A fibra de sisal é um importante produto agrícola usado na produção de cordas, tapetes e também como reforço de materiais compósitos poliméricos ou cimentícios. Durante sua produção, no entanto, é gerada uma grande quantidade de resíduos que atualmente tem pequeno potencial de aproveitamento comercial. O objetivo deste trabalho é caracterizar os resíduos agrícolas oriundos da produção e beneficiamento da fibra de sisal, denominados refugo e bucha de campo, e verificar a potencialidade de uso como reforço de argamassa. Os resíduos foram tratados com ciclos molhagem-secagem e avaliados através de ensaio de tração direta, microscopia eletrônica de varredura (MEV) e espectroscopia de infravermelho (FTIR). A compatibilidade com matriz a base de cimento foi avaliada através de ensaio de arrancamento de fibra e ensaio de flexão em compósitos reforçados com 2% de resíduos de sisal. Os resultados indicam que o uso do resíduo tratado permite a produção de compósitos com boas propriedades mecânicas, superiores aos compósitos tradicionais reforçados com fibra natural de sisal.

Sisal fiber is an important agricultural product used in the manufacture of ropes, rugs and also as a reinforcement of polymeric or cement-based composites. However, during the fiber production process a large amount of residues is generated which currently have a low potential for commercial use. The aim of this study is to characterize the agricultural residues by the production and improvement of sisal fiber, called field bush and refugo and verify the potentiality of their use in the reinforcement of cement-based composites. The residues were treated with wet-dry cycles and evaluated using tensile testing of fibers, scanning electron microscopy (SEM) and Fourier transform infrared (FTIR) spectroscopy. Compatibility with the cement-based matrix was evaluated through the fiber pull-out test and flexural test in composites reinforced with 2 % of sisal residues. The results indicate that the use of treated residue allows the production of composites with good mechanical properties that are superior to the traditional composites reinforced with natural sisal fibers.

To design building elements using sisal fibre reinforced mortar composites, the stress-strain curves of the composites both under tensile and compression load is needed. In this study short sisal fibre-cement based composites were developed and their stress-strain behaviour under compression characterized experimentally. The composites consisted of two mortar matrices, one self-compacting and one of normal consistency, reinforced with randomly distributed short sisal fibre (25 and 50 mm long) in volume fractions ranging from 2% to 6%. Based on the experimental results a compressive constitutive law for the composites was proposed based on the damage theory developed by Mazars (1986). This theory was used to model the ascending branch of the stress-strain curve and a damage parameter associated to the fibre-reinforcing index is proposed to allow the modelling of the post-peak behaviour of the composites. The modified model was then validated using results available in the literature. The experimental results obtained in the study indicated that the addition of short sisal fibres to cement matrices tends to reduce its elastic modulus, peak stress and strain and to increase its toughness. However, the use of a self-compacting matrix allowed better sisal fiber dispersion and composites with superior performance were obtained. The modified analytical model was able to predict with good accuracy the ascending and descending branch of the stress-strain curves of the sisal fiber-mortar composites and allowed evaluating the effect of fibre reinforcing index on material damage. In the ascending branch, an increase in the damage from 40% to 70% is recorded for fiber volume ranging from 2 to 6%. In the descending branch, on the other hand, the variation of fiber volume allowed a reduction of the damage from 65% to 60%.

O interesse pelo uso de fibras vegetais como reforço de matrizes, à base de cimento, tem crescido em todo o mundo nos últimos anos, sendo limitado pela baixa durabilidade das fibras no meio alcalino. Com o tempo, as fibras podem mineralizar devido à migração de hidróxido de cálcio (CH) da matriz para o lúmen e paredes das fibro-células. Procurou-se consumir, no presente estudo, o CH livre utilizando-se resíduo de tijolo moído e metacaulinita em substituição parcial, de 20 e 40% em peso, do cimento portland. Compósitos com fibras de sisal e matrizes cimento-pozolana foram submetidos a ensaios de resistência a flexão, após 28 dias de cura em água, 135 e 180 dias de envelhecimento natural e após 94 ciclos de molhagem e secagem. Os resultados indicaram que é possível consumir todo o CH da matriz, o que resultou na manutenção da tenacidade inicial do compósito e no aumento da sua resistência a flexão após exposição natural ou ciclos de molhagem e secagem.

In the last few years a growing interest in the use of sisal fibers as reinforcement in cement based composites has been observed. However, the main concern for its use is related with the durability of the fibers in the alkaline water of concrete as they can mineralize due to the migration of calcium hydroxide to the fiber lumen and cell walls. In this study, the alkalinity of the matrix was reduced using metakaolin and crushed waste calcined clay bricks as cement replacement. The percentage of cement replacement ranged from 20 to 40% on weight basis. Flexural tests were carried out in the composites after 28 days of cure in water, 135 and 180 days of ageing in the open air and after 94 cycles of wetting and drying. These results indicated that the mixture with cement replacement consumed all calcium hydroxide and kept the toughness over time.

Durable sisal fiber cement composites reinforced with long unidirectional aligned fibers were developed and their mechanical behavior was characterized in a multi-scale level. Tensile tests were performed in individual sisal fibers. Weibull statistics were used to quantify the degree of variability in fiber strength at different gage lengths. The fiber-matrix pull-out behavior was evaluated at several curing ages and embedded lengths. The composite's mechanical response was measured under direct tension while crack formation was investigated using a high resolution image capturing procedure. Crack spacing was measured using image analysis and correlated with the applied strain under both the tensile and bending response.

Com a proibição progressiva do uso de fibras de asbesto na fabricação de laminados à base de cimento, novos produtos têm sido desenvolvidos para suprir esta demanda do setor construtivo. A utilização de fibras de sisal como substituto ao asbesto, além de ser uma proposta ecológica tem grande importância socioeconômica, pois agregará valor a um produto cultivado com sucesso no semi-árido nordestino. Produziram-se, neste trabalho, placas laminadas com matriz de argamassa reforçadas com fibras longas de sisal. Ensaios de flexão em três pontos foram realizados com o objetivo de se estudar a influência da adição de fibras (3%), do número de camadas (2 e 3), da orientação das camadas (0 e 90°) e da pressão de moldagem (0 e 2 MPa) sobre o comportamento à flexão dos laminados. Os resultados indicam que a adição de fibras de sisal aumentou, para todos os casos estudados, a capacidade de absorver energia, a resistência à flexão pós-fissuração e a deflexão última do material. Os laminados reforçados com 3% de fibras de sisal, distribuídas em três camadas ortogonais à direção do carregamento e submetidos à pressão de moldagem de 2 MPa, apresentaram o melhor comportamento mecânico.

Because of hazards to human and animal health, the use of asbestos and its products is being prohibited all around the world and academic institutions and fibre cement producers have been engaged in intensive research to find asbestos-free cement products. The application of natural fibres such as sisal to replace asbestos fibres can bring economical and ecological benefits due to their availability, low cost, low consumption of energy and suitability to the semi-arid area of the Northeast of Brazil (where not many plants can grow). In this paper, cement-based laminates reinforced with continuous sisal fibre were produced. Three point bending tests were carried out to evaluate the influence of addition of fibre (3%), number of layers of reinforcement (2 and 3), fibre orientation (0 and 90°) and moulding pressure (0 and 2 MPa) on the flexural behaviour of the laminate. The results indicate that the fibre addition increased the toughness and post-cracking flexural strength of all composites studied. The laminate reinforced with 3% of sisal fibre arranged in three parallel layers and moulded at a compression pressure of 2 MPa presented the best mechanical behaviour.

Objetivando contribuir para maior conhecimento sobre as essências arbóreas existentes no nordeste brasileiro, buscou-se através deste trabalho determinar as características tecnológicas da algaroba (Prosopis juliflora (Sw.) DC e indicar alternativas de uso de sua madeira para construções rurais. A caracterização da espécie foi feita conforme valores, referentes à condição padrão de umidade (12%), obtidos em ensaios realizados de acordo com a NBR 7190 da Associação Brasileira de Norma Técnicas. Foram realizados ensaios de densidades básica e aparente, teor de umidade e de resistência à compressão paralela, tração paralela e cisalhamento, paralelo às fibras. Os resultados foram analisados pela comparação dos valores obtidos com aqueles encontrados na literatura, para outras madeiras. De acordo com os resultados, conclui-se que a madeira da algaroba se equipara em resistência e rigidez, às madeiras tradicionalmente utilizadas nas construções, no Brasil.

This work was carried out with the objective of increasing the knowledge on the existing wild trees species in north-eastern Brazil. The main purpose was to determine the technological characteristics of the Prosopis juliflora (Sw.) DC and to indicate alternative use of its wood for agricultural constructions. The procedures adapted for the characterization of the species were in agreement with the Brazilian Norm 7190 of Brasilian Association of Technical Norms referring to the standard conditions moisture content of 12%. Tests of basic and apparent densities were carried out, moisture content and parallel fibers resistance to compression, traction and shear, were measured. The results were analyzed through the comparison of the values obtained with those found in literature for other kinds of wood. In agreement with the results, it was concluded that the Prosopis juliflora's wood can be compared with other traditional kinds of wood used in Brazil.