diseño en ELU de elementos de CCARRFA bajo una exposición cíclica de cloruros. El modelo propuesto es capaz de reproducir el efecto del proceso de la corrosión a lo largo de los ciclos, siendo compatible con la actual filosofía propuesta en códigos para el diseño de estructuras de CCARRFA.

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Sarandily, A. "High strength autoclaved cementitious matrices and steel fibre reinforced composites." Thesis, University of Salford, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.374519.

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BRESCANSIN, JANAINA. "FRACTURE BEHAVIOR OF CEMENTITIOUS MATRIX COMPOSITES REINFORCED BY BAMBOO PULP." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2003. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=3720@1.

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CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO
O uso de todos os tipos de amianto na construção civil tem diminuído drasticamente devido a problemas sérios de saúde associados a sua manipulação. De fato é previsto banir totalmente o seu uso, dentro de um curto espaço de tempo, nos países desenvolvidos bem como nos em desenvolvimento. Na necessidade de se encontrar um substituto adequado para o amianto, tem-se pesquisado compósitos de argamassa reforçada com fibras vegetais e polpas celulósicas. Devido ao processo de polpação, que remove as impurezas não celulósicas, como a lignina e a hemicelulose, diminuindo o ataque às fibras, sem a necessidade de recorrer a modificações na matriz cimentícia, as polpas celulósicas podem ser o substituto ideal para o amianto. Assim sendo, o principal objetivo desta dissertação é determinar experimentalmente as características mecânicas e os parâmetros de fratura de compósitos de matriz cimentícia reforçada por polpa de bambu refinada e sem refino. As polpas celulósicas foram utilizadas nas porcentagens de 8 e 14 por cento em relação à massa do cimento, porcentagens estas que, conforme a literatura, são associadas à otimização da energia absorvida no ensaio de flexão. A avaliação do comportamento mecânico dos compósitos considerados neste trabalho foi realizada através de ensaios de compressão e impacto, bem como de flexão em três pontos em espécimes não entalhados e em outros contendo entalhes de raios de curvatura diferentes. Propriedades mecânicas, tais como módulo de elasticidade, resistência à compressão, ao impacto e à flexão, bem como integral J na carga máxima, são apresentadas e discutidas em termos de aspectos microestruturais e fractográficos dos corpos de prova ensaiados.
As handling and manipulation of asbestos pose grave health hazards, its use in civil construction has been drastically dwindling and will in fact be completely prohibited, in a few years, in developed countries. With the need arising to find an adequate substitute, vegetable fibers and cellulosic pulps have been considered to be viable alternatives. Taking into account the fact that the process for pulp production entails the removal of impurities, such as lignin and hemicellulose, cellulosic pulps seem to be the ideal substitute to asbestos, as their use does not necessitate modifications in the cementitious matrix. Accordingly, the purpose of this work is to experimentally determine basic mechanical characteristics and pertinent fracture parameters of bamboo pulp reinforced cement. Refined and non-refined pulps were used in the proportions of 8 and 14 percent of the weight of dry cement. These percentages were adopted as they imply, according to literature, in optimizing the energy absorbed by the composite in bend loading. Evaluation of the mechanical behavior of the composites considered in this work was realized by means of compression and impact testing. Three point bend tests were also carried out using unnotched as well as notched specimens of different notch root radii. Mechanical properties such as modulus of elasticity, compressive, impact and bend strengths, and J integral at maximum load are presented and discussed in terms of pertinent microstructural and fractographic aspects of test specimens.

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33

Errico, Carmine. "Determination of the influence of SRG anchors on the bond behavior of SRG/FRCM strips bonded to a quasi-brittle substrate." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2019.

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The use of FRCM composites (Fiber Reinforced Cementitious Matrix) is becoming more and more widespread. The inorganic matrix guarantees many advantages, especially when dealing with masonry substrates, including a good compatibility from both a physical and a chemical point of view and the lower sensitivity to debonding phenomena at the interface. Compared to FRP composites, which presents many data in the literature, FRCM composites must be studied in detail and research in this field has only begun in recent years. This work deals with an important problem: the realization of an anchorage system to improve the strength of composites and allow their use even in the absence of adequate development length. In this study, the effectiveness of the anchorage system and the interaction with an externally bonded FRCM were studied on masonry columns. The columns were tested until failure condition in the Laboratory of Structural and Geotechnical Engineering (DICAM – LISG) of the University of Bologna, via del Lazzaretto 15/5, Bologna. Test results demonstrate that the introduction of additional anchorages improves the effectiveness of the FRCM composites in terms of resistance and loading capacity.

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SALES, ANGELA TERESA COSTA. "SHRINKAGE, CREEP AND FRACTURE OF CEMENTITIOUS COMPOSITES REINFORCED WITH BAMBOO PULP." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2006. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=8663@1.

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COORDENAÇÃO DE APERFEIÇOAMENTO DO PESSOAL DE ENSINO SUPERIOR
A aplicação de compósitos cimentícios usando fibras vegetais, em substituição a fibras de asbestos, é uma realidade em indústrias de fibrocimento em vários países do mundo, pois, apesar das boas propriedades mecânicas e durabilidade, a utilização de asbestos acarreta problemas de insalubridade. Fibras vegetais, pela disponibilidade e adequação à preservação ambiental, apresentam vantagens sobre fibras sintéticas. O bambu é excelente fornecedor de fibras, pelo rápido crescimento, baixo custo e qualidade das fibras. Usando-se a polpa do vegetal, pode-se inserir maiores teores de fibras que, distribuídas aleatoriamente, conferem características isotrópicas ao compósito. Estudos são realizados, visando melhorar o desempenho dos compósitos com fibras vegetais. Retração e fluência se constituem em formas de deformação ao longo do tempo que podem comprometer o desempenho e reduzir a durabilidade do material. Tratando-se de materiais heterogêneos e sujeitos à presença de falhas, em diversos níveis, a aplicação da mecânica da fratura pode tornar-se valiosa ferramenta para projeto e controle da integridade desses compósitos, sendo a inibição da iniciação e propagação de trincas uma das principais funções do reforço de fibras curtas. Esse trabalho buscou analisar o comportamento de compósitos cimentícios reforçados com polpa de bambu, quanto à retração e à fluência, e obter parâmetros que descrevessem seu modo de fratura. Enquanto a capacidade de sofrer retração plástica foi reduzida, a retração livre na secagem cresceu com o aumento do teor de polpa de bambu no compósito, chegando a 40% de incremento para 14% de polpa, após um ano. Sob retração restringida, resultados mostraram melhor desempenho dos compósitos com fibras, pela ausência de fissuras detectáveis por fissurômetro, em relação à matriz sem reforço, que apresentou fissura em torno de 4 horas de exposição à secagem. Estudo da reversibilidade da retração mostrou que para os compósitos predominam as deformações de contração. Houve aumento da fluência sob compressão simples, com a inserção do reforço fibroso na mistura. Na fluência sob flexão, houve aumento da fluência específica na face comprimida com o aumento do teor de polpa na mistura. A fluência específica sob tração na flexão resultou maior para a matriz sem reforço do que para os compósitos com polpa de bambu. No estudo sobre mecânica da fratura, os corposde- prova entalhados de compósito com polpa apresentaram melhoria considerável no comportamento à flexão em relação à matriz sem reforço. Os compósitos com polpa mostraram-se menos sensíveis ao entalhe, com o incremento do teor de reforço fibroso. Observou-se considerável amolecimento (softening) precedendo a ruptura devido à propagação da trinca, nos compósitos. As curvas de resistência (curvas-R) permitiram identificar os valores de KIR que, nos compósitos, mostrou manter certa constância, com o aumento do comprimento da trinca. Nesse platô da curva, os valores médios para KIR foram de 1,88 MPa.m1/2 e 1,84 MPa.m1/2, respectivamente, para compósitos com 8% e 14% de polpa de bambu. Nos compósitos, os perfis dos caminhos trilhados pelas trincas no crescimento foram tortuosos, sendo o mecanismo de fratura mais intensamente dominado pela presença do entalhe inicial na matriz sem reforço que nos compósitos.
The application of cimentitious composites using vegetal fibers in substitution of asbestos is a worldwide fact in the fiber cement industry. Despite their good mechanical properties and durability, the use of asbestos fibers causes well-known health hazards. Although vegetal fibers have relatively poor mechanical properties compared with synthetic fibers, they have other advantages such as low cost and low energy demand during manufacture. Bamboo is an excellent fiber supplier, due to its fast growth and the quality of its fibers. Using vegetal pulp it is possible to insert considerable amounts of fiber in a cement matrix, which randomly distributed confer isotropic characteristics to the composite. Studies are carried out aiming to improve the performance of composites with vegetal fibers. Shrinkage and creep are sorts of time depending deformation that may significantly reduce the durability and performance of the cement based composite. Cementitious composites are essentially heterogeneous materials subject to the presence of flaws at different levels due to the presence of many internal microcraks in the material prior to loading. Therefore, the application of fracture mechanics could become a suitable tool for the design and control of the integrity of these composites, since the inhibition of crack initiation and propagation is one of the main functions of the short fiber reinforcement. This work sought to analyze the behavior of cimentitious composites reinforced with bamboo pulp under shrinkage and creep and to provide sufficient fracture parameters to describe the failure mode of the material. The results show that, whereas the plastic shrinkage reduces, the free drying shrinkage increases proportionally to bamboo pulp content in the composite, reaching a 40% increment for a 14% pulp content, after one year. Under restrained shrinkage, the composite with bamboo pulp presents better performance than unreinforced matrix. Namely, under same boundary conditions, while the unreinforced matrix presents cracks after about four hours, the composites present no cracks visible through a 10x magnifying glass, even after forty five days of drying. Study of the shrinkage reversibility of the composite showed that there is contraction deformation prevalence. Under simple compression, the creep capacity of the bamboo pulp composites increases proportionally with the fiber content. Under bending stress, there was an increase of the specific creep in the compressed face of the specimen, as the pulp content of the mixture increases. The specific creep under bending tension for the tensile face was greater for the unreinforced matrix than in the bamboo pulp composites. As revealed through the assessment of fracture behavior of composites with bamboo pulp, notched specimens presented a considerable improvement in bending behavior when compared to the unreinforced matrix. The composites with pulp became less sensible to the notch with the increment of pulp content. In the bamboo pulp composites, considerable softening was observed in the load-displacement curve, as load gradually decreases after the peak load and before the rupture due to crack propagation. Using resistance curves (R-curves) it was possible to identify the KIR values that, for the composites, kept certain constancy as the crack length increased. At this plateau of the curve, the average values for KIR reached 1,88 MPa.m1/2 and 1,84 MPa.m1/2 for composites with bamboo pulp content of 8% and 14% respectively. In the composites, crack profiles and crack surfaces were tortuous, while in the unreinforced matrix the fracture mechanisms were more intensely dominated by the presence of the initial notch.

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Bazkiani, Saeed Pourfalah. "Out-of-plane retrofitting of masonry wall using engineered cementitious composites." Thesis, Heriot-Watt University, 2017. http://hdl.handle.net/10399/3299.

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The contribution of infill masonry walls to the overall behaviour of frame structures has been acknowledged through numerous published experimental and numerical investigations. Both the in-plane and out-of-plane response of such walls have a significant effect on the overall structural performance of frames and can be subjected to a range of in-plane and out-of-plane actions (e.g. wind, earthquakes, impact and blast loads) characterised by different time-histories, loading-frequencies and intensities. Infill walls are particularly vulnerable to the application of loads in the out-of-plain direction and often sustain significant damage (in the form of cracking) which can result in failure and collapse. It is interesting to note that after sustaining a certain level of damage due to the load applied in the out-of-plane direction, an infill wall can no longer contribute to the in-plane response of a frame. In an attempt to enhance the overall behaviour of infill walls, present work sets out to develop a method for improving the out-of-plain behaviour of such elements. This is achieved through the use of a thin layer of engineered cementitious composite (ECC) which is fully or partially bonded on the face of the wall which is in tension (opposite to the face on which the out-of-plane action is applied) or on both faces of the wall. For this purpose, an ECC mix is initially developed employing materials available in the UK. Its behaviour is then established experimentally under increasing loading rates and temperatures. This material is then used to strengthen a series of beam-like masonry specimens under different loading rates by conducting a series of static and dynamic 4- point bending tests. The test data obtained is then employed to develop a numerical model of the problem at hand capable of realistically predicting the experimentally established behaviour through the use of nonlinear dynamic finite element analysis. Both, experimental and numerical studies, reveal that in all cases considered the use of ECC resulted in a significant enhancement of the out-of-plain behaviour of the specimens in terms of strength, stiffness and ductility. Furthermore, the specimens with a partially bonded ECC layer performed better compared to those with a fully ECC layer. In addition, the performance of these specimens under impact load was further enhanced when adding a second layer on the other face of the specimen. Finally, a parametric numerical investigation is conducted to assess the effect of a range of parameters (associated with the boundary conditions imposed onto the specimen, the properties of the materials involved, the geometry of the specimen and loading rate) on the behaviour of the specimens.

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36

De, Beer M. "Behaviour of cementitious subbase layers in bitumen base structures." Pretoria : [s.n.], 2009. http://upetd.up.ac.za/thesis/available/etd-08042009-115309/.

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Butler, Marko, Simone Hempel, and Viktor Mechtcherine. "Zeitliche Entwicklung des Verbundes von AR-Glas- und Kohlenstofffaser- Multifilamentgarnen in zementgebundenen Matrices." Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2009. http://nbn-resolving.de/urn:nbn:de:bsz:14-ds-1244045698955-31655.

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Mit zunehmendem Alter zeigt das Verbundverhalten von Multifilamentgarnen aus alkaliresistentem Glas (AR-Glas) oder Kohlenstoff in Abhängigkeit von der Zusammensetzung der zementgebundenen Matrix eine sehr unterschiedliche Entwicklung. Während bei AR-Glas teilweise drastische Verluste des Leistungsvermögens zu verzeichnen sind, treten diese bei Kohlefasern nicht auf. Zur Untersuchung der Phänomene wurden beidseitige Garnauszugversuche durchgeführt und die Interphase zwischen Filamenten und Matrix im Rasterelektronenmikroskop (ESEM) untersucht. Die unterschiedlichen mechanischen Eigenschaften stehen in Zusammenhang mit verschieden ausgeprägten Mikrostrukturen der Interphasen. Welche Ursachen die unterschiedliche morphologische Entwicklung der Interphasen hat, ist Gegenstand aktueller Arbeiten.

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Abdel-Monem, Ahmed El-Badawy Sayed. "The strength and fracture characteristics of autoclaved high-volume fraction steel-fibre reinforced cementitious composites." Thesis, University of Salford, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.280744.

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Carvalho, Milene. "Inclusão de compósitos cimentícios em blocos estruturais cerâmicos com foco em conforto térmico." reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2017. http://hdl.handle.net/10183/170229.

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Materiais aplicados na construção civil são importantes para fornecer segurança e conforto às pessoas. Quanto mais adequadas as propriedades térmicas, menos energia é necessária para aquecer ou resfriar uma área construída. A NBR 15575:2013 - Desempenho de Edificações Habitacionais, padronizou desempenhos térmicos para construções. Os blocos estruturais cerâmicos atendem o padrão mínimo, porém acredita-se que seu desempenho possa ser melhorado utilizando materiais de características isolantes dentro de seus furos verticais. Assim, o objetivo deste trabalho é investigar compósitos de matriz cimentícia com agregados leves para o aprimoramento térmico de blocos estruturais cerâmicos. Para o estudo, quatro corpos de prova foram produzidos preenchendo o vazado dos blocos com compósitos de matriz cimentícia utilizando 80% agregados leves (argila expandida, vermiculita, poliestireno expandido (EPS) e perlita expandida), 20% de cimento, além de uma amostra preenchida com graute estrutural que é comumente utilizado em edificações de alvenaria estrutural. Também foram produzidos corpos de prova com os compósitos, para a análise de massa específica, microscopia, resistência à compressão, absorção de água e desempenho térmico medido por termografia. Nos blocos, analisou-se massa final preenchido, absorção de água e desempenho térmico. No estudo termográfico, os blocos preenchidos foram comparados ao bloco cerâmico vazado padrão. Concluiu-se que o preenchimento dos vazados dos blocos com todos os compósitos leves e com o graute estrutural proporcionou um desempenho térmico melhor que o do bloco padrão, se destacando o EPS como melhor desempenho. O desempenho térmico dos prismas de compósitos confirmou o que foi observado nos corpos de prova de blocos. Assim foram feitos novos corpos de prova maximizando o teor de EPS para 85% e 90%. A análise térmica destas amostras apresentou melhor resultado para EPS 90%. O aumento do teor de EPS diminuiu a resistência à compressão e aumentou a absorção de água, porém, como o foco é o desempenho térmico e o bloco preenchido com o compósito EPS (90%) atende as características normativas, esta pode ser uma solução interessante.
Materials applied in civil construction are important to provide security and comfort to people. The more appropriate the thermal properties are, the less energy it is necessary to provide heat or cold to a constructed area. The NBR 15575:2013 standard, which deals with the Performance of Residential Constructions, has standardized thermal performances for buildings. Structural ceramic blocks meet the minimum standard, but it is believed that their performance can be improved by means of materials with isolating characteristics within their vertical holes. Thus, the aim of this paper is to investigate cementitious matrix composites with lightweight aggregates for thermal improvement of ceramic structural blocks. For the study, four specimens were produced by filling the hollow spaces of the blocks with cementitious matrix composites using 80% of lightweight aggregates (expanded clay, vermiculite, expanded polystyrene – EPS –, and expanded perlite), and 20% of cement. These were compared to a sample filled with structural grout, which is commonly used in structural masonry buildings. Specimens were also produced with the composites for specific mass analysis, microscopy, compression resistance, water absorption and thermal performance measured by thermography. In the blocks, the final, filled weight was analyzed, as well as water absorption and thermal performance. In the thermographic study, the filled blocks were compared to standard ceramic hollow blocks. It was concluded that filling the hollow spaces of the blocks with all the lightweight composites and structural grout provided a better thermal performance than that of standard blocks, highlighting EPS as having the best performance. Thermal performance of the composite prisms confirms what was observed in the block specimens. Thus, new specimens were made maximizing the EPS content to 85% and 90%. Thermal analysis of these samples presented better results for EPS 90%. The increase in the EPS content decreased compression resistance and increased water absorption. However, as the focus is thermal performance and as the block filled with EPS composite (90%) meets the requirements of the standard, this may be an interesting solution.

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França, Marylinda Santos de. "Rheological behavior of engineered cementitions composites reinforced with PVA fibers." Universidade de São Paulo, 2018. http://www.teses.usp.br/teses/disponiveis/3/3146/tde-03102018-140459/.

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The rheological behavior analysis of Engineered Cementitious Composites (ECC) is key to understand how the different preparation techniques affect the composite mechanical performance. However, the rheological assessment of reinforced materials becomes more complex since fibers usually cause flow disturbances not found in nonreinforced cementitious materials. Besides that, simple workability measurement techniques are not able to fully understand the composite behavior in the fresh state creating the need for more precise techniques to be employed. The main objectives of this study were to evaluate the ECC rheological behavior using different rheometer devices (Vane system and Ball measuring system) and investigate the influence of mixing processes on the fiber homogenization and rheological behavior. Additionally to this, a link between rheological behavior and mechanical performance was investigated. In the end, the ball measuring system revealed to be more efficient than the vane system when evaluating the composite rheological behavior. In addition, the mixing process influenced the rheological behavior of PVA-ECC especially regarding the moment which fibers are added. Fiber addition after mortar mixture improved fibers homogenization and reduced mixing energy by around 8%. Moreover, a correlation between rheological and mechanical properties showed that a 2-times variation in either yield stress or viscosity can lead to a variation of more than 50% in flexural strength without significantly affecting the composite compressive strength. It was also found that the lower the composite yield stress and viscosity the higher was its ultimate strain. To conclude, all those parameters contributed to understand the composite rheological behavior and globally optimize its performance.
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Mora, D. F. (Diego Fernando). "Multifield-based modeling of material failure in high performance reinforced cementitious composites." Doctoral thesis, Universitat Politècnica de Catalunya, 2013. http://hdl.handle.net/10803/117529.

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Cementitious materials such as mortar or concrete are brittle and have an inherent weakness in resisting tensile stresses. The addition of discontinuous fibers to such matrices leads to a dramatic improvement in their toughness and remedies their deficiencies. It is generally agreed that the fibers contribute primarily to the post-cracking response of the composite by bridging the cracks and providing resistance to crack opening. On the other hand, the multifield theory is a mathematical tool able to describe materials which contain a complex substructure. This substructure is endowed with its own properties and it interacts with the macrostructure and influences drastically its behavior. Under this mathematical framework, materials such as cement composites can be seen as a continuum with a microstructure. Therefore, the whole continuum damage mechanics theory, incorporating a new microstructure, is still applicable. A formulation, initially based on the theory of continua with microstructure Capriz, has been developed to model the mechanical behavior of the high perfor-mance fiber cement composites with arbitrarily oriented fibers. This formulation approaches a continuum with microstructure, in which the microstructure takes into account the fiber-matrix interface bond/slip processes, which have been recognized for several authors as the principal mechanism increasing the ductility of the quasi-brittle cement response. In fact, the interfaces between the fiber and the matrix become a limiting factor in improving mechanical properties such as the tensile strength. Particularly, in short fiber composites is desired to have a strong interface to transfer effectively load from the matrix to the fiber. However, a strong interface will make difficult to relieve fiber stress concentration in front of the approaching crack. According to Naaman, in order to develop a better mechanical bond between the fiber and the matrix, the fiber should be modified along its length by roughening its surface or by inducing mechanical defor-mations. Thus, the premise of the model is to take into account this process considering a micro field that represents the slipping fiber-cement displacement. The conjugate generalized stress to the gradient of this micro-field verifies a balance equation and has a physical meaning. This contribution includes the computational modeling aspects of the high fiber rein-forced cement composites (HFRCC) model. To simulate the composite material, a finite element discretization is used to solve the set of equations given by the multifield approach for this particular case. A two field discretization: the standard macroscopic and the micro-scopic displacements, is proposed through a mixed finite element methodology. Furthermore, a splitting procedure for uncoupling both fields is proposed, which provides a more convenient numerical treatment of the discrete equation system. The initiation of failure in HPFRCC at the constitutive level identified as the onset of strain localization depends on the mechanical properties of the all compounds and not only on the matrix ones. As localization criteria is considered the bifurcation analysis in combination with the localized strain injection technique presented by Oliver et al. It consists of injecting a specific localization mode during the localization stage, via mixed finite element formulations, to the path of elements that are going to capture the cracks, and, in this way, the spurious mesh orientation dependence is removed. Model validation was performed using a selected set of experiments that proves the via-bility of this approach. The numerical examples of the proposed formulation illustrated two relevant aspects, namely: 1) the role of the bonding mechanism in the strain hardening be-havior after cracking in the HPFRCC and 2) the role that plays the finite element formulation in capturing the displacement localization in the localization stage.

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Douglas, Kyle Scott. "Rate-dependence in high performance fiber-reinforced cementitious composites for seismic retrofits /." May be available electronically:, 2007. http://proquest.umi.com/login?COPT=REJTPTU1MTUmSU5UPTAmVkVSPTI=&clientId=12498.

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Abdallah, Sadoon Mushrif. "Bonding mechanisms and strength of hooked-end steel fibre reinforced cementitious composites." Thesis, Brunel University, 2017. http://bura.brunel.ac.uk/handle/2438/15827.

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Concrete is a strong material as to its compressive strength. However, it is a material with a low tensile and shear strength, and brittleness at failure. Concrete has to be reinforced with appropriate materials. Steel fibre is one of the most common materials currently being used to develop reinforced concrete, which may replace partially or completely conventional steel reinforcement. Successful reinforcement of concrete composite is closely related to the bond characteristics between the reinforcing fibre and matrix. The effective utilisation of steel fibre reinforced concrete (SFRC) requires in-depth and detailed understanding of bonding mechanisms governing the tensile behaviour. In response to this demand, this study embraced two main areas: understanding the reinforcing mechanisms of fibres in SFRC and material's post-cracking behaviour. Comprehensive experimental and theoretical programmes have therefore been developed: the experimental work is subdivided into three parts. The first part was to investigate the effect of various physical parameters, such as fibre characteristics (i.e. geometry, inclination angle, embedded length, diameter and tensile strength) and matrix strength which controls the pull-out behaviour of steel fibres. The second part is concerned with the assessment of the bond mechanisms of straight and hooked end fibres after exposure to elevated temperatures and varying matrix strength. The third part is devoted to gain further insight on the bond mechanisms governing the post-cracking behaviour through uniaxial and bending tests. It was found that the varying hook geometry and matrix strength each had a major influence on the pull-out response of hooked end fibres. As the number of the hook's bends increased, the mechanical anchorage provided by fibre resulted in significant improvement of mechanical properties of SFRC. The reduction in bond strength at elevated temperatures is found to be strongly related to the degradation in properties of the constituent materials, i.e. the fibre and concrete. The most effective combination of matrix strength and fibre geometry was found to be as follows: 3DH (single bend) fibre with normal-medium strength matrix, 4DH (double bend) fibre with high strength matrix and 5DH (triple bend) fibre with ultra-high performance matrix. Two analytical models to predict the pull-out behaviour of hooked end fibres were developed. Both models were able to predict the pull-out response of SFRC made from a variety of fibre and matrix characteristics at ambient temperature. This work has established a comprehensive database to illustrate the bonding mechanisms of SFRC and anchorage strengthening of various hooked end fibres, and this should contribute towards an increasing interest and growing number of structural applications of SFRC in construction.

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Sanjeevan, Poologanathan. "The effects of geometrical microstructure of cementitious composites on laser cleaning process." Thesis, Glasgow Caledonian University, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.443167.

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Pretorius, Jan Hendrik Christoffel. "The influence of PFA particle size on the workability of cementitious pastes." Pretoria : [s.n.], 2005. http://upetd.up.ac.za/thesis/available/etd-07082005-135427/.

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46

Arquez, Ana Paula. "Aplicação de laminado de polímero reforçado com fibras de carbono (PRFC) inserido em substrato de microconcreto com fibras de aço para reforço à flexão de vigas de concreto armado." Universidade de São Paulo, 2010. http://www.teses.usp.br/teses/disponiveis/18/18134/tde-29062010-114146/.

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O reforço de elementos estruturais de concreto armado com uso de polímeros reforçados com fibras de carbono (PRFC) está cada vez mais conhecido, seguro e acessível. Em todo o mundo, a aplicação do PRFC vem sendo estudada sob diversas técnicas. Características como elevada resistência à tração e à corrosão, baixo peso, facilidade e rapidez de aplicação são os principais fatores para essa disseminação. Em particular, a técnica aqui estudada é conhecida como Near Surface Mounted (NSM), que consiste na inserção de laminados de PRFC em entalhes realizados no concreto de cobrimento de elementos de concreto armado. Com dupla área de aderência, ela vem a suprir uma deficiência comum no reforço colado externamente, que é o seu destacamento prematuro. Como nas demais técnicas de reforço à flexão, o material é colado na região do concreto tracionado. Sabe-se que, na prática da intervenção, essa região frequentemente encontra-se danificada por razões diversas, como fissuração causada por ações externas, corrosão da armadura e deterioração do concreto, o que exige a sua prévia reparação. Considerando que a boa qualidade desse reparo é imprescindível à eficiência do reforço, propõe-se uma inovação técnica pela reconstituição da face tracionada da viga com um compósito cimentício de alto desempenho, que sirva como substrato para aplicação do PRFC e elemento de transferência de esforços à estrutura a ser reforçada. Produzido à base de cimento Portland, fibras e microfibras de aço, o compósito tem também potencial para retardar a abertura de fissuras e aumentar a rigidez da viga, melhorando o aproveitamento do reforço. Com apoio da mecânica do fraturamento, foi possível encontrar as taxas de fibras e microfibras de aço a serem adicionadas a uma matriz cimentícia especialmente desenvolvida. Foram realizados ensaios de aderência para estudar o processo de transferência de tensões cisalhantes do laminado para o compósito na zona de ancoragem da viga. Uma vez conhecido o comportamento do sistema, foram ensaiadas vigas de concreto armado de tamanho representativo de estruturas reais, em três diferentes versões de ancoragem do laminado, sendo duas delas com uso do compósito cimentício. Comprovou-se a eficiência da inovação proposta, constatando-se o aumento da rigidez e da capacidade de carga da viga reforçada, com excelente aproveitamento do laminado. Além disso, as fibras e microfibras diminuíram a abertura das fissuras em estágios mais avançados de carregamento, sem que se observasse fissuras horizontais próxima ao reforço, que poderiam indicar destacamento iminente do laminado de PRFC.
Strengthening of reinforced concrete elements with carbon fiber reinforced polymer (CFRP) is increasingly well known, safe and accessible. The application of CFRP has been studied worldwide using various techniques. Features like high tensile strength, corrosion resistance, lightweightness and easy and speedy application are the main factors for dissemination. In particular, the technique here analyzed is known as Near Surface Mounted (NSM), which involves inserting CFRP strips into grooves made on the concrete cover of reinforced concrete elements. With double bonding area, this technique avoids the premature peeling-off that usually takes place in externally bonded CFRP reinforcement. As in others flexural strengthening techniques, the material is bonded in the concrete tension region. It is known in strengthening practice that this region usually requires prior repair. Often it shows up damaged by several reasons such as cracking caused by external actions, reinforcement corrosion and deterioration of the concrete. Whereas the good quality of this repair is essential to strengthening efficiency, an innovative technique is proposed. A high-performance cementitious composite is used as a transition layer for insertion of CFRP strips. The composite is made of Portland cement, steel fibers and microfibers of steel. It also has the potential to delay crack opening and to increase the beam stiffness. Based on fracture mechanics, it was possible to find suitable volume fractions of steel fibers and microfibers to be added to the cementitious matrix. Bonding tests were performed to analyze the shear stress transferring from the CFRP laminate to the beam anchorage zone. Once known the system behavior, real size reinforced concrete beams were tested in three different versions of the anchorage conditions, two of them with use of cementitious composites. The efficiency of the proposed innovation was proved by confirming increased stiffness and load capacity of the strengthened beam. In addition, fibers and microfibers allowed the decrease of the crack opening in later loading steps. No horizontal cracks near to the reinforcement were noticed, which means that CFRP laminate peeling-off was not likely to occur.

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Garcez, Estela Oliari. "Investigação do comportamento de Engineered Cementitious Composites reforçados com fibras de polipropileno como material para recapeamento de pavimentos." reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2009. http://hdl.handle.net/10183/28642.

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Uma parcela substancial das rodovias do país apresenta processos de deterioração graves de seus pavimentos, fato que acarreta sérios impactos econômicos, sociais e ambientais, resultando em aumento do consumo de combustível, dos gastos com manutenção dos veículos, da frequência de engarrafamentos e do tempo gasto em deslocamentos. A utilização de recapeamentos ou overlays de concreto tem demonstrado ser uma alternativa sustentável e econômica para a reabilitação de pavimentos. No entanto, em muitos casos, os overlays de concreto não tem conseguido prevenir a ocorrência de fissuração por reflexão. Os Engineered Cementitious Composite (ECCs) são um tipo especial de compósitos cimentícios de alto desempenho reforçados com fibras, cuja principal característica é a altíssima ductilidade. Esta propriedade faz com que os mesmos sejam capazes de superar muitas das limitações dos overlays de concreto tradicionais. Fibras de PVA com uma camada superficial modificada foram especialmente desenvolvidas para serem empregadas no reforço de ECCs (ou PVAECC). O custo de tais fibras é o principal responsável pelo elevado custo dos ECCs, o que pode inviabilizar seu emprego em alguns casos. Buscando alternativas, este estudo se focou na investigação da possibilidade de uso de fibras de polipropileno (PP) de alto desempenho. Estas fibras, com custo mais atraente, já são produzidas comercialmente no Brasil, e usadas na produção de fibrocimento. As mesmas se demonstraram adequadas para uso como reforço em ECCs (ou PPECC), sendo capazes de garantir que se atinja um comportamento dúctil através do desenvolvimento de um processo de múltipla fissuração. Um resultado importante foi que a dimensão média da abertura das fissuras nos PPECC foi de 10 m, enquanto nos PVAECC a mesma era 60 m. Este resultado pode resultar em incrementos na durabilidade de estruturas. Além disto, o trabalho investigou o comportamento à flexão e fadiga dos ECCs reforçados com fibras de polipropileno. Os resultados demonstraram que os compósitos produzidos com cimento Portland tipo V-ARI não se comportam adequadamente à fadiga, uma vez que ocorre a deterioração das fibras. Por outro lado, os compósitos produzidos com cimento tipo I, já usualmente empregado em ECCs, apresentaram resultados satisfatórios. Um modelo de previsão de vida útil foi gerado para recapeamentos de PPECC, PVAECC e concreto, em função das espessuras dos revestimentos. O mesmo indicou que os ECCs requerem camadas 1,5 a 2,5 vezes mais finas que as usuais de concreto. O material foi, então, testado especificamente quanto à resistência à fissuração por reflexão. Os resultados demonstraram que o PPECC pode modificar o modo de ruptura frágil dos recapeamentos através do processo de múltipla fissuração. Na última etapa do trabalho foi realizada uma análise do ciclo de vida e dos custos do ciclo de vida de quatro diferentes sistemas de recapeamento – concreto, asfalto, PVAECC e PPECC. Os resultados mostram que os overlays de ECCs são bastante atrativos, pois diminuem tanto o consumo de energia associado aos processos de projeto, construção e manutenção do recapeamento, bem como reduzem a liberação de emissões gasosas à atmosfera, constituindo uma alternativa mais sustentável que as demais. Os sistemas de recapeamento com ECC também resultaram em vantagens econômicas. Apesar do alto custo inicial, a menor frequência de atividades de manutenção resulta em uma redução do custo total ao longo do período de 40 anos considerado. Isto representa uma importante economia em termos de custos diretos para os responsáveis pelas rodovias. De forma geral, o trabalho evidenciou a viabilidade de uso dos PPECCs para reabilitação de pavimentos.
Many old pavements in service today are approaching the end of their design service lives. Others are in dire need of major repair to continue serving, resulting in economical, environmental and social impacts by increasing vehicle fuel consumption and maintenance costs, traffic jam and delays. For pavements subject to moderate and heavy traffic, concrete overlays are increasingly being used as a cost effective and sustainable rehabilitation technique. However, concrete overlays have some physical limitations that contribute to durability concerns, which increase the probability of pavement overlay failure and maintenance frequency. Consequently, alternative materials are being developed to improve overlay performance. Engineered Cementitious Composites (ECC) are a special type of high performance fiber reinforced cementitious composites, designed for high ductility and damage tolerance which may overcome concrete overlay limitations. Polyvinylalcohol (PVA) fibers with special coating are typically used as reinforcement of ECC. Although some successful field application of PVAECC, the use of ECC is restrained by the high cost of the material, consequence of high PVA fibers cost. This research is focused on the investigation of using high tenacity polypropylene fibers as reinforcement of engineered cementitious composites (PPECC). Those fibers are produced and available in Brazil for fibrocement industry by less than half price of PVA fibers. PP fibers have demonstrated good performance in reinforcing ECC, assuring composite strain-hardening behavior through the development of multiple cracking processes. An important finding was the tinier crack opening of PPECC – 10 m average- comparing to PVAECC – 60 m average. This result may result in higher material durability. Furthermore, flexural and fatigue behavior or ECCs reinforced with PP fibers were investigated. Results have shown that Portland cement type V (high early strength) is not adequate for PPECCs subject to fatigue loading, resulting in fiber deterioration and premature rupture. By the other hand, promising results were found with cement ordinary type I, usually used in ECC production. A model of service life prediction was developed for PPECC, PVAECC and concrete overlays correlated to overlay thickness. Results have shown that ECCs may reduce overlay thickness in 1.5 to 2.5 times the usual thickness of overlay concrete. Reflective cracking resistance of PPECC was also testes. From the results it is possible to deduce that PPECC may modify typical rupture mode of concrete overlays through the development of multiple cracking. In the last stage of this work, life cycle analyses and life cycle cost analyses of four different overlays systems – concrete, hot mix asphalt, PVAECC and PPECC – were carried out. The results of this study have shown that an ECC overlay system have lower environmental burdens, reducing the energy consumption related to design, construction and maintenance activities, reducing green house effect as well. Life cycle costs analyses over a 40 years service life revealed that PPECC is the most economical overlay system compared to concrete, hot mix asphalt and PVAECC overlay systems. Agency costs are significantly reduced by adopting PPECC overlays. PPECC is a feasible alternative for pavement rehabilitation.

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48

Jeřábek, Jakub [Verfasser]. "Numerical framework for modeling of cementitious composites at the meso-scale / Jakub Jerabek." Aachen : Hochschulbibliothek der Rheinisch-Westfälischen Technischen Hochschule Aachen, 2011. http://d-nb.info/1018218130/34.

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49

Quartarone, Giovanni. "Confinement of masonry columns with Steel Fiber Reinforced Cementitious Matrix (S-FRCM) composites." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2017.

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The rehabilitation of existing masonry elements through jacketing of columns using composite materials is becoming a remarkable technique in several applications that aim to increase the strength of existing masonry building. An experimental campaign was conducted with Steel- and -Basalt Fiber Reinforced Cementitious Matrix (FRCM) systems, in order to test new products that might increase the advantages in terms of good adhesion to masonry substrate, breathability of the system, efficiency in aggressive environments, ease of installation and reversibility, which are essential for the preservation of historical buildings. The mean objective of this experimental study was to investigate the state of the improvement of square masonry columns, built in alternate stretcher and header bond configuration using as material confinement Steel- and-Basalt FRCM system, subjected to axial compression. Moreover, the effectiveness and influence of the confinement in terms of load-bearing capacity and strain distribution with respect to unconfined prisms was carried out. An optical technique, known as Digital Image Correlation (DIC), was employed to understand the interaction between the unit masonry components.

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SOUZA, LETICIA OLIVEIRA DE. "CRACKING MECHANISMS AND AUTOGENOUS HEALING CAPABILITY OF CEMENTITIOUS COMPOSITES REINFORCED WITH CURAUA FABRIC." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2017. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=33404@1.

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PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO
CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO
O presente trabalho tem como objetivo o estudo do comportamento mecânico, os mecanismos de fissuração e a autocicatrização de compósitos cimentícios reforçados com fibras de curauá. Desenvolveram-se três tipos de compósitos distintos, cada um reforçado com uma, três ou cinco camadas de tecido unidirecional de curauá. O comportamento mecânico foi avaliado por meio de ensaios de tração direta e flexão a quatro pontos. Estudaram-se os mecanismos de fissuração por meio de fotografias obtidas ao longo dos ensaios, além de análises por correlação digital de imagens (Digital Image Correlation - DIC). Estágios de carregamento foram identificados e associados com o espaçamento entre as fissuras formadas. Os corpos de prova de flexão foram instrumentados com strain gauges nas faces inferior e superior, a fim de medir as deformações de tração e compressão. Dessa forma, foi possível realizar um estudo sobre o desenvolvimento da linha neutra e correlacionar as deformações com espaçamento entre fissuras. A capacidade de autocicatrização dos compósitos foi avaliada por meio de ensaios mecânicos cíclicos e de carregamento contínuo, e também por acompanhamento da evolução das fissuras. Estas foram monitoradas com o auxílio de microscópio estereoscópico. As amostras foram expostas a diferentes ambientes (seco, ciclos de água borrifada, imersão em água) e a influência deles foi avaliada. Todos os compósitos apresentaram strain/deflection hardening com formação de múltiplas microfissuras. Fissuras na presença de água apresentaram cicatrização total e parcial, demostrando que o material desenvolvido é promissor para a ocorrência de autocicatrização.
The present work aims to study the mechanical behavior, cracking mechanisms and the autogenous healing capability of cementitious composites reinforced with curauá fabric. Composites with one, three and five fabric layers were produced. Their mechanical behavior was evaluated through direct tensile and four point bending tests. The cracking mechanisms were studied using image analysis of both photographs took during the tests and Digital Image Correlation (DIC). Various stages of loading were identified and associate with the crack formation. The effect of flexural cracking on the composite neutral axis position was analyzed using strain-gages and correlated with the crack spacing. The autogenous healing capability of the three layered composite system was analyzed by means of the mechanical behavior, in cyclic bending and constant load tests. The crack evolution was follow with microscope stereoscope. The samples were subject to several conditions (RH of 55 percent, cycles of spayed water, water immersion) and their influence was evaluated. All the composites presented strain/deflection hardening behavior with multiple microcrack formation. Cracks exposed to water were partially or totally healed, demonstrating that three layered composite is a promising material for autogenous healing.

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Dissertations / Theses on the topic 'Cementitious composite'

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