Resumo em Inglês:

Abstract Researches on building performance have been developed over time. The Brazilian Performance Standard - NBR 15575 - deals with the issues of durability applied to residential buildings, establishing criteria and parameters to classify the systems into minimum, intermediate and higher performance levels. In relation to the service life, studies are also associated with the building’s structural durability, in which the technical specifications and quality of materials, construction systems, building process, use and maintenance of the building are important factors for better performance. In order to evaluate the structural durability over the years, a case study was conducted in a building designed to meet the higher level established in the Brazilian Performance Standard, with service life of 75 years in the structural project, through the non-destructive surface hardness of concrete test by using a Schmidt hammer and semi-destructive carbonation tests. The superficial hardness test was conducted on a concrete column following the procedures of NBR 7584, while the carbonation samples were collected in 3 concrete columns in which a phenolphthalein solution was sprayed to observe the alkalinity of the samples. For all tests, three different heights were considered. The concrete testing hammer indicated an average surface hardness of approximately 50 MPa, and for carbonation tests, it was noted that the concrete was not carbonated at a depth of 5mm. So, the criteria of service life could be considered attended.

Resumo em Inglês:

Abstract The present research had as its basic objective to contribute with the improvement in the quality control evaluation of the compacting process in road works. The real contribution of the survey is to establish an innovative way of controlling the compaction process in the field, with employment of the Humidity versus Rigidity and the Humidity versus Elasticity Module curves, turning the methodology faster and more efficient than the conventional procedures. In fact, to date, the compacting control procedures contemplate methods that are inaccurate and limited by several constraints, rendering the technique unfeasible and time consuming, in detriment of the work schedule. Thus, this study proposes to define a rational correlation criterion between the geotechnical characterization with results obtained in the laboratory using conventional methods and the elastic parameters obtained by applying the rigidity meter of compacted soils, based on a statistical treatment of data concerning the infrastructure of experimental road and railway sections. The results obtained in the research were the correlation curves for Humidity versus Rigidity, and for Humidity versus Elasticity Module, for the material of the deposit, with the corresponding equations. Thenceforth, with the correlation curves, it will be much easier to obtain the moisture content that the soil requires on the earthworks. By measuring the modulus of elasticity or rigidity through the stiffness meter of compacted soils, the respective curve checks if the value of the soil moisture content is compatible with the variation of the moisture content in the project.

Resumo em Inglês:

Abstract High pressure abrasive water jets (HPAWJ) are an emergent excavation technology. Despite being used for several applications since the nineteenth century, it is only in recent decades that this excavation purpose has been considered. This is the result of evolution in high pressure pump technology and parameter investigation. Special highlight should be given to optimization works which improve knowledge about the main parameters. However, studies usually neglect the importance of HPAWJ cutting strategies, and only consider bidimensional approaches as options for nozzle movement. This article analyzes and proposes an operational cycle based on a tridimensional approach for HPAWJ. Higher removal rates and lower energetic consumption are expected in comparison with traditional strategies.

Resumo em Inglês:

Abstract The reduction of natural resources combined with a substantial increase in the generation of solid waste in large urban centers, justifies the search for methods of reusing the construction industry waste. The ceramic industry has a high disposal rate during the manufacturing, transportation and eventual replacement of its products. In this case, research on the reuse of ceramic materials is urgent. A possible solution is the employment of ceramic waste as a coarse aggregate in structural concrete. Therefore, the mechanical properties of this new mix of concrete have to be assessed. This study evaluates the bond strength between steel rebar and concrete with ceramic waste aggregates, by means of the pull-out test method, proposed by RILEM-FIP-CEB (1978). Three concrete mixtures were produced: a mixture without any replacement, and two other mixtures with gradual substitution of natural coarse aggregate by ceramic coarse aggregate (40% and 100% substitution, in volume). Nine cylindrical specimens, three for each of the concrete mixtures, were evaluated in laboratorial conditions. Results concerning bond stress between concrete and steel rebar indicated the feasibility of employing ceramic waste to replace part of the coarse aggregate in structural concrete.

Resumo em Inglês:

Abstract The Itabira Iron District, located at the northeastern end of the Iron Quadrangle, still presents some uncertainties regarding the tectonic origin of its macrostructure. The Itabira synclinorium is characterized by a large synformal structure in the NE-SW direction, with anticlines and synclines distributed "en echelon". The analysis of the relationship between the primary structures and the plane-axial schistosity, linear and planar structures, allowed the development of a three-dimensional model for the region. The increase in deformation from E to W, observed from the Cauê mine to the Conceição mine, and the rotation of the axes of the macrostructural folds, characterized by the Cauê, Dois Córregos, and Conceição synclines, are explained in this study by a model with six deformation phases. The increase in shortening from the Cauê mine towards the Conceição mine can be explained based on the flanking fold model. The application of this mechanism to explain kilometric-scale folding has been presented for the eastern flank of the Santa Rita Syncline in the Iron Quadrangle.

Resumo em Inglês:

Abstract The characterization presented in this study aims to identify and map the different types of pedogeomorphic units found in a 7th order, the Pandeiros river basin, in the upper São Francisco River (1st order basin), located in the North of Minas Gerais State. A general panoramic view of the geodiversity is presented, since the Pedogeomorphic Maps allow a visualization of the spatial distribution of the main pedogeomorphic classes, providing important information for various purposes, such as teaching, research and land-use planning. These Maps are relevant specifically for the territorial planning, even without providing data of the local use and occupation because they have strategic information for the understanding and evaluation of the landscape dynamics in region, offering subsidies to the understandings of the processes, phenomena and behaviors of the physical environment related to the different forms of interference of human actions. The Maps also provide support for environmental assessments that have been applied to identify, characterize and monitor trends in environmental aspects.

Resumo em Inglês:

Abstract The large amount of dust generated in electric arc furnace aligned with its chemical composition makes this dust a potential source of iron in the direct reduction iron process. Thus, the aim of this research is to investigate the reduction of pellets produced with electric arc furnace dust using hydrogen as the reducing agent. The kinetic investigation was examined applying the differential method. In addition, the influence of reducing gas stream and temperature in the reduction process were investigated applying the Forced Stepwise Isothermal Analysis technique. The temperature studied varied from 500 to 1000°C with isothermals in each 50°C. The reducing gas was a mixture of 10% of hydrogen and 90% of argon. Then, the product characterization was carried out via scanning electron microscope and X-ray analysis. A thermogravimetric test showed a mass loss of 42 wt% due to the reduction of iron and zinc oxides. Besides this, the reduction occurred in three steps: 550-650°C, 700-800°C, 850-950°C. Between 550-650°C, the reduction was controlled by a nucleation mechanism with an Ea of 41.1 kJ/mol. In the second step (700-800°C), a mixed control between nucleation and diffusion was obtained with an Ea of 89.1 kJ/mol. Furthermore, a crust of iron was formed around the pellet, which hindered the reducing gas diffusion into the pellet. In the third stage (850-950°C), the formation of a sintered structure was noted, which decreased pore volume. The internal diffusion of reducing gases was determined as the controlling mechanism, with an Ea of 130.9 kJ/mol.

Resumo em Inglês:

Abstract The demand for sustainable materials in the steel industry and the search for alternatives for the traditional ferriferous burdens utilized in siderurgy stimulated the development of this research. The briquetting process is a usual measure taken for recycling materials such as ironmaking waste (dust and sludge from blast furnaces), which can be reutilized in steel plants. The objective of this article is to investigate the influence of the use of organic and inorganic binders, blast furnace dust and sludge on the mechanical strength of briquettes for use in blast furnaces. The mechanical analysis was performed with the results from tumbling tests, executed to obtain the strength of each sample composition. The results exhibited adequate values of mechanical strength for samples that contained BBTL and BBTX binder, indicating that these materials acted as good binders in the briquetting process.

Resumo em Inglês:

Abstract The amount of Electric Arc Furnace Dust (EAFD) is continuously increasing in mini-mill steel plants. This dust is considered a hazardous waste because of the presence of elements like lead, cadmium and chromium. Among many different treatment processes for this issue, there is the possibility of returning the EAFD back to the Electric Arc Furnace. This article presents a study of the compressive strength of self-reducing cold bonded pellets as well as their zinc removal, in an agglomerate containing EAFD, petroleum coke (PET) and Portland cement. The effects of the reductant and binder employed were discussed. Moreover, an apparatus was built to prevent zinc gas reoxidation inside an electric vertical laboratory furnace. Thus, the fraction of weight loss complemented the result of a previous study indicating the optimal content of PET source usage between 10 to 15%, in mass. Zinc removal and additional X Ray Diffraction outcomes are shown and discussed, concluding that 80% of zinc removal for this system could indicate the possibility of the EAFD reuse.

Resumo em Inglês:

Abstract Organic matter-in-aqueous entrainment is a serious problem in the hydrometallurgical extraction of copper from ore. Current inefficiencies, changes in the morphology and orientation of cathode deposit are some of the problems when organic matter is present in the advance electrolyte. In addition, negative effects upon metabolic activity of bioleaching microorganisms are reported due to entrained organic matter in the raffinate electrolyte. In view of these problems, the objective of this study was to evaluate ozonation as an alternative method for the removal of entrained organic matter present in an advanced electrolyte. For this purpose, ozonation during 30 min of synthetic solutions using a bubble glass column reactor at different ozone concentrations, flow rates and temperatures were studied. It was found that the increase in all of these operating parameters is not necessarily associated with an increase of the removal efficiency, and their effects on the mass transfer rate, chemical reaction rate, ozone solubility and contact time play a decisive role in the ozonation process. Thus, the best operating conditions were found at 6.7 wt.%, 1 L min-1 and 27 °C and reached a removal efficiency of 94.5%. This result demonstrated that removal of entrained organic matter in strongly acid solution by ozonation could be an alternative technology.

Resumo em Inglês:

Abstract Blends of Polystyrene (PS) and Poly(ε-caprolactone) (PCL) were twin screw extruded, two PSs, with low and high melt flow rate (MFR) were used and their feasibility within PCL investigated by means of torque rheometry, mechanical tests, heat deflection temperature (HDT) and scanning electron microscopy (SEM); predictive models were utilized to evaluate interfacial adhesion in PS/PCL blends. Results show that no decreasing was verified in torque rheometry plots suggesting thermally stable blends; elastic modulus decreased and elongation at break increased in PS/PCL blends compared to neat PS. PS/PCL blends with low MFR PS and higher PCL amount are more thermodynamically stable. Higher HDT was verified in PS/PCL blends. The trends observed applying predictive models are indicative of poor adhesion between PCL and PS, agreeing with coalescence and phase segregation as verified in SEM images. PS/PCL systems with higher MFR PS presented the best results.

Resumo em Inglês:

Abstract Pitting corrosion resistance of two austenitic stainless steels, 18Cr8Ni (Type 304L or UNS S30403 stainless steel) and 17Cr6Mn5Ni, was evaluated in three electrolytic solutions containing a fixed concentration of 0.6M sodium chloride and different additions of sodium sulfate, 0.06M, 0.15M or 0.6M. Cyclic potentiodynamic polarization tests were performed on as-received samples and on specimens annealed at 1010°C, 1040°C, 1070°C or 1100°C. The best pitting corrosion resistance was presented by the 17Cr6Mn5Ni steel annealed at 1070°C or 1100°C, with lower delta ferrite contents, in the electrolyte with the highest sulfate concentration. It can be found that the addition of sodium sulfate inhibits pitting corrosion and has a better inhibitor effect in the high manganese steel.

Resumo em Inglês:

Abstract The use of the sediment deposited in the Candonga dam after the collapse of the Fundão dam is being considered as raw material for civil construction. Blocks were obtained by adding 5 % of sodium carbonate and 13 % of water to the dried dredged sediment, which was mixed and heat treated at 700 ºC and cooled slowly inside the oven to room temperature. The water absorption of the blocks was in the 12-16 % range, the loss of mass in water was (0.01±0.01) %, the density was (1.95±0.03) g/cm3, the compression strength was (11.05±1.29) MPa (reference value ≥ 1.7 MPa), and the flexural strength was (4.42±0.69) MPa (reference value ≥ 3.5 MPa). Small cracks and pores, as well as the growth of white spots (efflorescence) were observed on the surface of the blocks, which can be avoided or attenuated by improving the compaction pressure and the heat treatment.

Resumo em Inglês:

Abstract In order to increase competitiveness in the steel industry through reduction of the cost of coal mixtures and increase in the quality productivity of coke in the oven, this research was developed with the aim of increasing the bulk density through briquetting of low power coking coal using tar as a binding material. Initially an industrial scale double roller press was used to manufacture briquettes in the ellipsoid format. The physical properties of the briquettes were analyzed in relation to variation of the amount of tar and the curing time of briquettes. Through the process of coal briquetting using low amounts of tar, it is possible to obtain a fuel of greater density, greater use of soft coals, uniform granulometry and easy handling. The increase in the apparent density of coal through briquetting may reach 42.5%. The success achieved in these tests, through these briquettes, with good chemical and physical characteristics represents ease of production as well as economic gain and low investment when compared to other processes of charge densification in coke ovens.

Resumo em Inglês:

Abstract The injection of pulverized materials is a technique used in most of the blast furnaces in the world to reduce coke and charcoal consumption. In addition, injection is one of the main variables of the blast furnace heat control. Coal is the most used material for the injection, but some industries have been attempting to use other materials, usually mixtures, in order to reduce the total dependence on it. The quality of the injected material influences some operational parameters, such as the permeability, the heat control, and also the quality of the hot metal produced. Due to these factors, the strategy and quality of these materials should be planned and evaluated using quality indicators to achieve good production, with low cost and environmental impact. In this context, there is a large number of researches on different materials, especially waste from iron and steelmaking processes, among others. Herein, some quality indicators of different materials tested on industrial and laboratory scales were analyzed compared, and the feasibility of using new materials injected into the blast furnace was discussed.

Resumo em Inglês:

Abstract Pulverized coal injection (PCI) into blast furnace tuyeres is widely used by integrated steel mills worldwide to reduce the consumption of coke and costs. High injection rates are desirable. The big challenge is to achieve them with cheaper and lower quality raw materials, without losing the quality of the hot metal and the productivity of the blast furnace. An increase in the injection rate leads to improved fuel selection. Thus, it is important to have knowledge of the injected fuel quality variables that affect the burning efficiency and the replacement rate of the coke into the furnace, as well as the quality of the hot metal and the stability of the furnace. In this context, the present study is based on the chemical characterization and combustibility behavior of four fuels: Australian coal (CMA), North-American coal (CMN), charcoal fines (MCV) and green petroleum coke (CVP) and fuel blends. Results of chemical analysis show that the CMA, CMN, MVC and CVP are within the ranges of acceptable values in the PCI process for the ash and sulfur contents. The order of combustibility by thermogravimetric analysis was MCV>CMN>CMA>CVP. However, the combustion rate obtained by the simulator test, performed under extreme conditions of short residence time and high temperature, presented a different order of combustion rate of MCV>CVP>CMA>CMN, which may be related to the mineral on char. The blend that presented the best burning efficiency was obtained for the composition containing 20%MCV+80%CVP, followed by blends containing 80 and 90% of CMA, respectively.

Resumo em Inglês:

Abstract The design of room-and-pillar mines relies on the correct estimation of the safety indicator of the underground structures formed by the excavation of drifts. Thus, the study of the geomechanical behavior is of vital importance. The mathematical models play an important role in the identification of problematic areas and allows different configurations to be tested in a safe manner. This article presents the development and application of a flexible and automatic routine to quantify the safety of room-and-pillar mines in terms of the safety factor of pillar and room convergence. The commercial software package FLAC3D was used to implement a computation routine in FISH language that can automatically represent the main characteristics of the geomechanical conditions, lithology and geometric features of a room-and-pillar project in a fast and accurate manner. A case study was performed on a manganese ore mine in order to demonstrate the capabilities of the developed routine.

Resumo em Inglês:

Abstract Rock blasting is the first phase of comminution, completed by mechanical means downstream in the crushing and milling phases. Nevertheless, mineral processers and blasters seldom work together. The total energy of mechanical comminution depends on feeding grain size and on the internal resistance of the material to grinding. Blasting heavily influences both of these aspects: i) it induces visible fracturing: this is the particle size distribution visible to the naked eye, that is measurable by means of image analysis or sieving; ii) it induces invisible fracturing: this is the system of micro-fractures, invisible to the naked eye, that are detectable only by microscopic analysis but show their direct effect by reducing the grinding energy ("softens" the material). A proper management of blasting can greatly benefit the comminution circuit. In this article, the author analyzes data from literature and from field experiments and discusses the benefits that rock blasting can produce for the comminution process.

Resumo em Inglês:

Abstract The application of the centrifugal concentration gains importance in the world scenario, considering the low environmental impact and the concentration of fine particles. Literature does not present articles using centrifugal concentration (Falcon) for chromite. The material used in the tests is the tailings from a Northeastern Brazil concentration plant, which was homogenized in the laboratory. In the process assays, the number of G (25-300 G) and the fluidization water pressure (20-100 kPa) were optimized. The initial tests used a wide range of particle size of 1 kg mass, with the "best results" being for 50 and 100 G at a pressure of 60 and 80 kPa, respectively, where a metallurgical recovery of 25% and grade close to 20% of Cr2O3 were obtained. The amount of mass showed to be a significant variable in the process, being 250 g the ideal for the material used, which obtained considerable recoveries, even though the grade is still low. These results led to a cut at 250 µm, considering that the liberation of the chromite is of the order of 77 %. The best result was with 150 G and fluidization water pressure of 60 kPa for a metallurgical recovery of 72% and a grade of 28% Cr2O3.

Resumo em Inglês:

Abstract Researchers have found that a valuable alternative for predicting the mechanical behavior of landfill construction is numerical simulation based on the finite element method. The results of such a numerical simulation for a sandy tailings deposit from the iron mining coupling flow and deformation are presented herein. This study investigates the influence of the construction rate, drainage system, and anisotropy of permeability on the magnitude of pore pressures generated during the construction process. The study also presents the results from different analyses considering different constitutive models including elastic, nonlinear elastic and nonlinear elastoplastic. In obtaining the constitutive parameters, the numerical results highlight the importance of having a more detailed set of conventional triaxial compression tests. Also highlighted by the numerical results is the importance of having an efficient drainage system and the necessity of taking into account the water level variation in the hydro-mechanical behavior of numerical simulations of landfills that are hydraulically constructed.

Resumo em Inglês:

Abstract Grinding has become one of the most important unitary operations for producing pellet feed for direct reduction from low-grade ores and small liberation size, such as compact itabirites. The aim of this study was to evaluate and compare two grinding circuits in an industrial iron ore plant, by evaluating the current operation through sampling, industrial data analysis and mass balancing. The flows analyzed were the grinding circuit, flotation throughput and desliming hydrocyclone overflow. In total, two grinding circuits were tested. One circuit had two mills installed in series, with the first mill operating in an open circuit and the second mill, in a reverse closed circuit. The second grinding circuit involved two mills operating in parallel, both in direct closed circuits. The results indicated that the parallel circuit produced 20% less slime than the series circuit, with an additional 4.3% throughput in the flotation feed. No circuit produced particles (> 0.15mm). The parallel circuit spent less 8.3% of energy by not using one of the hydrocyclone batteries.

Resumo em Inglês:

Abstract High anomalous grades are very common in gold deposits, whose presence requires careful treatment to prevent overestimation of metal content. Mineral resource analysts have worked on the estimation of several gold deposits, and none of the classical methods were able to avoid manual interventions, such as cutting high grades for local estimation or using more information beyond the data for the variogram inference. The Field Parametric Geostatistics (FPG) is presented as an alternative for the application of linear kriging methods to estimate highly skewed distributions, proposing a mathematical model which incorporates the grades and its representativeness into a new variable, reducing the influence of high grades without empirical manual interventions. In this article, the mathematical formulation of the FPG theory is presented, as well as its application in datasets with outliers and high skewed distributions: the Walker Lake dataset and the Amapari gold deposit. The results are compared to results obtained by the application of standard techniques, demonstrating that FPG is a feasible alternative to estimate local grades and local reserves for highly skewed variables.