Paulo Henrique Ribeiro Borges

Full factorial design analysis of carbon nanotube polymer-cement composites

The work described in this paper is related to the effect of adding carbon nanotubes (CNT) on the mechanical properties of polymer-cement composites. A full factorial design has been performed on 160 samples to identify the contribution provided by the following factors: polymeric phase addition, CNT weight addition and water/cement ratio. The response parameters of the full factorial design were the bulk density, apparent porosity, compressive strength and elastic modulus of the polymer-cement-based nanocomposites. All the factors considered in this analysis affected significantly the bulk density and apparent porosity of the composites. The compressive strength and elastic modulus were affected primarily by the cross-interactions between polymeric phase and CNT additions, and the water/cement ratio with polymeric phase factors.

Propriedades mecânicas de materiais compósitos à base de cimento Portland e resina epoxi

The study of multi-functional materials of high performance, as the polymeric-cementitious composites, has been the focus of several researches in the industry of the civil engineering. This work investigates the effect of the combination of a thermorigid epoxy phase and the white Portland cement, followed by the evaluation of its compressive strength and modulus of elasticity. This composite, when the phases are individually compared, provides an increase of the compressive strength, a reduction of the density, and a significant change of the mechanical behaviour. The changes in mechanical behaviour are associated with the hydration of cement in the presence of resin, which was evident after infrared spectroscopy analysis.

The position effect of structural Eucalyptus round timber on the flexural modulus of elasticity

Round timber has great use in civil construction, performing the function of beams, columns, foundations, poles for power distribution among others, with the advantage of not being processed, such as lumber. The structural design of round timber requires determining the elastic properties, mainly the modulus of elasticity. The Brazilian standards responsible for the stiffness and strength determination of round timber are in effect for over twenty years with no technical review. Round timber, for generally present an axis with non-zero curvature according to the position of the element in the bending test, may exhibit different values of modulus of elasticity. This study aims to analyze the position effect of Eucalyptus grandis round timber on the flexural modulus of elasticity. The three-point bending test was evaluated in two different positions based on the longitudinal rotation of the round timber element. The results revealed that at least two different positions of the round timber element are desired to obtain significant modulus of elasticity.

Numerical evaluation of the modulus of longitudinal elasticity in structural round timber elements of the Eucalyptus genus

Currently, the standards that deal with the determination of the properties of rigidity and strength for structural round timber elements do not take in consideration in their calculations and mathematical models the influence of the existing irregularities in the geometry of these elements. This study has as objective to determine the effective value of the modulus of longitudinal elasticity for structural round timber pieces of the Eucalyptus citriodora genus by a technique of optimization allied to the Inverse Analysis Method, to the Finite Element Method and the Least Square Method.

Estudo comparativo da análise de ciclo de vida de concretos geopoliméricos e de concretos à base de cimento Portland composto (CP II)

A Analise de Ciclo de Vida (ACV) e um metodo que inclui a compilacao e avaliacao das entradas, saidas e dos impactos de um produto ao longo do seu ciclo de vida. Os resultados desta analise sao utilizados para escolher alternativas favoraveis para uma aplicacao especifica. Este artigo utilizou as ferramentas de ACV, apoiada pelo software Umberto, para comparar o processo de obtencao de concretos de cimento Portland com o de concretos geopolimericos, obtidos da ativacao alcalina de aluminossilicatos. O impacto ambiental foi avaliado considerando 1 m 3 de cada concreto, sendo (i) as emissoes de CO 2 (kg CO 2 / m 3 ) e (ii) a demanda energetica (MJ/m³) as variaveis para determinar o potencial sustentavel de ambos materiais. O objetivo principal foi avaliar se os concretos geopolimericos sao mais sustentaveis do que os concretos tradicionais. Os resultados obtidos mostraram que o consumo energetico e reduzido em 45,8% na producao do concreto geopolimerico, quando comparado a producao do concreto de cimento Portland de desempenho mecânico equivalente. Com relacao as emissoes de CO 2 , o concreto geopolimerico reduz as emissoes em 72,4%, em comparacao ao concreto tradicional de cimento Portland CPII. Assim, o primeiro se mostra uma alternativa a ser considerada, na producao de materiais de construcao de menor impacto ambiental.

The effect of silica microparticles and maleic anhydride on the physic-mechanical properties of epoxy matrix phase

Abstract Thermoset polymers, especially epoxy resin, have been applied in several industrial applications in which high stiffness and adhesive strength are demanded. On the other hand, epoxy resin is rather brittle and has poor fracture toughness. For this reason, the addition of fibres/particles into thermoset polymer can be used to enhance strength and toughness for several structural applications. This work investigated the addition of silica microparticles and maleic anhydride (as a coupling agent between the phases) into epoxy resin, which will be used as the matrix phase of hybrid biocomposites. A full factorial design was conducted to evaluate the effect of silica microparticles and chemical additive into the epoxy matrix under compressive loadings. Apparent density was also evaluated. Experimental factors such as weight fraction of silica microparticles (0, 20, and 33.3 wt%) and weight fraction of maleic anhydride (0 and 2 wt%) were investigated. The statistical analysis revealed that the main factors ‘chemical additive’ and ‘silica addition’ significantly affected the compressive modulus of the composites.

Cement - steatite composites reinforced with carbon fibres: an alternative for restoration of brazilian historical buildings

Steatite is a mineral which has been employed in the carving of elements in facades of Brazilian historical buildings and churches since the 17th century. Over the years, many of those historical buildings suffered the consequences of weathering with a current need for restoration. Recently a special cement-based mortar containing additions of fine powder waste from mineral extraction of steatite has been developed in Brazil, as a composite material for restoration of steatite elements. However, the incorporation of steatite waste reduces the flexural strength of the mortar and compromises the restoration of elements where gravity imposes tensile stresses. The addition of carbon fibres may overcome this issue and increase the flexural strength of the cement-steatite composite mortar. This work investigates the effect of carbon fibre addition on the bulk density and flexural strength of compacted precast cement-steatite composites. The results show that the addition of carbon fibres (i) effectively increases the mechanical strength, allowing for a higher amount of steatite powder waste in the mixes; (ii) reduces the weight of the structural elements. This new composite material would help to develop restoration techniques of historical buildings and serve as a disposal route of steatite powder waste in Brazil.

Investigations on Wood–Plastic Composites Reinforced With Silica Particles Using Design of Experiment

Incineration and landfilling of waste from the timber industry are practices condemned and unused. The reuse of wood waste as a dispersive phase in composite materials has been the focus of much research to develop new products, mainly for the automotive and construction industries. The wood–plastic composites (WPC) present characteristics, such as moderate strength, light weight, and high durability. Besides, they are inexpensive and sustainable, which make them attractive for innovative design. This work investigates the effect of eucalyptus sawdust, a chemical admixture and silica particles on the physical and mechanical properties of WPC upon a statistical methodology. The silica-particle addition was added by the matrix phase replacement to reduce the overall costs, because the latter is nearly 87 % more expensive. A microstructural analysis was conducted to better assess the variables studied. Results have shown that the composites made with 20 wt. % of sawdust addition, 10/50 US-Tyler sawdust particle size and maleic anhydride addition appeared to have acceptable properties for engineering applications.

Influência da rigidez de ligações parafusadas em estruturas planas de madeira do tipo treliça

Trusses are structural systems commonly used in projects, being employed mainly in roof structures, present in most rural buildings. The design of trusses, as well as other structural systems, requires the determination of displacements, strains and stresses. However, the project is developed from an ideal model of calculation, considering free rotation between the elements of a connection. This paper presents a computer program for the analysis of bidimensional wooden trusses with connections formed with two screws per node. The formulation is based on the flexibility method, taking into account the influence of the effect of semi-rigid connections formed by two screws. An example of a structure is presented and analyzed by the program developed here, highlighting the importance of behavior analysis on semi-rigid connections.

The Influence of Rice Husk Ash Addition on the Properties of Metakaolin-Based Geopolymers

This paper investigates the replacement of metakaolin (MK) with rice husk ash (RHA) in the production of alkali-activated binders or geopolymers. The influence of the RHA addition on compressive and flexural strength, as well as water absorption and apparent porosity were determined, in terms of the percentage of RHA in the mixture and molar ratios of the mixes. Fourier Transform Infrared (FTIR) spectroscopy and Energy Dispersive spectroscopy (EDS) were carried out to assess the changes in the microstructure of the geopolymer matrices with the RHA addition. Results have shown that RHA may be a supplementary precursor for geopolymers. The composition of the geopolymer matrices containing 0-40% RHA is very similar, which indicates that the additional Si provided by RHA is not incorporated to the geopolymer matrix. In addition, geopolymers with RHA content higher than 40% present a plastic behavior, characterized by extremely low strength and high deformation, which can be attributed to the formation of silica gel in formulations containing variable Si/Al ratio.