Paulo Roberto Lopes Lima

Recycled lightweight concrete made from footwear industry waste and CDW

In this paper two types of recycled aggregate, originated from construction and demolition waste (CDW) and ethylene vinyl acetate (EVA) waste, were used in the production of concrete. The EVA waste results from cutting off the EVA expanded sheets used to produce insoles and innersoles of shoes in the footwear industry. The goal of this study was to evaluate the influence of the use of these recycled aggregates as replacements of the natural coarse aggregate, upon density, compressive strength, tensile splitting strength and flexural behavior of recycled concrete. The experimental program was developed with three w/c ratios: 0.49, 0.63 and 0.82. Fifteen mixtures were produced with different aggregate substitution rates (0%, 50% EVA, 50% CDW, 25% CDW-25% EVA and 50% CDW-50% EVA), by volume. The results showed that it is possible to use the EVA waste and CDW to produce lightweight concrete having semi-structural properties.

Effect of Sisal Fiber Hornification on the Fiber-Matrix Bonding Characteristics and Bending Behavior of Cement Based Composites

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 fiber-matrix 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.

Influência de ciclos molhagem-secagem em fibras de sisal sobre a aderência com matrizes de cimento Portland

RESUMO Visando a reducao da capacidade de absorcao de agua de fibras ligno-celulosicas, ciclos de molhagem e secagem sao usualmente utilizados na industria de papel e celulose. Esse procedimento enrijece a estrutura polimerica das fibro-celulas (processo conhecido como hornificacao) resultando assim em maior estabilidade dimensional da fibra. No presente estudo foi avaliada a influencia da hornificacao de fibras de sisal no seu comportamento fisico (variacoes dimensionais e absorcao de agua), mecânico (comportamento sob cargas de tracao direta) e microestrutural (modificacoes superficiais da fibra e da estrutura das fibro-celulas). Ensaios de arrancamento da fibra de sisal em matriz de cimento portland foram realizados, utilizando comprimentos de embebimento de 25 mm e 50 mm, com o objetivo de verificar se a possivel estabilidade dimensional decorrente da hornificacao aumentava a adesao fibra-matriz. Os resultados indicaram maior estabilidade dimensional, reducao na capacidade de absorcao de agua, aumento na resistencia a tracao e capacidade de deformacao e reducao no modulo de elasticidade da fibra de sisal com a hornificacao. Acrescimos na carga de arrancamento foram observados indicando uma maior aderencia da fibra hornificada a matriz de cimento. Palavras-chave: Fibras naturais, Sisal, Interface, Resistencia ao arrancamento, Hornificacao

Mechanical behavior of recycled lightweight concrete using EVA waste and CDW under moderate temperature

Muitos beneficios podem ser obtidos com o aproveitamento de residuos na producao de materiais para construcao, como a reducao do custo dos componentes construtivos, a reducao do consumo de energia e a diminuicao do uso de recursos naturais. Alem do aproveitamento do proprio residuo de construcao e demolicao (RCD), a industria da construcao civil pode tambem incorporar residuos de outras industrias, como o residuo de etileno acetato de vinila (EVA) da industria calcadista. O EVA e um residuo proveniente do excedente do processo de producao de solas de sapatos e pode ser utilizado, apos moagem, como agregado para producao de concreto. Neste trabalho, concretos reciclados foram produzidos com utilizacao de RCD e EVA, em substituicao ao agregado graudo natural. O objetivo foi avaliar a influencia do uso destes agregados reciclados sobre o comportamento mecânico do concreto sob compressao direta, em temperatura ambiente e apos ser submetido a temperaturas moderadas (50, 70 and 100o C). Foram produzidas quatro misturas com diferentes teores de substituicao, em volume, do agregado natural pelo reciclado (0, 50%EVA, 50%RCD e 25%EVA-25%RCD) e duas relacoes agua-cimento (0,49 e 0,82). A partir dos ensaios de compressao direta foi possivel avaliar a influencia do agregado reciclado sobre a resistencia a compressao, modulo de elasticidade e coeficiente de Poisson. O efeito da temperatura foi avaliado tambem sobre o comportamento tensao-deformacao dos concretos. Os resultados demonstram que e possivel utilizar agregados provenientes de RCD e EVA para produzir concretos leves e que a mistura com 50%EVA apresentou, de forma mais acentuada, reducao do modulo de elasticidade com o aumento da temperatura.

CHARACTERIZATION AND TREATMENT OF SISAL FIBER RESIDUES FOR CEMENT-BASED COMPOSITE APPLICATION

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.

Influence of Recycled Aggregate on the Rheological Behavior of Cement Mortar

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.

Morphological Characterization of Natural and Artificial Sands Through Image Analysis

This article proposes a simple methodology for the morphological characterization of sand particles through scanning electron microscopy (SEM) and image analysis. It was tested on comparison of natural sands, and artificial sands composed by construction and demolition waste (CDW) from mortar, ceramic, and concrete.The samples were segregated by a sieve series, mounted with epoxy resin and subsequently ground and polished. For each sample, at least 500 particles were imaged.The particles were segmented and a morphological separation method was employed to disconnect touching particles. Then, shape and texture description parameters were measured for each particle.The samples of natural sands presented a particle shape slightly more rounded, as described in the literature. On the other hand, the textures of natural and artificial sands were clearly different. The particles of artificial sands were mainly agglomerates of particles, sometimes composed by different minerals. Besides, they exhibited much more pores.

Effect of Natural Fiber Hornification on the Fiber Matrix Interface in Cement Based Composite Systems

Several fiber treatments can be applied to mitigate the high water absorption of vegetal fibers. Wetting and drying cycles are usually performed in the industry of paper and cellulose to reduce the volume variation of the natural fibers. This procedure stiffens the polymeric structure of the fiber-cells (process known as hornification) resulting in a higher dimensional stability. The aim of this study is to determine the effect of the hornification on the interface of natural fibers. For this purpose, cycles of wet and drying was applied on Sisal, Curaua and Jute fibers. Fiber pull-out tests were performed in embedment lengths of 25mm. Furthermore, the influence of the hornification in the fibers mechanical (under tensile loading) and microstructural (surface modifications of the fiber and changes in the fiber-cell structure) behavior were investigated. The results indicate changes on the tensile strength and strain capacity of the studied fibers, showing that morphology and chemical composition play an important role on the efficiency rate of hornification.

Effect of calcined clay on aging of sisal short fiber reinforced mortar

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.

Effect of Treatment of Sisal Fiber on Morphology, Mechanical Properties and Fiber-Cement Bond Strength

The dimensional instability of vegetable fibers due to hygroscopicity results in a gradual loss of adherence in cement based composites which, when in service, are submitted to a natural variation of humidity. Such an effect reduces the contribution of the fiber as a reinforcement and can cause the early rupture of the material. In this work, a treatment of the sisal fibers is performed with the applying of wetting-drying cycles in order to alter their crystalline structure and improve the dimensional stability of the fiber to withstand the variation of humidity: 6, 10, 20, 30 and 34 cycles were applied in order to evaluate the effect on the properties of fiber; a tensile test, the morphological characterization (MEV) and the evaluation of the chemical structure of fiber were carried out. The effect of the treatment on fiber-matrix behavior was evaluated using the pull-out test. Embedded lengths of 16, 20, 30, 40 and 44 mm were defined through a factorial design and used in the test. It is verified that the use of 10 wetting-drying cycles causes less damage to the tensile strength and the elastic modulus of the fiber and contributes to a better adherence with the matrix, with an increase of up to 23 % compared with the untreated fiber. The statistical analysis of the interaction effect between the studied factors, using 2K factorial design with central composite design, indicates that the number of cycles can be decreased when using a longer length of the embedded fiber.Keywords: wetting-drying cycles, pull out test, tensile strength..