Abstract in English:Abstract This article evaluates the impact of different fiber types on the flexural creep of self-compacting concretes (SCC). The study focuses on the effects of vegetable fibers (Hemp, [H] and Dis [D]) and synthetic fibers (Polypropylene [P]) on SCC. To assess the SCC, various tests such as spreading, J Ring, compressive strength, and flexural strength are conducted. The authors developed a test configuration and methodology to subject beams measuring 120 cm in length to sustained flexural stresses for 200 days. Two curing modes of the beams are also studied: total creep (beams exposed to air) and endogenous creep (beams protected from air). Moreover, the plant fibers were previously subjected to two treatments separately; the first involves immersing them in a 5% alkaline solution of NaOH (HN and DN) and the second in a solution of the polymer styrene-butadiene rubber (SBR) (HS and DS). The findings show that the treatment of vegetable fibers by SBR reveals high mechanical properties as well as a good capacity for endogenous and total creep. SCC-DS shows an increase in flexural strength of 9% and 13% with a decrease in total creep of 4% and 16% compared to SCC without fiber and SCC-DN, respectively. These results are promising for further reflection on a large scale to explore the issue of strengthening SCC with treated vegetable fibers.
Abstract in English:Abstract The current advanced analysis techniques for steel frames generally use structural analyses with geometric and material nonlinearities to capture the collapse strength of the steel frame. Unfortunately, the true strength of a steel frame cannot be predicted with accuracy because of the uncertainties of the most significant design variables. Building codes of steel structures apply a resistance factor to account for the uncertainties present in the design variables and thus ensure a target level of structural reliability. This article examines the reliability of planar steel frames subject to gravitational loads by advanced structural analysis (second-order inelastic analysis). To calculate the collapse probability of planar steel frames, we utilized the first-order reliability method (FORM). The advanced analyses were performed using the program MASTAN2 and considered the geometric nonlinearities and inelasticity of the steel. The collapse probabilities of planar steel frames were evaluated and the adequacy of the resistance factor applied was discussed. The current inelastic design procedure of ANSI 360 reduces the yield strength and stiffness of all members by a factor of 0.90. Thus, the present study suggests that the adopted resistance factor must be equal to 0.85 for the target reliability index equal to 3.0, or it must be equal to 0.69 for the target reliability index equal to 3.8.
Abstract in English:Abstract RCC using hematite as an aggregate has interesting characteristics for use in massive structures or structures for radiation shielding. In Brazil, there is a considerable amount of hematite ore tailings without practical use, which makes this material an environmental problem and a matter of public safety. Thus, the search for alternatives to use these tailings is a priority environmental concern. An RCC containment dam with hematite aggregate was constructed to protect the basin of the Barao de Cocais River, including the city of Barao de Cocais in the State of Minas Gerais in Brazil, from a possible rupture of the Sul Superior tailings dam in the Congo Soco iron mine. Approximately 150,000 m3 of RCC was deposited in three months. In this article, the results of the technological control tests during the construction of the containment are presented and compared with the results of the cores extracted after the construction, showing their coherence and strength performance compared with RCC using conventional aggregate. Also, studies related to the performance of radiation shielding of this RCC are presented. An attenuation of 10% of 1.6 MeV gamma radiation in relation to conventional concrete was observed.
Abstract in English:Abstract For a soil to be granulometrically stable, it must present low plasticity and a granulometric composition that conforms with the limits regulated by standards. This article presents a study of the clay fraction activity and plasticity of three laterites from the Triângulo Mineiro region, aiming to use them in a granulometrically stabilized base. The experimental phase contained the determination of liquidity limit, plastic limit, sand equivalent and silica sesquioxide ratio, in addition to a Methylene Blue spot test, linear shrinkage, MCT classification and X-ray diffraction. The results show that the sand equivalent alone is not able to evaluate the content of impurities of the clay fraction; it needs to be performed along with the Methylene Blue spot test. Linear shrinkage proved to be an important indicator of plasticity, capable of measuring small values of plasticity. Finally, the MCT classification precisely indicated the lateritic behavior of the samples.
Abstract in English:Abstract Heterogeneous catalysts, especially those produced with functionalized clays, can be used for methyl transesterification at moderate temperatures. The use of bentonite clay functionalized by potassium compounds (KF, KOH, K2CO3, KCl and K2SO4) in the methyl transesterification of cottonseed oil is the object of the present study. The catalysts were produced by contacting aqueous solutions with the clay and subsequent drying. The catalysts were characterized by Hammett indicators to determine alkalinity. The methyl transesterification reactions were made in a flask with stirring and reflux at 70°C for 2 h. The performance evaluation of the reaction was carried out using regression between the absorption band area and the concentration of a biodiesel-oil mixture by infrared spectroscopy. The catalytic activity is directly associated with the alkaline character of the catalysts. The catalysts produced with KCl and K2SO4 did not show conversion in the methyl transesterification reaction, while the catalysts produced with KF, KOH and K2CO3 showed a conversion greater than 90%.
Abstract in English:Abstract This article proposes to evaluate the application of Seismic Hazard methodologies for the study of falls of ground (FOG) that occurred in the Cuiabá underground mine. Specifically, a fall of ground that occurred in 2018 in the Serrotinho mineralized body (level 18) was elected as the object of study, since it had characteristics common to other FOGs that occurred deep in the mine. Because of the close proximity and timing of the events, another three FOGs were considered in order to understand the relationship between these rock detachment events and microseismicity. Regarding seismic hazard methods, the apparent stress ratio (ASR) could provide an overview of the evolution of apparent stress in the region. The interpolation of the ASR of microseismic events to the mine levels, in 3 of the 4 cases studied, mapped the FOG region as having a high apparent stress ratio before its occurrence. A rockburst early warning methodology, in turn, proved to be helpful in the identification of precursor conditions of a microseismic event of greater local magnitude (ML = 0.5) in the analyzed period. Although, during application of this method, some difficulties were found in identifying the right precursors patterns of the microseismic parameters.
Abstract in English:Abstract Sampling is an important tool for gathering information about mineral deposits, helping to estimate the ore grade, and has great relevance at any stage of a mining project, to ensure reliable results and consequently, to project a better mining planning. There are several errors to which the sampling is exposed and among them we can mention the fundamental sampling error (FSE). This error cannot become zero as it is related to the constitutional heterogeneity of the ore, so it represents the minimum sampling error. This study applies Pierre Gy’s theory of sampling (TOS) to estimate the values of K and α sampling constants at different deposits of bauxite in Brazil and compare them with the calculated factors, then calculate the relative standard deviation of the fundamental sampling error s(FSE) based on the results of the heterogeneity test (HT) in each deposit. The deposits are located in: Barro Alto - State of Goiás, Juruti - State of Pará, and Poços de Caldas - State of Minas Gerais. The weathering process is the main reason of the alteration of the physical and chemical factors diversifying bauxites in Brazil and worldwide. However, when sampling is carried out correctly, the Gy’s formula becomes a powerful tool for improving mining processes as long as the factors are estimated correctly for each ore.