Bernardo Fonseca Tutikian

Coal emissions adverse human health effects associated with ultrafine/nano-particles role and resultant engineering controls

Abstract There are multiple elements which enable coal geochemistry: (1) boiler and pollution control system design parameters, (2) temperature of flue gas at collection point, (3) feed coal and also other fuels like petroleum coke, tires and biomass geochemistry and (4) fuel feed particle size distribution homogeneity distribution, maintenance of pulverisers, etc. Even though there is a large number of hazardous element pollutants in the coal‐processing industry, investigations on micrometer and nanometer‐sized particles including their aqueous colloids formation reactions and their behaviour entering the environment are relatively few in numbers. X‐ray diffraction (XRD), High Resolution‐Transmission Electron microscopy (HR‐TEM)/ (Energy Dispersive Spectroscopy) EDS/ (selected‐area diffraction pattern) SAED, Field Emission‐Scanning Electron Microscopy (FE‐SEM)/EDS and granulometric distribution analysis were used as an integrated characterization techniques tool box to determine both geochemistry and nanomineralogy for coal fly ashes (CFAs) from Brazils largest coal power plant. Ultrafine/nano‐particles size distribution from coal combustion emissions was estimated during the tests. In addition the iron and silicon content was determined as 54.6% of the total 390 different particles observed by electron bean, results aimed that these two particles represent major minerals in the environment particles normally. These data may help in future investigations to asses human health actions related with nano‐particles. Graphical abstract Figure. No Caption available.

Microstructure of concrete subjected to elevated temperatures: physico-chemical changes and analysis techniques

Resumo The exposure of concrete to high temperatures, such as in a fire, leads to physical and chemical changes, which may cause deterioration of mechanical properties, cracking and spalling. This paper presents a critical review of microstructural changes in concrete exposed to high temperature. The transformations developed in the cement paste, aggregates and interfacial transition zone were studied, as well as the experimental techniques of microanalysis presented in recent related researches. Lastly, a critical analysis of experimental results from literature was performed. It was verified that microstructural changes are related to concrete properties and the heating process. The experimental techniques has a potential use for assessment of thermally damaged concrete, however, these techniques must be applied simultaneously and specific methods must be established.

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.

A influência das baixas temperaturas na evolução das resistências do concreto

The mechanical strength of concrete can be affected by many conditions, among them the proportion of the mixture and the influence of external agents, such as external temperatures. Thus, the objective of the paper is to analyze the influence of low temperature on the evolution of concrete strength, from the molding of tests specimens cured at various temperatures. The specimens were submitted in the first 7 days, as curing temperatures ranging from 0oC to 25oC, simulating the lowest possible value for the start of the cement hydrations reactions to the considered ideal for development resistances. The results of the experimental program demonstrated at lower cure temperatures the strength of the mixture develops more slowly, as might be expected, but also found after 14 days, the strength of the mixtures was reversed, i.e., concretes cured at higher temperatures lower values. Thus, it was concluded the concrete in cold weather can be beneficial to its mechanical performance to over time, at the expense constructive steps in normal temperature.

Impact Sound Insulation of Lightweight Concrete Floor with EVA Waste

This study presents an evaluation of acoustic performance of lightweight concrete with EVA waste to reduce impact noise on floors. Three types of concrete with three different mix proportions were evaluated and were made relationships between impact noise levels and results of water absorption, voids and density of the samples. The experimental study of noise impact followed the procedures of ISO 140. The results indicate that the lightweight concrete with EVA recycled aggregate can reduce impact noise levels by up to 15 dB and the highest percentage of coarse aggregate EVA does not entail a higher acoustic performance.

Comparativo da aderência do concreto com aço sem proteção e o aço galvanizado a quente

O aumento da vida util de estruturas e de grande importância para a construcao civil, seja por aspectos economicos quanto de seguranca aos usuarios. A corrosao de armaduras e um dos problemas mais recorrentes, principalmente em ambientes com alto teor de cloretos. Uma das alternativas mais eficientes para proteger as armaduras contra a corrosao e a galvanizacao a quente das barras de aco, com a incorporacao de uma camada de zinco que sera consumida antes do aco entrar em reacao, prolongando a vida util da estrutura. Porem, esta camada de zinco nao deve prejudicar a aderencia das barras de aco com o concreto. Neste trabalho, foi investigada esta relacao, comparativamente com a armadura sem protecao, com a analise de tres diâmetros de barras, 8, 12,5 e 16mm, atraves de ensaio de flexao em viga, com o procedimento da Rilem, de 1978 [1]. Observou-se que nao houve perda de aderencia significativa em nenhum dos diâmetros, apos analise estatistica, mostrando que a aderencia entre o concreto e o aco galvanizado a quente nao e inferior do que com os acos sem protecao, para estes materiais.

Study of Pressure and Curing Temperature in Reactive Powder Concretes (RPC) with different amounts of Metallic Microfibers

Reactive powder concrete (RPC) is one of the greatest breakthroughs in concrete technology, as it enables the manufacturing of thinner structures without passive reinforcement. That reduces the load in buildings and increases durability, especially in aggressive environments. The use of metallic microfibers is what provides the increase in tensile stress and the resulting elimination of reinforcements. However, it is also the most expensive material as well as the most difficult to obtain, which requires its maximum optimization. Therefore, the aim of this study was to compare the mechanical properties of the RPC with three amounts of metallic fibers, 1%, 3%, and 5% in volume in relation to the material total, after having determined the best curing temperature and effectiveness of the confining pressure in the fresh state. The mechanical properties studied were the axial compressive strength, flexural strength, tensile strength by splitting tensile test, and capillary absorption. The results showed that the fibers have little influence on compressive strength, since there was only a small increase as the amount of fibers was increased. However, for tensile strengths, either flexural or by splitting tensile test, the incorporation of microfibers allowed a significant improvement, obtaining gains of 392% for the flexural strength for the 5%, reaching 59MPa, in comparison with the 0%, which was 12MPa. There was also a decrease in capillary absorption. Keywords: Reactive Powder Concrete (RPC); Metallic Microfibers; Mechanical properties, Construction Materials.

Estudo de grautes produzidos com agregado reciclado de resíduo de bloco cerâmico incorporando teores de cal hidratada

Em geral, um volume significativo de residuo proveniente de blocos cerâmicos e gerado na execucao de alvenaria de vedacao ou estrutural, mesmo quando o sistema construtivo e racionalizado. Assim, incorporar este residuo sob a forma de agregado reciclado aos grautes pode ser uma boa alternativa. Comumente utilizada em argamassas, a cal hidratada tambem tem uso recomendado em grautes, objetivando manter a trabalhabilidade da mistura e melhorar a aderencia com o substrato, ao auxiliar na hidratacao do cimento. Aliando essa capacidade de retencao e absorcao de agua ao aproveitamento do residuo cerâmico em grautes, este estudo apresenta uma avaliacao da influencia do teor da cal hidratada em grautes produzidos com substituicao de 30% de agregado graudo natural por reciclado. Foram utilizados os teores de 2%, 4% e 6% de cal hidratada, alem de produzir um graute referencia, sem adicao. No estado fresco foi verificada a perda de abatimento. Os tracos com cal hidratada apresentaram maior manutencao de consistencia. No estado endurecido foram realizados ensaios de velocidade de propagacao de onda ultrassonica, compressao axial e absorcao de agua por capilaridade. Os melhores resultados em ambos os estados foram obtidos com 4% de adicao, para os tracos pobre e rico, e com 2%, para o traco pobre.

Experimental analysis of the spalling phenomenon in precast reinforced concrete columns exposed to high temperatures

Resumo Among the processes that involve the degradation of concrete structures subject to the high temperatures of a fire there is the spalling phenomenon. Its mechanisms are related to the thermal stress of the materials dilatations and pore pressure the process of vaporization of water during heating. The factors that influences in its occurrence are related to concrete properties, structural member characteristics or the exposure conditions, and their parameters are not clearly known yet. This paper aimed to study the influence of three concrete mixtures, four coating thicknesses and two bars diameters of longitudinal reinforcement in the spalling phenomena exposed to ISO 834 fire curve. The characterization of concrete were performed either of the axial compression strength tests, water absorption by capillary and mercury intrusion porosimetry, besides the fire resistance tests in real-scale specimens. It was concluded that the diameter of the bar does not have influence, while the mixture and the concrete cover thickness does. More spalling was recorded for the columns with thicker concrete cover and concrete compressive strength at 61,9 MPa, and although higher strength concrete have less permeability, this characteristic can be balanced with the higher tensile strength of this type of concrete.

Especificação frente à durabilidade para atender nível superior de desempenho em elementos estruturais enterrados

The performance standard NBR 15575-1: 2013 [1] states that to achieve the higher level of performance for durability, buried concrete structures must achieve a minimum service life (VUP) of 75 years. However, the NBR 6118:2014 [2] does not specify the minimum project properties for the structure fulfill this VUP. The objective of this study is to provide recommendations for structural designers to meet higher performance requirements of NBR 15575:2013 [1] in durability. It was conducted a research of national and international standards and reference publications about the durability and VUP 75 years for structural elements buried. The paper was divided into three parts: (1°) the analysis of the Brazilian and international legal system, as well as reference publications in the area; (2°) discussion of service life prediction models; and (3°) specifications to meet the superior level of durability of structural elements buried.