Autor(a/res): João Queiroz Krause, Flávio de Andrade Silva, Khosrow Ghavami, Otávio da Fonseca Martins Gomes, Romildo Dias Toledo Filho

Resumo: This paper reports the experimental results of the investigation on the microstructure of Dendrocalamus giganteus bamboo laminae and the influence on its mechanical properties. The laminae were extracted from the central culm sector and from specific wall thickness positions in order to identify the fiber volume fraction, porosity and other matrix constituents, due to the functionally gradient characteristic. Samples were prepared from each set of laminae, both for microanalysis and for mechanical testing, under proposed configurations. The microscale morphology was observed and characterized both qualitatively and quantitatively through transmitted and reflected light microscopy, scanning electron microscopy and X-ray microtomography. An original method was proposed to quantify porosity through a humidity variation test. Tension and compression tests were carried out and their results were discussed with respect to the bamboo microstructure. Additionally the modes of failure were registered and analyzed. Results show that voids constitute an expressive portion of the culm. The mechanical properties are dictated by the fiber volume fraction when the specimens were tested under tensile load and by the density variation when tested under compressive load.

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Autor(a/res): G.C. Cordeiro, L.M. Tavares, R.D. Toledo Filho

Resumo: Selective grinding was identified as a potential technology to reduce the content of quartz in sugar cane bagasse ash (SCBA), so as to assist in developing an improved supplementary cementitious material. The selective grinding strategy comprised of a ball mill and two classifiers, where a quartz-rich waste is discharged as a coarse waste by the first one. The amenability of two distinct SCBA samples to selective grinding was first demonstrated on the basis of measurements of strength of individual particles. The samples were then analyzed with respect to chemical and mineralogical compositions and pozzolanic activity. Results showed that the quartz content decreased significantly as a result of selective grinding and classification, thus increasing the amorphous content and, consequently, the pozzolanic activity for both of the studied SBCA samples. Moreover, good correlations were observed between the amorphous content and SCBA reactivity considering electrical conductivity and pozzolanic activity index tests.

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Autor(a/res): Saulo Rocha Ferreira, Enzo Martinelli, Marco Pepe, Flávio de Andrade Silva, Romildo Dias Toledo Filho

Resumo: This paper analyzes the bond behavior of natural fibers in cement-based matrix. First, it presents the results of pull-out tests carried out on jute fibers embedded in a cementitious mortar. Then, the experimental results are employed in identifying the bond-slip relationship which describes the interaction between fiber and matrix. A theoretical model, capable of simulating the various stages of a pull-out test, is formulated and applied for an inverse identification of the bond-slip law. Finally, the obtained results demonstrate the soundness of the proposed theoretical interpretation for the bond behavior of jute fibers embedded in a cementitious matrix.

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Autor(a/res): Vivian Karla Castelo Branco Louback Machado Balthar, Romildo Dias Toledo Filho, Eduardo de Moraes Rego Fairbairn e Cristiane Richard de Miranda.

Resumo: In a deepwater environment, unconsolidated formations at seabed and naturally fractured carbonates at reservoir zones with high permeability are commonly found. In this context, the use of lightweight slurries is necessary to effectively cementing these formations, in order to mitigate slurry losses to the formations and to prevent their fracture. This work investigates the mechanical properties and durability of high performance lightweight slurries to be used in this environment. The mixtures were formulated within the framework of the Compressible Packing Model and were extended using hollow ceramic or glass microspheres. Tests were carried out to determine the slurries apparent density, rheology, free fluid, sedimentation, fluid loss, resistance to acid attack, sorptivity and total water absorption. A mechanical characterization was performed by uniaxial and triaxial compression and splitting tensile strength tests and were correlated with the durability tests. The reference slurry, extended with bentonite, presented a 1.46 g/cm3 density and compressive strength of 3 MPa (cure at 27oC/ 2.7 days). The slurries containing glass and ceramic microspheres were slightly lighter and presented a higher mechanical performance as compared to ordinary slurry. Besides, these mixtures presented a higher resistance to acid attacks and lower sorptivity, especially the lightweight slurry containing ceramic microspheres.

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