Flávio de Andrade Silva

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

The Influence of Fiber Treatment on the Mechanical Behavior of Jute Textile Reinforced Concrete

In the present work a natural textile reinforced concrete (TRC) was developed and mechanically characterized. A fabric made of jute, a natural occurring fiber, was used as reinforcement in a fine grained cementitious matrix with a low content of calcium hydroxide. Tensile tests were performed on TRC reinforced with 3 and 5 layers of jute fabric. The mechanical tensile tests were coupled with image analysis in order to measure the crack spacing and the results were correlated with the applied tensile strain. Various stages of loading corresponding to initiation, propagation, distribution, opening, and localization of a crack system in the specimen are discussed. In order to improve the fiber-matrix interface the jute fabric was treated with a polymer based coating.

Mechanical Behavior of Self-Compacting Soil-Cement-Sisal Fiber Composites

The aim of this research is the development and mechanical characterization of self-compacting soil cement composites with the incorporation of fly ash, metakaolin and sisal fibers. The mentioned composites, based on natural raw materials (raw earth and vegetable fibers), which are abundant in nature and have low cost and low environmental impact could be used as a more sustainable alternative than conventional industrialized materials for applications that don ́t require high structural performance (minimum strength equals to 2 MPa). A residual soil, constituted by 35% of fines and 65% of granular material was selected and the matrix was designed using a computational routine, based on the compressible packing model (CPM). The rheology of the matrix was adjusted by the slump flow test having as a target the spreading value of 600 mm. The matrix presented uniaxial compression strength of about 3.3 MPa after 28 days of curing. After 240 days of curing it was noticed an increase in the compressive strength to 7.5 MPa. This can be traced back to the pozzolanic reactions that takes place in the system. The soil cement composites were produced with three different sisal fiber contents: 0.5, 1.0 and 1.5% (in relation to the weight of dry soil) and a fiber length (Le) of 20 mm. Under compression, the incorporation of fibers has significantly influenced the post-peak behavior, increasing the toughness and the strain capacity. Under four point bending loading, the presence of fibers have contributed to increase the peak strength and the residual strength with expressive gains of toughness. The composites presented strength values as high as 1.8 MPa (1.0% of fibers) when they were subjected to bending loads. The use of sisal fibers as reinforcement modified the fracture mechanisms of the composites, changing it from a brittle to a ductile behavior.

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.

Flexural behavior of hybrid steel fiber reinforced self-consolidating concretes

The simultaneous use of different types of fibers as reinforcement in concrete, mortar or pastes, can avoid the propagation and widening of cracks at different stages of their load-deflection or stress-strain behavior. The purpose of this article is to evaluate the flexural behavior in the material and structural scale of self-compacting concretes reinforced with meso and macro steel fibers. Two tests were used to mechanically characterize the concretes reinforced with volume fractions of 1 and 1.5% hybrid steel fibers: four point bending tests (material scale) and round panel tests (structural scale). The results indicated that hybridization of fiber reinforcement raised the serviceability limit state of concrete, contributing to increased toughness and load bearing capacity for small levels of displacement and crack openings. Such benefits were more evident in the structural tests considering the degree of hyperstaticity and multiple cracking potential of the panels. In the descending branch of the load-displacement curves, where macro-cracks were predominant, macro-fibers were more efficient in increasing the overall capacity for energy absorption of the composites.

A multi-scale investigation of the mechanical behavior of durable sisal fiber cement composites

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.

Influence of Elevated Temperatures

In this chapter, the effect of elevated temperatures on strain-hardening cement-based composites (SHCC) is reported. Key features of SHCC such as tensile strength and strain capacity, compressive strength, failure modes, the fiber–matrix interface, and spalling behavior are discussed. Different testing conditions are covered, including not only residual but also high temperature tests. Experimental results addressing various temperature levels (ranging from ambient temperature to 1000 °C) were used to investigate basic knowledge of the thermomechanical response of SHCC under conditions of both uniaxial tension and compression.

Addition of Paper Sludge Waste into Lime for Mortar Production

Civil construction materials such as brick, concrete and mortar have been incorporated with compatible wastes aiming at both reducing costs and providing an environmentally correct destination for the waste. In the present work, a sludge waste from a paper industry was added in different amounts, up to 20 wt%, into the lime used to produce mortar in mixture with sand and cement. Standard consistency tests of the pasty, as-prepared, mortar as well as flexural and compressive tests of the solid, as-cured, mortar were performed. The results indicated that the addition of up to 10 wt% of paper sludge waste into the lime increased the mortar consistency and up to 20 wt% addition also improved the mechanical strength of the cured mortar.

Enhanced silk performance by enriching the silkworm diet with bordeaux mixture

Abstract This work evaluated the effect of different concentrations (5, 10, and 20%) of Bordeaux mixture (Bm) in the diet of the silkworm caterpillars in order to improve the cocoon production and structural and mechanical properties of the ensuing silk. The cocoon yield, tensile properties, and microstructure (X-ray diffraction, surface fracture, and qualitative composition) of the obtained silk fiber threads were determined. The mortality levels of caterpillars fed on mulberry leaves with Bm were up to 80% higher than the rates observed on caterpillars fed on non-treated leaves. The consumption of leaves decreased as the amount of Bm introduced to the caterpillars’ diets was increased. However, the lower demand of leaves by caterpillars fed on leaves treated with 5 and 10% of Bm did not imply in obtaining lower cocoon productivity, as the raw silk rates were not different in comparison to the control group. The tensile strength and maximum strain of the fiber were greatly improved, whereas the toughness was not statistically improved by the presence of Bm in the diet. There was an increase in the concentration of Ca and Cu in the silk fiber threads treated with Bm, leading to higher crystallinity. If the cocoon producers were rewarded with an increase in cocoon quality, the application of Bm could be interesting, despite the increase in caterpillars’ mortality.