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Autor(a/res): Saulo Rocha Ferreira, Paulo Lima, Flávio de Andrade Silva e Romildo Dias Toledo Filho.
Resumo: Cycles of wetting and drying can change the microstructure of vegetable fibers through a mechanism known as hornification, which modifies the polymeric structure of the fiber-cells resulting in a higher dimensional stability. In the present work the influence of hornification on the sisal fiber-matrix bond adhesion as well as in the sisal fiber dimensional stability and mechanical behaviour under direct tension was evaluated. Furthermore, cementitious composites reinforced with randomly dispersed hornified sisal fibers were developed and characterized under bending loads. The results show that the tensile strength and strain at failure of the hornified sisal fibers were increased by about 5% and 39%, respectively, whereas the modulus of elasticity was reduced by 9%. The fibers also presented higher dimensional stability with the hornification process. The fibermatrix bonding was improved and the pull-out resistance of the fibers submitted to ten cycles of wetting and drying was increased by about 40% to 50%. The higher fiber-matrix bond strength contributed to an increase in the ductility and post-cracking behaviour of the composite. The fracture process was characterized by the formation of multiple cracks with the hornified sisal fibers presenting a higher ability to bridge and arrest the cracks.
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Autor(a/res): Dimas Alan Strauss Rambo, Flávio de Andrade Silva e Romildo Dias Toledo Filho.
Resumo: In the present work the effect of steel fiber hybridization on the mechanical and rheological behavior of self-consolidating concretes was studied. Straight and hooked end steel fibers with different lengths and diameters were used as reinforcement in fiber volume fractions of 1.0% and 1.5%. The viscosity and shear yield stress of the concretes was determined using a parallel plate rheometer. The mechanical behavior was determined by means of compression, tension and bending tests. The movement of the neutral axis under bending load was experimentally determined by strain-gages attached to compression and tensile surfaces. The mechanical response of the material under bi-axial bending was addressed using the round panel test in three different boundary conditions. The obtained results indicated that the fiber hybridization improved the behavior of the composites for low strain and displacement levels increasing the serviceability limit state of the same through the control of the crack width.
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Autor(a/res): Flávio de Andrade Silva, Marko Butler, Simone Hempel e Romildo Dias Toledo Filho.
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Autor(a/res): Marco Pepe, Romildo D. Toledo Filho, Eduardus A.B. Koenders e Enzo Martinelli.
Resumo: As sustainability is becoming a fundamental requirement for all modern industrial activities, upcoming environmental research efforts should be intended at both enhancing the efficiency in the use of raw materials and reducing the carbon footprint. The present research activity has been launched at the Federal University of Rio de Janeiro (UFRJ, Brazil) for demonstrating the feasibility of “ecological concrete” for structural use, characterised by a significant replacement of natural aggregates with recycled ones, which are produced from processing Construction Demolition Waste (CDW). Particularly, this work explores alternative processing procedures and investigates their influence on the relevant physical and mechanical properties of the resulting aggregates and concrete mixtures. Therefore, particle size distribution, bulk density attached mortar content as well as the associated water absorption capacity of recycled aggregates were monitored to scrutinise the effect of such processing procedures. Subsequently, a series of concrete batches was produced for evaluating the influence that alternative processing procedures for recycled aggregates have on the main mechanical performance in a fresh and hardened state. Results reported in this paper show the feasibility of “autogenous cleaning”, which removes surface impurities and reduces particle heterogeneities, usually characterising the morphology of a recycled aggregate matrix. It shows that the considered cleaning procedure significantly reduces the gap between the performance of recycled aggregate concrete (RAC) and ordinary ones, both in terms of workability at the fresh state and strength at the hardened state of concrete mixtures.
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