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The influence of two types of polypropylene fibres on the mechanical properties of shotcrete
No full textModel of Probabilistic Analysis of Pile Capacity Based on the Extrapolation of Load-Settlement Curves
No full textThis paper formulates a mathematical model using the extrapolation of load-settlement curves with a rational function for analyzing the capacity of piles obtained from the static load test (SLT). In preliminary analyses, the extrapolation was based on the application of a number of mathematical functions that were gradually eliminated by iterative selection and filtering. The solution was obtained by extrapolation with a rational function. Using a rational function in the extrapolation of the load-settlement curve, a clearly identifiable part is obtained in which the asymptote is vertical, indicating the reached limit state of capacity in the soil and/or in the pile. The probabilistic analysis showed that no unique value for pile capacity was obtained, and that the spectrum of capacity values depends on the probability of occurrence of the corresponding event
Immobilization of heavy metal ions Zn2+, Ni2+, Pb2+ and Cu2+ in the structure of cement-based materials
Get PDFPrirodni zeolit i bentonit korišćeni su kao mineralni dodaci u mešavinskom dizajnu ekološki sigurnih građevinskih materijala na bazi cementa. Ispitane su adsorptivne sposobnosti ove dve glinene sirovine, tj. njihov afinitet da imobiliziraju jone teških metala Zn2+, Ni2+, Pb2+ i Cu2+. Za eksperiment su pripremljeni pojedinačni i multi-rastvori Zn2+, Ni2+, Pb2+ i Cu2+ . Dobijeni rezultati su analizirani pomoću kinetičkih modela pseudo prvog i pseudo drugog reda. Analizirane su izoterme Langmuira i Freundlicha. Bentonit je pokazao bolji adsorpcioni afinitet od zeolita prema sva četiri ispitivana katjona. Kao dokaz, ispitano je ispitivanje ispiranja na sedam različitih veziva za cement sa različitim mineralnim dodacima (leteći pepeo, zeolit, bentonit). Eluati dobijeni na uzorcima cementa sa dodatkom letećeg pepela i gline (bilo zeolita ili bentonita) sadržavale su niže koncentracije jona Zn2+, Ni2+, Pb2+ i Cu2+ u odnosu na eluat dobijen na uzorcima cementnog veziva sa letećim pepelom. Razlog za dobijanje ovakvih rezultata su adsorpcioni i hidratacioni mehanizmi koji imobiliziraju teške metale u cementnim kompozitima.Natural zeolite and bentonite were utilized as mineral additives in the mix-design of environmentally safe cement-based building materials. The adsorptive abilities of these two clayey raw materials, i.e. their affinity to immobilize heavy metal ions Zn2+, Ni2+, Pb2+ and Cu2+ were investigated. Singleand multi-solutions of Zn2+, Ni2+, Pb2+ and Cu2+ were prepared for the experiment. The obtained results were submitted to analysis via pseudo-first and pseudo-second order kinetic models. Langmuir and Freundlich isotherms were analyzed. Bentonite exhibited better adsorption affinity than zeolite towards all four investigated cations. As a proof, a leaching test was conducted on seven different cement binders with different mineral additives (fly ash, zeolite, bentonite). The leachates obtained on the samples of cement with addition of fly ash and clay (either zeolite or bentonite) contained lower concentrations of Zn2+, Ni2+, Pb2+ and Cu2+ ions than leachates obtained on the samples of cement binder with fly ash solely as a result of adsorption and hydration mechanisms that immobilized heavy metals within cementitious composites
Studija stanja ugroženosti Beograda bukom iz ugostiteljskih objekata
No full textMasovno ugrožavanje bukom iz ugostiteljskih objekata dobro je poznat ekološki
probem u Beogradu. Buka koju oni stvaraju najvećim delom potiče iz uređaja za reprodukciju
muzike. Međutim, problem je kompleksniji jer činjenica da su takvi objekti mesto okupljanja
većeg broja ljudi, i to dominantno u noćnom periodu, donosi ugrožavanje bukom zbog žamora i
drugih zvučnih pojava koje to prate. U ovom radu prikazani su neki rezultati studije koja ima za
cilj sagledavanje tog problema i predlaganje postupaka koji taj problem mogu da umanje. U
radu je prikazana prostorna distrubucija ugostiteljskih objekata koji su u protekle četiri godine
bili predmet žalbi inspekcijskoj službi i analiza rezultata dobijenih kontrolnim merenjima buke
koja su u istom periodu obavljana po nalogu inspektora
Optimizacija kvaliteta suvih opeka na osnovu karakteristika polaznih sirovina pomoću matematičkog modela zasnovanog na veštačkim neuronskim mrežama
No full textKorisnik/naručilac: Institut za ispitivanje materijala a.d., Beograd, 202
Problematika upravljanja rudarskim otpadom u podzemnim rudnicima uglja u Republici Srbiji
No full textNumerical determination and experimental validation of the fracture toughness of welded joints
No full textMost of the serious weldment failures lead to catastrophic consequences in terms of damage of other equipment, loss of production, and risks to workers' health and safety. Hence, there is motivation to find margin between safety and disaster. This necessitates guaranteeing the integrity of a welded structure even if a crack is present. Therefore, influence of the material inhomogeneity and residual stresses on deformation and fracture behavior needs to be described precisely. Fracture mechanics parameters J - integral and CTOD have attracted great interest in recent years. Two three point bending specimens of base metal (BM) and weld metal (WM) were tested according to standard BS EN ISO 15653. Than, a two dimensional finite element analysis was performed in Ansys Workbench software to calculate J-integral, and compare with experimental results. The aim of this work is to explore the possibility of using the test results in the reliable prediction of weldment fracture
Performances of Vermiculite and Perlite Based Thermal Insulation Lightweight Concretes
Get PDFThis experimental study was conducted with an aim to investigate the effect of the elevated temperature on the mineral phase composition, microstructure and mechanical properties of the thermal insulation lightweight concretes. The first group of experimental concretes was based on the expanded vermiculite and expanded perlite used as lightweight aggregates (in 65 wt%) in combination with either ordinary Portland cement or refractory calcium aluminate cement. The mix-design of the second group of concretes comprised standard quartz aggregate, vermiculite or perlite as aggregate replacement (25 wt%) and binder (PC or CAC). A total of 10 concrete mix-designs were fabricated in form of 40x40x160 mm samples which were submitted to heat-treatment at 400 degrees, 600 degrees, 800 degrees and 1000 degrees C upon standard 28-days period of curing and hardening. The changes in crystallinity and mineral phase composition induced by temperature were monitored by X-ray diffraction technique. Microstructural visualizations of the non-fired and fired concrete samples were conducted by scanning electron microscopy accompanied with EDX analysis. The results indicated that despite the decrease in compressive strengths upon firing, investigated lightweight concretes can be categorized both as thermal insulators and structural materials
Improvement and modification of the energy-dispersive X-ray fluorescence method for the determination of metal elements in cement leachates - A chemometric approach
Get PDFA modification of an analytical procedure for the energy-dispersive X-ray fluorescence (EDXRF) quantification of ten chemical elements (As, Ba, Cd, Co, Cr, Cu, Mo, Ni, Pb and Zn) in the leachates obtained from cement binders was developed. Twenty-nine testing samples were used in the experiment. All samples were based on Portland cement. Fly ash of different origin, zeolite and bentonite were employed as mineral additives in the cement binders. Distilled water was used as the leachate. Validation of the modified EDXRF procedure was conducted in terms of limits of detection and quantification, working range, linearity, selectivity, precision, trueness, and robustness. Traceability of the procedure was established using certified reference materials. Uncertainty of measurement was confirmed via an "in-house" laboratory validation approach. The expanded uncertainties for the ten analysed elements were obtained for the entire working range of the EDXRF method. Robustness of the modified EDXRF procedure was assessed by means of a chemometric in-house approach. The results obtained by the modified X-ray fluorescence method were additionally correlated to those acquired by inductively coupled plasma optical emission spectrometry to confirm that EDXRF could be used as an effective and reliable alternative method for analysis of cement leachates
Characterization of drying behavior and modeling of industrial drying process
Get PDFThe general method for industrial chamber dryer optimization was reported in this paper. The first step in finding the most suitable drying regime is to characterized the clay raw material, especially its water loss at 2000C and to determine the critical drying rate inside the specially constructed laboratory dryer. These data provides us information if the product or the dryer is the bottleneck for the optimisation. If the optimization is justified geometry of the dryer, air mass flows, temperature, and humidity profiles inside the dryer as well as initial water content in the drying material, initial temperature of the products and the load of the dryer are required. Some of the previously mentioned data are only used to check if the chamber dryer is working properly, while the others are used as the initial parameters necessary for software simulation. In this paper two models for calculating the optimal drying parameters were used. The first model was developed from the comprehensive theory of the moisture migration during isothermal drying. The calculation software for setting up the non - isothermal drying regimes was reported in our previous papers. It is important to say that this model was not able to adequately predict the temperature raise within the drying products. In order to simulate the raise of the temperature of the roofing tiles during drying the second model was used. This simple receding drying front model was firstly reported by Kitcher. If both models are used simultaneously it is possible to calculate air temperatures, product temperature, absolute and relative humidity of the drying air, moisture content of the product, drying rate etc ... It is important to mention that this approach can lead to the recommendations for changes inside the dryer before an optimized situation is achieved. One example of such situations is described in this paper in details