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Autor(a/res): Juliana Malta, Jardel Pereira Gonçalves, Romildo Dias Toledo Filho, Vanessa Silva Silveira
Resumo: The different treatments given to recycled aggregates influence the properties of mortars in fresh and hardened states. As these aggregates have characteristics different from those of natural aggregates, such as high absorption, lamellar form, rough texture and lower density, there is a need to study the different procedures used in the dosage of mixtures containing these residues and their influence on the physical and mechanical behavior of mortars. Two procedures were used in this study: partial compensation of the water absorbed by the recycled fine aggregates (RFA) through their pre-saturation and use of aggregates dried in an oven. The main aim of this study is to evaluate the influence of these dosage procedures on the viscosity, chemically combined water content and compressive strength of mortars containing 25% and 50% of recycled aggregates replacing (by mass) natural aggregates. The results showed that the pre-saturation procedure influences the properties of the mortars in the fresh and hardened states. The presence of the RFA promotes mixtures with higher viscosity, higher content of free water and less resistance to compression.
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Autor(a/res): Paulo Lima, Romildo Dias Toledo Filho, Otavio Gomes
Resumo: In this work it was studied the influence of recycled fine aggregate obtained from construction and demolition waste (CDW) on the rheological properties of Portland cement mortars. The CDW was initially separate in their main constituents (mortar, ceramic and concrete debris) at the laboratory and then grinded separately to the sand size in order to generate more homogeneous fine aggregates. The characterization of the natural and recycled sands was carried out through physical tests, X-ray diffraction, scanning electron microscopy (SEM), and image analysis (shape and texture description parameters). A conventional mortar and three mortars containing recycled sands were produced with a sand/cement ratio of 4 and consistency index of 255±5 mm. The consistency was kept constant by ranging the water-cement ratio from 0.58 to 1.14. The rheological study was performed using a rotating viscometer to obtain torque-rotation ratio and to calculate the yield stress and plastic viscosity. The results indicate that the presence of recycled aggregate causes a lowering of both yield stress and plastic viscosity with respect to the mortar containing natural aggregate.
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Autor(a/res): Lourdes Maria Silva de Souza, Eduardo de Moraes Rego Fairbairn, Romildo Dias Toledo Filho, Guilherme Chagas Cordeiro
Resumo: This work presents the results of a study on the hydration of pastes containing calcium hydroxide and either rice husk ash (RHA) or sugar cane bagasse ash (SCBA) in various initial CaO/SiO2 molar ratios. The products of the reactions were characterized by thermal analyses X-ray diffraction, and scanning electron microscopy. In the case of the RHA pastes, the product was composed of CaO-SiO2-H2O (type I C-S-H) or CaO-SiO2-H2O (type II C-S-H) according to the CaO/SiO2 ratio of the mixture. In contrast, in the case of the SBCA pastes, the product was composed primarily of CaO-SiO2-H2O that differed from both the previous types; the product also contained inclusions of calcium aluminate hydrates.
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Autor(a/res): Margareth da Silva Magalhães, Romildo Dias Toledo Filho, Eduardo de Moraes Rego Fairbairn
Resumo: This paper addresses the results of an investigation on the influence of the Brazilian raw materials on the mechanical performance of Strain Hardening Cementitious Composites (SHCC). The mixtures were produced with variations of fly ash/cement and sand/cement proportions and with different maximum sand particle. Mechanical properties were evaluated by direct tension, bending and compression tests. Crack formation under direct tension and bending loads was also investigated. The results indicate that the use of high quantities of fly ash with low quantities of fine sand is the ideal combination to obtain strain hardening composites with tensile strain capacity superior to 3% using local materials. The increase in the sand content and particle size affects the behavior of the composites and tended to reduce the strain capacity of the specimens by up to 30%. Keeping constant the fly ash/cement and sand/cement rates it was found that the crack density and width measured under direct tension are only affected by the diameter of the sand for tensile strains in the range of 2%. The same general trends were observed for specimens submitted to compressive and bending loads.
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Autor(a/res): Saulo Rocha Ferreira, Andréa Maria da Silva, Fernando Gomes de Souza Jr, Romildo Dias Toledo Filho e Flávio de Andrade Silva.
Resumo: The work at hand presents an experimental investigation on the chemical and mechanical behavior of coir fibers treated with aniline polymerization (PAni), H2O2 and as-received. The fibers were characterized using Fourier transform infrared spectroscopy, X-ray diffraction, thermogravimetry analysis and scanning electron microscopy. The obtained data shows that the presence of H2O2 produces some extension of oxidation of the hydroxyl groups. After the formation of PAni new characteristic bands are formed. Additionally, the electrical resistivities and respective sensitivities to variations of the applied pressure were evaluated. Finally, a state-of-the-art micromechanical testing machine was used to study the tensile behavior of treated and as-received fibers. The cross-sectional area of the fiber was measured using scanning electron microscope micrographs and image analysis. The failure mechanisms are described and discussed in terms of the fiber microstructure.
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