Fernanda Pacheco

Multifaceted processes controlling the distribution of hazardous compounds in the spontaneous combustion of coal and the effect of these compounds on human health

Abstract Pollution generated by hazardous elements and persistent organic compounds that affect coal fire is a major environmental concern because of its toxic nature, persistence, and potential risk to human health. The coal mining activities are growing in the state of Santa Catarina in Brazil, thus the collateral impacts on the health and economy are yet to be analyzed. In addition, the environment is also enduring the collateral damage as the waste materials directly influence the coal by‐products applied in civil constructions. This study was aimed to establish the relationships between the composition, morphology, and structural characteristics of ultrafine particles emitted by coal mine fires. In Brazil, the self‐combustions produced by Al–Ca–Fe–Mg–Si coal spheres are rich in chalcophile elements (As, Cd, Cu, Hg, Pb, Sb, Se, Sn, and Zn), lithophile elements (Ce, Hf, In, La, Th, and U), and siderophile elements (Co, Cr, Mo, Fe, Ni, and V). The relationship between nanomineralogy and the production of hazardous elements as analyzed by advanced methods for the geochemical analysis of different materials were also delineated. The information obtained by the mineral substance analysis may provide a better idea for the understanding of coal‐fire development and assessing the response of particular coal in different combustion processes. HighlightsElectron bean reveals the interactions among nanoparticles and hazardous compounds.Samples were obtained from the most big Brazilian coal power plant.Overall, exposure to hazardous compounds in coal fire pose health risks.

Aplicação de MEV e microtomografia 3D na investigação da distribuição de fibras em compósitos cimentícios avançados

Resumo The incorporation of fibers on cement composites reduces its fragility, turning it a ductile material. The amount of fibers and its distribution presents a large influence on the composite performance, especially by the fact that it is self-consolidating, which facilitates the fiber distribution. 3D microtomography is an efficient tool for determining the fibers distribution, generating images and creating a representation in three dimensions of the sample. Moreover, the scanning electron microscopy (SEM) can be used to analyze the interaction of fibers with the cement composite. The purpose of this paper is to investigate the application of these techniques to visualize the distribution and interaction of metallic and polypropylene fibers inserted into an advanced cementitious composite, at 3% in volume content. The results presented these techniques’ efficiency in the verification of fibers distribution within the mixture and the absence of flaws in the composition.

Ethylene vinyl acetate (eva) aggregates usage evaluation for lightweight concrete subfloor to reduce impact sound in flooring systems

Civil construction, nowadays has to deal with comfort and habitability requirements and raw material lack. Thus, it is desired to reuse materials. In this context, the subfloor plays an important role in providing users with comfort, being an interesting object of analysis. Thus, this study aims to design lightweight concrete slabs with ethylene vinyl acetate (EVA) aggregates for subfloors, with two grain sizes of conventional sand replaced with EVA. The experimental program is composed of four unit mixes, three of them varying the ratio between EVA coarse and natural fine aggregates, and the one with higher quantity of EVA coarse aggregates was replaced sand for EVA fine aggregates. The subfloor slabs were molded with three thickness of 3, 5 and 7 centimeters, and a set of 3cm slabs plus 1cm of conventional coating. Slabs were submitted to specific mass tests and L’nT,w mean standardized impact sound pressure level tests. Results showed a correlation between two variables, being that 7cm thickness slabs with smaller specific mass, with total aggregate replacement, presented noise intensity reductions of 17dB in comparison to 7cm slabs with natural sand and smaller content of EVA coarse aggregate; and 28dB reduction in relation to the reference.

ANÁLISE DAS PROPRIEDADES MECÂNICAS DE COMPÓSITOS AVANÇADOS À BASE DE PÓS-REATIVOS COM HIBRIDIZAÇÃO DE MICROFIBRAS METÁLICAS E DE POLIPROPILENO

The pursuit of higher quality materials is necessary to ensure the construction durability and performance, increasing comfort and living conditions for users. The advanced cementitious composite of reactive powder concrete (RPC) is a result of this effort, by which the coarse aggregate is replaced with a compacted fine aggregate and integrated with structural microfibers, reducing voids, providing mechanical packing and increasing compressive strength, tensile strength and ductility, in comparison to the conventional concretes. This paper analyzed the physical and mechanical properties of hybrid composites with metal and polypropylene microfibers, with content values of 100%, 75% and 50% of metal fibers and 0%, 25% and 50% of polypropylene fibers, besides the reference composition, with no fibers. The mixtures behavior was evaluated concerning specific gravity, total absorption, void ratio, compressive strength and tensile flexure, and surface abrasion wear, with the aid of scanning electron microscopy (SEM). The results showed improved mechanical properties by the combination of fibers. When evaluating the different percentages of microfibers, it was found that RPC 100/0 showed better properties for the mechanical characterization tests. Regarding material performance in the physical tests, RPC 75/25 displayed reduction of voids and increase of specific gravity, and lesser damages in the surface abrasion test because of its homogeneity and surface density. Keywords: microfiber, reactive powder concrete, durability. RESUMO A busca por materiais de maior qualidade e necessaria para garantir a durabilidade e desempenho das construcoes, aumentado o conforto e condicoes de moradia para os usuarios. Portanto, materiais inovadores com potencial para este fim estao sendo pesquisados. O composito cimenticeo avancado a base de Concreto de Pos-Reativos (CPR) e resultado deste esforco, onde agregados graudos sao substituidos por agregados miudos empacotados e com a incorporacao de microfibras metalicas, reduzindo vazios, promovendo refinamento dos poros e aumentando a resistencia a compressao, tracao e ductilidade, quando comparado com os concretos convencionais. Este artigo analisou as propriedades fisicas e mecânicas de compostos hibridos com microfibras metalicas e de polipropileno, com os valores de 100%, 75% e 50% de fibras metalicas e 0%, 25% e 50% de fibras de polipropileno, alem da mistura referencia, sem fibras. O comportamento das misturas foi avaliado em funcao da massa especifica, absorcao total e volume de vazios, resistencia a compressao e tracao na flexao e resistencia a abrasao, alem da analise da microscopia eletronica de varredura (MEV). Os resultados mostraram que as propriedades mecânicas aumentaram com a hibridizacao das fibras. Quando comparados os diferentes percentuais de microfibras, concluiu-se que o CPR 100/0 apresentou os melhores resultados nos ensaios mecânicos. Com relacao ao desempenho das misturas nos ensaios fisicos, o CPR 75/25 apresentou uma reducao de vazios e aumento da massa especifica, e menos defeitos apos o ensaio de abrasao, devido a homogeneidade e densidade superficial. Palavras-chave: microfibras, compositos cimenticeos avancados, durabilidade.The pursuit of higher quality materials is necessary to ensure the construction durability and performance, increasing comfort and living conditions for users. The advanced cementitious composite of reactive powder concrete (RPC) is a result of this effort, by which the coarse aggregate is replaced with a compacted fine aggregate and integrated with structural microfibers, reducing voids, providing mechanical packing and increasing compressive strength, tensile strength and ductility, in comparison to the conventional concretes. This paper analyzed the physical and mechanical properties of hybrid composites with metal and polypropylene microfibers, with content values of 100%, 75% and 50% of metal fibers and 0%, 25% and 50% of polypropylene fibers, besides the reference composition, with no fibers. The mixtures behavior was evaluated concerning specific gravity, total absorption, void ratio, compressive strength and tensile flexure, and surface abrasion wear, with the aid of scanning electron microscopy (SEM). The results showed improved mechanical properties by the combination of fibers. When evaluating the different percentages of microfibers, it was found that RPC 100/0 showed better properties for the mechanical characterization tests. Regarding material performance in the physical tests, RPC 75/25 displayed reduction of voids and increase of specific gravity, and lesser damages in the surface abrasion test because of its homogeneity and surface density.