Microstructural and cavitation erosion testing was carried out on Cu-12.8Al-4.1Ni (wt. %) shape memory alloy (SMA) samples produced by continuous casting followed by heat treatment consisting of solution annealing at 885 °C for 60 min and, later, water quenching. Cavitation resistance testing was applied using a standard ultrasonic vibratory cavitation set up with stationary specimen. Surface changes during the cavitation were monitored by metallographic analysis using an optical microscope (OM), atomic force microscope (AFM), and scanning electron microscope (SEM) as well as by weight measurements. The results revealed a martensite microstructure after both casting and quenching. Microhardness value was higher after water quenching than in the as-cast state. After 420 min of cavitation exposure, a negligible mass loss was noticed for both samples. Based on the obtained results, both samples showed excellent cavitation resistance. Mass loss and morphological analysis of the formed pits indicated better cavitation resistance for the as-cast state (L).

In this study, a mixture of magnesium oxide and titanium dioxide was mechanically activated in order to investigate the possibility of mechanochemical synthesis of magnesium titanate. Mechanical activation was performed for 1000 min in a high-energy vibro mill (type MH954/3, KHD Humboldt Wedag AG, Germany). The mill is equipped with housing having a horizontally placed shutter. The cylindrical stainless steel working vessel, with inner dimensions of 40 mm in height and 170 mm in diameter, has working elements consisting of two free concentric stainless steel rings with a total weight of 3 kg. The engine power is 0.8 kW. Respecting the optimal amount of powder to be activated of 50-150 g and the stoichiometric ratio of the reactants in the equation presenting the chemical reaction of magnesium titanate synthesis, the starting amounts were 20.2 g (0.5 mol) of MgO and 39.9 g (0.5 mol) TiO2. During the experiments, X-ray diffraction analysis of the samples taken from the reaction system after 60, 180, 330, and 1000 min of mechanical activation was performed. Atomic absorption spectrophotometry was used for chemical composition analysis of samples taken at different activation times. Based on the X-ray diffraction analysis results, it can be concluded that the greatest changes in the system took place at the very beginning of the mechanical activation due to the disturbance of the crystal structure of the initial components. X-ray diffraction analysis of the sample after 1000 min of activation showed complete amorphization of the mixture, but diffraction maxima characteristic for magnesium titanate were not identified. Therefore, the mechanical activation experiments were stopped. Evidently, the energy input was not sufficient to overcome the energy barrier to form a new chemical compound - magnesium titanate. The failure to synthesize magnesium titanate is explained by the low negative Gibbs energy value of -25.8 kJ/mol (despite the theoretical possibility that the reaction will happen), as well as by the amount of mechanical energy entered into the system during activation which was insufficient to obtain the reaction product. Although the synthesis of MgTiO3 was not achieved, significant results were obtained which identify models for further investigations of the possibility of mechanochemical reactions of alkaline earth metals and titanium dioxide.

Milica VLAHOVIĆ,, Aleksandar SAVIĆ, Sanja MARTINOVIĆ, Nataša ĐORĐEVIĆ, Zoran STEVIĆ, Tatjana VOLKOV HUSOVIĆ 1 University of Belgrade, Institute of Chemistry, Technology and Metallurgy, Belgrade, Serbia 2 University of Belgrade, Faculty of Civil Engineering, Belgrade, Serbia 3 Institute for Technology of Nuclear and Other Mineral Raw Materials, Belgrade, Serbia 4 University of Belgrade, Faculty of Electrical Engineering, Technical Faculty Bor, CIK Belgrade, Serbia 5 University of Belgrade, Faculty of Technology and Metallurgy, Belgrade, Serbia

Due to the Portland cement chemical reaction, which always takes place in a hardening concrete, a certain amount of heat is released. This heat should be quantified, as it can harm or aid the concrete itself, depending on the concrete components, structure element, ambient and building site conditions. There are number of possible setups for the monitoring of heat of hydration, two of which have been applied in the case presented in this paper. Four concretes were monitored with the use of the two stated techniques for 24 hours. First technique used is thermo-vision camera which monitored the surface, and the second is thermosensor - used for monitoring of interior of fresh concrete hardening mass. The potential of the applied setup lays in the ease of installation, low price, and possibilities of mass application, which could substantially aid the monitoring and prevent concrete failure.

Although the most prominent material in contemporary construction practice due to its obvious advantages, concrete possesses a number of drawbacks. One of the advantageous principles for decades is to enable a large scale on-site application of this material with acceptable properties, needed to withstand specific conditions. A concept of 3d printing concrete presents a promising ground for further improvement of this principle. While maintaining as much as possible of the prerequisite and common properties to answer the construction demands, this material has to evolve as much as possible to fulfill the 3d concept, which would, in turn, pave a way for the next level of its construction applications. This paper presents the main principles of 3d printing concrete, by discussing the main goals and the drawbacks that have to be solved prior to wider application. Also, one specific facility- wind tower will be reconsidered as a potentially promising ground for this old construction material dressed in a new suit.

This paper investigated the effect of the tenon length on the strength and stiffness of the standard mortise and tenon joints, as well of the double mortise and tenon joints, that were bonded by poly(vinyl acetate) (PVAc) and polyurethane (PU) glues. The strength was analyzed by measuring applied load and by calculating ultimate bending moment and bending moment at the proportional limit. Stiffness was evaluated by measuring displacement and by calculating the ratio of applied force and displacement along the force line. The results were compared with the data obtained by the simplified static expressions and numerical calculation of the orthotropic linear-elastic model. The results indicated that increasing tenon length increased the maximal moment and proportional moment of the both investigated joints types. The analytically calculated moments were increased more than the experimental values for both joint types, and they had generally lower values than the proportional moments for the standard tenon joints, as opposed to the double tenon joints. The Von Mises stress distribution showed characteristic zones of the maximum and increased stress values. These likewise were monitored in analytical calculations. The procedures could be successfully used to achieve approximate data of properties of loaded joints.

The intent in this paper is to define how the batch equilibrium results of copper removal from a synthetic solution on natural zeolite can be used for prediction of the breakthrough curves in the fixed-bed system for both a synthetic solution and wastewater. Natural zeolite from the Vranjska Banja deposit, Serbia, has been fully characterized (XRD, chemical composition, DTA/TG, SEM/EDS) as a clinoptilolite with cation exchange capacity of 146 meq/100 g. The maximum adsorption capacity (qm) in the batch of the mono-component system (synthetic copper solution) obtained using the Langmuir isotherm model was 7.30 and 6.10 mg/g for particle size below 0.043 and 0.6–0.8 mm, respectively. Using the flow-through system with the 0.6–0.8 mm zeolite fixed-bed, almost double the adsorption capacity (11.2–12.2 mg/g) has been achieved in a saturation point for the copper removal from the synthetic solution, compared to the batch. Better results are attributed to the constant high concentration gradient in flow-through systems compared to the batch. The complex composition of wastewater and large amounts of earth alkaline metals disturb free adsorption sights on the zeolite surface. This results in a less effective adsorption in flow-through systems with adsorption capacity in breakthrough point of 5.84 mg/g (~0.95 × qm) and in a saturation point of 7.10 mg/g (~1.15 × qm).

This study analyzes the feasibility of valorizing industrial by-product, fly ash from a thermal power plant as a partial replacement of mineral filler-limestone for the production of self-compacting concrete (SCC). Three types of SCC mixtures with different portions of fly ash and the reference mixture with limestone were designed. The synthesized SCCs in the fresh state were examined for density, entrained air content, flowability (Slump flow, Slump flow time (t500), V-funnel time (tv)), passing ability (L-box), and segregation resistance, while hardened state testing included: density, compressive and flexural strength, static modulus of elasticity, water permeability, resistance against freezing in the presence of de-icing salt, and SEM analysis. Taking into account the obtained results it can be concluded that the addition of fly ash has a positive impact on the concrete properties and that the optimal content of fly ash is 20 % with respect to the total filler mass.

High-temperature materials are used in a wide range of industries and applications such as gas turbine engines for aircrafts, power and nuclear power plants, different types of furnaces, including blast furnaces, some fuel cells, industrial gas turbines, different types of reactors, engines, electronic and lighting devices, and many others. Demands for high-temperature materials are becoming more and more challenging every year. To perform efficiently, effectively and at the same time to be economically viable, the materials used at high temperatures must have certain characteristics that are particularly expected for applying under such extreme conditions, for example, the strength and thermal resistance. In the present review, some important requirements that should be satisfied by high temperature materials will be discussed. Furthermore, the focus is put on refractory concretes, ceramics, intermetallic alloys, and composites as four different categories of these materials, which are also considered in respect to possibilities to overcome some of the current challenges.

Self-compacting concrete (SCC) contains fine mineral fillers such as limestone powder. The idea of this study was to partially replace limestone with waste sulfur since it is hydrophobic, insoluble in water and therefore chemically inert and to compare the properties of produced concrete samples. Fresh concrete proper­ties included: slump-flow, t500, V-funnel time, L-box ratio, segregation ratio, density, and entrained air content. Hardened concrete was tested for compressive, flexural and bond strengths, ultrasonic velocity, dynamic elas­ticity modulus, dynamic Poisson’s ratio, and microstructure. Flowability and segregation increased, while bulk density, compressive and flexural strength, dynamic elasticity modulus and ultrasonic velocity slight declined. Times t500 and V-funnel time, L-box ratio and entrained air changed insignificantly. Considering that all proper­ties should remain or improve in case of waste valorization and the criteria should set to satisfy requirements for SCC, this study proved that all mixtures can be used for structural applications.

Aleksandar SAVIĆ, Zoran STEVIĆ, Sanja MARTINOVIĆ, Milica VLAHOVIĆ3, Tatjana VOLKOV HUSOVIĆ 1 University of Belgrade, Faculty of Civil Engineering, Belgrade, Serbia 2 University of Belgrade, Faculty of Electrical Engineering, TF Bor, CIK, Belgrade, Serbia 3 University of Belgrade, Institute of Chemistry, Technology and Metallurgy, Belgrade, Serbia University of Belgrade, Faculty of Technology and Metallurgy, Belgrade, Serbia

In this paper, the stress and strain analysis of common laminated wood seat shell is performed. Experimental stiffness evaluation is conducted by measuring displacement of the point on the backrest, and experimental stress analysis is carried out by tensometric measuring at the critical transition area from the seat to the backrest. Finite element analysis is carried out layer by layer with a “2D linear elastic model” for orthotropic materials. Good matching is found between numerical and experimental results of displacement. It is also shown that the results of the principal stress in the measurement points of the seat shell compare favourably with experimental data. The applied in-plane stress analysis of each individual veneer is not applicable for interlaminar stress calculations that are a significant factor in curved forms of laminated wood. Curved forms of laminated wood products require more complex numerical analysis, but the method can be used to achieve approximate data in early phase of product design.