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Autor(a/res): Maria Fidelis, Flávio de Andrade Silva, Romildo Dias Toledo Filho
Resumo: In the present work a natural textile reinforced concrete (TRC) was developed and mechanically characterized. A fabric made of jute, a natural occurring fiber, was used as reinforcement in a fine grained cementitious matrix with a low content of calcium hydroxide. Tensile tests were performed on TRC reinforced with 3 and 5 layers of jute fabric. The mechanical tensile tests were coupled with image analysis in order to measure the crack spacing and the results were correlated with the applied tensile strain. Various stages of loading corresponding to initiation, propagation, distribution, opening, and localization of a crack system in the specimen are discussed. In order to improve the fiber-matrix interface the jute fabric was treated with a polymer based coating.
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Autor(a/res): Juliana C. Ferreira, Thiago M. Grabois, Gabrielle C.S. Calcado, Romildo D. Toledo Filho
Resumo: In this paper it was investigated how the use of recycled fine aggregate influences the stress-strain behavior of mortar mixtures with different strengths. The mix design composition of the studied mortars, expressed by mass, were 1:2:0.45, 1:4:0.68 and 1:6:1.05 (cement: sand: water/cement ratio). The substitution percentages by mass of the natural aggregate by recycled aggregate were 15, 25 and 50%. The recycled aggregate had a grain size distribution comparable to that of natural sand and was obtained by grinding the waste produced by the partial demolition of UFRJ’s University Hospital. The mortars were evaluated under uniaxial compressive strength test after 28 days of curing. The results indicated that for the two higher strength classes the substitution rates affects its mechanical response by decreasing the strength. Besides, for the lower strength class the recycled aggregate could promote an increase of strength in the case of 25% of replacement.
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Autor(a/res): F Vitorino; RD Toledo Filho
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Autor(a/res): Daniel de Lima Araújo, Fernanda Gabrielle Tibúrcio Nunes, Romildo Dias Toledo Filho, Moacir Alexandre Souza de Andrade
Resumo: This study analyzed the mechanical behavior of shear strength of steel fiber-reinforced concrete beams. Six beams subjected to shear loading were tested until failure. Additionally, prisms were tested to evaluate fiber contribution to the concrete shear strength. Steel fibers were straight, hook-ended,35 mmlong and aspect ratio equal to 65. Volumetric fractions used were 1.0 and 2.0%. The results demonstrated a great contribution from steel fibers to shear strength of reinforced concrete beams and to reduce crack width, which can reduce the amount of stirrups in reinforced concrete structures. Beam capacity was also evaluated by empirical equations, and it was found that these equations provided a high variability, while some of them have not properly predicted the ultimate shear strength of the steel fiber-reinforced concrete beams.
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Autor(a/res): Maria Gorett dos Santos Marques, João de Almeida Melo Filho, Julio Cesar Molina, Romildo Dias Toledo Filho, Raimundo Pereira de Vasconcelos, Carlito Calil Junior
Resumo: Composites of high mechanical performance reinforced by fibers need a well set arrangement of them in the matrix so that under reinforcement which they can be submitted, a desirable performance can be shown. Thus, the cement composite studied has a cement matrix which received a reinforcement made by arumã fibers, shaped in bidirectional frames distributed in three layers. Arumã is a typical plant from the Amazon, species from the genus Ischnosiphon polyphyllus, part of the family Marantaceae. This study had the purpose of assessing the cement composites mechanical behaviour from the bending tests in four points and puncture tests in sheets which were supported by the four edges. Having presented mechanical results, a numerical simulation was made through the SAP2000 NonLinear® software, with the aim to obtain a numerical computational model able to represent the composites behaviour up to the point where the loading reaches the greatest amount. The numerical results present a good correlation with those obtained in the experimental tests.
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