Prediction model for calculation of the limestone powder concrete carbonation depth

The efficient way to mitigate the impact of the concrete industry on climate change is to reduce the clinker content in the concrete mix. Beside incorporating supplementary cementitious materials (SCMs), it is possible to use high filler content combined with concrete mix optimisation. Limestone powder emerges as a promising filler mineral due to its availability and ready-to-use technology. In this work, the carbonation resistance of concrete with a high limestone powder content (45–65% of the powder phase) was experimentally tested. Test results showed that, with an optimized mix design featuring low water content and increased paste and plasticizer volume, concrete mixes satisfied high workability and strength demands for commonly applied strength classes. However, carbonation resistance remains a challenge. After two years in indoor natural conditions, carbonation depths were 8%, 28%, and 67% greater than referent Portland cement concrete for mixes with 47%, 58%, and 65% limestone powder content, respectively. Further analyses showed the inapplicability of the existing fib Model Code 2010 service life prediction model to limestone powder concrete. Based on a comprehensive database of experimental results, the modification of the fib prediction was proposed. A full probabilistic service life analysis revealed that for concrete with more than 20% limestone powder content and for both 50 and 100-years’ design service life, the currently prescribed concrete cover depths in European standards should be increased, depending on the carbonation exposure class

Effect of rib-to-beam angle on the shear resistance of headed studs in composite slab

Headed stud shear connectors are commonly implemented in steel-concrete composite floors for connecting the concrete slab to the steel beam and providing composite action between those two elements. The orientation of profiled sheeting is usually transverse or parallel to the supporting beam, and for those cases, design codes provide specific detailing requests and relations for obtaining headed stud resistance. Nevertheless, design codes do not recognise specific configurations when the angle between profiled sheeting ribs and the beam is in the range between 0° and 90°, which is characteristic of irregular-shaped floor structures. Due to the lack of design recommendations for headed stud resistance in these cases, investigations of the effect of the rib-to-beam angle on headed stud shear performance were conducted and presented in this paper. Experimental work included push-out tests conducted on specimens with rib-to-beam angles of 45° and 60°, as well as control specimens with ribs transverse to the beam. The influence of varied rib-to-beam angles on shear connector properties such as shear resistance, stiffness, ductility, and failure mode was discussed. According to experimental research, finite element models of push-out tests were created and verified. The parametric numerical analysis covered key parameters such as concrete class, headed stud height and diameter, and rib-to-beam angle. According to the results, an analytical relation for obtaining headed stud resistance in profiled steel sheeting with a rib-to-beam angle between 30° and 90° was proposed

Challenges in teaching mathematics in Serbia

The purpose of this paper is to address the critical issue of the shortage of mathematics teachers and professors in Serbia. The old teaching staff is drying up, and there is a lack of new teaching potential. The demoralization of current math teachers is an ongoing concern and as a result, hardly any student want to become math teacher. Soon we will only be able to realize that no one wants to teach mathematics anymore. We will focus on the causes and consequences of the perceived problem

Economic assessment of nature-based solutions to reduce flood risk and enhance co-benefits

Flooding is expected to increase due to climate change, urbanisation, and land use change. To address this issue, Nature-Based Solutions (NBSs) are often adopted as innovative and sustainable flood risk management methods. Besides the flood risk reduction benefits, NBSs offer co-benefits for the environment and society. However, these co-benefits are rarely considered in flood risk management due to the inherent complexities of incorporating them into economic assessments. This research addresses this gap by developing a comprehensive methodology that integrates the monetary analysis of co-benefits with flood risk reduction in economic assessments. In doing so, it aspires to provide a more holistic view of the impact of NBS in flood risk management. The assessment employs a framework based on life-cycle cost-benefit analysis, offering a systematic and transparent assessment of both costs and benefits over time supported by key indicators like net present value and benefit cost ratio. The methodology has been applied to the Tamnava basin in Serbia, where significant flooding occurred in 2014 and 2020. The methodology offers valuable insights for practitioners, researchers, and planners seeking to assess the co-benefits of NBS and integrate them into economic assessments. The results show that when considering flood risk reduction alone, all considered measures have higher costs than the benefits derived from avoiding flood damage. However, when incorporating co-benefits, several NBS have a net positive economic impact, including afforestation/reforestation and retention ponds with cost-benefit ratios of 3.5 and 5.6 respectively. This suggests that incorporating co-benefits into economic assessments can significantly increase the overall economic efficiency and viability of NBS

Comprehensive review of the structural behaviour and numerical modelling of recycled aggregate concrete-filled steel tubes

This paper summarises current research findings related to the behaviour and simulation of a relatively new type of structural component: recycled aggregate concrete-filled steel tube columns (RACFST). The first part of the paper presents a review of the latest experimental campaigns on RACFST columns subjected to a variety of loading conditions. For each of loading condition, highlight observations about the behaviour of RACFST columns are presented. The second part of the paper provides a summary of numerical modelling approaches developed for simulating the structural behaviour of RACFST columns. Special attention is paid to the selection and calibration of material models for recycled aggregate concrete. Finally, directions for future investigations in this area are outlined and discussed. The review will benefit researchers and professionals seeking to gain an indepth understanding of the behaviour of RACFST columns, and fills a gap in existing literature regarding a number of practical issues related to the numerical modelling of these components

Determination of Mode I fracture properties of European spruce

In this paper an efficient procedure for obtaining a cohesive law for Mode I timber fracture (crack opening), based on the Double Cantilever Beam (DCB) tests is given. DCB tests were performed on ten European spruce specimens in order to determine the energy release rate vs crack length (R curves). Two crucial parameters - crack length during the experiment and the crack tip opening displacement were obtained using 2D Digital Image Correlation (DIC) technique. In order to determine accurate fracture resistance (R curve), procedure which includes calculating cumulative released energy was employed. The cohesive law for Mode I fracture of wood was obtained by differentiation of the strain energy release rate as a function of the crack tip opening displacement. This cohesive law is further implemented in the successful numerical modelling of failure modes in large-scale end-notched glulam beams which were experimentally tested in four-point bending configuration

Transfer learning approach based on satellite image time series for the crop classification problem

This paper presents a transfer learning approach to the crop classification problem based on time series of images from the Sentinel-2 dataset labeled for two regions: Brittany (France) and Vojvodina (Serbia). During preprocessing, cloudy images are removed from the input data, the time series are interpolated over the time dimension, and additional remote sensing indices are calculated. We chose TransformerEncoder as the base model for knowledge transfer from source to target domain with French and Serbian data, respectively. Even more, the accuracy of the base model with the preprocessing step is improved by 2% when trained and evaluated on the French dataset. The transfer learning approach with fine-tuning of the pre-trained weights on the French dataset outperformed all other methods in terms of overall accuracy 0.94 and mean class recall 0.907 on the Serbian dataset. Our partially fine-tuned model improved recall of crop types that were poorly classified by the base model. In the case of sugar beet, class recall is improved by 85.71%

Sectorization of water distribution network into dmas with performance indices comparison

Sektorizacija odnosno podela vodovodne mreže na osnovne zone bilansiranja (eng. District Meter Areas – DMAs) predstavlja najisplativiju i opšte prihvaćenu strategiju za kontrolu vodnog bilansa, pritisaka i smanjenje gubitaka u mreži. Izbor zona bilansiranja nije jednoznačan zbog čega je identifikacija njihovog optimalnog rasporeda u mreži izuzetno zahtevan zadatak, naročito u slučaju postojećih distributivnih sistema. Pored osnovnih kriterijuma (npr. veličina zona i dužina mreže) postupak sektorizacije treba da obuhvati i dodatne „lokalne“ kriterijume specifične za mrežu koja se razmatra kao što su minimalni broj dovoda, zadovoljenje protivpožarnog opterećenja itd. Metodologija za sektorizaciju primenjena u ovom radu zasnovana je na primeni indeksa uniformnosti mreže (eng. Uniformity Index) čime se omogućava identifikacija zona u mreži ujednačenih po potrošnji. Efikasnost, upotrebljivost i primena razvijene metodologije obezbeđena je kroz implementaciju sledećih celina u jedinstveni hidroinformacioni alat: 1) algoritm za automatsku sektorizaciju mreže na klastere, 2) efikasni model za hidrauličke simulacije i 3) višekriterijumska optimizacija. Osnovni kriterijumi za vrednovanje i izbor optimalnog rešenja su minimalna ulaganja u neophodne intervencije u mreži i očuvanje pouzdanosti sistema. Za poređenje stanja sistema pre i nakon sektorizacije usvojeni su sledeći indikatori performasi: 1) indeks sposobnosti adaptacije sistema (eng. Resilience Index), 2) pokazatelj zadržavanja vode u mreži (eng. Water Age) i 3) prosečan pritisak u zonama. Rezultati testiranja metodologije na realnom primeru distributivne mreže naseljenog mesta u Holandiji, sa primenom lokalnih kriterijuma, potvrđuju da metodologija može biti od značajne koristi u inženjerskoj praksi u procesu sektorizacije.Sectorization of Water Distribution Network (WDN) into District Meter Areas (DMAs) is a proven measure for proactive leakage and pressure control. Sectorization of WDN into an optimal system of DMAs is a hard task to achieve, especially for the existing and continuously operating WDN. Beside general criteria (e.g. DMA size, network length), sectorisation process should be driven by the case-specific criteria such as required number of feeds, fire flow regulations etc. This paper presents sectorization algorithm that utilizes newly developed uniformity index which drives the sectorization process and identifies clusters in the network with uniform demand. The efficiency, usability and succesufull application of the developed methodology is ensured through its’ implementation in comperhensive hydroinformatics tool encompasing: 1) algorithm for automatic sectorization of the network into clusters, 2) efficient model for hydraulic simulations and 3) multicriteria optimization. Least investment for field implementation and maintaining the same level of WDN’s operational efficiency are adopted as main criteria for solution evaluation and selection of preferable solution. To compare the state of the system before and after sectorization, the following performance indices were adopted: 1) Resilience Index, 2) Water Age and 3) average pressure in zones. Testing algorithm on a real-life WDN in Netherlands, subjected to the specific local design criteria, proved it can be a valuable decision support tool for sectorization process

Measuring Chandler Wobble amplitude variations using IERS EOP C04 data

We analyzed the Earth's long-term polar motion using the time series IERS EOP C04 (from 1984 to 2023) to determine the variation of amplitude of the Chandler wobble. To compare the results based on the C04 with the Belgrade latitude data (BLZ series 1949-1985) results, we calculated the variations of latitude at BLZ point using the C04 coordinates (x, y). The secular part of these latitude variations was determined by use of the least-squares method (LSM) and removed from the data to get residuals. We used the Fourier transforms (DFT) to obtain annual and semiannual oscillations and to remove them from the residuals (to get a new set of residuals). These new residuals were divided into 33 independent 1.2 years subintervals. For each subinterval, we calculated the amplitude, period and phase of the Chandler nutation using the LSM. The quasi-periodic instability of 33 values of the amplitude of the Chandler wobble is detected with a period of 54.5 years using LSM (it was 38.5 years from BLZ data 1949-1985); the amplitude of that quasi-periodic variation is 0.″087 (0.″06 from BLZ data). The amplitude of the Chandler nutation varies with a minimum of 0.″012 (at 2019.3) and a maximum of 0.″230 (at 1994.1); the period is stable, but the phase is not stable. We applied the Abbe criterion to explain the variability in 33 values of the Chandler wobble amplitude, and the hypothesis that there is no trend in these 33 values is rejected. The obtained amplitude modulation is in accordance with other published papers about similar subject (and with our results based on BLZ data). Probably, the cause is lying in the hydro-atmospheric circulation that could influence calculated quasi-periodic variation. A possible explanation can be found in changes of core-mantle electromagnetic coupling (in line with the last few years investigations). In recent papers, it has been noticed that the effects of geomagnetic jerks are more important for exciting free nutation than the atmosphere and oceans.Editors: Luka Popović, Ana Vudragović and Milena Jovanovi