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Changes in the Vibrational Characteristics of Clay Samples During the Drying Process
No full textThis paper investigates the changes in the mechanical and acoustic properties of clay samples during drying. Variations in resonant behaviour over time were analysed using impulse excitation, with particular focus on the emergence and evolution of the fundamental vibration mode under free boundary conditions. During the drying process, there is a significant decrease in internal damping and an increase in the effective modulus of elasticity, which enables the appearance of clearly defined resonant frequencies only in the later stages of drying. Due to the relatively large thickness compared to the width of the sample, classical thin plate models are not fully applicable, so the results are interpreted while considering the limitations of the theory. Experimental data indicate that the first vibration mode becomes the dominant signal component only after the sample reaches a certain level of dryness. The results are relevant for the development of a methodology for non-destructive monitoring of the mechanical properties of clay and similar materials during drying
Resistance of fire improving of steel elements insulated by fire protection material
No full textThe use of wood in In modern construction, due to its high mechanical properties, controlled quality,
flexibility, durability, economy of application and a large selection of solutions in the design of buildings,
steel is one of the most commonly used materials. In the event of a fire, in a very short time unprotected steel
can reach a critical temperature at which it loses its stability and load-bearing capacity, which can cause the
collapse of the structure and significant social and economic consequences. An unprotected steel support
during a fire relatively quickly reaches a critical temperature, which is about 400°C, after which there is a loss
of mechanical properties, progressive deformations, and then the collapse of part of the structure or the entire
building. The deformation of the steel support is the result of a sudden decrease in the strength of the steel,
which occurs already at 200°C, while at 400°C it drops to half of the initial value. Deformation of steel
columns causes buckling and crushing; the beams bend and in some cases break, so after plastic bending, a
part of the building or the building as a whole collapses. Depending on the type and quantity of combustible
materials and ventilation conditions, a fire can have very different dynamics, thermal power and strength,
which affects the thermal load of structures. For this reason, in order to avoid unwanted consequences, the
steel elements of the structure need to be protected from fire, which is usually done with fire-resistant coatings,
plates or plasters. In this paper the experimental and numerical analysis of three groups of the steel elements
insulated by fire protection material are shown. The first group of samples consists of samples protected with
systems based on fire boards type: AESTUVER thickness of 60 mm, the second group of samples consists of
samples protected with systems based on fire boards type: FIREPANEL A1 thickness of 45 mm thick and the
third group of samples consists of samples protected with systems based on fire boards type: AESTUVER 30
mm and 40 mm thick and with hard-pressed mineral stone wool 80 mm thick. All specimens have been
exposed to standard fire test defined by the standard SRPS EN 1363-1. Experimental determination of fire
resistance was performed in the standard vertical test furnace on ten samples according to the standards SRPS
U.J1.042 and SRPS U.J1.043. The fire resistance was determinate numerically according to the simple
calculation models according to the standard EN 1993 part 1-2 for the samples which is unprotected and
protected by fire protection material. The results obtained numerically and experimentally were compared.
The significant deviation was obtained
Chemical, technological, and radiological characteristics of raw clay and shale mixtures for ceramic brick production
No full textThis study evaluates the suitability of shale for ceramic brick production, focusing on mechanical, thermal, and radiological properties. Incorporating 10% and 20% shale into raw clay decreases the plasticity and fired strength. Radioactivity levels of key radionuclides were measured before and after firing, with hazard indices and effective dose estimations assessing safety. Findings confirm the potential of shale as a sustainable clay substitute while identifying necessary precautions. This research offers insights into mitigating environmental impact and optimizing shale-based ceramics for safer construction applications
Supplementary material to "The intra-Mesozoic bauxite-bearing truncations of the peri-Neotethyan realm (Dinarides/Vardar Zone): A multidisciplinary approach shedding new light on the Neocimmerian event"
No full textOnce coupled with global eustatic levels, bauxites, breccias, unconformities, and hiatuses are significant markers of compressional geodynamics. Most Balkan intra-Mesozoic bauxites, embedded within widespread Triassic carbonate parental sequences, are dominantly distributed in the tectonically exhumed broader Neotethyan realm (Dinarides s.l.). The same mid-Mesozoic stratigraphic interval within the Vardar Zone contains fewer bauxites (East Vardar Zone), exposing abundant corresponding depositional truncations, with occasional nappe stacking configuration and metamorphism. This study, which initially acquired data from a large number of mid-Mesozoic unconformities, carbonate breccias, and similar age bauxites spreading across Dinarides s.l., Serbia, Bosnia and Herzegovina, Montenegro, Croatia (Inner and External Dinarides, Western and East Vardar Zone), including Hellenides in Greece, has provided valuable paleogeographic and geodynamic insights. The findings of this study, combined with the available mineralogical and geochemical data, deformation, including the resulting provenances of intra-Mesozoic bauxite deposits, have led to a complex and intriguing discussion on the tectonic origin of similar age unconformities across Dinaride-Hellenide and Vardar Zone Neotethyan regions. These Dinaride-Hellenide intra-Mesozoic unconformities, carbonate breccias, and widespread bauxites are a fascinating puzzle as no study deals with the complex and controversial processes of repeated regional-scale uplifts, erosion, and bauxite formation. The ambiguity revolves around the geodynamic origin of the Jurassic ophiolites in the first place and its connection with mid-Mesozoic Cimmerian orogenic events (Neocimmerian stage). Thus, the Triassic – Jurassic(Lower Cretaceous) Inner Dinaride Ophiolite belt is particularly interesting accounting for the absence of the latest Jurassic – earliest Cretacous stratigraphic interval. Many of the bauxite ores are produced on Middle Triassic to Jurassic parental limestones, whereby the hiatus can last until the beginning of the Upper Cretaceous. The Triassic rifting and opening of “Dinaric Tethys”, which likely caused the pre-Neocimmerian Late Triassic shoulder uplift of early passive margins, continued into the Jurassic mid-oceanic spreading. The Triassic and Jurassic-aged zircon grains in bauxites, including new data extracted from the bauxite geochemical database, corroborate a volcanic parental affinity originating from exposed Jurassic volcanic rocks. The new geochemical analysis allowed the separation of ultramafic from mafic bauxite sources, whereby acidic sources are absent or well hidden within Inner Dinarides. Bauxite deposits at the southern edge of the Inner Dinaride area show an abundance of incompatible Mn, demonstrating a significant transgressional Oxfordian eustatic high-stand episode (precipitation of Mn on top of submerged paleokarst/bauxites). This, a Red Sea-type small ocean basin with a NE-vergent suprasubduction (“Dinaric Tethys”), lasted until the end of the Jurassic (also dated by metamorphic imprints). The tectonic exhumation processes of Inner Dinaride ophiolites involving the Neocimmerian compressive event caused the widespread uplift episode in the latest Jurassic – earliest Cretaceous, occasionally lasting until the Albian (Austrian unconformity). As a result, mid-Mesozoic long-lasting hiatuses allowed intense weathering of numerous uplifted parental limestone sites, frequently producing at least two cycles of laterites and bauxite ores. The Neocimmerian episode includes the limited length (shorter cross- lithospheric across-strike width) of the latest Jurassic ophiolite obduction on top of abutting continental crust, inclusive of the onset of Lower Cretaceous Vranduk turbidites (another marker of the closing “Dinaric Tethys”)
Balancing weight and strength of 3D printed, PETG and PLA cantilever beams through topology optimization
No full textTopology optimization is a computational method used in the design of elements to achieve optimal
performance, such as maximizing stiffness and minimizing weight. Therefore, it is considered a potent tool
that enables engineers to design elements that are both lightweight and strong. In this study, cantilevers made
of thermoplastic materials (PLA and PETG) were analyzed before and after applying topology optimization.
Afterwards, the cantilevers were 3D printed. By removing unnecessary mass, the structural integrity is not
compromised; instead, a lighter structure is obtained without losing strength. It is a significant challenge when
it comes to parts for the aerospace or automotive industry manufactured through 3D printing. A new model
shape is obtained, meaning that material is retained in areas where it is most needed to resist stresses, thereby
preventing cracks or failure. Therefore, topology optimization provides a prediction of where and how cracks
may occur, as well as how they propagate under specific loads. In this study, beams (PLA and PETG)
measuring 50 × 20 × 8 mm were analyzed under a load of 100 N applied to the free end. Two scenarios of
mass reduction were considered: 50% (factor 0.5) and 70% (factor 0.3), respectively. The initial masses of the
base (non-optimized) parts were 10.00 g (PLA) and 10.16 g (PETG), while the deflections after load
application were 0.2604 mm and 0.3551 mm for PLA and PETG, respectively. The analysis of both scenarios
showed significant weight savings (around 5 g for 50% reduction, and around 3 g for 30% reduction), while
the maximum bending stress for 50% and 70% retention amounted to 18.75 MPa and 31.25 MPa, respectively.
Although the maximum stress value at 70% is still below the typical tensile strength for both materials, it is
essential to consider that the safety factor decreases as the stress increases.
It demonstrated that PLA is more brittle, while PETG is a more rigid material. However, there are still
limitations related to the selection of printing parameters and technology. Nevertheless, it is essential to
emphasize that topology optimization plays a significant role in reducing manufacturing costs and minimizing
environmental impact
Reutilizing rubber tire waste in building industry with implementation of net zero principles: From waste to advanced materials
No full textThe rapid deterioration of concrete structures is often caused by flaws in structural design or by the
improper selection of component materials. This study addresses the existing knowledge gap regarding the
combined effect of frost and de-icing salts as a potential major cause of premature deterioration of concrete
structures. The underlying concept is to mitigate concrete degradation by optimizing its mix design and
incorporating waste resources (waste rubber tires – WRT) to achieve enhanced durability and resistance to
aggressive environments. In this novel, tailor-made concrete, WRT is used as a substitute for air-entraining
admixture. The objective is to establish a methodology for assessing the impact of WRT on the physicomechanical
and durability properties of concrete, as well as to identify the exact mechanisms by which WRT
modifies and enhances rubberized concrete at the microstructural level. Fine WRT particles control structural
water movement during freeze-thaw cycles, absorbing part of the internal stresses and resulting in a
significantly more stable and durable material. The ductility of WRT particles, replacing fine aggregate,
reduces concrete brittleness, while also balancing strains caused by ice expansion within the cement matrix
pores, similar to the function of air voids in air-entrained concrete. To validate this hypothesis, three types of
concrete were prepared: ordinary Portland concrete without admixtures (OPC), modified concrete with
admixtures (superplasticizer Sika® ViscoCrete 4077 and air-entraining admixture Sika® Control 100 AER
RS) (AER), and concrete with WRT (CRC). WRT with a grain size of 0/1 mm (manufacturer: Eco Recycling,
Novi Sad) was used. Two parameters were varied in the mix design: water-to-cement ratio (0.40 and 0.50) and
(in CRC) fine aggregate replacement (7.5% by volume). The replacement ratio was determined based on
previous research where WRT (0.08–3 mm) was used as a partial sand replacement at weight ratios of 5, 10,
and 15%. Specimen surfaces were exposed to 56 freeze-thaw cycles in the presence of de-icing salts. Results
showed increased freeze-thaw resistance and reduced surface scaling for the concrete with 7.5% volumetric
replacement of fine aggregate. Compared to the OPC control sample, this replacement increased the retained
air content from 2.0% to 3.2% at the time of water addition. Air voids were predominantly located around
rubber particles. The higher ductility of rubber grains compared to sand explains why WRT inclusion
improved freeze-thaw resistance in the presence of salts—the ductility of the concrete increased, enabling the
7.5% WRT mix to exhibit lower mass loss due to surface scaling after freeze-thaw cycling. The outcomes of
this study support the long-term management of WRT, the development of new utilization pathways for this
waste, and the preservation of concrete performance robustness, while contributing to environmental
protection in accordance with Net-zero principles. This approach can help scientists, engineers, policymakers,
civil society, and other stakeholders (e.g., WRT manufacturers, environmental NGOs, trade associations,
construction companies) to better understand the challenges and benefits of reusing waste rubber in concrete,
as well as its impact on various performance metrics over the service life, thereby fostering the development
of low-impact products that support waste-to-wealth concepts and the circular economy
Procena kvaliteta podzemne vode i pogodnosti za piće na području Zapadne Srbije
No full textPodzemne vode predstavljaju ključni resurs za snabdevanje vodom za piće, međutim održivo korišćenje podzemnih voda suočava se sa sve većim izazovima usled industrijalizacije i urbanizacije. Da bi se procenio kvalitet i pogodnost vode za piće i druge namene, u radu su analizirani uzorci podzemne vode iz hidrogeološke bušotine koja doseže dubinu > 400 m. Pored poznatih hidrogeoloških karakteristika akvifera i litološkog profila bušotine, sprovedena su fizičko-hemijska, mikrobiološka, biološka, parazitološka i radiološka ispitivanja vode. Rezultati analiza pokazali su da ispitivani parametri zadovoljavaju kriterijume propisane normativom, osim sa aspekta povišene koncentracije Fe, Mn, B, i blago snižene pH vrednosti.Groundwater is a vital resource for drinking water supply; however, its sustainable use is increasingly threatened by industrialization and urbanization. To assess suitability for drinking and other purposes, this study analyzes the quality of groundwater samples obtained from a hydrogeological borehole reaching depths > 400 m. In addition to the known hydrogeological characteristics of the aquifer, and the lithological profile of the borehole, and physicochemical, microbiological, biological, parasitological, and radiological analyses of the water were conducted. The results showed that the examined parameters met the regulatory standards, except for elevated concentrations of Fe, Mn, B, and a slightly decreased pH value
Sustainability and Structural Integrity in Seismic Design: The Role of Reinforcement Ratios in Life Cycle Impact and Building Safety
No full textThe construction sector faces increasing pressure to decarbonize, as embodied emissions
from structural materials often dominate the environmental footprint of reinforced concrete
(RC) buildings. Although reinforcement ratios are key drivers of structural capacity,
their environmental implications under seismic design remain insufficiently quantified.
This study investigates the relationship between longitudinal reinforcement ratios and
both seismic performance and life-cycle environmental impacts in RC frame buildings.
Three code-compliant reinforcement configurations (1%, 3%, and 5%) were analyzed for
three- and nine-story structures designed under Eurocode 8. Mechanical performance was
evaluated using nonlinear pushover analysis, while embodied impacts were quantified
through Life Cycle Impact Assessment (LCIA) using the ReCiPe 2016 midpoint and endpoint
methods. Results show that increasing steel content reduces concrete volume and
increases lateral capacity, but may significantly decrease ductility and increase environmental
burdens. Optimal performance is achieved with moderate reinforcement ratios, which
reduce embodied impacts while preserving seismic safety. Furthermore, reducing the
amount of concrete while increasing the amount of steel reduces the weight of structures by
between 19% (3 stories) and 22% (9 stories), improving their seismic resistance due to the
reduction in seismic forces in areas of moderate seismicity. These findings demonstrate that
reinforcement selection introduces a measurable trade-off between structural integrity and
sustainability, providing designers with quantitative guidance for low- and medium-rise
RC buildings in seismic regions
Application of the 10R strategy and 7S tools in the development of wearable sensors
No full textThis paper presents the integration of the 10Rs of the circular economy (CE) strategy with the 7S tools of Lean manufacturing, and lifecycle management of wearable sensors. The presented algorithm, based on CE, and the application of additive manufacturing (AM) in the realization of a modular enclosure from biodegradable polymer material, demonstrate a strategy for the sustainable development of prototypes with low material waste, rapid design changes, ease of disassembly and assembly, reuse, repair, and revitalization. The stated algorithm closes the circle between design, use, maintenance, and end-of-life of a product, incorporating sustainability into everyday engineering decisions through the example of wearable sensors. The electronic enclosure shown in the work is compact; it can be worn around the waist or secured to the head with a flexible tape. The results showed that the 10R/7S connection raises the enterprises’ competitiveness through efficient production, extended product life, and reduced waste, while simultaneously addressing challenges such as regulatory observation, affordability, and user feedback after long-term product use. The study confirms a practical methodology for applying CE principles to wearable sensor systems and highlights opportunities for modular improvements, serviceability, and the use of environmentally friendly materials. The work contributes to engineering and product design by gathering sustainable product development and more effective product lifecycle management