Resumo em Inglês:

Abstract The procedures for design and reinforcement projects regarding flexible pavements available in Brazil are mostly based on empirical models developed from studies carried out in specific localities, and therefore, should only be used in cases where equivalent climatic and traffic conditions are observed. The national highway agencies in partnership with universities and research centers have been working to change this scenario through the development of a mechanistic-empirical method that is more compatible with the Brazilian geographic and technical-scientific realities. The first outcome of this task force is the computer program MeDiNa, which is still under assessment. In this present study, the new flexible pavement software in Brazil (MeDiNa) was used by the Federal University of Juiz de Fora to calculate the overlay asphalt of its the ring road, aiming to recover its functional proprieties. This pavement was evaluated functionally by Computerized Continuous Visual Survey (CCVS) and tests of longitudinal cracks, and structurally by survey deflection measurements (FWD) and shaft sinking. With the data collected from the structural evaluation, the homogeneous segmentation of the stretch and the back-calculation of the data was carried out, aimed at the acquisition of needed parameters for the calculation. After the appropriate design, it was concluded that the best solution for the overlay is resurfacing along its entire length, with the use of the project’s asphalt mixture with single thickness of 5.0 cm, observing the application of the anti-reflective cracking layer in some stretches.

Resumo em Inglês:

Abstract This article introduces a hassle-free methodology for geotechnical parameters to be obtained from correlations between geophysics and CPT field tests in tailings dams undergoing the decommissioning process, which are reasonably representative of site conditions, from the very early project stages, with extensive coverage of all impoundment parts, without the requirement for large-size drilling programs. The development methodology consists of running direct (CPT) and indirect (geophysics) tests within the same area of the tailings dam to be decommissioned, with information crosschecking, thus allowing for results to be presented as adjustment equations, capable of describing tailings undrained shear strength based on geophysical survey data. A dam within the region known as Iron Quadrangle, in the state of Minas Gerais, Brazil, was selected to pilot the tests. The results obtained showed consistent adjustments, thus validating the proposed methodology as a complementary geotechnical investigation tool, and also enabling an optimized investigation plan to be proposed for similar tailings dams undergoing a mining process, so as to provide better assessment of the safety conditions of the proposals for deactivation with reduced schedule and resource savings.

Resumo em Inglês:

Abstract This article presents a study on the performance of semi-empirical methods based on the Standard Penetration Test (SPT) for the prediction of bearing capacity already disseminated in the practice of Brazilian Foundation Engineering (Aoki and Velloso, 1975; Décourt and Quaresma, 1978, 1996; Teixeira,1996), together with the recent method proposed by Pereira (2020), and the theoretical method known as a Method (disseminated around the world). These were applied to precast concrete piles based on sandy clay in the Uberlândia-MG region. In the performance analysis, the ultimate shaft and tip resistances and the bearing capacity values, which were utilized as references, were mobilized in the dynamic loading tests performed on ten piles. The results of these tests were compared with those obtained using the mentioned methods. In general, both methods yielded robust results, with relatively accurate predictions, except the a Method, which was found to perform below the semi-empirical methods considered. The research still highlights the need for discretion in the application of semi-empirical/theoretical methodologies because there are certain scenarios wherein these methods can yield inaccurate results.

Resumo em Inglês:

Abstract The reutilization of waste is a valuable alternative for the preservation of natural resources and the environment. In this sense, Basic Oxygen Furnace (BOF) steel slag is one of the most residues generated in steel the industry. It is estimated that for each ton of steel produced, about 150 kg of steel slag is generated in the BOF process. Generally, the newly produced BOF steel slag is volumetrically unstable, presenting expansive characteristics, and for this reason, its application should be based on stabilization studies. The main objective of this research was to analyze the chemical stabilization process of BOF steel slag by means of carbonation of the material. For this purpose, an experimental method based on hydration and carbonation in 2-meter high slag piles, moistened with sprinklers and instrumented with leaf wetting, temperature, precipitation and carbon dioxide content sensors was used. A control stack was also set up to accompany the stabilization process through the conventional procedure, in which the material is disposed of in large stacks and subjected to the weather conditions for long periods. The laboratory campaigns were developed in the laboratories of the Federal University of Ouro Preto. Thus, through the results obtained, it was possible to conclude that the stabilization method based on hydration and carbonation for the BOF steel slag was efficient, reducing the free lime content to values well below those prescribed internationally.

Resumo em Inglês:

Abstract Landslides can substantially impact the fluvial systems, which is why the continuous mapping of their extent, evolution and stability assessment is crucial. However, in such environments, material identification (e.g. colluvium) and subsurface characterization by the methods used for geologic mapping and geotechnical investigation is often a challenging task. Thus, these classical invasive methods may benefit from geophysical techniques to enable and enhance our understanding of the subsurface in these areas. To examine such integrated approach, Multi-Channel Analysis of Surface Waves (MASW) combined with Electrical Resistivity Tomography (ERT) were applied on a geomorphologically active fluvial valley in Sobradinho (the Federal District of Brazil). The subsurface materials showed a specific range of resistivity values as dry soil, saprolite, and landslide slip surface. The 1D shear wave velocity (Vs) model showed an increasing trend of Vs with depth at a location away from the landslide mass, while the longitudinal profile (over the landslide) showed an anomalous change in Vs (~ 250 to 400 m/sec). Based on the existing information about the landslide, the ERT appeared to be an effective method over MASW. This study shows how the integration of geophysical data with the geological and geotechnical investigation helps to obtain a more realistic or unambiguous model of the subsurface.

Resumo em Inglês:

Abstract The Guacuí and Batatal lineaments in the southern region of the state of Espírito Santo (southeastern Brazil) can be traced from satellite images for tens of kilometers. They are considered shear zones associated to the final tectonic stages of the Araçuaí-West Congo (A-WC) Orogen during the Ediacaran-Cambrian period. In order to understand their nature and tectonic implications for the development of the orogeny, we integrated geological and structural data based on fieldwork and detailed microstructural analysis. Data was collected along two profiles located at the central segments of both structures. The results demonstrated that the Guaçuí shear zone (GSZ) is a typical ductile transpressive shear zone with approximately 9 km width that shows numerous dextral kinematic indicators and records metamorphism of upper amphibolite facies. The GSZ shows different levels of intensity of dynamic deformation. The Batatal shear zone (BSZ) is a narrow brittle shear zone that shows essentially brittle microstructures (intercrystalline microfractures) revealing deformation at low-grade conditions (frictional regime). Based on their characteristics and the level of erosion of the rocks exposed in the region, we interpret that GSZ developed prior to BSZ.

Resumo em Inglês:

Abstract Synthetic slag has been added during BOF tapping in order to modify the physicochemical properties of resulting slag with the aim of assessing the influence on inclusion density, composition and size distribution. Viscosities and activities of slag oxides were calculated by FactSage 7.2, using the FToxid database and Viscosity module. All heats were treated under vacuum in an RH degasser for 15 minutes. A comparative analysis of top slags with two levels of FeO+MnO (> 10% and ≤ 10%) was carried out. The higher level of FeO+MnO led to almost thrice more inclusion than the lower level. Top slags after treatment with synthetic slag brought the best result of inclusions features thanks to their higher CaO activity, lower viscosity and lower activity of Al2O3. These heats presented smaller inclusions and lower initial inclusion density at ladle arrival at RH. Based on these evidences, top slags with synthetic slags added during the tapping and FeO+MnO content ≤ 10% conferred the best condition in steel cleanliness.

Resumo em Inglês:

Abstract The microstructure of the main structural elements (Phoenix columns, transversal beams and tie-rods) of the Simón Bolivar iron bridge, located in Arequipa (Peru), was investigated. The bridge was supposedly designed by Gustave Eiffel and opened to the public in 1882. The characterisation revealed that the columns, beams and tie-rods are made of puddled iron (ferritic matrix of equiaxial grains and numerous slag inclusions). The tensile properties were estimated by hardness and nanohardness measurements, and the tensile strength varied between 285 and 390 MPa and the Young's modulus from 187 to 198 GPa. The components of puddled iron with the same provenance, Phoenix Iron Company, showed typical variations in the chemical composition and microstructure of the slag inclusions. The microanalysis results of the slag inclusions indicated that the wüstite phase presented qualitatively the same composition with pronounced variations in the ratio between V2O5 and TiO2 contents, confirming that a single parameter cannot be used to determine the provenance of iron artefacts. The intense presence of slag inclusions in the puddled iron components (~ 10% in volume fraction) heterogeneously distributed in the iron illustrates the technological limits of the iron refining technique of the time.

Resumo em Inglês:

Abstract Gas injection in the tundish has been considered as an alternative to optimizing inclusion removal from steels. In the present study, physical and mathematical modeling were used to investigate the effect of gas injection in the tundish on the inclusion removal efficiency. The physical model is a 1/3 reduced scale of an industrial two-strand tundish of 40 tons. The inclusion removal efficiency was quantified using the APS III probe, which counts particles leaving the tundish during the test. Different locations for the gas injection plug were evaluated. Additionally, a mathematical model was developed using commercial CFD software CFX. The predictions of the mathematical model were validated by the physical model results, comparing the efficiency of inclusion removal. The proposed model includes a new boundary condition to describe the behavior of the particles at the free surface, implemented by a special subroutine. The model enabled the identification of appropriate conditions: plugs located at 0.56 or 0.84m from the tundish inlet with gas injection with the flow rate of 3NL/min.

Resumo em Inglês:

Abstract The microstructures of steels are altered when exposed to high working temperatures for long periods, which results in varied physical and chemical proprieties. This study evaluates the erosive wear behavior of ASTM A106 steel after it is exposed to high temperatures for long durations. Samples of normalized ASTM A106GrB steel were placed in a muffle furnace at 530 and 630 °C for 50, 100, and 200 h. The erosive wear test was conducted at a speed of 20 m/s for 30 min at 450 °C with an incidence angle of 30°. Irregular alumina was used as the erodent material. The surface characterization was performed using scanning electron microscopy to determine the distribution homogeneity, morphological conditions, quantity, and spheroidization degree of the carbides. The erosive wear test results indicated that there was no volume loss after 50 h of heat treatment at 530 °C. The maximum spheroidization degree was 0.71 after 200 h at 630 °C, which decreased the hardness from 220 to 140 HV. Additionally, the volume loss reached 2.52 cm3. Therefore, the use of the ASTM A106GrB steel at working temperatures higher than 530 °C for more than 50 h decreased the mechanical behavior and the wear resistance, thereby decreasing the lifetime of the system.

Resumo em Inglês:

Abstract Reconciliation plays a key role in controlling and analysing mine operations. It consists in comparing model estimates with actual results produced by the plant, being used as an indicator, a monitoring tool. Discrepancies between these values are common in the mining industry and they highlight problems during processing steps. However, these discrepancies do not necessarily need to be brought to zero, as long as their order of magnitude is understood. Prognostication, a new concept that seeks to replace reactive reconciliation, aims to raise and correct the real causes of these variations. A common cause of this type of problem is sampling, which in most cases is not performed correctly, providing biased samples and compromising reconciliation analyses. The present study reports, evaluates and improves reconciliation in a bauxite mine located in the city of Poços de Caldas/MG, in Brazil and reports on a study of the heterogeneity of the ore. A common practice of the bauxite mines in Poços de Caldas is to carry out the last stage of sampling manually from the trucks before the ore goes to the treatment plant. The data evidenced that this sampling is biased and systematically overestimates the planned ore grades. In addition, it has been confirmed that the best alternative for the company is to implement a conveyor belt sampler collecting increments every 15 minutes. This method shows the best adherence to the plan, that is 100.7% for available alumina and 83% for reactive silica.

Resumo em Inglês:

Abstract In an underground mine, the ventilation is responsible for 25% to 50% of its electrical energy consumption. In countries such as South Africa, United States and Canada researchers have started to achieve a significant reduction in energy consumption without neglecting aspects of the quantity and quality of air required for the best performance of the system, in compliance with safety standards and worker comfort. In Brazil, on demand this ventilation application began in 2013 at the Ipueira mine (Bahia, controlled by Ferbasa company), and was soon after applied by the Cuiabá, Córrego do Sitio I and Lamego mines; all three mines administered by Anglo Gold Ashanti. Each mine adopted frequency inverters for the main ventilation, whereby the fan rotation is adjusted according to demand and speed drivers. This measure resulted in the saving of thousands of reais, since the flow is proportional to the velocity, the pressure is proportional to the square of the velocity, and the power is proportional to the cubed velocity. Therefore, a reduction of 20% in the flow will save about 50% of the energy required. The Cuiabá mine presents the most modern and automated system in the country. The fans are controlled and monitored through a control room. In addition, sensors scattered in the mine, control the required flow rate. The Lamego mine has a similar but simpler system. This article proposes to discuss the application and improvement of the process of ventilation on demand in Brazilian mines where this system is applied.

Resumo em Inglês:

Abstract Finite/discrete element methods (FDEM) are hybrid numerical models that use algorithms to analyze the transition from continuous to discontinuous. This type of formulation allows modeling physical laboratory tests with greater proximity to reality. This article proposes to simulate the average behavior of a uniaxial compression test campaign. The tests were modeled and calibrated based on the strength and the fracture pattern using Geomechanica Inc. Irazu two-dimensional software. The simulated results were analyzed by the mean standard deviation of approximately 3000 elements in the middle third of the model, the same region where the clip gages are located in the physical test. The obtained results show that FDEM can replicate the laboratory test with great similarity.

Resumo em Inglês:

Abstract Knowing the quantity and the quality of products and tailings generated by a beneficiation plant, even before ore processing, can make the mining operations more sustainable, more profitable, and safer. To forecast these values, it is necessary to submit samples to batch tests which mimic the processing workflow used on an industrial scale. Then, the results need to be analysed with the aim of finding a statistical model able to comprehend how Run of Mine (ROM) characteristics impact the performance at the beneficiation. After developing a model, it is possible to apply it to blocks where the ROM characteristics are known, but the metallurgical information is not, making it possible to estimate these. With this goal, a geometallurgical model was developed with a neural network technique using 37 samples collected at two Brazilian gold mines. The Au and S grades in ROM, and the mine from where the sample was collected, were used as input variables. The model was able to forecast the following variables with a Pearson correlation coefficient on the cross validation test set equal to the value in parenthesis: mass (0.55) and metallurgical (0.54) recovery in the gravimetric concentrate, mass (0.80) and metallurgical (0.12) recovery in the flotation tailings, mass (0.77) and metallurgical (0.11) recovery in the leaching tailings, mass recovery (0.84) of gas sent to the sulphuric acid plant, and metallurgical recovery (0.65) in the leaching concentrate. The results obtained with neural networks were superior to the ones obtained when three alternative techniques were tested.

Resumo em Inglês:

Abstract This article evaluates the efficiency, benefits and limitations of pre-concentration by density separation for process mineralogy studies of low-grade gold ore. The pre-concentration by density aims to generate a product with a high content of gold and to maximize the number of gold-bearing particles characterized, thereby increasing the representativity and reducing the number of polished sections to be analyzed. Pre-concentration by density was carried out for a low-grade sulfide gold ore (0.96 ppm) from the north of Brazil. The sample was ground to below 1.7 mm, sieved down to 0.037 mm and subjected to density separation, amalgamation of the heavy product and cyanide leaching of all products. Gold was assessed in each product to evaluate the separation recovery and distribution. The finer the particle size, the higher the gold distribution in the heavy product, due to a higher degree of liberation of gold and sulfides; these values varied from 65% to 84% in fractions below 0.60 mm and decreased from 40% to 13% in the coarser fractions. Regarding gold distribution, fractions finer than 0.84 mm indicates a notable increase on gold recovery by amalgamation, indication higher surface exposure.

Resumo em Inglês:

Abstract Coal mine waste rocks produced during mining and beneficiation can affect the environment due to land degradation and acid mine drainage generation. However, proper characterization and treatment of mineral processing wastes creates options for safe disposal, enhancing the environmental performance. The aim of this study was to use static and kinetic tests to assess properties of coal waste produced at the Moatize Mine in Mozambique, one of the largest "world-class" coal deposits. The study included sampling and characterization of coarse and fine wastes generated during coal beneficiation. Both materials were analyzed in terms of granular properties, static procedures - immediate composition, sulfur forms, mineralogical composition, elemental composition, acid-base balance - and kinetic behavior in humidity cell tests. The conjugation of these techniques indicates that these wastes have a low water acidification potential and low geochemical mobility of toxic elements. Therefore, it was concluded that fine and coarse wastes could be used in land shaping procedures.