Resumo em Inglês:

Abstract New materials and technologies used in construction constantly need improvements, whereby the leveraging of new raw materials for the manufacture of products already in use, such as paving, is required. Thus, this study aimed to determine the mechanical and thermal behavior of pavers containing waste glass and São Tomé stone waste to verify their potential application as cold diffraction. Thereafter, they were comminuted and added to the mixtures for making the pavers having glass waste and São Tomé stone in the range of 0-30% by weight. Mechanical compressive strength and thermal heat absorption tests were performed. Results showed that the replacement of fine aggregates with waste glass and São Tomé stone waste in pavers reached a mechanical resistance of approximately 85% and 73% of that of the reference paver, respectively. The results show that reducing the waste content of pavers can increase the mechanical strength to reach the NBR 9781/87 values. However, pavers with lower mechanical strength can be used in paving pedestrian sidewalks, where the loads are low. Pavers with 30% glass waste achieved a 5.5% reduction in the maximum temperature, which could contribute to the reduction of urban heat islands.

Resumo em Inglês:

Abstract Cellular beams are an attractive engineering solution due to their high strength to weight ratio, allowing for a design even lighter and more cost efficient in steel structures. These beams possess enhanced strength and stiffness compared to regular I-section beams of similar weight, due to their higher second moment of area. However, their variable cross-sections along the length introduce different modes of failure, making further research necessary, since there is a lack of standardized processes for their design. This paper investigates the design and verification procedures proposed by Ward (1990), Annex N (1998), Veríssimo et al. (2013), Fares et al. (2016), and Grilo et al. (2018) through a parametric study of cellular beams with varying geometries. To assess the buckling characteristics of cellular beams, shell finite element models are employed, which were previously validated, using experimental tests conducted by other researchers. The results obtained from a Python code implementing these design methods are then compared with Finite Element Method (FEM) analysis results for 80 beams. It can be concluded that the design methods provide conservative results for beams with intermediate or long spans. On the other hand, for beams with short spans, these methods may yield values that compromise safety. Finally, based on the FEM analysis results, a Hybrid Design Method (HDM) is proposed, which incorporates the verification procedures analyzed. This proposed method presents a better failure mode detection and limited load capacity when applied to cellular beams made from regular Brazilian I-section beams.

Resumo em Inglês:

Abstract At high temperatures, concrete may exhibit adverse mechanical behavior that compromises the safety of structures. Thus, it is necessary to study and develop concrete that can obtain greater performance in situations of exposure to high temperatures. In this regard, the present study investigates the replacement of 25% of sand by expanded vermiculite in different types of concrete and its performance when subjected to room temperature and punctual temperatures, of little content in literature, such as 200°C, 400°C and 800°C. This study also innovates by proposing the evaluation of prototypes exposed to high temperatures exclusively according to the perspectives of Brazilian technical standards, without resorting to international guidelines. Thus, the consistencies of the mixtures were determined and analyzed, as well as physical and mechanical tests that were carried out with the produced concrete. Among the results found are: vermiculite reduces the workability of the concrete mixture; vermiculite is not recommended for high-performance concrete, as it can significantly reduce its mechanical properties; in general terms, concrete that has a design strength of 50 MPa benefits from replacing the fines aggregate with vermiculite. From 400°C of exposure, all of the concrete samples showed cracks. The spalling phenomenon was also noticed in some specimens. The developed concrete samples cannot be characterized as lightweight concrete according to Brazilian standards, but o can be recommended as structural concrete given that their apparent specific mass is greater than 2000 kg/m3.

Resumo em Inglês:

Abstract Despite presenting several advantages in relation to the mortar coating performed by hand labor traditionally carried out in Brazil, there is little knowledge available about mortar pumping systems. Thus, selecting a mortar pump system is not a trivial procedure, and there are no significative studies published in the specialized literature to fully understand the decision criteria applying to this equipment selection. Therefore, the present study aimed to identify the relevant criteria and quantify their importance in the selection of this equipment, by developing a framework combining both mortar pump specialists expertise and fuzzy analytic hierarchy process method to aid this decision making process. Results showed that acquisition cost and quality are the most relevant criteria, representing togheter around 2/3 of the decision weight, while technical and operational aspects account for aproximatelly 1/10 of relevance in the equipment selection.

Resumo em Inglês:

Abstract In the past decade, machine learning techniques were responsible for a revolution in classification and regression tasks, making it possible to automate some laborious activities, saving time and reducing errors. It is known that the geological logging process is one of the most time-consuming activities accomplished by mining companies. Additionally, it is a subjective activity, and changes in the staff directly affect the geological databases due to different human log interpretation. By developing an automatic log classifier, a company can avoid problems related to the turnover of the staff by standardizing the criteria used to label an interval and can save time by avoiding manual log description. The proposed solution is: given the well log data containing the coordinates, resistivity and natural gamma, the model will be able to predict the presence or absence of coal, and its lithology. The innovation of the methodology proposed, considers not only the geophysical logging values, but additionally inserts the neighbourhood of a given depth as valuable input information, using Fully Convolutional Network. It performs a semantic segmentation using the well log data, which means that model´s input is the complete well log data curve and the trained model will return an output curve giving the probability of the presence of coal, by interval. The results showed good prediction for the binary problem (F1-score 0.79). The multi-class modelling suffers from the lack of data for each class, resulting in a F1-score from 0.38 for the worst result to 0.76 for the best.

Resumo em Inglês:

Abstract Biodiesel serves as a biodegradable, non-toxic, and renewable fuel option that offers an alternative to traditional fossil fuels. This study aimed to examine the impact of elevating biodiesel content to 20% and 50% within regular diesel, with a focus on comprehending how these fuel mixtures influence variations in soot composition using Raman spectroscopy. The soot samples under analysis originated from commercial S10 diesel, as well as fuel blends containing 20% and 50% portions of sunflower and macaúba biodiesel, whereupon the use of this methodology for these fuels characterizes the novelty of this work. The outcomes derived from analyzing the soot samples revealed distinct characteristics in the G, D1, D3, and D4 bands. The ratio between the intensities of these D and G bands is closely indicative of the soot's structure. Consequently, this ratio was analyzed in this investigation to assess the effects of biodiesel concentration and engine rotation speed on soot characteristics. The conclusions found in this study indicated that there was minimal variation in the spectral characteristics of the soot samples across the different fuels and varying engine speeds. As a result, it is inferred that increasing the proportion of biodiesel in commercial diesel S10 did not have a significant impact on the structural composition of soot.

Resumo em Inglês:

Abstract The effect of graphene oxide (GO) on the concrete quality and the corrosion resistance of carbon steel reinforcement was evaluated. The concrete mix was calculated at a ratio of 1: 1.86: 2.14: 0.46 (cement: sand: gravel: water); the dosages of GO were 0.03 wt.% and 0.05 wt.% and the superplasticizer (PC) concentration was 0.6 wt.% concerning the cement mass. Compressive strength tests (7, 28, and 91 days), water absorption tests, determination of voids index (WATIDVI), ultrasonic pulse velocity (UPV) testing, and optical microscopy analysis were carried out. All concrete samples showed excellent compactness and low porosity. Open circuit potential measurements and linear polarization resistance (LPR) were performed during 15 cycles of partial immersion and drying of concrete in a 3.5 wt.% NaCl solution. A beneficial effect of 0.03 wt.% of GO addition on the corrosion resistance of the reinforced concrete was identified in the saline medium and the corrosion inhibition efficiency obtained was 79.3%.

Resumo em Inglês:

Abstract Graphene and reduced graphene oxide are promising materials that are increasingly used in the field of polymer materials. In this study, reduced graphene oxide was prepared by chemical exfoliation of graphite, and subsequently, used in different amounts of 0.05, 0.2 and 2.0 wt.% in poly(ethylene-co-vinyl acetate) - EVA nanocomposites and foams. The approach used to prepare the reduced graphene oxide showed good efficiency with nanometer-scale particles and an average number of eight layers. Reduced graphene oxide in water suspension was introduced into the EVA by thermofusion using a closed mixer. Subsequently, sheets and foams were prepared by thermocompression molding using chemical expansion and crosslinking agents. The leading results suggest that the presence of reduced graphene oxide could change the cell morphology of the foam by increasing the cell density and decreasing its size. The sample containing 2 phr of reduced graphene oxide exhibited lower density and higher resistance to compression compared to pure EVA.

Resumo em Inglês:

Abstract The consumption of coals without coking properties in coal blends for coke production is a challenge, precisely because of their lack of coking properties, and in some cases, high contents of macerals from the inertinite group, which are known to contribute to a reduction in the mechanical strength of coke when present in high size dimensions. With the constant search for the use of non-coking coal in the coal blends, the main objective of the study was to investigate the effect of increase inertinite-rich coal content in multi-component coal blends. To achieve this, selective crushing was performed to obtain 1.5 mm as the critical inertinite size for the coke’s mechanical strength, decreasing the amount of microcracks at the boundary between reactive maceral-derived components (RMDC) and inert maceral-derived components (IMDC). The microstructural characterization for the industrial metallurgical coke was studied using optical microscopy associated with image analysis (ImageJ software). It was established that a 25 % content of inertinite-rich coal addition in the blend caused systematic changes in the coke’s microstructural features, decreasing the mechanical strength. Additionally, the segmentation between RMDC and IMDC was studied to achieve better correlation from the coke’s microstructural parameters, predicting mechanical strength (DI150/15). A new equation was proposed describing both microstructural features from reactive and inert components.

Resumo em Inglês:

Abstract The state of Espirito Santo is the most important producer and exporter of ornamental quarry stone. In its various quarries, it uses bench heights that range from 5, 20, 50 and 100 meters. The high altitudes raise concerns about the stability of the slopes. Therefore, the study focuses on determining the value of the safety factor (SF) for these heights using the limit equilibrium method. To make this possible, the values of simple uniaxial compression, Geological Strength Index (GSI), the disturbance factor, and intact rock parameter must be obtained. To obtain the GSI, it is necessary to establish a correlation with the Rock Mass Rating, the values of which are determined using a scan line. The uniaxial compression values were treated statistically, obtaining classes at 75, 100, 125, 150, 175, and 200 Mpa. The 2D slide software was used to obtain the SF values for the respective heights. With the results obtained, these rocks do not present stability problems. The correct choice of GSI is of paramount importance for a good analysis, as it directly affects the results. Using this technique to determine safety factors is appropriate, but it is necessary to analyze more robust methods to compare the results.

Resumo em Inglês:

Abstract This study develops briquettes from fines generated in the processing of manganese ore from a strategic manganeferous district of Minas Gerais-Brazil. The briquettes were produced based on the following variables: compaction pressure (20 and 25MPa), curing time (7 and 28 days), percentage by mass of binder (5% and 10%), and replacement with tailings (0% and 10%). Technological tests evaluated the compressive, abrasion, impact strength and water absorption. The best conditions for briquette included 10% Portland cement, 10% Mn tailings, compaction pressure of 25MPa and 7 days of curing, as well as 10% Portland cement, compaction pressure of 25MPa and 28 days of curing. The briquettes primarily contained the spessartine, todorokite, quartz, and pyrolusite minerals. The storage time tests indicated that the briquettes responded satisfactorily to storage for three months in a dry environment and at room temperature. Through crackling tests, the briquettes have potential to be commercially used.

Resumo em Inglês:

Abstract The main objective of this study is to evaluate the hanging wall stability of the mining stopes resulting from the open stope underground mining method, taking into account the exposure time of the wall sans any support, through numerical simulation, using an elasto-viscoplastic model formulated for the finite element method. In order to carry out the simulation, a real application case was chosen: the extraction of a mining block from the underground zinc mine of Nexa Resources, in the municipality of Vazante-MG, which operates through the open stope mining method, where the values of unplanned dilution are known. The stability of the stope’s hanging wall was analyzed through two instability indicators, the horizontal displacements and the minor principal stress, simulated in a two-dimensional perpendicular section and in the center of the stope. The results obtained in the simulations were coherent with the real results that occurred in the stope, and with the rheological behavior of the rocks, since the unstable regions increase with the exposure time without any type of support used, which shows that the model used is a good alternative for prediction of the dilution and the evolution of instability areas of the stope wall according to its exposure time.

Resumo em Inglês:

Abstract As historical waste has accumulated in dams, the interest in studying the feasibility of reusing mining tailings has grown, offering both environmental and economic advantages. However, given the unique characteristics of each site, conducting site-specific assessments is crucial. Building on a detailed evaluation of the Cocoruto Dam in Nova Lima, Minas Gerais, this study presents a technical feasibility and financial viability analysis of three potential reprocessing scenarios. The primary objective was to assess the viability and potential benefits of reusing Au tailings. The proposed methods involve grinding, calcination and leaching, with designs adaptable for existing metallurgical plants. Considering the economic potential of Au in these inactive mine tailings (with an average grade of 0.95 mg/kg and a total resource of 3,350.55 tonnes), multiple factors were analyzed to determine the feasibility of Au production from this source. Analyzed variables included: cut-off grades and tonnage for each scenario; net present value (NPV) calculated with an 8% annual discount rate; a general slope angle of 20 degrees; three possible final pit configurations; different annual production rates (400,000 t, 800,000 t and 1,000,000 t), and various Au ounce values ($1300/oz, $1500/oz, and $1700/oz). From a financial perspective, for all ounce values and an annual production of 400 tonnes, all scenarios prove profitable. However, other risks and parameters should be further evaluated.