Thesis (Ph. D.)--University of New South Wales, 2005. / Also available online.

Thesis (Ph.D.)--Civil and Environmental Engineering, Georgia Institute of Technology, 2008. / Committee Co-Chair: Kahn, Lawrence F.; Committee Co-Chair: Zureick, Abdul-Hamid; Committee Member: Armanios, Erian A.; Committee Member: Gentry, Russell T.; Committee Member: Leon, Roberto T.

Thesis (M.S.)--Florida State University, 2006. / Advisor: Kamal Tawfig and Primus Mtenga, co-advisors, Florida State University, College of Engineering, Dept. of Civil & Environmental Engineering. Title and description from dissertation home page (viewed Sept. 15, 2006). Document formatted into pages; contains ix, 87 pages. Includes bibliographical references.

Thesis (M.S.)--West Virginia University, 2006. / Title from document title page. Document formatted into pages; contains xi, 117 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 115-117).

Orientador: Itamar Ferreira / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecanica / Made available in DSpace on 2018-08-13T02:49:59Z (GMT). No. of bitstreams: 1 Carnio_MarcoAntonio_D.pdf: 4129193 bytes, checksum: 27ed4b4a807f05043017033527f2d6f8 (MD5) Previous issue date: 2009 / Resumo: O concreto reforçado com fibras (CRF) é um compósito constituído de duas fases: concreto (matriz) e fibras (reforço). As fibras são elementos descontínuos de vários aspectos geométricos e materiais, destacando-se atualmente as fibras metálicas (aço) e as fibras sintéticas (polipropileno). Em geral, os teores de fibras em volume adicionados à matriz se dividem em: baixos teores - até 0,5%; médios teores - entre 0,5% e 1% e altos teores - acima de 1%. Dentre as aplicações do CRF com baixos teores, a utilização em pavimentos de concreto é a mais significativa, cuja solicitação predominante é cíclica. O estudo da fadiga se divide em iniciação da trinca, propagação da trinca e fratura final, e a vida em fadiga (Nf) é caracterizada pela soma do número de ciclos até a fratura. Dessa forma, como no estudo da fadiga do CRF a maioria dos trabalhos se concentra na obtenção de seu comportamento por meio das curvas S-N (tensão em função do número de ciclos até a fratura), este trabalho tem como objetivo estudar experimentalmente a propagação da trinca por fadiga dos CRFs com baixos teores, por meio de ensaios de flexão em corpos-de-prova prismáticos de seção quadrada, submetidos a carga cíclica com freqüência de 20 Hz e razão de carga R = 0,1, representando seu comportamento pelas curvas da/dN-_K (taxa de propagação de trinca por fadiga em função da variação do fator de intensidade de tensão), ensaios de flexão em corpos-de-prova prismáticos de seção quadrada, submetidos a carga monotônica, representando seu comportamento pelas curvas carga monotônica-deslocamento de abertura da boca da trinca (CMOD) e o estudo macroscópico da seção fraturada desses concretos, após cargas cíclicas e monotônica para avaliação dos mecanismos de fratura da seção, visando melhor entender a contribuição dessas adições nos CRFs submetidos a cargas cíclicas. Os resultados indicam que o CRF com fibras de polipropileno de 54 mm apresenta melhor desempenho à propagação de trinca por fadiga, com comportamento equivalente aos CRFs com fibras de aço de 60 mm e que, o CRF com fibras de aço de 35 mm apresenta melhor desempenho dentre todos tipos e teores de fibras estudadas. Quanto ao comportamento à carga monotônica, o desempenho dos CRFs com fibras de aço de 60 mm se mostrou melhor dentre os estudados, desempenho esse não confirmado quanto à propagação de trinca por fadiga. Também se conclui que a ancoragem das fibras interfere no comportamento dos CRFs às cargas monotônica e cíclica, sendo que a degradação da ancoragem mecânica nas fibras de aço submetidas a cargas cíclicas penaliza mais os CRFs com fibras de aço de 60 mm quanto ao desempenho à propagação de trinca por fadiga. Na avaliação da superfície de fratura dos CRFs, verificou-se que a adição de fibras interfere nessa superfície, apresentando-se mais plana para os CRFs com fibras sintéticas e mais irregular para os CRFs com fibras de aço. / Abstract: The fibers reinforced concrete (FRC) is a composite formed by two phases: concrete (matrix) and fibers (reinforce). The fibers are discontinuous elements of several geometric aspects and materials, currently detaching the metal fibers (steel) and the synthetic fibers (polypropylene). In general, the contents of fibers in volume added to the matrix are separated in: low contents - up to 0.5%; medium contents - between 0.5% and 1% and high contents - above 1%. Among the applications of the FRC with low contents, the usage in concrete pavements is the most significant, which predominant request is cyclic. The study of fatigue is divided into initialization of crack, propagation of crack and final fracture and the life in fatigue (Nf) is characterized by the sum of number of cycles up to the fracture. In this way, as in the study of fatigue of FRC the majority of the work focuses on obtaining their behavior through the S-N curves (tensile due to the number of cycles up to the fracture) this work has as objective to study experimentally the fatigue crack propagation of the low contents FRC, by means of testing the flexure in prismatic samples of square section, subjected to a cyclic load of 20 Hz frequency and load ratio R=0.1, representing their behavior through the da/dN-_K curves (rate of fatigue crack propagation in lights of the variation of the intensity of the tensile), by testing the flexure in prismatic samples of square section, subjected to a monotonic load, representing their behavior through the curves monotonic load - cracking mouth opening displacement (CMOD) and the macroscopic study of the fracture section, to better understand the contribution of these additions into the FRC subjected to a cyclic load. The results indicate that the FRC with synthetic fibers of 54 mm size shows a better performance for fatigue crack propagation, with equivalent behavior as of the FRCs with steel fibers of 60 mm size and that the FRC with steel fibers of 35 mm size shows even a better performance among all types and contents of fibers studied. About the behavior of the monotonic load, the performance of the FRCs with steel fibers of 60 mm size was better among all studied behaviors, but that performance is not confirmed regarding the fatigue crack propagation. Also concludes that the anchorage of the fibers interfere in the behavior of both FRC subjected to monotonic load and cyclic load, and the degradation of the mechanic anchorage in the steel fibers, subjected to a cyclic loads punish more the FRCs with the steel fibers of 60 mm regarding to their performance of fatigue crack propagation. Evaluating the fracture surfaces of the FRC, verify that the addition of fibers interfere on these, resulting in a more flat to the FRC with synthetic fibers and more irregular to the FRCs with steel fibers. / Doutorado / Materiais e Processos de Fabricação / Doutor em Engenharia Mecânica

Este trabalho apresenta um estudo para a previsão de comportamento quanto à fissuração e seu controle pelo uso das fibras de aço, em elementos de superfície de concreto restringidos, ou seja, submetidos às tensões de tração induzidas pela retração restringida. Neste estudo, foi desenvolvido um método analítico para calcular o consumo de um determinado tipo de fibra de aço em função do potencial de retração da matriz de concreto e da máxima abertura de fissura, determinada em função de parâmetros de durabilidade e aceitabilidade sensorial. Posteriormente, foram realizados ensaios para caracterização do potencial de fissuração de matrizes de concreto utilizadas em obras de elementos de superfície, onde testou-se um método de estimativa das tensões induzidas por retração restringida no concreto, no momento da primeira fissura. Na etapa final do trabalho, foi realizado um programa experimental, com a construção de pistas de concreto reforçado com fibras de aço (CRFA), com consumos de fibras de 10 kg/m3, 30 kg/m3 e 60 kg/m3, construídas sobre bases com duas condições de restrição: superfície desempenada e superfície jateada com exposição dos agregados. A fissuração destas pistas, nas primeiras idades, foi monitorada através da medida da abertura e do comprimento das fissuras. Com os resultados desta etapa experimental, foi realizada uma retroanálise do método onde concluiu-se que a consideração de valores característicos na previsão da resistência à tração do concreto era um ajuste necessário e coerente com a observação prática. Com o ajuste, os resultados experimentais de abertura de fissura ficaram dentro da faixa de previsibilidade do método, considerando um intervalo de confiança de 90%. Com o desenvolvimento deste método, buscou-se contribuir para a aplicação do CRFA no controle da fissuração por retração restringida de elementos de superfície, ampliando a fronteira do conhecimento no aspecto da escolha e dosagem da fibra para um determinado desempenho esperado quanto à fissuração. / This work presents a study for crack prediction and use of steel fibers to crack control in concrete surface elements submitted to tension stress induced by restrained shrinkage. In this study, a method was developed where a certain steel fiber type could be quantified, as function of concrete matrix shrinkage potential and maximum crack width, determined from human sensorial and durability criteria. Afterwards, an experimental program was done in order to characterize the crack potential of concrete matrices commonly used in surface elements. In this program, a method to predict tension stress induced by restrained shrinkage, at first crack moment, was tested. In the final step of this work, another experimental program was done, where steel fiber reinforced concrete (SFRC) tracks were built, with fiber contents of 10 kg/m3, 30 kg/m3 and 60 kg/m3, over substrates with two restriction conditions: smooth surface and rough surface, with exposition of surface aggregates. Lengths and widths of the early age shrinkage cracks in the tracks were monitored. The results obtained in this program were useful to analyze the method, adjusting it with the consideration of characteristic values in prediction of tension strength. With this adjust, experimental crack width results were more compatible with 90% confidence interval for crack width values predicted by the method. With this study, the goal was the contribution to use SFRC in the control of restrained shrinkage cracks in surface elements, amplifying the knowledge border in the aspect of fiber selection and proportioning, for a determined and expected performance in terms of crack width.

Cuenca Asensio, E. (2012). ON SHEAR BEHAVIOR OF STRUCTURAL ELEMENTS MADE OF STEEL FIBER REINFORCED CONCRETE [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/18326 / Palancia

Concrete technology has been in changeful evolution since the Roman Empire time. It is remarkable that the technological progress became of higher magnitude from the second part of the XX Century. Advances in the development of new cements, the appearance of the fibers as a reinforcement for structural applications, and specially the grand progress in the field of the water reducing admixtures enabled the emergence of several types of special concretes. One of the lasts is the Ultra High Performance Fiber Reinforced Concrete (UHPFRC), which incorporates advances of the Self-Compacting Concrete (SCC), Fiber-Reinforced Concrete (FRC) and Ultra High Strength Concrete (UHSC) technology. This exclusive material requires a detailed analysis of the components compatibility and a high control of the materials and processes. Mainly patented products have been used for the few structural elements carried out so far today, but the costs makes doubtful the development of many other potential applications. In accordance with the previously explained, a simplification of the UHPFRC components and processes is needed. This becomes the first main goal of this Ph.D. thesis, which emphasizes in the use of local available components and simpler mixing processes. Moreover, the singular properties of this material, between ordinary concrete and steel, allow not only the realization of slenderer structures, but also the viability of new concepts unthinkable with ordinary concrete. In this field is focused the second part of the Ph.D. thesis, which develops a bolted connection system between UHPFRC elements. This research summarizes, first of all, the subfamilies belonging to the HPC-UHPC materials. Afterwards, it is provided a detailed comparison between the dosage and properties of more than a hundred of mixtures proposed by several authors in the last ten years of technology. This becomes a useful tool to recognize correlations between dosages and properties and validate or no preconceived ideas about this material. Based on this state of art analysis was performed the later development of mixtures, on Chapter 4, which analized the effect of use of simpler components and processes on the UHPFRC. The main idea was use local components available in the Spanish market, identifying the combinations that provide the best rheological and mechanical properties. Steam curing use was avoided since a process simplification is intended. Diferent dosages were developed to be adapted to various levels of performance, and always trying to be as economical as possible. The concretes designed were selfcompacting and mainly combined two fiber types (hybrid), as the flexural performance was of greater relevance. The compressive strength obtained varied in the range between 100 and 170 MPa (cube L=100 mm), and the flexural strength between 15 and 45 MPa (prism 100 x 100 x 500 mm). Some of the components introduced are very rarely used in UHPFRC, as limestone coarse aggregate or FC3R, a white active residue from the petrol industry. As a result of the research, some simple and practical tips are provided for designers of UHPFRC dosage. At the end of this chapter, five dosages are characterized as examples of useful concretes for different requirement applications. In a second part, the idea of a bolted joint connection between UHPFRC elements was proposed. The connection system would be especially useful for struts and ties elements, as truss structures. The possible UHPFRC failure modes were introduced and two different types of tests were designed and performed to evaluate the joint capacity. The geometry of the UHPFRC elements was modified in order to correlate it with the failure mode and maximum load reached. Also a linear finite element analysis was performed to analyze the UHPFRC elements connection. This supported the results of the experimental tests to deduce formulations that predict the maximum load for each failure mode. Finally, a real size truss structure was assembled with bolted joints and tested to verify the good structural behavior of these connections. To conclude, some applications designed and developed at the Universitat Politècnica de València with the methods and knowledge acquired on UHPFRC are abstracted. In many of them the material was mixed and poured in a traditional precast concrete company, providing adequate rheological and mechanical results. This showed the viability of simpler UHPFRC technology enabling some of the first applications in Spain with this material. / Camacho Torregrosa, EE. (2013). Dosage optimization and bolted connections for UHPFRC ties [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/34790 / TESIS

In order to study the mechanical performance of dry-cast synthetic fiber reinforced concrete (SynFRC), samples of varying geometry, fiber content, and environmental exposure were developed and tested using the modified indirect tensile test. The samples created consisted of three different thicknesses (with two different geometries), and six different fiber contents that differed in either type, or quantity, of fibers. Throughout the duration of this research, procedures for inflicting detrimental materials into the concrete samples were employed at a number of different environments by implementing accelerated rates of deterioration using geometric adjustments, increased temperature exposure, wetting/drying cycles, and preparation techniques. The SynFRC samples studied were immersed in a wide range of environments including: the exposure of samples to high humidity and calcium hydroxide environments, which served at the control group, while the sea water, low pH, and barge conditioning environments were used to depict the real world environments similar to what would be experienced in the Florida ecosystem. As a result of this conditioning regime, the concrete was able to imitate the real-world effects that the environments would have inflicted if exposed for long durations after an exposure period of only 20-24 months. Having adequately conditioned the samples in their respective environments, they were then tested (and forensically investigated) using the modified indirect tensile testing method to gather data regarding each sample’s toughness and load handling capability. By analyzing the results from each sample, the toughness was calculated by taking the area under the force displacement curve. From these toughness readings it was found that possible degradation occurred between the fiber-matrix interface of some of the concrete samples conditioned in the Barge environment. From these specimens that were immersed in the barge environment, a handful of them exhibited multiple episodes of strain softening characteristics within their force displacement curves. In regard to the fibers used within the samples, the PVA fibers tended to pull off more while the Tuff Strand SF fibers had the highest tendency to break (despite some of the fibers showing similar pull off and breaking failure characteristics). When it comes to the overall thickness of the sample, there was clear correlation between the increase in size and the increase in sample toughness, however the degree to which it correlates varies from sample to sample. / Includes bibliography. / Thesis (M.S.)--Florida Atlantic University, 2020. / FAU Electronic Theses and Dissertations Collection

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