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Determinationof the salt distribution in the lime-based mortar samples using XRF and SEM-EDX characterization
No full textAlthough, the salt crystallization is one of the most common causes of the deterioration of lime-based mortars, testing of their resistance to the soluble salt action has not yet been standardized. The problems following the development of the globally accepted testing method are, among others: defining the type of mortar samples, ways of samples’ contamination, the type and the concentration of the salt solutions used, environmental conditions during testing, determination of the damage development and the durability assessment. Another task of the testing method is to explain and connect the processes developing in the materials when they are applied in laboratory and real conditions. In this paper, soluble salt resistance testing of lime mortars on the composite samples is presented. The main focus of the paper is on the determination of the salt distribution in this type of samples after the five wetting and drying cycles. Samples consisted of two lime rendering layers (inner – 1/3 and outer -1/1), both prepared according to the experiences found in the literature for these types of lime mortars when applied on historical structures, placed on the natural stone bases. They were cured in laboratory conditions for 90 days, before drying and exposing to soluble salts action. Two types of 10% salt solutions were used for the test: sodium-chloride and sodium-sulfate. Salt contamination was performed by capillary action only in the first cycle, while in the other cycles samples were wetted by deionized water. After the finalization of the cycles, the detached pieces of mortar and efflorescence were removed from the samples. One of the samples from both groups were then cut in two halves, from which one was used for X-Ray Fluorescence (XRF) and another for Scanning Electron Microscopy with Energy Dispersive X-Ray Analysis (SEM – EDX) characterization. For the XRF analysis samples were divided into four layers, and then crushed and sieved through 0.5 mm sieve before testing. For the SEM-EDX analysis the polished thick cross sections were prepared. The paper presents the results of these two analyses, and discusses the advantages and disadvantages of their application for this purpose. Mineralogical analysis of the samples was performed using XRD analysis. It was shown that XRF analysis provides more precise quantification of the elements within one sample, while SEM-EDX analysis gives possibilities for testing of layers with smaller depth within one cross – section
Estimation of rating curve in non-prismatic compound channel using Ackers method and exchange discharge model – Sana River example –
Get PDFVeć trideset godina razmatraju se mogućnosti za poboljšanje metoda za procjenu krive protoka u slučajevima kada se voda izlije iz glavnog korita na plavne površine. Tradicionalne metode zasnovane na podjeli korita za veliku vodu na hidraulički homogene segmente i primjeni Maningove jednačine, vrijednost protoka precjenjuju za više od 60% [1]. Empirijske i fizički zasnovane metode koje su razvijene i unaprijeđene na osnovu mjerenja u laboratorijskim kanalima u uslovima ustaljenog jednolikog i nejednolikog tečenja pokazuju dobro slaganje sa mjerenjima. U ovom radu razmatraju se mogućnosti primjene empirijskog Ekersovog metoda i fizički zasnovanog metoda razmjene količine kretanja (MRKK), između glavnog korita i plavnih površina. Kao primjer primjene navedenih metoda koristi se profil hidrološke stanice Prijedor na rijeci Sani za koju postoje podaci osmatranja u domenu velikih voda. Vrijednosti protoka koje se dobiju na osnovu korišćenih metoda porede se sa vrijednostima sa krive protoka dobijena na osnovu terenskih mjerenja.Possibilities for the improvement of the methods for the estimation of rating curves in compound channels in the range of overbank flows have been analysing for thirty years now. It was shown that traditional methods, which divide a compound channel into segments with uniform rougness and use Manning’s equation overestimate the discharge by more than 60%. Empirical and physically based methods that have been developed and improved based on the data collected in laboratory channels under the steady uniform and non-uniform flows show good agreement with new measurements. This paper discusses the possibilities of applying the empirical Ackers method, and the physically based exchange discharge model for the estimation of the overbank rating curve at the river gauging station. The Prijedor gauging station on the Sana River is used in this paper as an example. The choice is based on the availability of the measurement data of high flows. The discharge data obtained by the two methods are compared to the data from the official rating curve for the gauging station
Procjena efekata primjene rješenja bliskih prirodi (NBS) za umanjenje rizika od poplava u slivu rijeke Vrbanje
Get PDFAn evaluation of numerical integration methods for constitutive relations of HASP soil model
No full textFor the application of complex constitutive models for soil in incremental - iterative numerical
analysis using the Finite Element Method, the integration of constitutive relations is of particular importance. Considering that deformations are the basic variables in FEM, to determine the stress state it is necessary to carry out a numerical integration of the stress from the constitutive relations of the model. There are several classes of numerical integration methods that are not equally appropriate for every constitutive model. In this paper, two integration methods were evaluated for the HASP (Hardening State Parameter) constitutive model: governing parameter method (a variant of a first order implicit return mapping algorithm) and first order explicit forward Euler integration scheme. HASP is a critical state bounding surface constitutive model for describing the behavior of overconsolidated clays. The two algorithms were compared with respect to a boundary value
problem – ground settlement calculation under embankment construction in undrained conditions. The results show that both integration methods give similar results with comparable CPU times
Mogućnost primene poroznih betonskih ploča sa udelom otpadnih materijala za smanjenje površinskog oticaja u urbanim sredinama
No full textGlobalne klimatske promene, kao posledica ljudskih aktivnosti, dovode do negativnih efekata, kao što su: iscrpljivanje prirodnih resursa, zagađenje eko-sistema i narušavanje prirodne ravnoteže procesa na Zemlji. Kao pokušaj da se ublaži odgovor na pomenute fenomene pojavio se koncept održivog razvoja koji podrazmeva da se prirodni resursi i već nastala dobra koriste tako da se uvaže i potrebe budućih generacija.
Jedna od preporuka, u duhu održivog razvoja, je primena reciklaže. Za primenu reciklaže građevinarstvo je pogodna industrijska grana. Mogućnost primene cementnih kompozita sa recikliranim materijalima višestruko pospešuje primenu postulata održivog razvoja i koncepta bez otpada, jer se istovremeno zbrinjava otpad, smanjuje upotreba prirodnih resursa i emisija štetnih materija (prevashodno ugljen-dioksid) u životnu sredinu.
U radu su prikazane karakteristike poroznih betonskih ploča, izrađene sa recikliranim materijalima (neutral) i mogućnost primene u urbanim sredinama, za unapređenu kontrolu i usmeravanje atmosferskih padavina.
Prikazane i analizirane ploče zadovoljavaju kriterijume po pitanju zapreminske mase, čvrstoće pri pritisku, čvrstoće pri savijanju, upijanju vode i vodopropustljivosti, ali potreban je njihov dalji razvoj po pitanju otpornosti na habanje i otpornosti na dejstvo mraza i soli
Modeling of vertical gravity gradient for purposes of gravimetric survey
No full textThe knowledge of the vertical gradient of the gravity field is of great importance in gravimetry
and consequently in geodesy, since the gravity acceleration measured with the instrument
must be reduced to a stabilized point. We can model vertical gravity gradient by using
normal gravity field and different digital terrain models. In this research, we used an approach
that belongs to the group of “forward modeling” methods and differs from the known and
used vertical gravity gradient modeling procedures, as it does not contain data about the
Earth's gravity field. We created various combinations of models from which we calculate the
vertical gravity gradients. For all calculations, we assumed a constant density of topographic
masses above the ellipsoid and included the effect of the Earth's curvatures, while using a
square to determine the area of calculation and division into zones, all with the aim of
improving calculation speed. In our approach, we model the gravitational influence of the
topographic masses as the summation of the topographic masses between the ellipsoid and
the geoid and the topographic mass between the geoid and the physical Earth surface, using
the rectangular prism as the elementary body.
Based on the deviations between the measured and modeled values, we were able to
perform analyzes and statistical evaluations of the results. This allows us to determine the
optimal model and data selection criteria for modeling vertical gravity gradients
Practical ANN prediction models for the axial capacity of square CFST columns
No full textIn this study, two machine-learning algorithms based on the artificial neural network
(ANN) model are proposed to estimate the ultimate compressive strength of square
concrete-filled steel tubular columns. The development of such prognostic models is
achievable since an extensive set of experimental tests exist for these members. The
models are developed to use the simplest possible network architecture but attain
very high accuracy. A total dataset of 1022 specimens with 685 stub columns and 337
slender columns subjected to pure axial compression is collected from the available literature.
This is significant for the development of the initial model considering that for
this field it falls under the scope of big data analysis. The ANN models are validated by
comparison with experimental results. The validation study has shown the superiority
of surrogate models over the Eurocode 4 design code. The empirical equation derived
from the best-tuned Bayesian regularization algorithm shows a better agreement with
the experimental results than those obtained by the Levenberg–Marquardt algorithm,
and Eurocode 4 design code. A similar conclusion applies to stub and slender columns
independently. The Bayesian regularization-based model is negligibly slower than the
one developed on the Levenberg–Marquardt algorithm but gives a better generalization
even with simplified ANN. Generally, besides its high accuracy, one of the key
benefits of the presented ANN model is its applicability to a broader range of columns
than Eurocode 4 and other studies
Influence of Fly Ash as Cement Substitution on Accelerated and Natural Carbonation of Concrete
No full textThe use of fly ash (FA) for the production of new concrete seems to be a promising solution for “greening” of construction industry. However, re-placement of cement with supplementary cementitious materials such as fly ash influences concrete performance especially in terms of durability. One of major durability problems worldwide is carbonation-induced corrosion, given that a large number of infrastructural objects are exposed to a CO2-rich environment. The objective of this research was to analyse the influence of cement substitution level on accelerated and natural carbonation of concrete. Experimental program considered testing of 10 concrete mixtures selected in two groups – with water to binder ratio of 0,5 (400 kg/m3 of binders) and 0,6 (300 kg/m3 of binders), while in each group the cement substitution ratio was varied from 0% to 50%. Carbonation depth was measured after 14, 21 and 28 days of exposure to 2% CO2 in carbonation chamber, while the twin samples were exposed to natural carbonation. It was shown that accelerated carbonation depths were similar in both groups for mixtures up to 30% of FA, but they were doubled and tripled for larger replacement levels. Using the previously modified fib carbonation model for service life design, the prediction of natural carbonation was made. A reliability of proposed modification was assessed by comparison between pre-dicted and measured values of natural carbonation after 19 and 34 months of exposure
Combining size distribution spectrums of ambient aerosols using equivalent optical properties of nanosized particles selected examples from the Bay of Kotor
Get PDFAtmospheric aerosols in urban areas typically consist of particles of different
diameters, which can range in size from a few nanometers to a few micrometers and can have
a strong impact on human health [1,2]. This motivates the need to measure aerosol
concentration accurately, but it is often also necessary to combine results from several
instruments, with fundamentally different measurement principles. In this work, methods
based on the measurement of the electrical mobility of particles, for the range of diameters
from 10nm to 420nm, and the measurement of the equivalent optical diameter, for the range
of diameters from 300nm to 10um, were used. Combining the overlapping region in two size
distribution spectra can be used to infer equivalent optical properties of the ambient aerosol,
and examples of measured and combined spectra in several urban hot spots in Bay of Kotor
are analyzed in some detail. These examples will illustrate several aspects of urban aerosol
properties not readily available in a typical regulatory monitoring setting, such as distribution
of modes in number and mass concentration, as well as optical properties of measured aerosol.
As the main result, examples of combining particle size spectrums are presented. In the
process of combining the particle size spectra, it is possible to modify the distribution
obtained by optical measurements by searching for the optimal value of the refractive index
of the particles to obtain the best possible agreement with the size distribution obtained by
measuring the electrical mobility. An equivalent refractive index as well as the equivalent
shape factor of the ambient aerosol is obtained using Mie scattering theory as a theoretical
framework [3]. The measurement results from the mobile monitoring campaign in Bay of
Kotor in 2017 were used to elucidate the main principles of size spectrum combination, as
well as to showcase diversity of equivalent optical properties of urban aerosols.
Funding for this work has been provided by the EU H2020 Framework Programme for
research and innovation under grant agreement no 952433 (VIDIS); Ministry of Education,
Science and Technological Development of the Republic of Serbia under contract number
451-03-47/2023-01/ 200017 which is being realized in Vinca Institute of Nuclear Sciences