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Sustainable Cement Design with Hybrid SCMs: Integrating Recycled Concrete, Eggshells and Calcined Clay
No full textThe cement industry faces urgent challenges in reducing carbon emissions while maintaining performance standards. This study explores the development of sustainable cementitious systems using hybrid supplementary cementitious materials (SCMs) derived from recycled concrete powder (RCP), thermally activated clay, and eggshell waste. These materials were selected based on their local availability, reactivity potential, and environmental value. Comprehensive characterization of the raw components was carried out using X-ray fluorescence (XRF) and inductively coupled plasma optical emission spectrometry (ICP-OES) to determine chemical composition, while Fourier-transform infrared spectroscopy (FTIR) was employed to identify functional mineral phases. Physical properties such as specific surface area, particle size distribution, and density were also measured. Cement mortars were prepared with 10–30% replacement of ordinary Portland cement by the hybrid SCM blend. Compressive strength was tested after 7, 28, and 90 days of curing. The mixture with 20% SCM substitution exhibited the best performance, achieving up to 18% higher compressive strength than the reference mix. The synergy of RCP, eggshells, and calcined clay provided enhanced reactivity and microstructural refinement. The results confirm that combining recycled and biogenic waste streams offers a promising route toward eco-efficient cement design, aligning with global goals for circular construction and carbon footprint reduction.poste
Temperaturski impulsni odziv dvoslojne građevinske pregrade
No full textU radu je analizirana dvoslojna građevinska pregrada poznatih toplotnih i fizičkih karakteristika i određen je temperaturski impulsni odziv na zadate granične uslove na spoljašnjoj i unutrašnjoj površini. Odziv je određen rešavanjem Furijeove jednačine za zadati problem u frekventnom domenu. Temperaturski odziv u vremenskom domenu je dobijen određivanjem polova prenosne funkcije u frekventnom domenu
Determination of the lifetime by the finite element method of round smooth specimen exposed to low cyclic fatigue
No full textIn the paper, based on the results of experimental research on the behavior of samples made of high-strength
low-alloy steel (HSLA), Nionicral 70 (NN-70), in the form of a round smooth specimen (RSS) under conditions
of low cyclic fatigue (LCF), a computational stress analysis was performed using the finite element method
(FEM), in the Cosmos module of the SolidWorks program.
Based on the analysis of the results of the stress-strain state and determination of the service life via the
service life isolines, Fig. 1, for a certain load cycle that affects the entire RSS ligament for a certain load in a
wide range of LCF loads and comparison with the results of experimental tests, conclusions were drawn that
justify the efforts to solve the service life assessment of a machine element loaded with low-cycle fatigue
numerically.
The results of experimental tests and test simulations (FEM, LCF in the SolidWorks program) also provided
us with important data on understanding the LCF behavior of HSLA steel, NN-70
Analysis of pile integrity executed in improved soil
No full textPile integrity testing (PIT) is a widely applied and straightforward method for assessing the geometric characteristics and quality of constructed piles. However, its reliability strongly depends on the availability of comprehensive data regarding geological conditions and the construction process. This paper presents a practical case where the absence of information on soil improvement by jet grouting initially led to misinterpretation of pile reflectograms, with piles classified as potentially defective. The heterogeneities introduced by jet grouting significantly affected the reflectograms, creating apparent negative reflections that complicated interpretation. To address this uncertainty, comparative analysis of multiple signals was performed, supported by available geotechnical data. Furthermore, static load tests were conducted on selected piles, confirming their bearing capacity and proving that the initial assessment based solely on reflectograms was misleading.Ispitivanje integriteta šipova (Sonic Integrity Test – SIT) predstavlja jednostavnu i široko primenjivanu metodu za ocenu geometrijskih karakteristika i kvaliteta izvedenih šipova. Pouzdanost ove metode u velikoj meri zavisi od raspoloživih podataka o geološkim uslovima i samoj tehnologiji izvođenja šipa. U ovom radu prikazan je praktični primer u kojem je izostala informacija o sanaciji tla metodom jet grouting-a, što je dovelo do pogrešne interpretacije reflektograma i klasifikacije šipova kao potencijalno oštećenih. Heterogenosti izazvane jet grouting-om značajno su uticale na izgled reflektograma stvarajući negativne refleksije koje otežavaju tumačenje. Radi smanjenja neizvesnosti izvršena je uporedna analiza većeg broja signala, uz oslanjanje na dostupne geotehničke podatke. Dodatno, sprovedena su statička probna opterećenja odabranih šipova, koja su potvrdila njihovu nosivost i pokazala da je prvobitna ocena zasnovana samo na reflektogramima bila pogrešna
Analiza rada redovne i incidentne ventilacije u garažama sa simulacijom požara
No full textGarages can be equipped with advanced smoke extraction and ventilation systems. A notable characteristic is that the same ductwork and fans are typically used for both regular ventilation and emergency ventilation. Consequently, smoke extraction ducts and fans must be certified for adequate fire resistance. Regular ventilation refers to the conditioning of air within the garage to reduce emissions of carbon monoxide and other harmful gases generated by vehicles. Emergency ventilation, on the other hand, is activated in the event of a fire, requiring the same smoke extraction infrastructure to maintain operational integrity under elevated temperature and fire conditions. National regulations prescribe the required air exchange rate and permissible exposure duration to carbon dioxide concentration in enclosed parking facilities. In this study, the temporal variation of harmful gas concentrations during a simulated fire was analyzed, confirming that the modeled garage complies with the parameters stipulated by the regulations. Particular emphasis is placed on the fluid mechanics equations that describe turbulent smoke flow at high temperatures. These equations are applied in algebraic form to solve the flow field inside the garage using Computational Fluid Dynamics (CFD) methods. The commercial software PyroSIM (FDS) was employed for geometric modeling of the garage and for simulating the fire scenario. Boundary conditions describing the fire load were defined in detail, and a fire growth curve was developed for a burning vehicle positioned at the most disadvantageous location for smoke extraction. In addition to the main extraction fans, the simulation considered the presence of axial (JET) fans, which are used exclusively during emergency ventilation. Their influence on the velocity field, temperature distribution, and visibility within the garage was assessed. The simulation results demonstrate that complete smoke extraction can be achieved within 33 minutes, providing sufficient time for firefighting intervention and suppression
Novi pristup modelovanju ekološki održivih maltera sa pucolanskim dodacima i recikliranim agregatom primenom PLS regresije
No full textU ovom radu predstavljena je primena metode delimičnih najmanjih kvadrata sa strukturnim jednačinama (Partial Least Squares, PLS) za optimizaciju sastava maltera sa ciljem postizanja balansa između mehaničkih svojstava i ekološkog otiska. Ispitivani su malteri sa dodatkom pucolanskih (metakaolin, zeolit) i recikliranih materijala, uz variranje sadržaja cementa i vode. Hemijska karakterizacija sirovina izvršena je metodama rendgensko fluorescentne spektrometrije (EDXRF) i optičko emisione spektrometrije sa indukovanom spregnutom plazmom (ICP-OES), čime je omogućen uvid u sadržaj ključnih oksida (SiO 2, Al 2O 3) koji utiču na pucolansku aktivnost. Na osnovu eksperimentalnih podataka o sastavu i čvrstoći maltera, kao i proračunate emisije CO 2 po jedinici zapremine, konstruisan je PLS model kojim su kvantifikovani uticaji pojedinačnih komponenti na željene osobine. Rezultati su pokazali da određeni udeli metakaolina i zeolita mogu doprineti smanjenju CO 2 emisije, bez značajnog kompromisa u mehaničkim performansama. Takođe, primena recikliranog betona kao zamene za deo prirodnog agregata omogućava efikasnije korišćenje resursa i smanjenje građevinskog otpada, bez narušavanja ključnih svojstava maltera. Predloženi model predstavlja alat za efikasan dizajn ekološki optimizovanih receptura maltera, sa potencijalom za dalju primenu u inženjerskoj praksi i industriji građevinskih materijala
How sodium silicate affects self-compacting concrete qualities with various aggregates and mineral additions
No full textSelf-compacting concrete (SCC) was developed with the goal of minimizing the human factor in concrete placement. SCC improves the quality and durability of the structures because it does not require vibration after being poured into the formwork and molds. The use of construction and demolition waste (C&DW) as a source of aggregates for the production of new concrete is the result of increasing environmental awareness and responsibility for future generations lives, as well as recognizing the economic interest expressed through lower transportation costs and avoidance of landfill fees. Given the foregoing, the fact that interest in recycled aggregate (RCA) from concrete waste is steadily increasing is unsurprising, but it is just evidence and an indicative of the future direction of material use. This research investigates the idea of treating recycled aggregates with sodium silicate to improve their qualities in high-strength concrete. Silica fume and fly ash, the industrial byproducts, are used as mineral additives. Throughout the experiment, several different self-compacting concrete compositions were tested. The reference combination was made entirely of natural aggregate, whereas the remaining four mixtures used 50% recycled aggregate in the II (4/8) and III (8/16) fractions. The physical and mechanical properties of fresh and hardened concrete were investigated, as well as the feasibility of employing treated recycled aggregate in high-strength structural concrete. The fresh qualities of concrete were assessed using consistency, entrained air percentage, and concrete temperature. Compressive strength, flexural strength, static and dynamic modulus of elasticity, ultrasonic pulse velocity, adhesion, water impermeability, and surface hardness were all measured in hardened concrete. The results show that there is a possibility of improving properties of fresh and hardened self-compacting concrete with recycled concrete aggregate, paving a way to a more sustainable construction
Application of Deff–MR curve analysis to external drying data for identifying the moisture transport mechanisms
No full textThe Deff–MR (effective diffusivity vs. moisture ratio) curve approach, developed by the authors, has been successfully used over the past 15 years to optimize drying regimes for clay-based materials. While its practical value in industrial and laboratory settings is well-established, its theoretical contribution to identifying internal moisture transport mechanisms remains underutilized in broader drying applications. To assess its universal relevance, this study applies Deff–MR curve analysis to digitized drying and shrinkage data from multiple external sources. The data were extracted from literature graphs and reanalysed using the proposed Deff–MR framework. Despite differences in experimental procedures and diffusivity calculation methods, the analysis revealed consistent transition points corresponding to known moisture transport mechanisms, including capillary flow, vapor diffusion, and Knudsen diffusion. These findings support the broader applicability of the Deff–MR method as a diagnostic tool for identifying dominant internal moisture movement mechanisms across different drying scenarios and materials
An Analysis of Transition Temperature for Real and Simulated Heat Affected Zone of HSLA Steel
No full textThe aim of this paper is to present the analysis of the influence of different test temperatures on the impact toughness of the real heat affected zone (RHAZ) and
the simulated heat affected zone of the welded joint (SHAZ) of high strength low-alloy steel. Through thermal cycle simulation, which includes heating to a certain temperature
and programmed cooling, the microstructure of different areas of the heat-affected zone was obtained on the samples, which allows us to directly draw appropriate
conclusions regarding the real heat-affected zone of the welded joint. Based on the previous text, a comparison of the brittleness transition temperature values for RHAZ
and SHAZ as a very important factor for structural steels was made. It has been observed that with a decrease in temperature many metals exhibit a sudden decrease in
toughness, so the temperature at which the material transits from ductile to brittle fracture is called brittle transition temperature (ductile-brittle transition temperature). This
indicator is very important regarding further design and exploitation of welded steel structures
Analiza kvaliteta sirovina za proizvodnju keramike u Srbiji
No full textSpecifična svojstva gline kao sirovine određuju mogućnost primene u različitim vrstama
keramičkih proizvoda. U ovom radu dat je prikaz različitih tipova sirovina iz Srbije, na osnovu
hemijskog, mineraloškog sastava, kao i ponašanja tokom pečenja. Ispitivane gline se mogu podeliti
na one pogodne za proizvodnju opekarskih proizvoda i tzv. fine keramike. Iz svake grupe glina
prikazan je po jedan primer i dati su hemijski i mineraloški sastav, kao i ponašanje pri zagrevanju
(pečenju). Posebna pažnja posvećena je uticaju nečistoća, kao što su karbonati, oksidi gvožđa i
organski materijali, na finalne karakteristike gotovih proizvoda