The innovative method for determining the approximate value of the Bond work index

: In this study, we examine an innovative approach to determining the Bond work index, a key parameter in the mining and cement production industry that indicates material grindability. The method relies on the first-order kinetics law and allows for the estimation of approximate index values with any number of grinding cycles, depending on the desired data accuracy. An important aspect of this approach is the multiplication of parameters G and P80 for each cycle by specific coefficients, achieving values close to those of the last grinding cycle when equilibrium is reached in the standard test. In this paper, we compare the results obtained by the innovative method with the standard Bond procedure on various samples of mineral materials. Our analysis shows a significant reduction in the mean square error as the number of grinding cycles increases, indicating increased precision of the new approachhttp://www.serbianceramicsociety.r

The application of the thin and lumped appreoach for comparision of the drying kinetic registered for various thin clay slabs

The main goal of this paper was to compare the lumped and thin layer modelling approach for describing the drying kinetics of clay slabs extruded from various clays. Four drying regimes were firstly designed. The drying velocity was fixed to 3 m/s in all experiments. The drying temperature and humidity were hold at 400C and 60% in the first drying regime. These parameters were raised for 100C and 10% in each following experiment. Eight thin-layer models, including the new one, was used. The non-linear regression analysis was applied for fitting the experimental data. The lumped approach is relatively new and it assumes that different drying mechanisms which affects the internal moisture transport are combined and presented in a form of the effective diffusivity constant. The lumped modelling approach has retained and reused the form of the Crack’s diffusion equation with only one update. The pure diffusion coefficient was replaced with the effective one. Since the effective moisture diffusivity can vary with time the most advanced lumped models are taking this into account by defining the relationship between the effective diffusivity coefficient and the Fourier number. This model was adopted in this paper. Results have shown that the best thin layer model was the new one. It was found that this model has up to 5 % deviation from the experimentally registered data at the beginning of the first drying segment. The lumped model was deviating from the experimental data for only 2%. This was another confirmation that the conjugation degree in thin layer modelling is lower than in the case of the lumped approach. This means that thin layer model application is actually very limited, especially for porous materials which predominantly shrinks during drying, due to theoretical assumptions which simplifies the boundary conditions for which the equations were originally developed

Raw clays in the production of ceramic and refractory tiles

Raw clay samples from Serbia, mainly of kaolinitic, illitic and mixed nature, were tested for their possible application in the production of ceramics. Using various triaxial diagrams, the samples were sorted according to their chemical and bulk mineralogical makeup, and also particle size distribution to determine whether they could be employed in the production of ceramics and refractories. The areas in the ternary graphs determined in earlier studies concerning the expected color after firing and the applicability of the raw clays are checked and extended. The samples' water absorption and flexural strength were assessed using EN standard procedures after they had been hydraulically semi-dry pressed and fired at several peak temperatures between 1100 and 1300 °C. A novel triaxial diagram considering the position of the samples based on firing temperature, water absorption and modulus of rupture is proposed, and the areas of different kinds of ceramic tiles are defined. It is discovered that the different raw clays can be utilized to create refractory, as well as wall and floor tiles. This study supports the rational use of natural sources of raw materials

Properties of concrete with crumb rubber in relation to ordinary and aerated concrete

Waste tires have long been a challenge for waste disposal. In an effort to mitigate the impact of solid waste on the environment and recycle it as much as possible, research has been conducted into the possibility of using this waste in concrete mixes. However, the use of these waste materials in concrete is still not popular due to the lack of knowledge of the properties that can be obtained with this material. Hence, the aim is to use waste material in the production of concrete, and that concrete mixes with this material have satisfactory performance. The paper presents the results of research on concrete in which volume replacement of fine aggregate with crumb rubber was performed in the amount of 5%, and this concrete was compared with the control concrete mix and aerated concrete. All concrete are made with a water-cement factor of 0.45. The performance of fresh concrete was monitored for 10, 30 and 60 min. In the case of concrete with the addition of crumb rubber, after 60 min, higher values of air content were obtained, and lower values of volume mass of fresh concrete compared to the initial measurements. The obtained test results of hardened concrete indicate that concrete with crumb rubber has a lower compressive strength compared to the control concrete mix, while compared to aerated concrete, they obtain approximate compressive strength values

Metodologija određivanja plastičnog i elastičnog dela opterećenja čelika kod ispitivanja nisko cikličnim zamorom

KORISNIK TEHNIČKOG REŠENJA: Univerzitet u Beogradu, Mašinski fakultet, Laboratorija za dinamička ispitivanj

Feasibility study on utilization of pulverized construction and demolition waste as alternative raw material for Portland cement clinker production

A number of beneficial characteristics are displayed by ordinary Portland cement (OPC), including workability, appropriate setting and hardening behavior, superior mechanical performance, and good chemical resistance. OPC has been used as the major bonding agent in the building industry for more than 200 years due to these reasons. OPC is commercially produced by heating limestone, quartz, clay, and slag in a specially designed rotary kiln. The goal of this study is to use waste materials (construction and demolition waste) and alternative clayey materials to produce cement clinker. When it comes to the resources needed to make cement clinker, caution has been applied because substitute raw materials need to be accessible in adequate quantity and quality. Carbon dioxide is a byproduct of the chemical reactions in a rotary kiln. One kilogram of CO2 is released into the atmosphere during the cement-making process. Up to 9% of global human CO2 emissions are produced annually by the manufacture of cement and concrete. An attempt has been made to decrease the sintering temperature and the duration of thermal treatment in order to decrease the carbon emissions of the process. Therefore, in this study, cement clinker was synthesized at temperatures ranging from 1100°C to 1400°C upon mechanical activation of the raw material. Four cement clinkers were produced based on different raw materials: 1) recycled concrete, kaolinitic-illitic clay, Fe-slag, and limestone; 2) recycled concrete, zeolite, Fe-slag, and limestone; 3) recycled concrete, bentonite, Fe-slag, and limestone; and 4) recycled concrete, refined kaolinitic-illitic clay, Fe-slag, and limestone. The obtained clinkers were characterized by DTA/DCS/TG, XRD, FTIR, and SEM methods. The results indicated that the obtained clinkers exhibited four main cement clinker phases, namely C3S, C2S, C3A, and C4AF, identical to commercial ordinary Portland cement (OPC). The obtained results pointed out that the production of cement clinker based on recycled waste resources and alternative clayey materials is feasible.http://www.serbianceramicsociety.r

Experimental Investigation of Elastic Modulus of Ultra-High Performance Concrete on Small-Scale Specimens

Modulus of elasticity of concrete and other cement-based materials is experimentally obtained through a static load test, which generally involves cyclic preloading in the elastic range, before recording the final measurements of force and deformation. Due to heterogeneity of concrete, certain minimal size of a specimen is needed. This requirement is addressed in relevant standards, where specimen sizes are prescribed. Ultra-high performance concrete (UHPC) mixes contain fine quartz aggregates, which may permit a smaller specimen size, such as those used with mortars, which would reduce costs and waste associated with laboratory testing, while retaining satisfactory confidence in results. In the investigation presented in the paper, testing procedure for concrete was modified to accommodate a smaller specimen size (40x40x160mm prism) and used to obtain the stabilized elastic modulus of three UHPC mixes with varying amount of steel fiber reinforcement. The results exhibit a relatively small dispersion and a reasonable agreement with dynamic moduli obtained by pulse velocity method. To validate the results, a numerical investigation is carried out to examine the influence of imperfect specimen geometry on strain readings. Technical aspects of the testing method, potential improvements and prospects of application to other fine-grained cement-based materials are outlined and discussed.http://www.serbianceramicsociety.r

Determination of the ductile-to-brittle transition temperature of NIOMOL 490 K steel welded joints

This paper is dedicated to the ductile–brittle transition behaviour of the microalloyed structural steel NIOMOL 490 K. This steel grade is used for welded pressure vessels subjected to dynamic loads and operating at sub-zero temperatures. Therefore, it must have an acceptable toughness. Due to its importance for the safety assessment of pressure vessels, a characterization of this steel was carried out using the Charpy V-notch impact test in the temperature range between - 60 ◦C and + 60 ◦C. The notches were located in parent material, heat affected zone and weld metal. In this paper, the tensile strength properties at ambient temperature and the nil ductility temperature in the temperature range from - 60 ◦C to + 60 ◦C are presented

Modelovanja transporta toplote u višeslojnim strukturama u nestacinarnom režimu korišćenjem Grin-ove funkcije i ekvivalnentnih električnih RC kola

Predstavljena je analiza transporta toplote kroz višeslojne građevinske pregrade u nestacionarnom slučaju u vremenskom domenu. Razamatrani su pristupi bazirani na Grin-ovim funkcijama i konvoluciji kao i modelovanje nestacinarnih termičkih procesa korišćenjem ekvivlaentnog RC kola. Pokazano je da je sa praktičnog stanovišta, pri analizi termalnih gubitaka u građevinskim objektima, metod baziran na Grin-ovim funkcijama i konvolucionom integralu u vremenskom domenu pogodoniji za određivanje fluksa toplotnih gubitaka kroz višeslojne pregrade u slučajevima kada su poznate vemenski promenljive temperature vazduha sa spoljašne i unutrašnje strane posmatrane strukture, dok je modelovanje bazirano na ekvivalentnom električnom RC kolu pogodnije u slučajevima kada su poznate vremenski zavisna spoljašnja temperatura vazduha i snaga unutrašnjih grejnih tela. U modelu baziranom na RC kolu moguće je uzeti u obzir i toplotne gubitke kroz pod kao i toplotni kapacitet prostorije, što je u slučaju pristupa baziranog na Grin-ovim funkcijama u vremenkom domenu znatno složenije. Na osnovu razvijenog numeričkog RC modela dobijene su toplotne dinamičke karakteristike posmatranog višeslojnog zida u vidu vremenskih konstanti za različite delove konstrukcije