Abstract in English:Abstract The use of slate waste can help to reduce the impacts caused to the environment due to the decrease of the appropriate disposal areas and the disordered consumption of raw material. This article presents an analysis of the Resilient Modulus (RM) and the California Bearing Ratio (CBR) of this waste in mixtures with clayey soil. To analyze variations in RM and CBR due to the increase in the slate waste content, tests were carried out on reference mixtures (REF) and mixtures containing slate waste (SLT). The tests were carried out for mixtures of granular material (gneiss for REF and slate waste for SLT) and clay soil, containing different levels of granular materials (50%, 60%, 70%, 80% and 90%) It was observed that the values of Resilient Modulus and California Bearing Ratio of the SLT mixtures increased 62.8% and 127.0% with the addition of the slate waste between the SLT 50/50 and SLT 90/10 mixtures, respectively. This behavior was similar to that presented by the REF mixtures, which increased 125.0% in RM and 60.1% in CBR for the same addition of granular material. The results obtained indicate that the mixtures containing slate waste presented RM and CBR similar to those of conventional materials (such as the REF mixtures) used in layers of sub-base and the base of pavements. Finally, it was concluded that the relationship between RM and CBR is non-linear for both mixtures (REF and SLT) in function of granular material addition.
Abstract in English:Abstract The use of steel in construction is an alternative that has changed the panorama of this sector, contributing to an increase in productivity, and a reduction in waste and construction time. The Light Steel Framing (LSF) system, introduced in Brazil at the end of the 1990s, is undergoing a process of technical development and acceptance in the national civil construction market, but there are still shortcomings regarding the design, itemization and implementation of the complementary closing systems, and also regarding its thermal performance. This study employs an analytical approach that uses the isothermal planes method to calculate the resistance and thermal transmittance, and a numerical approach that uses the ANSYS software (version 15) to verify and compare these analyses. Multi-layer closures are considered, with the outer layer being made up of cement board and the inner layer of gypsum board, brokered by fiber glass insulation and air, with studs formed by C-section profiles in galvanized steel. The isothermal planes method revealed the value of 0.77 (m2.K)/W for the equivalent thermal resistance, 1.3 W/(m2.K) for the thermal transmittance, and 13.04 W/m2 for the heat conduction flux. The difference of the results when comparing the isothermal planes and numerical solution methods was 9% for thermal resistance and 8% for heat conduction flux. The obtained results showed that the heat flux is equivalent to a value around 54% greater than the heat flux value for a closure without the presence of steel profile.
Abstract in English:Abstract The chord length is an essential geometric property that must be defined in the analysis of isolated joints composed of hollow steel sections, as well as the boundary conditions of the test. The analysis of these parameters’ effect on the behavior of joints has been addressed by other studies, mostly with joints between circular hollow sections with compact or semi-compact cross-sections. Recent research about tubular joints has addressed cases with slender sections, where the design of joints containing these sections is still in development. In this context, this study aimed to evaluate the effect of the chord length in the behavior of T-joints between circular hollow section braces and slender rectangular hollow section chords through experimental tests and a numerical study considering the application of axial compression at the braces. The joint behavior was examined through the load-strain and load-deformation curves and the von Mises stress distribution, which allowed the failure mode's determination and the joint resistance value. Chord face failure was observed in the prototypes. It was concluded that a minimum chord length of 0.6m would be the adequate value for the study of the T-joints containing the geometric properties used in this study, which would be equivalent to a chord length five times higher than the width of the cross-section (5b0).
Abstract in English:Abstract Over the last decades, the capability of a desulfurizing mixture to remove sulfur has been widely studied. The hot metal desulfurization efficiency represents the percentage of sulfur removed from the bath and the development of parameters that predict the process efficiency is fundamental for selecting the best desulfurization mixture without the need for experimental tests. Therefore, this research aims to develop a new parameter to predict the hot metal desulfurization mixture efficiency, which was called the desulfurization factor (FDeS). Desulfurizing mixtures from CaO-Fluorspar and CaO-Sodalite systems were used for this purpose. The phases present in the heating of the mixtures at 1400°C as well as the liquid and solid percentage were determined by ThelmoCalc software. These data were used in the desulfurization factor construction. Experiments were carried out in an electric resistance furnace with mechanical stirring. Different mixtures from these systems were added in molten hot metal at 1400°C. Sampling was made to measure the sulfur content variation with time. It was possible to apply the desulfurization factor to the proposed mixtures and to determine the influence of the solid and liquid phases on the desulfurization efficiency.
Abstract in English:Abstract The Direct Reduction (DR) process has been growing worldwide, and there are strong context suggestions that it will grow even more. One of these factors is the environmental pressure that occurs worldwide, and there are already projects to migrate Blast Furnace route steel plants to the Direct Reduction (DR) route, due to its smaller carbon footprint. Considering the importance of this process and the challenges of carrying out experimental tests on a pilot scale, an adequate way to evaluate the process and its impacts is through numerical simulations. There are different techniques applied to models that describe the counter-current reactor in the DR process, but none of them account for the clustering phenomenon. Clustering occurs because of the sintering of the metallic iron on the surface of the pellets in such a way that they attach to each other, forming clusters that hinder the gas flow through the shaft. The present study attempted to adapt a numerical model of a DR process to account for the effect of the cluster formation. Some clustering index equations from literature and some developed as part of this study were used and tested in the model, as a function of temperature, by varying the solid volume fraction in the control unit. The equation that resulted in the adjusted output closest to the current empirical value was implemented in the model and proved to be successful.
Abstract in English:Abstract This study evaluated the as-cast microstructure of three alloys based on Fe-25%Cr-5%Ni weight (wt.) composition whose carbon content is 0.02 wt.%, 0.12 wt.%, and 0.37 wt.%, respectively. Thermocalc was applied to predict the possible phases that could be formed during the cooling of each alloy and then the cross-sections of the ingots were characterized. The first alloy, with 0.02 wt.%C, presented a microstructure composed of ferrite and austenite, which was formed through solid-state precipitation. The second alloy, with 0.12 wt.%C, showed a microstructure formed by ferrite, austenite from the peritectic reaction (L + δ → γ) and M23C6 (M=Fe, Cr) carbide. Finally, the third alloy, with 0.37 wt.%C, exhibited a microstructure formed by dendrites of ferrite and austenite, also formed according to the peritectic reaction (L + δ → γ), with an M23C6 (M = Fe, Cr) and M7C3 (M = Fe, Cr) carbide network in the interdendritic regions.
Abstract in English:Abstract Biomass was the first material used as a fuel by humanity, being replaced by fossil fuels after the industrial revolution. With the growing of environment discursions and the effects of CO2 emissions, biomass has been gaining strength as a potential alternative to fossil fuels, especially for steelmaking, which is responsible for about 5 to 10% of all CO2 emitted. It is known that biomass, compared to fossil fossils, has a higher volatile content, high moisture and lower calorific value. On the other hand, it has a higher hydrogen content and lower sulfur content (important for the steel industry), in addition it is considered neutral in CO2 emissions. Torrefaction, heating biomass at a temperature between 200-280°C in an oxygen free atmosphere, is an interesting treatment to adapt biomasses for use in the steelmaking processes, mainly in the pulverized material injection into the blast furnace. PCI is an extremely important process for the production of iron in the blast furnace, due to its ability to reduce coke consumption and optimize the operation of the reactor. This article comes with the purpose of presenting a bibliographic review about PCI technique, torrefaction process, biomasses and its applicability in the steel industry. In addition, an economic and environmental analysis of the possible use of biomass in steelmaking processes will be presented. Results shows that the use of torrefied biomass in the injection process is interesting, generating savings of 10 dollars and reduction of 264kg in CO2 emissions per ton of hot metal, with a replacement of 50% of the coal used by biomass.
Abstract in English:Abstract The article reviews the metallurgical processes used in the first industrial ironworks operated in Brazil, the Patriótica Iron Factory, from 1812 to 1831. It discusses its impact on the ironmaking plants that spread in Minas Gerais's state during the XIX century. The remnants of this Factory in Ouro Preto were the first industrial site listed by the Brazilian Historic Heritage Authority (SPHAN) in 1938. Vale SA, owner of the site, and the National Historic and Artistic Heritage Institute (IPHAN) authorised collecting samples from two ferrous artefacts found in the old Factory, a hammer and an eyebolt nailed to the remnants of one of the reduction furnaces. The eyebolt’s microstructure suggests that this part was produced in the Patriótica Iron Factory, while the hammer’s microstructure indicates that this component was not produced in the Patriótica Iron Factory.
Abstract in English:Abstract A Brazilian Tensile Strength (BTS) laboratory test for meta-andesite was modeled using a Finite/Discrete Element Method (FDEM or FEM-DEM). These hybrid methodologies allow modeling the transition from continuous to discontinuous that happens on mechanical tests of rock samples. This article presents the calibration and the simulation of BTS tests using some parameters previously calibrated on UCS modeling of the same material. Irazu, a two-dimensional software developed by Geomechanica, was used to simulate the tests based on the tensile strength and the fracture pattern. The model shows that, in BTS test simulation, the mode II (shear) happens mainly on the rock-platen contact. The mode I (traction) rules the fractures on the BTS test as observed in laboratory tests. The model represents, with great fidelity, the results obtained in the physical test.
Abstract in English:Abstract The creation of tridimensional models that represent the quality and geomechanical characteristics of the rock mass to be excavated can be made by using spatial interpolation techniques. The aim of this research is to improve the safety in underground activities, as well as to spread and popularize the use of spatial interpolation methods to represent both the spatial continuity of the quality of the rock mass and the geomechanical variables through geostatistical methods. This article presents and demonstrates the viability of using Q-System block models estimated from the borehole data for previous classification of the rock mass surrounding the underground excavation and rock support design. The block model for the support design of galleries is justified because it allows to previously forecast the kind and quantity of support necessary for the stability of the excavation, as well as the costs with these devices, besides increasing the safety in the operations. Techniques of indicator kriging and ordinary kriging were used to build the Q-System index block model. The model was validated through the techniques of visual inspection and cross validation. The data used in this study were collected from the geotechnical description of 39 borehole core samples with a total measurement of 4,015 meters in Fazenda Brasileiro Mine, located in the town of Teofilândia, Bahia State, Brazil.
Abstract in English:Abstract Knowledge of the physical properties of rock masses is fundamental for the economics and safety of mining projects. The determination of these properties in rock samples in the laboratory requires time, expensive equipment and qualified personnel, which considerably increases the information's cost. Indirect methods were developed to obtain properties related to rock masses, which have been shown to be a viable alternative to traditional procedures. The determination of the compressional mechanical wave velocity (Vp) and subsequent correlation with lithological mechanical properties are indirectly obtained. This study’s objective was to obtain correlations between Vp and the resistance to uniaxial compression, UCS (Unconfined Compressive Strength), as well as the density and porosity of the siltstone and sandstone lithologies present in the coalfield of Candiota, located in the southern region of Rio Grande do Sul, Brazil. The Vp records were obtained in laboratory samples, using ultrasonic velocity sensors, and in-situ by geophysical well logging (directly in boreholes). The results indicate the possibility of using Vp to determine the physical parameters of the investigated lithologies. In the specific case of the correlations between Vp and Unconfined Compressive Strength, determination coefficients R2 above 0.70 were obtained, indicating sufficiently high reliability for using this information (e.g. in roof support projects). The correlation between Vp and density was also high.