Navegando por Assunto "Silica ativa"

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Acesso aberto (Open Access)
Compósitos cimentícios reforçados com fibras de curauá (Ananas erectifolius) impregnadas com sílica ativa
(Universidade Federal do Pará, 2019-02-01) PINTO, Renata Godinho; PICANÇO, Marcelo de Souza; http://lattes.cnpq.br/4535052395600357
Vegetal fibers are an alternative for reinforcement in cementitious mortars, unlike the synthetic fibers, they are renewable, biodegradable and low cost. The great limitation of these composites concerns the low durability of the fibers inserted in the cementitious matrix. Therefore, the present research aim to analyze the properties of reinforced mortars with curaua fibers previously impregnated with silica fume. The mix design ratio of the composites was determined with a pilot study. The composites were prepared with mix design ratio 1:3:0.61 and with addition of 2% fibers with 25 mm length. Six families were molded using CP-IV cement and CP-II E. The properties of the composites were verified at 28 days and after natural aging at 180 and 270 days. The characteristics of the curaua fiber used were: density of 1.33 g/cm³, tensile strength of 422.89 MPa and modulus of elasticity of 28.83 GPa. For compressive strength, the composites fibers previous treatment provided a better result than that obtained for mortars with natural fibers. For the tensile strength, inclusion of fibers provided the desired reinforcement improving this property in 45 %. The modulus of elasticity indicated that the addition of the fibers reduced the stiffness of the material. For flexural strength the composite AFCS:IV showed a 57.95 % increase compared to the reference, but it was identified with the natural aging the decrease of the resistance for composites with untreated fibers. The proposed treatment was effective to preserve the toughness of the composites after natural aging. Due to the composites X-ray diffraction, it was verified that the previous treatment of the fibers was effective in limiting the formation of the portlandite in the matrix. This corroborates with micrographs of the mortars, where degradation signals were identified in composites with untreated fibers, while the previously treated fibers remained intact even after natural aging. Thus, it can be considered that the impregnation of the fibers with silica fume improved the properties of the composites and increased the durability of the curaua fibers.
Acesso aberto (Open Access)
Compósitos cimentícios reforçados com fibras do epicarpo do coco babaçu para aplicação em placas cimentícias.
(Universidade Federal do Pará, 2022-08-25) ARAÚJO, Myrela Vieira de; SANTANA, Audirene Amorim; http://lattes.cnpq.br/7431678688628387; PICANÇO, Marcelo de Souza; http://lattes.cnpq.br/4535052395600357
The search for new materials for civil construction based on renewable sources has contributed to sustainable development. Lignocellulosic fibers are possibilities for strengthening cementitious mortars, since they are low cost, easy to reach, and renewable, unlike artificial fibers. However, when added to the cement matrix, they reach low durability and undergo degradation. Thus, the present research aimed to analyze the physical, mechanical, morphological and mineralogical properties of cement composites reinforced with fibers from the epicarp of the babassu coconut of the species Attalea Speciosa Mart. Ex Spreng in 0natura and impregnated in silica fume paste. The composites trace was established through a pilot study, using the trace 1:3:0.62 and addition of 1% of fibers with length ≤ 25 mm. Three families of mortar were molded, the first without the addition of fibers (REF), the second with the addition of in natura fibers (AFST) and the third with the addition of treated fibers (AFCT). The babassu coconut epicarp fibers had a specific mass of 1.398 g/cm³, a moisture content of 6.93% and an average tensile strength of 141.9 MPa. After 28 days of wet curing, the properties of the composites were analyzed, reaching an increase of 46.68% for theflexural tensile strength after the addition of in natura fibers and for composites with treated fibers a decrease of 14.16%. For the apparent density, both AFST and AFCT conditions, there was a decrease in the property and in the water absorption, there was an increase of 8.20% and 11.49%, respectively. In the permeability test, there was no formation of droplets in all samples and the thermometry analysis showed fiber compatibility with the cement. Through the micrographs of the mortars, it was observed in the AFST samples the presence of waxes that offer protection against water penetration, while in the AFCT samples there was a loss of waxes. From the diffractograms, it was verified that the impregnation of the fibers in silica paste caused the loss of calcite and portlandite, producing samples with greater porosity. Thus, the addition of fibers in natura provided improvements in the properties of the composites, but the treatment in silica fume paste caused a decrease in properties, not being suitable for use.
Acesso aberto (Open Access)
Dosagem experimental de concreto massa com adição de sílica ativa aplicado em barragem
(Universidade Federal do Pará, 2017-11-10) SOUZA, Grazielle Tigre de; GOUVEIA, Fernanda Pereira; http://lattes.cnpq.br/1772072130947378
The study of concrete dosage for large constructions, specifically of dams, has its own peculiarities due to the large volumes involved, intensifying the care with the supply and quality of materials used for these concretes, compositions with pozzolan additions are generally used in order to reduce the heat of hydration. In this sense, the main objective of this research is the elaboration of a mix design of concrete with the substitution of 8% of the cement per silica fume, the experimental study of the mix design was based on the Method of the Fineness Module of the Aggregates. To meet the proposal of this research, the methodology based primarily on the characterization of concrete constituent materials (fine and coarse aggregates, and silica fume), concrete mix design study by the Method of the Fineness Module (MFM) and subsequent analysis of the properties of the concrete mass obtained, making it possible to elaborate the concrete mix design, according to the requirements specified in the design of hydroelectric power plant structures. In this sense, with regard to the characterization of the aggregates, the results demonstrated the feasibility of the use of these in the production of concrete for dams. In relation to cement and silica fume the characteristics of these materials attend the normative requirements. The experimental dosage based on the MFM method, made it possible to compose the dosage graphs needed to define the mix design of concretes and consequently the verification of their applications in dams. It can be affirmed, thus, that the MMF approach developed in this research can be considered an important contribution, for the dissemination of the dosage methodology for concrete application in dams.