Resumo A cinza do bagaço da cana-de-açúcar é um resíduo produzido pela cogeração de energia a partir da queima de biomassa. Diferentes processos podem ser aplicados a esse material para adequar suas caracteríscitcas químicas e físicas ao emprego como pozolana. Este trabalho visa avaliar a efetividade do processo de fracionamento densimétrico na produção de uma cinza do bagaço da cana-de-açúcar de elevada pozolanicidade. Inicialmente, uma cinza rica em quartzo foi coletada em caldeira industrial e submetida ao fracionamento densimétrico para remoção das partículas de quartzo por meio de decantação. Em seguida, a parcela de cinza potencialmente pozolânica foi submetida à moagem ultrafina. Os resultados mostraram elevado teor de amorfos (94,8%) na cinza após fracionamento. Ensaios de condutividade elétrica e índice de desempenho confirmaram a adequada pozolanicidade das cinzas processadas. Além disso, pastas com 20% de substituição por cinzas do bagaço (em massa) mostraram redução do calor de hidratação. Portanto, o fracionamento densimétrico foi eficiente na produção de um material de elevada reatividade em comparação com a cinza original devido à redução de contaminantes e, consequentemente, pelo aumento da concentração de sílica amorfa.

Abstract Sugarcane bagasse ash is a by-product produced by the energy cogeneration from biomass burning. Different processes can be applied to this material to adapt its chemical and physical characteristics to its use as pozzolan. This work aims to evaluate the effectiveness of the densimetric fractionation process in production of sugarcane bagasse ash with high pozzolanicity. Initially, a quartz-rich ash was collected in an industrial boiler and subjected to densimetric fractionation to remove the quartz particles through decantation. Then, the potentially pozzolanic ash portion was subjected to ultrafine grinding. The results showed high amorphous content (94.8%) in the ash after fractionation. Electrical conductivity and performance index tests confirmed the adequate pozzolanicity of the processed ashes. In addition, cement-based pastes with 20% cement replacement by bagasse ash (in mass) showed a reduction in the heat of hydration. Thus, the densimetric fractionation was efficient in producing a material with high reactivity compared to the original ash due to the reduction of contaminants and, consequently, the increase in the amorphous silica concentration.

Resumo Este trabalho objetiva estudar a produção e as características físicas e químicas de cinzas da casca de arroz, do bagaço da cana-de-açúcar, da folha de milho e da folha de bambu com vistas à aplicação como pozolanas. As etapas de produção das cinzas consistiram basicamente de coleta e preparação das matérias-primas, tratamento químico por lixiviação com ácido cítrico, queima conjugada (beneficiamento térmico) e moagem ultrafina das cinzas produzidas (beneficiamento mecânico). Os resultados indicaram que todas as cinzas atenderam aos requisitos de normas específica e foram classificadas como adições pozolânicas. A elevada pozolanicidade das cinzas foi confirmada em ensaios de condutividade elétrica, de índice de desempenho e pelas mudanças na cinética de hidratação de pastas cimentícias por calorimetria isotérmica. Portanto, os mecanismos de beneficiamento utilizados na produção das diferentes cinzas foram eficazes para geração de materiais pozolânicos altamente reativos.

Abstract This paper aims to study the production and the physical and chemical characterization of rice husk, sugarcane bagasse, corn straw, and bamboo leaf ashes to use as pozzolans. The ash production steps basically consisted of raw material collection, chemical treatment by citric acid leaching, conjugated burning (thermal processing) and ultrafine grinding (mechanical processing) of the produced ashes. The results indicated that all ashes could be classified as pozzolanic additions based on specific standards. The high pozzolanicity of the ashes was confirmed by testing the electrical conductivity, mechanical performance index, and hydration kinetics of cement pastes by isothermal calorimetry. Therefore, the production processes used in this work were effective in producing highly reactive pozzolanic materials.

This work systematically describes a laboratory study on different pretreatments of sugar cane straw to produce pozzolanic ash. Two procedures were used to accelerate the hydrolysis of celluloses and hemicelluloses and remove metallic impurities present in significant levels in sugar cane straw: hot water washing and acid leaching. Proximate analysis by thermogravimetry was carried out to cover volatile matter, fixed carbon, and ash content of the different straws. Detailed measurements of X-ray diffraction, oxide percentages, loss on ignition, and BET specific surface area were performed to compare hot water washed, acid leached, and non-pretreated ashes, after controlled processes of burning and grinding. The pozzolanic activity of the ashes was evaluated from the modified Chapelle and electrical conductivity methods. The results revealed that ashes with a high content of amorphous silica were produced, in spite of the straw pretreatments. However, both straw pretreatments induced a significant increase in pozzolanic activity, mainly associated with the removal of impurities, especially CaO, SO3, K2O, and carbon compounds. The effect of the hot water washing treatment was relatively small in relation to the acid leaching, but the hot washed ash was significantly more pozzolanic than non-treated ash.

The objective of the present study was to evaluate the influence of two different environmental conditions on the quantitative change of color and mass, tensile strength and modulus of elasticity of glass fiber reinforced polymers (GFRP) produced in Brazil. For this purpose, specimens were taken from pultruded composite profiles with two different matrices (vinylester and phenolic resins) reinforced with glass fibers. The first condition consisted of exposing them to cycles of ultraviolet radiation followed by water spray. In the second environment, the specimens were continuously exposed to alkaline solution at a constant temperature of 40 °C. After the exposure, both vinylester and phenolic composites were characterized according to the following parameters: variation of mass, tensile strength and modulus of elasticity. The CIE 1976 L*a*b* color system was used to determinate the color variation of the specimens after degradation using a spectrophotometer. Results indicated significant reductions in tensile strength values for both composites, in addition to expressive variations of mass and color. However, the color variation was not directly related with the loss of mechanical strength.

This work presents the results of a study on the hydration of pastes containing calcium hydroxide and either rice husk ash (RHA) or sugar cane bagasse ash (SCBA) in various initial CaO/SiO2 molar ratios. The products of the reactions were characterized by thermal analyses X-ray diffraction, and scanning electron microscopy. In the case of the RHA pastes, the product was composed of CaO-SiO2-H2O (type I C-S-H) or CaO-SiO2-H2O (type II C-S-H) according to the CaO/SiO2 ratio of the mixture. In contrast, in the case of the SBCA pastes, the product was composed primarily of CaO-SiO2-H2O that differed from both the previous types; the product also contained inclusions of calcium aluminate hydrates.

As membranas biológicas são biomateriais de origem orgânica, geralmente constituídas por colágeno. São utilizadas em diversos fins, dependendo da característica de cada material conservado. A túnica albugínea está sendo mais utilizada atualmente como uma membrana biológica e suas características ainda precisam ser estudadas. O objetivo deste trabalho foi avaliar as características estruturais relacionadas à biomecânica da túnica albugínea bovina conservada em glicerina 98% para utilização como membrana biológica. Para a análise da influência da idade do animal doador sobre a resistência da membrana, foram separados dois grupos. Foram testadas 34 amostras, sendo 17 amostras de membranas oriundas de animais com até um ano e onze meses de idade e o mesmo número de amostras oriundas de animais com idade entre dois e quatro anos. Sendo assim, formou-se um subgrupo com corpos de prova testados a partir de um corte transversal ao sentido longitudinal da membrana com 12 amostras, e outro constituído por corpos de prova testados a partir de cortes feitos na direção longitudinal da membrana, também com 12 amostras. Os resultados de resistência à tração não mostraram diferenças entre os grupos em nenhuma das comparações.

The biological membranes are biomaterials formed by structures of organic origin, usually collagen. They are used for many purposes depending on the characteristics of this material. The tunica albuginea is being used recently as a biological membrane and its characteristics however need to be studied and discussed. The aim of this study was to evaluate the structural features related to the biomechanics of bovine túnica albugínea preseved in 98% glycerin for use as a biological membrane. To analyze the influence of age on the resistance of the membrane, they were separated in two groups. There were tested 34 samples, 17 samples of membranes from animals up to one year and eleven months and 17 samples from animals with two until four years old. Two groups were formed in order to sense the correlation of membrane tension and resistance of the material. Thus was formed a sub-group with specimens tested from a longitudinal cross-section of the membrane with 12 samples and another sub-group composed of samples tested from cuts made in the longitudinal direction of the membrane with 12 samples. The results of tensile strength test did not show differences between groups in any of the comparisons.

O concreto com agregado leve tem sido cada vez mais empregado em razão da reduzida massa específica, do elevado isolamento térmico e acústico e da melhoria na resistência estrutural a carregamentos cíclicos. Neste trabalho foram estudados concretos com agregados leves com resistência à compressão em torno de 20 MPa e seu desempenho estrutural em lajes treliçadas pré-moldadas. Utilizaram-se três diferentes concretos com valores de massa específica entre 1.200 e 1.600 kg/m³. Os concretos foram avaliados com relação à resistência à compressão (aos 3, 7 e 28 dias) e à absorção total de água (aos 28 dias). Com os três tipos de concreto foram produzidas e ensaiadas à flexão lajes pré-moldadas (duas lajes para cada tipo de concreto), com a avaliação de seu comportamento no estado limite de serviço (ELS) para cargas de curta duração, ou seja, sem considerar efeitos ao longo do tempo. Os resultados mostraram o potencial do uso de concretos com agregados leves nesse tipo de laje estrutural.

Lightweight aggregate concrete has been widely used due to its low density, high thermal and acoustic insulation properties, and also due to its improved structural strength under cyclic loading. In this study, concretes containing lightweight aggregates of compressive strength about 20 MPa were studied and its use in precast truss slabs was evaluated. Three different concretes with density values between 1,200 and 1,600 kg/m³ were investigated. The concretes were evaluated taking as basis the compressive strength (at 3, 7 and 28 days) and the total water absorption (at 28 days). Using the three types of concrete, precast slabs were produced and tested under bending (two slabs for each type of concrete) and their behavior at the serviceability limit state (SLS) for short-term loading was evaluated, without considering time-dependent effects. The results showed the potential of using lightweight aggregate concretes in this type of structural slab.

This paper presents a study on the production of silica gel in hydrothermal process using residual rice husk ash. Measurements of the chemical composition, X-ray diffraction, infrared spectroscopy, particle size distribution, and pozzolanic activity were carried out in order to characterize the obtained material, and the optimal silica gel was selected for use as a mineral additive in cement pastes. The compressive strengths were determined for cement pastes containing silica gel (0.0, 2.5 or 5% by mass) in different times. The results indicate that the mixtures containing silica gel showed improved mechanical behavior over all time periods evaluated.

This work presents the results of morphological and physical-chemical characteristics of a sugar cane bagasse ash material sample produced under controlled burning conditions. The investigation was carried out by analyzing chemical composition, X-ray diffraction, 29Si nuclear magnetic resonance, morphology, thermal analysis, particle size, specific surface, and density. Moreover, the pozzolanic activity of the ash was evaluated by pozzolanic activity index and Chapelle's method. The results suggest that the sugar cane bagasse ash has adequate properties to be used as pozzolan in construction materials.