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Influence of coal ashes on fired clay brick quality: Random forest regression and artifcial neural networks modeling
No full textFinding a solution to the problem of the large buildup of coal ashes is a vital necessity. Although the use of coal
ashes in fired clay bricks has been thoroughly investigated, there is insuffcient information on their industrial
utilization and researchers do not agree on whether or not this addition improves the quality of the fnal
products. Therefore, a database has gathered 20 years of research containing key factors related to the quality of
the bricks (i.e., chemical composition, fring temperature, soaking time, open porosity, water absorption and
compressive strength). Then, random forest regression and artifcial neural networks (ANN) modeling were used
to separately predict the parameters concerning the quality of the fnal products. The overall conclusions were
that the compressive strengths were the highest when using fly ashes and that class F ashes were highly suitable
to be used in the brick industry as a replacement material for brick clay. In addition, the ANN models showed
higher coeffcients of determination and an overall better fit to the experimental data. By changing the chemical
makeup of the initial materials and their proportions, the particle size of the ashes, the firing temperature and
soaking time, as well as the size of a product, the created models can be used to estimate the quality of the brick
containing coal ash. That is crucial because the inconsistent chemical composition of ash is generally the main
obstacle to its utilization. The local sensitivity analysis revealed the highest influence of the content of the alkali
oxides in the initial clay on the fired clay bricks due to their fluxing effect. In the case of ash-clay bricks, the
decisive factors were the type of furnace used, the ashes’ class, the Na2O content in raw clay, and the K2O
introduced with the ash. The F class ashes containing about 2–3% of K2O and <5% of CaO gave the highest
compressive strength in bricks fred at 1000–1100 ◦C.
Additional analyzes were made for 50% pond ash and 50% clay bricks to test the best-suited model and fill in
the knowledge gap. The results obtained in this study are important for supporting the decision in the selection of
materials and process parameter values that will increase the quality of the ash-clay-fired bricks
Edelweiss Applied Science and Technology
No full texthttps://learning-gate.com/index.php/2576-8484/editorialtea
Pure Iodide Multication Wide Bandgap Perovskites by Vacuum Deposition
No full textThe CsPbI3 perovskite has a suitable bandgap (≈1.7 eV) for
application in tandem solar cells. One challenge for this compound is that the
semiconducting perovskite phase is not stable at room temperature, when it tends
to form a yellow nonperovskite phase with a bandgap of approximately 2.8 eV.
Therefore, many reports have been focused on the stabilization of the CsPbI3 black
perovskite phase through the use of additives during solution processing. Vacuum
deposited CsPbI3 has been seldom reported, as in this case, the insertion of
stabilizing agents is more challenging. In this work, we demonstrate the vacuum
processing of CsPbI3 perovskite films at room temperature, obtained by
incorporating dimethylammonium iodide by cosublimation with CsI and PbI2. As-prepared films were applied in planar
solar cells, leading to an average power conversion efficiency (PCE) exceeding 12%. In order to improve the device
performance, we introduced a third A-site cation (methylammonium) in a four-source deposition process. This pure iodide
formulation can be used in wide bandgap solar cells with a PCE up to 14.8%
Occurrence of cracks due to inadequate turbine shaft construction
Get PDFAfter several decades of constant exploitation of the horizontal bulb turbine, which is an integral
part of the hydroelectric power unit, empirically, the formation of a crack occurs in the turbine shaft
due to the influence of corrosion, erosion and cavitation.
Through experimental tests and calculations it has been determined that values of bending stresses
of the turbine, which occur due to the action of fatigue and corrosion, as well as stress concentration,
are bigger than 25 MPa for flanges exposed to water, and in other case bigger than 40 MPa for
flanges exposed to `corrosive water` and can cause the occurrence of surface cracks on the transition
radius between the cylindrical part of the shaft and the flange. It has been determined that stress
values in the zone under the influence of bending stresses were bigger than allowable values, which
led to the occurrence of many cracks due to fatigue corrosion. One of those cracks caused the failure
of the shaft and of the whole turbine
Raw kaolinitic-illitic clays for the production of refractory ceramics
No full textThe study makes a unique effort to characterize all the necessary characteristics of refractory clays and products fired at temperatures between 1100 and 1300 °C on a laboratory level. For 19 composite samples from the recently opened reservoir, thorough instrumental and ceramic-technological data are presented. The potential for using Serbian raw refractory clays from the recently discovered deposit is investigated. The composites had a variety of qualities and varied in composition, but they were majorly composed of kaolinite and illite and had a significant share of fluxes. The samples had high quantities of clay minerals and organic matter, which is seen as the most intense mass loss in the 400–600 °C range. Low-duty and high-duty refractories could be distinguished by their refractoriness over 1581 °C. This parameter was mostly influenced by the content of alumina and kaolinite within the materials. Hydraulically-pressed ceramic tiles, following firing stage showed water absorption was between 9.02–1.42 % and and modulus of rupture of 16.5 – 53.6 MPa. Color is determined by spectrophotometer and correlated to the composition of the initial clay and fired products. For the lining of ceramic and glass furnaces, the majority of these clays can be employed as natural refractory materials. Some of the samples' organic content has a detrimental effect on the fast-firing procedure, since the occurrence of the entrapped air (bloating)
Pile capacity distribution analysis for SLT with reactive system
Get PDFIn the paper, the analysis of the bearing capacity of the pile and the redistribution of the
load on the pile toe and shaft was carried out. The tests were carried out by a static load test (SLT)
incrementally increasing the compressive force on the test pile, and the tension force on the anchor
piles. The test system consisted of one test pile and two anchor piles with a reaction beam. Two
tests were conducted according to the same test program, where the test piles were of the same
length, while the length of the anchor piles in the second test was increased. In the first test, the
anchor pile failed, while in the second test, the test pile failed. Based on the achieved limit values of
settlement of the test and anchor pile, the bearing capacity of the test pile at the toe and shaft was
determined. Subsequently, a CPT test was carried out and the bearing capacity was calculated
according to the LPC-CPT method
Procedure for correction of bearing capacity of piles examined by the Dynamic Load Test (DLT) according to the Static Load Test (SLT)
Get PDFThe paper shows the comparative analysis of behavior and bearing capacity of piles examined using the Dynamic Load Test (DLT) according to Static Load Test (SLT) results. The pile testing methodology is based on the existing ASTM standards and experiences of the authors of the paper. The pile tests were carried out using counterweights, reactive system, dynamic testing equipment, hardware and software for SLT and DLT. The data obtained by testing were statis-tically processed, and also a regression analysis of the linear function was conducted, resulting in the creation of the model for the change of mobilized static bearing capacity from DLT according to SLT. In addition, a procedure for correcting the solution of mobilized static bearing capacity from DLT according to SLT, is made by observing provisions of standard EN 1997-1:2004, so the average deviation of solutions from DLT according to SLT is reduced. Apart from that, through iterations, the value of correlation factor ξ5 is determined, taking into consideration solutions presented by SLT and DLT of piles of the real structures
Influence of different types of fibers on properties of concrete
No full textThe paper presents the influence of the use of different types of fibers on the properties of concrete. All concrete samples were made with same component materials and compositions, except for the amount of fibers, which was varied. After hardening, the concrete samples were tested for compressive strength, tensile splitting strength and water penetration depth under pressure. Based on the test results, depending on the type, shape, amount and arrangement of fibers, the tensile and compressive strength values as well as the depth of water penetration under pressure were analyzed. Based on the tests performed, the best mechanical properties were achieved with the use of "Dramix 3D" steel fibers
An augmented approach for the determination of the particle size effect on energy dispersive X-ray fluorescence analysis outcomes for alumina-based refractory materials
No full textThe chemical compositions of refractory materials, such as high-alumina concrete, bricks, and putty, were analyzed using an energy-dispersive X-ray spectrometer (EDXRF). An improved methodology for investigating the effect of particle size on the outcomes of EDXRF chemical analysis is presented. Eight independent refractory samples (refractory concrete, brick, and putty) were pulverized utilizing seven milling times (30, 60, 120, 180, 240, 300, and 360 s) and compared to non-pulverized samples. Thus, sixty-four refractory samples were obtained and analyzed using EDXRF. The method for measuring the fundamental EDXRF characteristics was then tested with ten certified reference materials. The acquired data were compared using inductively coupled plasma atomic emission spectrometry (ICP-OES). Univariate and multivariate statistics are used to evaluate EDXRF data. The particle size of the tested samples affected the z-scores of SiO2, Al2O3, Fe2O3, TiO2, CaO, MgO, Na2O, K2O, and P2O5 concentration measurements. Grinding times for refractory concrete, brick, and putty samples were determined in order to validate the robustness of the EDXRF technique and provide reliable chemical analyses. The ideal milling times for the samples studied ranged from 180 to 360 s, depending on the type of refractory material