Lightweight concrete shows good insulation properties, depending on several parameters such as mi... more Lightweight concrete shows good insulation properties, depending on several parameters such as mix design and aggregate type. Perlite aggregate is one of the most effective aggregates for such a purpose, mainly because of its low thermal conductivity (0.04 W/m.°C), but is not available globally. This paper explores the potential use of another source of thermal efficient aggregate, vermiculite (0.058 W/m.°C) which is available in Brazil and other countries where perlite is absent. Cylindrical samples were cast by using two lightweight aggregates, perlite and vermiculite, and treated with supercritical carbon dioxide. Supercritical carbonation (SCC) of concrete can improve mechanical, thermal and durability features. In this paper, the effect of SCC on the thermal behavior of lightweight mortars was investigated with regards to physical and microstructure features and thermal behavior due to cooling.
Materials Research-ibero-american Journal of Materials, 2021
The world is moving at a fast pace in the consumption of non-renewable natural resources, causing... more The world is moving at a fast pace in the consumption of non-renewable natural resources, causing several ecological problems. The search for the cost reduction by implementing renewable energies implies in the optimization of the manufacturing processes parameters of consolidated technologies, such as solar thermal energy collectors. One of the applications of selective surfaces is to improve performance of solar absorbers. The purpose of this work is to produce selective coatings with high absorption in range of UV/Vis and low emittance in the IR range. It was prepared a selective surface composed of ilmenite deposited on substrates of AISI 304 stainless steel using technique of cathodic cage plasma nitriding/deposition for application in solar thermal absorbers. Ilmenite was initially characterized by X-Ray Diffractometry (XRD), X-Ray Fluorescence (FRX) and Thermal Analysis (TGA). The coatings produced were optically characterized in range UV/Vis/IR and emittance and data on the ...
Revista Principia - Divulgação Científica e Tecnológica do IFPB, 2021
Life Cycle Assessment (LCA) quantifies the environmental impacts associated with products through... more Life Cycle Assessment (LCA) quantifies the environmental impacts associated with products throughout their life cycle. LCA also assists in the interpretation of impact assessment results, enabling improvements in a product or process. This paper applied the LCA methodology to quantify and compare the greenhouse gas emissions associated with different types of concrete: with a traditional binder (Portland cement) and with alkali-activated materials (Metakaolin, Lateritic Soil, and Lateritic Concretion) as precursors. The environmental impact was evaluated by means of greenhouse gas emissions (kg CO2-eq/m³), considering 1m³ of each binder and resistance of approximately 30 MPa, obtained by a recommended mix ratio. The main objective is to evaluate whether alkali-activated binders present lower emissions than Portland cement. The results demonstrated that Portland cement is responsible for over 92% of the environmental impacts of traditional concrete production. The use of alternative materials in civil construction, such as laterite soil, reduces carbon dioxide emissions by 79% compared to Portland cement concrete emissions. Keywords: Life Cycle Assessment. Carbon Footprint. Concrete. Portland cement. Alkali-activated materials. Resumo A Avaliação de Ciclo de Vida é um método que permite quantificar os impactos ambientais de um produto ou processo ao longo do seu ciclo de vida. Ele também auxilia na interpretação dos resultados, com a finalidade de permitir melhorias no produto ou processo. Este artigo aplicou a metodologia em questão para comparar o processo de obtenção do concreto com o ligante tradicional, o cimento Portland, e os materiais alcalinamente ativados tendo como precursores o Metacaulim, o Solo Laterítico e a Concreção Laterítica. O impacto ambiental foi avaliado por meio das emissões de carbono (kg CO 2 /m 3) considerando 1m 3 de cada aglomerante, em função do traço recomendado para se obter concreto com resistência de aproximadamente 30 MPa. O objetivo principal desse trabalho foi avaliar se os aglomerantes alcalinamente ativados são mais sustentáveis do que o cimento Portland. Os resultados obtidos nesse trabalho mostraram que, na construção civil, a utilização de materiais alternativos como o solo lateritico torna possível uma redução de 79% das emissões de dióxido de carbono, quando comparado com as emissões do concreto de cimento Portland. O cimento Portland é responsável por pouco mais de 92% dos impactos ambientais ocasionados na produção do concreto tradicional.
Known since the 70's, geopolymers are synthetic materials of acknowledged interesting chemic... more Known since the 70's, geopolymers are synthetic materials of acknowledged interesting chemical, mechanical and thermal performance. As far as environmental issue is concerned, the use of alkali-activated industrial by-product precursors and the near-room casting temperature (around 60oC) can be seen as an advantageous choice for many applications such as in thermo-mechanical ecient steel coatings. Whereas most epoxy resin would char at temperatures above 300oC, geopolymers can upheld good mechanical performance in temper- atures as high as 1000oC. Although they have mostly been studied for coatings, the number of studies on their adhesion mechanisms is considerably less then those regarding its other properties. The main thrust of this work is to evaluate the binding potential of alkali-activated clay-based waste in steel bonded plates. The adhesion of steel plates (40x160x5mm) was evaluated using three clay-based wastes and metakaolin (MK) as precursors, provided by X-Ray fluo...
Geompolymers and their engineering applications have attracted significant attention of the scien... more Geompolymers and their engineering applications have attracted significant attention of the scientific community. This is due to properties such as good thermal stability and high resistance to aggressive environments. Most studies on this subject are based on traditional precursor materials such as calcined kaolinite clay (metakaolinite) and fly ash. The iron content is significant, reaching around 10% in metakaolinite, for instance. The role of iron in geopolymers still lacks systematic investigation. This can be attributed to the limitations presenting nuclear magnetic resonance (NMR) spectroscopy, which is a widely used technique to study geopolymers structure. Ferromagnetic elements such as iron, which is often present in some precursors, affect the magnetic response of the material, compromising the proper analysis of its structure by NMR results. Iron content in some industrial residues may be several times higher as it is often found in metakaolinite. This work presents x-ra...
The main purpose of this work is to perform a thermal analysis in an air conditioning duct to ver... more The main purpose of this work is to perform a thermal analysis in an air conditioning duct to verify the influence of the thermal properties of the insulating material on the minimum thermal insulation thickness necessary to avoid the condensation of water vapor present in the air. The mathematical formulation is based on Fourier’s law and the first law of thermodynamics. A response surface, a contour plot and a mathematical model for the analyzed response variable, were obtained from an experimental design. Results indicate that the reduction of thermal conductivity and increase of emissivity of the insulating material contribute to the reduction of the minimum thermal insulation thickness.
Alkali-aggregate reaction is a pathology directly linked to interactions between solubilized alka... more Alkali-aggregate reaction is a pathology directly linked to interactions between solubilized alkali hydroxides in the pore structure concrete and other chemical species from aggregates. In the presence of excessive water, these chemical interactions lead to the precipitation of gel-like phases within aggregates, paste-aggregate interface and cement matrix, causing expansion due to internal pressure in concretes that can promote disruption. It appears that the volume expansion of silica gels tends to have a maximum at the total dissolved silica. Both alkali and silica are needed to chemically stabilise alkaline activated cements (AAC-geopolymers). Therefore, this study aims to evaluate the potential use of geopolymers as mitigating agent of AAR. Four formulations were carried out in the study, three metakaolin based AAC were synthesized with different alkali types (100% sodium silicate, 100% potassium silicate and 50% of sodium silicate and 50% potassium silicate). Portland cement mo...
The present study evaluated the influence of two sugarcane bagasse ash (SCBA) beneficiation proce... more The present study evaluated the influence of two sugarcane bagasse ash (SCBA) beneficiation processes (sieving and high-energy milling) as an alternative to evaluate its absorption potential for application as a raw material for the production of solar absorber films. It was noticed that the absorption levels of all the samples were higher than 90% and that the SBCA has predominance of SiO2 corroborated by the mineralogical analysis. The thermal behavior of all the samples was similar among each other, presenting a total mass loss corresponding to 8.5%. As the ash is able to maintain a thermal stability in the temperature range of 100°C to 1000°C, and the chemical and mineralogical composition favors the absorption of solar energy, SCBA has proven to be favorable for application as raw material of selective solar surfaces.
Thermo-Fluid Dynamics Analysis of Fire Smoke Dispersion and Control Strategy in Buildings
Smoke is the main threat of death in fires. For this reason, it becomes extremely important to un... more Smoke is the main threat of death in fires. For this reason, it becomes extremely important to understand the dispersion of this pollutant and to verify the influence of different control systems on its spread through buildings, in order to avoid or minimize its effects on living beings. Thus, this work aims to perform thermo-fluid dynamic study of smoke dispersion in a closed environment. All numerical analysis was performed using the Fire Dynamics Simulator (FDS) software. Different simulations were carried out to evaluate the influence of the exhaust system (natural or mechanical), the heat release rate (HRR), ventilation and the smoke curtain in the pollutant dispersion. Results of the smoke layer interface height, temperature profile, average exhaust volumetric flow rate, pressure and velocity distribution are presented and discussed. The results indicate that an increase in the natural exhaust area increases the smoke layer interface height, only for the well-ventilated compar...
Titanium is considered the fourth most widely used material in industry worldwide. Titanium miner... more Titanium is considered the fourth most widely used material in industry worldwide. Titanium minerals are currently being applied in various branches of industry, mainly in the field of pigmentation. Ilmenite (FeTiO3) is an iron and titanium oxide of more common and abundant occurrence, with theoretical composition of Fe (36.8%), Ti (31.6%) and O (31.6%). Having regard to the potential of titanium minerals and the abundance of ilmenite, together with the importance of validating direct applications of this ore, since the processing of titanium is still complex and expensive, it is necessary to study this mineral and the knowledge of its main characteristics. This work brings thermal, chemical and mineralogical characterizations of ilmenite, in order to know the potential of application of this ore as a solar absorbing material. The characterization techniques used were: X-ray diffraction (XRD) and Rietveld refinement for phase quantification, X-ray fluorescence (XRF), optical spectro...
The cement industry is the second-largest single industrial emitter in the world and therefore ha... more The cement industry is the second-largest single industrial emitter in the world and therefore has an important role to play in reducing the intensity of its carbon emissions: participation of the sector is important to contribute to the goal of the Paris Climate Change Agreement to limit global warming. One of the strategies for reducing the carbon footprint of the cement industry is substitution of Portland cement, which is a component of the concrete mix widely used as a construction material worldwide. Geopolymer cement has emerged as an alternative for Portland cement, with several advantages. This study applied the Life Cycle Assessment methodology to quantify the carbon emissions associated with 1m 3 of two types of concrete (concrete PC-II cement-based Portland cement vs. geopolymer concrete). Geopolymer concrete presented almost 43% less carbon emissions, while also presenting high physic-chemical performance. It was verified that geopolymer concrete has the potential to help mitigate climate change, and can be employed as part of the plan to minimize the emissions associated with the construction sector.
Selective surfaces have the function of absorbing strongly the sunlight, while ideally losing lit... more Selective surfaces have the function of absorbing strongly the sunlight, while ideally losing little heat to the environment via convection and radiation. The present study sought to obtain a selective surface of black chromium coated with an antireflective (AR) layer based on sugarcane bagasse ash using copper as a substrate. From this selective surface the electrodeposition parameters (time, working distance, voltage) as well as the surface behavior were analyzed in order to determine if the AR layer provided an increase in the absorption levels of the film. By means of the present study it was possible to conclude that, in terms of the electrodeposition parameters evaluated, the anode-cathode distance of 5 cm stimulated the obtaining of higher levels of absorption. The addition of the antireflective layer on the black chromium films favored the increase of the absortance average in all the adopted parameter sets, besides reducing the standard deviation around the average. As for the microstructure of the obtained films, the increase of the parameter Ra promoted the increase of the absorption, due to the formation of optical traps.
The search for the reduction of costs for the implementation of renewable energies implies in the... more The search for the reduction of costs for the implementation of renewable energies implies in the optimization of the parameters of the manufacturing processes of consolidated technologies. Among these technologies are the solar collectors composed of absorber films characterized by high absorption in the spectrum range corresponding to solar radiation and low emittance in the infrared range, allowing an increase in the collector's operating temperature (300 to 700°C). The present work produced selective surfaces based on black chrome absorber films on stainless steel substrate by electrodeposition. The substrates were immersed in a chromium trioxide bath with hexafluorosilicic acid using a Pb-Sn electrode. In the project some parameters of deposition were evaluated (time, distance and voltage) and their influence on the surface roughness of the coatings obtained by correlating them with the absorptions of the produced surfaces. For this, the surfaces produced were characterized by UV-Vis-NIR, profilometry and SEM. The results indicate that the working distance directly influenced the increase of the films absorption and that the influence of the surface roughness on the film absorption is related to the electrodeposition time as the voltage is raised.
fissura do tipo MMF em placas metálicas (aço) coladas foram realizados. Os resultados apontam par... more fissura do tipo MMF em placas metálicas (aço) coladas foram realizados. Os resultados apontam para a possibilidade de utilização desses novos adesivos, mostrando em certos casos uma aderência mais eficiente do que aquela obtida com a resina epóxi. Palavras-chave: Aderência, geopolímero, metal. INTRODUÇÃO Juntas coladas são consideradas a principal alternativa às juntas mecânicas convencionais, tais como: rebites, parafusos e soldagem. Na indústria automotiva, de quatro a cinco quilos de cola são atualmente empregados na união de diferentes peças do carro e a tendência é de que essa quantidade vá aumentar ainda mais. Esse aumento se deve, dentre outras razões, a melhor distribuição de tensões na junta, a redução de custos, 18º CBECiMat -Congresso Brasileiro de Engenharia e Ciência dos Materiais, 24 a 28 de Novembro de 2008, Porto de Galinhas, PE, Brasil.
Stabilization is a common practice to improve the properties of earth used in the different ways ... more Stabilization is a common practice to improve the properties of earth used in the different ways in the field of construction. Nowadays, the most utilized products to stabilize the earth are lime, Portland cement and bituminous emulsions. In the last decades, geopolímers appeared as an alternative binder, being used also to produce concrete. Geopolimers are synthetic material made by alkaline activation of solid particles rich in silica and alumina. For good activation, it is necessary that these materials are in the amorphous form, as in metakaolin, slag and fly-ash. The earth clay fraction is composed by aluminum-silicates. So both the desirable materials are available, even if the great part of them is in the crystalline form. This work presents the first results about compressed earth stabilized by geopolymers. The geopolymeric binder was composed by metakaolin activated by sodium silicate and sodium hydroxide. Three percentages of geopolymers were used. Earth compressed prism o...
Alcaline activation of alumino-silicate materials have attracted significant attention of the sci... more Alcaline activation of alumino-silicate materials have attracted significant attention of the scientific community. This is chiefly due to properties such as good thermal stability and high resistance to aggressive environments. Most studies on this subject are based on traditional precursor materials such as calcined kaolinite clay (metakaolinite) and fly ash. In the tropical regions of the earth, there are other aluminosilicate containing materials, such as red tropical soils (RTS). In this type of soil, alongside with the presence of other alumino silicate phases such as kaolinite, the levels of iron (Fe 2 O 3) are as high as 60%. Their alkaline activation potential is, still, needed of systematic evaluation. The aim of this work is to evaluate the potential of RTS as a precursor for the development of geopolymers. The mechanical properties and the structural characteristics of the samples were evaluated by means of compressive strength and x-ray diffraction, x-ray fluorescence, ...
Lightweight concrete shows good insulation properties, depending on several parameters such as mi... more Lightweight concrete shows good insulation properties, depending on several parameters such as mix design and aggregate type. Perlite aggregate is one of the most effective aggregates for such a purpose, mainly because of its low thermal conductivity (0.04 W/m.°C), but is not available globally. This paper explores the potential use of another source of thermal efficient aggregate, vermiculite (0.058 W/m.°C) which is available in Brazil and other countries where perlite is absent. Cylindrical samples were cast by using two lightweight aggregates, perlite and vermiculite, and treated with supercritical carbon dioxide. Supercritical carbonation (SCC) of concrete can improve mechanical, thermal and durability features. In this paper, the effect of SCC on the thermal behavior of lightweight mortars was investigated with regards to physical and microstructure features and thermal behavior due to cooling.
Materials Research-ibero-american Journal of Materials, 2021
The world is moving at a fast pace in the consumption of non-renewable natural resources, causing... more The world is moving at a fast pace in the consumption of non-renewable natural resources, causing several ecological problems. The search for the cost reduction by implementing renewable energies implies in the optimization of the manufacturing processes parameters of consolidated technologies, such as solar thermal energy collectors. One of the applications of selective surfaces is to improve performance of solar absorbers. The purpose of this work is to produce selective coatings with high absorption in range of UV/Vis and low emittance in the IR range. It was prepared a selective surface composed of ilmenite deposited on substrates of AISI 304 stainless steel using technique of cathodic cage plasma nitriding/deposition for application in solar thermal absorbers. Ilmenite was initially characterized by X-Ray Diffractometry (XRD), X-Ray Fluorescence (FRX) and Thermal Analysis (TGA). The coatings produced were optically characterized in range UV/Vis/IR and emittance and data on the ...
Revista Principia - Divulgação Científica e Tecnológica do IFPB, 2021
Life Cycle Assessment (LCA) quantifies the environmental impacts associated with products through... more Life Cycle Assessment (LCA) quantifies the environmental impacts associated with products throughout their life cycle. LCA also assists in the interpretation of impact assessment results, enabling improvements in a product or process. This paper applied the LCA methodology to quantify and compare the greenhouse gas emissions associated with different types of concrete: with a traditional binder (Portland cement) and with alkali-activated materials (Metakaolin, Lateritic Soil, and Lateritic Concretion) as precursors. The environmental impact was evaluated by means of greenhouse gas emissions (kg CO2-eq/m³), considering 1m³ of each binder and resistance of approximately 30 MPa, obtained by a recommended mix ratio. The main objective is to evaluate whether alkali-activated binders present lower emissions than Portland cement. The results demonstrated that Portland cement is responsible for over 92% of the environmental impacts of traditional concrete production. The use of alternative materials in civil construction, such as laterite soil, reduces carbon dioxide emissions by 79% compared to Portland cement concrete emissions. Keywords: Life Cycle Assessment. Carbon Footprint. Concrete. Portland cement. Alkali-activated materials. Resumo A Avaliação de Ciclo de Vida é um método que permite quantificar os impactos ambientais de um produto ou processo ao longo do seu ciclo de vida. Ele também auxilia na interpretação dos resultados, com a finalidade de permitir melhorias no produto ou processo. Este artigo aplicou a metodologia em questão para comparar o processo de obtenção do concreto com o ligante tradicional, o cimento Portland, e os materiais alcalinamente ativados tendo como precursores o Metacaulim, o Solo Laterítico e a Concreção Laterítica. O impacto ambiental foi avaliado por meio das emissões de carbono (kg CO 2 /m 3) considerando 1m 3 de cada aglomerante, em função do traço recomendado para se obter concreto com resistência de aproximadamente 30 MPa. O objetivo principal desse trabalho foi avaliar se os aglomerantes alcalinamente ativados são mais sustentáveis do que o cimento Portland. Os resultados obtidos nesse trabalho mostraram que, na construção civil, a utilização de materiais alternativos como o solo lateritico torna possível uma redução de 79% das emissões de dióxido de carbono, quando comparado com as emissões do concreto de cimento Portland. O cimento Portland é responsável por pouco mais de 92% dos impactos ambientais ocasionados na produção do concreto tradicional.
Known since the 70's, geopolymers are synthetic materials of acknowledged interesting chemic... more Known since the 70's, geopolymers are synthetic materials of acknowledged interesting chemical, mechanical and thermal performance. As far as environmental issue is concerned, the use of alkali-activated industrial by-product precursors and the near-room casting temperature (around 60oC) can be seen as an advantageous choice for many applications such as in thermo-mechanical ecient steel coatings. Whereas most epoxy resin would char at temperatures above 300oC, geopolymers can upheld good mechanical performance in temper- atures as high as 1000oC. Although they have mostly been studied for coatings, the number of studies on their adhesion mechanisms is considerably less then those regarding its other properties. The main thrust of this work is to evaluate the binding potential of alkali-activated clay-based waste in steel bonded plates. The adhesion of steel plates (40x160x5mm) was evaluated using three clay-based wastes and metakaolin (MK) as precursors, provided by X-Ray fluo...
Geompolymers and their engineering applications have attracted significant attention of the scien... more Geompolymers and their engineering applications have attracted significant attention of the scientific community. This is due to properties such as good thermal stability and high resistance to aggressive environments. Most studies on this subject are based on traditional precursor materials such as calcined kaolinite clay (metakaolinite) and fly ash. The iron content is significant, reaching around 10% in metakaolinite, for instance. The role of iron in geopolymers still lacks systematic investigation. This can be attributed to the limitations presenting nuclear magnetic resonance (NMR) spectroscopy, which is a widely used technique to study geopolymers structure. Ferromagnetic elements such as iron, which is often present in some precursors, affect the magnetic response of the material, compromising the proper analysis of its structure by NMR results. Iron content in some industrial residues may be several times higher as it is often found in metakaolinite. This work presents x-ra...
The main purpose of this work is to perform a thermal analysis in an air conditioning duct to ver... more The main purpose of this work is to perform a thermal analysis in an air conditioning duct to verify the influence of the thermal properties of the insulating material on the minimum thermal insulation thickness necessary to avoid the condensation of water vapor present in the air. The mathematical formulation is based on Fourier’s law and the first law of thermodynamics. A response surface, a contour plot and a mathematical model for the analyzed response variable, were obtained from an experimental design. Results indicate that the reduction of thermal conductivity and increase of emissivity of the insulating material contribute to the reduction of the minimum thermal insulation thickness.
Alkali-aggregate reaction is a pathology directly linked to interactions between solubilized alka... more Alkali-aggregate reaction is a pathology directly linked to interactions between solubilized alkali hydroxides in the pore structure concrete and other chemical species from aggregates. In the presence of excessive water, these chemical interactions lead to the precipitation of gel-like phases within aggregates, paste-aggregate interface and cement matrix, causing expansion due to internal pressure in concretes that can promote disruption. It appears that the volume expansion of silica gels tends to have a maximum at the total dissolved silica. Both alkali and silica are needed to chemically stabilise alkaline activated cements (AAC-geopolymers). Therefore, this study aims to evaluate the potential use of geopolymers as mitigating agent of AAR. Four formulations were carried out in the study, three metakaolin based AAC were synthesized with different alkali types (100% sodium silicate, 100% potassium silicate and 50% of sodium silicate and 50% potassium silicate). Portland cement mo...
The present study evaluated the influence of two sugarcane bagasse ash (SCBA) beneficiation proce... more The present study evaluated the influence of two sugarcane bagasse ash (SCBA) beneficiation processes (sieving and high-energy milling) as an alternative to evaluate its absorption potential for application as a raw material for the production of solar absorber films. It was noticed that the absorption levels of all the samples were higher than 90% and that the SBCA has predominance of SiO2 corroborated by the mineralogical analysis. The thermal behavior of all the samples was similar among each other, presenting a total mass loss corresponding to 8.5%. As the ash is able to maintain a thermal stability in the temperature range of 100°C to 1000°C, and the chemical and mineralogical composition favors the absorption of solar energy, SCBA has proven to be favorable for application as raw material of selective solar surfaces.
Thermo-Fluid Dynamics Analysis of Fire Smoke Dispersion and Control Strategy in Buildings
Smoke is the main threat of death in fires. For this reason, it becomes extremely important to un... more Smoke is the main threat of death in fires. For this reason, it becomes extremely important to understand the dispersion of this pollutant and to verify the influence of different control systems on its spread through buildings, in order to avoid or minimize its effects on living beings. Thus, this work aims to perform thermo-fluid dynamic study of smoke dispersion in a closed environment. All numerical analysis was performed using the Fire Dynamics Simulator (FDS) software. Different simulations were carried out to evaluate the influence of the exhaust system (natural or mechanical), the heat release rate (HRR), ventilation and the smoke curtain in the pollutant dispersion. Results of the smoke layer interface height, temperature profile, average exhaust volumetric flow rate, pressure and velocity distribution are presented and discussed. The results indicate that an increase in the natural exhaust area increases the smoke layer interface height, only for the well-ventilated compar...
Titanium is considered the fourth most widely used material in industry worldwide. Titanium miner... more Titanium is considered the fourth most widely used material in industry worldwide. Titanium minerals are currently being applied in various branches of industry, mainly in the field of pigmentation. Ilmenite (FeTiO3) is an iron and titanium oxide of more common and abundant occurrence, with theoretical composition of Fe (36.8%), Ti (31.6%) and O (31.6%). Having regard to the potential of titanium minerals and the abundance of ilmenite, together with the importance of validating direct applications of this ore, since the processing of titanium is still complex and expensive, it is necessary to study this mineral and the knowledge of its main characteristics. This work brings thermal, chemical and mineralogical characterizations of ilmenite, in order to know the potential of application of this ore as a solar absorbing material. The characterization techniques used were: X-ray diffraction (XRD) and Rietveld refinement for phase quantification, X-ray fluorescence (XRF), optical spectro...
The cement industry is the second-largest single industrial emitter in the world and therefore ha... more The cement industry is the second-largest single industrial emitter in the world and therefore has an important role to play in reducing the intensity of its carbon emissions: participation of the sector is important to contribute to the goal of the Paris Climate Change Agreement to limit global warming. One of the strategies for reducing the carbon footprint of the cement industry is substitution of Portland cement, which is a component of the concrete mix widely used as a construction material worldwide. Geopolymer cement has emerged as an alternative for Portland cement, with several advantages. This study applied the Life Cycle Assessment methodology to quantify the carbon emissions associated with 1m 3 of two types of concrete (concrete PC-II cement-based Portland cement vs. geopolymer concrete). Geopolymer concrete presented almost 43% less carbon emissions, while also presenting high physic-chemical performance. It was verified that geopolymer concrete has the potential to help mitigate climate change, and can be employed as part of the plan to minimize the emissions associated with the construction sector.
Selective surfaces have the function of absorbing strongly the sunlight, while ideally losing lit... more Selective surfaces have the function of absorbing strongly the sunlight, while ideally losing little heat to the environment via convection and radiation. The present study sought to obtain a selective surface of black chromium coated with an antireflective (AR) layer based on sugarcane bagasse ash using copper as a substrate. From this selective surface the electrodeposition parameters (time, working distance, voltage) as well as the surface behavior were analyzed in order to determine if the AR layer provided an increase in the absorption levels of the film. By means of the present study it was possible to conclude that, in terms of the electrodeposition parameters evaluated, the anode-cathode distance of 5 cm stimulated the obtaining of higher levels of absorption. The addition of the antireflective layer on the black chromium films favored the increase of the absortance average in all the adopted parameter sets, besides reducing the standard deviation around the average. As for the microstructure of the obtained films, the increase of the parameter Ra promoted the increase of the absorption, due to the formation of optical traps.
The search for the reduction of costs for the implementation of renewable energies implies in the... more The search for the reduction of costs for the implementation of renewable energies implies in the optimization of the parameters of the manufacturing processes of consolidated technologies. Among these technologies are the solar collectors composed of absorber films characterized by high absorption in the spectrum range corresponding to solar radiation and low emittance in the infrared range, allowing an increase in the collector's operating temperature (300 to 700°C). The present work produced selective surfaces based on black chrome absorber films on stainless steel substrate by electrodeposition. The substrates were immersed in a chromium trioxide bath with hexafluorosilicic acid using a Pb-Sn electrode. In the project some parameters of deposition were evaluated (time, distance and voltage) and their influence on the surface roughness of the coatings obtained by correlating them with the absorptions of the produced surfaces. For this, the surfaces produced were characterized by UV-Vis-NIR, profilometry and SEM. The results indicate that the working distance directly influenced the increase of the films absorption and that the influence of the surface roughness on the film absorption is related to the electrodeposition time as the voltage is raised.
fissura do tipo MMF em placas metálicas (aço) coladas foram realizados. Os resultados apontam par... more fissura do tipo MMF em placas metálicas (aço) coladas foram realizados. Os resultados apontam para a possibilidade de utilização desses novos adesivos, mostrando em certos casos uma aderência mais eficiente do que aquela obtida com a resina epóxi. Palavras-chave: Aderência, geopolímero, metal. INTRODUÇÃO Juntas coladas são consideradas a principal alternativa às juntas mecânicas convencionais, tais como: rebites, parafusos e soldagem. Na indústria automotiva, de quatro a cinco quilos de cola são atualmente empregados na união de diferentes peças do carro e a tendência é de que essa quantidade vá aumentar ainda mais. Esse aumento se deve, dentre outras razões, a melhor distribuição de tensões na junta, a redução de custos, 18º CBECiMat -Congresso Brasileiro de Engenharia e Ciência dos Materiais, 24 a 28 de Novembro de 2008, Porto de Galinhas, PE, Brasil.
Stabilization is a common practice to improve the properties of earth used in the different ways ... more Stabilization is a common practice to improve the properties of earth used in the different ways in the field of construction. Nowadays, the most utilized products to stabilize the earth are lime, Portland cement and bituminous emulsions. In the last decades, geopolímers appeared as an alternative binder, being used also to produce concrete. Geopolimers are synthetic material made by alkaline activation of solid particles rich in silica and alumina. For good activation, it is necessary that these materials are in the amorphous form, as in metakaolin, slag and fly-ash. The earth clay fraction is composed by aluminum-silicates. So both the desirable materials are available, even if the great part of them is in the crystalline form. This work presents the first results about compressed earth stabilized by geopolymers. The geopolymeric binder was composed by metakaolin activated by sodium silicate and sodium hydroxide. Three percentages of geopolymers were used. Earth compressed prism o...
Alcaline activation of alumino-silicate materials have attracted significant attention of the sci... more Alcaline activation of alumino-silicate materials have attracted significant attention of the scientific community. This is chiefly due to properties such as good thermal stability and high resistance to aggressive environments. Most studies on this subject are based on traditional precursor materials such as calcined kaolinite clay (metakaolinite) and fly ash. In the tropical regions of the earth, there are other aluminosilicate containing materials, such as red tropical soils (RTS). In this type of soil, alongside with the presence of other alumino silicate phases such as kaolinite, the levels of iron (Fe 2 O 3) are as high as 60%. Their alkaline activation potential is, still, needed of systematic evaluation. The aim of this work is to evaluate the potential of RTS as a precursor for the development of geopolymers. The mechanical properties and the structural characteristics of the samples were evaluated by means of compressive strength and x-ray diffraction, x-ray fluorescence, ...
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