Carlito Calil Junior

Microstructure and mechanical properties of gypsum composites reinforced with recycled cellulose pulp

The use of waste fibers for the reinforcement of brittle matrices is considered opportune for the sustainable management of urban solid residues. This paper examines the microstructure and mechanical properties of a composite material made of gypsum reinforced with cellulose fibers from discarded Kraft cement bag. Two different kinds of gypsum were used, natural gypsum (NG) and recycled gypsum (RG), both with an addition of 10% by mass of limestone. For the production of samples, slurry vacuum de-watering technique followed by pressing was evaluated revealing to be an efficient and innovative solution for the composites under evaluation. The composite was analyzed based on flexural strength tests, scanning electron microscopy (SEM) imaging, secondary electron (SE) detection, and pseudo-adiabatic calorimetry. The morphology of the fractured surfaces of flexural test samples revealed large gypsum crystals double the original size surrounding the fibers, but with the same overall aspect ratio. Natural fibers absorb large amounts of water, causing the water/gypsum ratio of the paste to increase. The predominance of fiber pullout, damaged or removed secondary layers and incrusted crystals are indicative of the good bonding of the fiber to the gypsum matrix and of the high mechanical resistance of composites. This material is a technically better substitute for the brittle gypsum board, and it stands out particularly for its characteristics of high impact strength and high modulus of rupture.

Vibração transversal: um método eficiente para classificação de peças estruturais de madeira

A classificacao de pecas estruturais de madeira e uma tendencia mundial, mas ainda deficiente no Brasil. O uso de metodos nao-destrutivos para classificacao e, consequentemente, para racionalizacao do uso de madeira em estruturas, melhora a posicao da madeira quando em competicao com materiais estruturais mais uniformes. Este trabalho mostra a existencia de forte correlacao linear entre o modulo de elasticidade estatico e o modulo de elasticidade dinâmico, obtidos a partir de testes de flexao estatica e de vibracao transversal, em 326 pecas estruturais de madeira da especie Southern Pine, e indica a eficiencia do metodo de vibracao transversal para determinacao do modulo de elasticidade e para classificacao de pecas estruturais de madeira.

Tenacidade da madeira como função da densidade aparente

The knowledge on the behavior of wood in situations of short load contributes to the development of a safer structural design. However, toughness is not part of the mechanical properties commonly investigated in the characterization of this material. Therefore, the present study aimed to evaluate, the possibility to estimate the toughness with the knowledge of the apparent density of 6 Brazilian tropical wooden species (Angico, Eucalyptus, Jatoba, Parica, Pine and Teak), by using linear, quadratic and cubic polynomial regression models. The results highlighted the significance and representation of all adjustments investigated, and the cubic polynomial was the most efficient for estimating the wood toughness.

Permeability Measuremens of Brazilian Eucalyptus

The permeability of Brazilian Eucalyptus grandis and Eucalyptus citriodora wood was measured in a custom build gas analysis chamber in order to determine which species could be successfully treated with preservatives. Liquid permeability was tested using an emulsion of Neen oil and a control of distillated water. Air was used to test the gas phase permeability. For both Eucalyptus grandis and Eucalyptus citriodora, the longitudinal permeability of gas was shown to be about twice as great as the liquid phase permeability. No radial permeability was observed for either wood. The permeability of air and water through the sapwood of Eucalyptus grandis was greater than that through the sapwood of Eucalyptus citriodora. The permeability of neen oil preservative through the sapwood of Eucalyptus grandis was also greater than through the sapwood of E. Citradora, but the difference was not statistically significant. Scanning Electron Microscopy images showed that the distribution and obstruction in the vessels could be correlated with observed permeability properties. Irrespective of the causes of differences in permeability between the species, the fluid phase flux through the sapwood of both species was significant, indicating that both Eucalyptus grandis and Eucalyptus citriodora could be successfully treated with wood preservative.

Strength and stiffness of thermally rectified eucalyptus wood under compression

The aim of this work was the evaluation of the thermal-rectification process of reforestation wood Corymbia citriodora Hook by measuring of mechanical properties under compression parallel to the grain and also determining of chemical composition. The tested samples were thermally treated in a furnace with nitrogen-atmosphere at heating rate of 0.033 oC.min-1, at temperatures of 160, 180, 200, 220 and 240 oC. The chemical components and mechanical properties were affected with the thermal rectification process. The contents ranged from 17.85 to 3.51% extractives, 30.44 to 53.86% lignin, 69.56 to 46.14% holocellulose and 0.31 to 0.47% ashes. The samples strength decreased from 20% to 50% and the elasticity modulus increased about 47%. The characteristic values of strength under compression were determined and these changes were about 23% lower than Brazilian standard. The best mechanical properties of Corymbia citriodora were obtained at 180 oC.

Pullout strength of axially loaded steel rods bonded in glulam at a 45º angle to the grain

This paper presents an experimental analysis of the pullout strength of bonded and axially loaded steel rods used as connector elements in log-concrete composite bridge decks. Static and cyclic tests were carried out to evaluate the fatigue of the connectors using two species of reforested wood, three types of commercial adhesives and three levels of wood moisture content. It was found that six failure modes (rod interface failure, timber interface failure, combined timber interface/rod interface failure, combined rod interface/timber substrate failure, rod failure, and adhesive failure) can occur in the geometry of a single test specimen. The results indicate the good performance of epoxy glued steel rod connectors for use in log-concrete composite bridge decks.

Análise estrutural de silos metálicos prismáticos

Nos ultimos anos, o crescimento da agricultura brasileira tem forcado varios setores a se adequarem aos padroes produtivos com o intuito de se manterem competitivos, frente ao processo de globalizacao economica. Nesse contexto, as fabricas de racao avicola tendem a buscar novas alternativas que favorecam a producao e reduzam custos sem afetar a qualidade do produto final. Entre essas alternativas, destaca-se o uso de silos verticais por facilitar o processo de confeccao das racoes e eliminar os grandes depositos horizontais. Diante dessa possibilidade, objetivou-se, com a presente pesquisa, estudar as tensoes nas paredes em conformacao ziguezague de um silo metalico prismatico 2m x 1m e comparar os resultados obtidos com teorias e normas. Para o calculo das tensoes, utilizaram-se os metodos simplificados de Ravenet e Troitsky. Para a obtencao dos esforcos reais nas paredes, utilizaram-se extensometros eletricos. Dessa forma, conclui-se que, tanto a teoria de Ravenet quanto de Troistky, podem ser recomendadas para o dimensionamento de silos prismaticos por apresentarem boa aproximacao com valores experimentais.

Wood cross-arms coated with polyurethane resin - tests and numerical simulations

Brazils electric power utilities have commonly employed native timbers as the main material for manufacturing cross-arms for distribution lines. However, the increasingly high costs of these timbers and Brazils new environmental laws have contributed to change this situation, spurring research on new materials for application in transmission and distribution systems. This paper discusses two reforested wood species, Pinus elliottii and Eucalyptus citriodora, coated with castor oil-based polyurethane resins, as an alternative material for distribution line cross-arms, from the standpoint of their mechanical and electrical properties and their low cost. Numerical simulations and a complete description of the entire coating process are also part of this work.

Pre-stressed timber bridges: economic choice for rural roads

The demand of new bridges and rehabilitation of the existing ones in Brazil is evident, in the municipal, state and federal scope. The construction of efficient roads can provide, besides comfort to the users, a cost decrease for the transportation of food and other products, since almost all the transportation in the country is made through highways. According to the estimate made by the Wood and Timber Structures Laboratory (LaMEM) of Sao Paulo University, more than 100,000 of short and medium span bridges are necessary to improve Brazilian roads. Therefore, the study of competitive technologies is of extreme importance, in order to minimize the budget needed to these improvements. This work reports on a technical and economical viability analysis of transversally pre-stressed timber bridges, for the use in rural and secondary roads. The analysis was made through design, construction and monitoring of the first pre-stress-laminated timber bridge in South America. The results show high performance, low cost, easy and quick execution.

Metodologia alternativa para o cálculo do módulo de elasticidade em vigas de madeira de dimensões estruturais

This study aims to present an alternative calculation methodology based on the Least Squares Method for determining the modulus of elasticity in bending wooden beams of structural dimensions. The equations developed require knowledge of three or five points measured in displacements along the piece, allowing greater reliability on the response variable, using the statistical bending test at three points and non-destructively, resulting from imposition of measures from small displacements L/300 and L/200, the largest being stipulated by the Brazilian norm NBR 7190:1997. The woods tested were Angico, Cumaru, Garapa and Jatoba. Besides obtaining the modulus of elasticity through the alternative methodology proposed, these were also obtained employing the Brazilian norm NBR 7190:1997, adapted to the condition of non-destructive testing (small displacements) and for pieces of structural dimensions. The results of the modulus of elasticity of the four species of wood according to both calculation approaches used proved to be equivalent, implying the good approximation provided by the methodology of calculation adapted from the Brazilian norm.