Introduction. Defects that occur during the operation of monolithic transport structures, in particular overpasses, rectangular pipes and cattle drives, are considered. A comprehensive approach to ...the selection of constructive solutions, materials and technologies is proposed for their prevention and improvement of some provisions of the current norms for the design of such structures. Problem Statement. In the constructions of span structures of monolithic rectangular pipes, overpasses and cattle runs, during their operation under load, transverse cracks of the span structure appear, as well as shrinkage cracks, which can harm their normal operation. Purpose. The purpose of the work is the need to draw the attention of balance-keepers of structures, work customers and project organizations to the importance of ensuring proper indicators of the operational condition of transport structures at all stages of the life cycle, from project development and construction to the performance of regular work on their operational maintenance. Materials and methods. Research methods consist in identifying the influence of structural defects of monolithic transport structures on durability and safe operation. Analytical materials were used, in particular, based on the results of supervision of monolithic transport structures during the implementation of scientific support for their construction or reconstruction, as well as based on the results of survey and diagnostic work during the updating and filling of the analytical expert bridge management system (AESUM) at the facilities Poltava region. Results. The paper analyzes and provides recommendations for preventing cracking and eliminating defects in the constructions of monolithic transport structures. Conclusions. Monolithic transport facilities require complex solutions for the design of span structures and coverings, ensuring the proper organization of water drainage and compliance with the requirements of current regulatory documents and technological regulations during construction and operational works. When performing calculations of monolithic span structures of transport facilities, stricter requirements should be put forward regarding crack resistance indicators when calculating the formation and opening of cracks. It is also necessary to pay more attention to the technology of installing a cement-concrete coating. In order to reliably establish the bearing capacity of monolithic span structures, it is proposed to investigate dynamic effects during the inspection of structures and take into account the actual forces from moving loads in the presence of irregularities formed on the carriageway.
În cadrul articolului cu titlul „Beton monolit versus beton prefabricat la execuția în consolă a podurilor” vor fi abordate o serie de probleme care apar atât la proiectarea cât şi la execuţia ...structurilor de poduri din beton precomprimat utilizând metoda execuţiei în consolă.
Această metodă a revoluţionat podurile din beton, din punct de vedere al deschiderilor şi al uşurinţei traversării unor obstacole dificile. În afara avantajelor realizării unor structuri din beton monolit prin execuţie în consolă, utilizarea elementelor prefabricate conduce la micşorarea semnificativă a timpului de execuţie şi la diminuarea problemelor care pot apărea din cauza curgerii lente şi a contracţiei betonului.
Materialul prezentat în cadrul articolului cu titlul „Beton monolit versus beton prefabricat la execuția în consolă a podurilor” va prezenta principiul metodei de execuţie în consolă, avantajele utilizării acestei metode, cazurile particulare pentru care se pretează o astfel de structură, scheme statice şi secţiunile transversale adoptate pentru acest tip de structuri, cât şi modul de îmbinare al tronsoanelor prefabricate în funcţie de generaţia din care fac parte.
De asemenea, se va prezenta un studiu de caz în care vor fi analizate cele doua variante de execuție în consolă (turnare monolită a tronsoanelor respectiv montare de tronsoane prefabricate) și vor fi prezentate concluzii privind oportunitatea utilizării uneia dintre cele două variante.
In the article "Monolithic Concrete vs Precast Concrete for the Construction of Bridges by the Cantilever Method", there are approached a number of issues that come out in the design and execution of prestressed concrete bridge structures using the cantilever method.
This method has revolutionized concrete bridges, in terms of spans, and the ease of crossing some difficult obstacles. In addition to the advantages of making monolithic concrete structures by the cantilever method, using prefabricated elements leads to significant decrease in execution time and reducing problems that may occur due to creep and shrinkage of concrete.
The material presented in the paper "Monolithic Concrete vs Precast Concrete for the Construction of Bridges by the Cantilever Method" shows the principle of the cantilever method, the advantages of using this method, the particular cases that are suitable for such a structure, static diagrams and cross sections adopted for this type of structures, and the way to join the prefabricated sections according to the generation they belong .
There is also presented a case study in which the two solutions are analysed (monolithical casting on site or assembling prefabricated sections) and conclusions regarding the opportunity of using one of them.
The influence of the cross‐linker (concentration), the porogen (lyotrophic salt) and the solvent type as well as the type and concentration of up to three “functional”, i.e., interactive monomers on ...the morphology and the chromatographic properties of acrylamide‐based hydrophilic monoliths are investigated. High total monomer concentrations favored polymers with a rigid rather than gel‐like structure. High cross‐linker concentrations also favor the formation of a nodular structure. The addition of a lyotrophic salt favors the formation of small nodules especially at higher monomer concentration; the pore size of the polymer can also be modulated through the salt concentration. Suitable monoliths were further investigated as potential stationary phases for capillary electrochromatography (CEC). Depending on the type and concentration of the monomers, plate numbers between 50 000 and 100 000 were routinely obtained. The standard deviation of the run‐to‐run reproducibility was below 2% and that of the batch‐to‐batch reproducibility below 5%. A set of nine hydrophobic and polar aromatic compounds (all noncharged) was used to investigate the retention mechanism. Possible candidates for chromatographic interaction and retention in these monoliths are the hydrophobic polymer backbone itself and the alkyl, carbonyl, hydroxy, amino, amide, and charged groups introduced by the various functional monomers. Judging from our results, the carbonyl and the hydroxy functions, as well as the hydrophobic polymer backbone can be supposed to be the main sites of interaction. The charged but also the alkyl functions seem to be less important in this regard. The polymerization conditions and especially the composition of the reaction mixture have a strong influence on the behavior of the final column.
Fertilizing intensively plants with fertilizers a part of unspent nutritional elements of plants and not being mobilized into steady compounds migrates into deeper layers, consequently causing a ...danger to underground waters’ pollution. The aim of the work is to define a migration of alimentary materials ((NH4+), (NO2), (NO3), (PO43) in soil after using ecological fertilizers (Biofer and Activit). The base of the research is 35 samples in model systems of unmoved soil, top-dressed with ecological fertilizers (Biofer and Activit). Results of the research have shown that in the average heavy clayey soil the concentration of nitrogen compounds and phosphate in the soil depends on the amount of used ecological fertilizers (Biofer and Activit). After using Activit and Biofer fertilizers in 1 soil’s layer (10 cm) it has been set that the highest concentration of nitrites and nitrates is in 30 days after the soil was fertilized. The highest concentration of ammonium ions and phosphates has been set in 1 soil’s layer (10 cm) in 10 days after the soil was fertilized with fertilizers (Biofer and Activit).
Divovske kamene građevine širom svijeta, svojom višetisućljetnom starošću, veličinom, trajnošću, načinom gradnje koji nadmašuje tehničke mogućnosti tadašnjih kultura, ali i zagonetnom namjenom, ...godinama pobuđuju zanimanje stručne i šire javnosti. Megalitska arhitektura, koja predstavlja dio istoimene kulture, najdugotrajnije i najraširenije graditeljske kulture u ljudskoj povijesti, obilježena je postavljanjem monumentalnih kamenih blokova raznih oblika - megalita, pojedinačnih ili grupiranih u različite strukture/građevine. Ovakva preširoka definicija uključuje neolitičke (i kasnije) megalitske spomenike (dolmeni, menhiri, kromleki i drugi), ali i kasnije građevine tzv. „razvijenije arhitekture“, koje su imale arhitektonska obilježja, izgrađene od megalita pravilnog geometrijskog oblika, mase desetke i stotine tona. Često se nazivaju „kiklopskom“, što neki autori osporavaju koristeći taj naziv samo za građevine tzv. „mikenske civilizacije/kulture“. Stoga su autori odlučili koristiti univerzalni naziv „divovske kamene građevine“, te ovu tematiku podijeliti u zasebne radove, pokušavajući potaknuti čitatelje na daljnje proučavanje obimne raspoložive literature u potrazi za odgovorima na brojne dvojbe koje nam svima i dalje ostaju…
Due to the fact that surface characteristics of carbon material depend of carbon precursor nature and manufacturing parameters, the main objective of this work was to find appropriate carbonization ...and activation parameters in order to obtain activated hemp fibers (ACh) and carbon monolith (CM) with good adsorption properties toward pesticides. Chemical modification of short hemp fibers prior to carbonization was used to examine the influence of carbon precursor chemical structure and morphology on carbonized material characteristics. The factor of the influence on the final porous texture and adsorptive properties of activated carbon materials by production conditions are as follows: carbonization temperature, activating agent/carbon material ratio and activation temperature. Optimal production conditions were selected based on the adsorption properties of carbonized materials toward pesticides. Activated hemp fibers and carbon monolith surface were characterized by specific surface area and porosity, obtained from adsorption and desorption isotherms of N2 and by the amount and nature of surface oxygen groups, obtained by temperature-programmed desorption (TPD). As a specific test for surface activity, adsorption of silver was used. Obtained carbon materials impregnated with silver were also used for water disinfection. The possibility of using obtained materials in water purification was tested through adsorption of heavy metals and pesticides. Adsorption of heavy metal ions was tested through adsorption isotherms and kinetics. The experimental data obtain in this way was used for development of the mathematical model that would describe both the phenomenon of metal ions transport through the porous matrices, and the structure of carbonized hemp fibers. For the pesticides adsorption study, pesticides with different chemical structure were chosen: acetamiprid, dimethoate, nicosulfuron, carbofuran and atrazine. Decrease of pesticide concentration, as a consequence of the adsorption, was determined by liquid chromatography–tandem mass spectrometry technique. The possibility of using carbonized and activated hemp fibers as a sorbent in the solid-phase extraction (SPE) for pesticide analysis in water samples were also tested. Abstract The removal of lignin by chemical modification of carbon precursor brings the increase in the amount of surface oxygen groups, while polymorphic transformation of Cell I to Cell II increases specific surface area. Scanning electron microscopy (SEM) showed that the main feature of the carbonized samples are partial or complete fibrillation, caused by alteration of carbon precursor chemical structure. By varing the parameters of carbonisation and activation, different ACh and CM samples were obtained. Based on the adsorption capacities of ACh and CM samples toward pesticides, the optimal production parameters were chosen: carbonization temperature of 1000ºC, activated agent/carbon material ratio of 2/1 and activation temperature of 900ºC. It was shown that by following optimal production parameters microporous samples with high specific surface area (SBET, = 2192 m2/g) and amount of surface oxygen groups were obtained. Surface oxygen groups have dominant influence on silver deposition on the carbon material surface. Increased amount of CO yielding groups leads to the increased amount of Ag deposit and decreases its crystallite sizes. Activated hemp fibers and carbon monolith impregnated with silver are suitable for water disinfection due to the strong antimicrobial activity against Escherichia coli, Staphylococcus aureus and Candida albicans. Carbonized hemp fibers show good adsorption properties toward heavy metal ions, which is mostly influenced by specific surface area. A good agreement between model prediction and the experimental data indicates that the proposed mathematical model can be used for optimization of heavy metal ions adsorption process by correlating the model parameters to the carbonized hemp fibers performances. All tested samples have good adsorption properties toward pesticides. The nature and the amount of surface oxygen groups show dominant effect on pesticide adsorption, while specific surface area is not the crucial factor. Due to the good adsorption properties toward heavy metals and pesticides, along with the strong antimicrobial effect, examined materials could be successfully used as filter materials in water purification. Also, results obtained from SPE experiments indicate that the activated hemp fibers could be successfully applied as a solid-phase sorbent for the pesticides analysis in water samples. For same pesticides, recoveries obtained by these cartridges were even higher than recoveries obtained by commercial cartridges.
Cilj ovog rada je razvoj metode dobijanja i funkcionalizacije površine nanostrukturisanih ugljeničnih materijala različitih morfologija u cilju postizanja maksimalne adsorpcije pesticida na tako dobijenim materijalima. Hemijska modifikacija kratkih vlakana konoplje pre karbonizacije, korišćena je u cilju ispitivanja uticaja hemijske strukture i morfologije ugljeničnog prekursora na svojstva karbonizovanog materijala. U cilju ispitivanja uticaja parametara dobijanja na površinske karakteristike rezultujućih ugljeničnih materijala, variranjem temperature karbonizacije, temperature aktivacije i odnosa količina aktivirajućeg agensa i karbonizovanog materijala, dobijeni su uzorci ugljeničnih materijala različitih površinskih karakteristika, a optimalni parametri dobijanja izabrani su na osnovu efikasnosti uklanjanja pesticida iz vodenih rastvora. Aktivirana vlakna konoplje i karbon monolit okarakterisani su sa aspekta specifične površine i poroznosti, određenih na osnovu adsorpcionih i desorpcionih izotermi azota, i količine površinskih grupa, dobijene metodom temperaturnoprogramirane desorpcije. Kao specifičan test za ispitivanje površinske aktivnosti dobijenih ugljeničnih materijala, korišćena je adsorpcija srebra na njihovoj površini, a potom je ispitana i mogućnost dezinfekcije vode ugljeničnim materijalima impregnisanim srebrom. Mogućnost korišćenja dobijenih ugljeničnih materijala u prečišćavanju vode ispitana je i sa aspekta adsorpcije teških metala i pesticida. Adsorpcija teških metala okarakterisana je adsorpcionim izotermama i adsorpcionom kinetikom. Dobijeni eksperimentalni podaci iskorišćeni su za matematičko modelovanje samog procesa transporta jona kroz poroznu matricu, kao i za karakterizaciju površinske strukture karbonizovanih vlakana konoplje. Za ispitivanje adsorpcije pesticida, korišćena je smeša rastvora pet pesticida različitih hemijskih struktura: acetamiprida, dimetoata, nikosulfurona, karbofurana i atrazina. Koncentracija pesticida u rastvoru određivana je metodom tečne hromatografije u kombinaciji sa tandem masenom spektrometrijom. Takođe, ispitana je i mogućnost korišćenja karbonizovanih i aktiviranih vlakana Rezime konoplje kao sorbenata u metodi ekstrakcije na čvrstoj fazi, pri analizi pesticida iz vodenih rastvora. Pokazano je da hemijska struktura ugljeničnog prekursora ima višestruki uticaj na karakteristike karbonizovanog materijala. Značajnije uklanjanje lignina iz strukture prekursora utiče na povećanje količine kiseoničnih površinskih grupa, dok polimorfna transformacija celuloze iz Cell I u Cell II izaziva povećanje specifične površine karbonizovanog materijala. Promene hemijskog sastava prekursora indirektno utiču i na morfologiju karbonizovanih vlakana konoplje, što je detektovano skenirajućom elektronskom mikroskopijom (SEM). Variranjem parametara karbonizacije i aktivacije dobijeni su različiti uzorci aktiviranih vlakana konoplje i karbon monolita. Optimalni parametri proizvodnje odabrani su na osnovu kapaciteta materijala za adsorpciju pesticida: temperatura karbonizacije od 1000ºC, odnos aktivacioni agens : karbonizovani materijal – 2:1 i temperatura aktivacije od 900ºC. Na ovaj način dobijeni su mikroporozni materijali visokih vrednosti specifične površine (SBET, = 2192 m2/g) i količine kiseoničnih površinskih grupa. Pokazano je da kiseonične grupe imaju dominantan uticaj na adsorpciju srebra, i da se povećanjem količine kiseoničnih grupa koje termalnom dekompozicijom otpuštaju CO može povećati količina i smanjiti veličina kristalita depozita Ag. Aktivirana vlakna konoplje i karbon monolit impregnisani srebrom pokazuju jako antimikrobno dejstvo na smešu Escherichia coli, Staphylococcus aureus i Candida albicans. Karbonizovana vlakna konoplje pokazuju dobre karakteristike u adsorpciji jona teških matala, pri čemu je efikasnost sorpcije uslovljena veličinom specifične površine. Matematički model razvijen u cilju opisivanja samog procesa transporta jona teških metala, kao i strukture adsorbenta pokazuje jako dobra slaganja između eksperimentalnih podataka i predikcije modela, pa se na zadovoljavajući način može koristiti za modelovanje procesa adsorpcije teških metala na karbonizovanim vlaknima konoplje. Svi ispitivani uzorci pokazuju visoku efikasnost adsorpcije pesticida, pri čemu vrsta i količina površinskih grupa imaju dominantan uticaj na adsorpciju pesticida, dok specifična površina nema presudnog uticaja u ovom procesu. Visoka efikasnost u uklanjanju pesticida i teških metala, kao i mogućnost dezinfekcije vode, omogućavaju uspešno korišćenje ovih materijala u izradi filtera za prešišćavanje vode. Rezime Rezultati dobijeni u SPE eksperimentu pokazuju da se aktivirana vlakna konoplje mogu koristiti kao sorbent za predkoncentrisanje pesticida, što ih čini adekvatnom zamenom za skupe komercijalne kertridže.
SažetakU razdoblju od 2011. do 2013. godine u Hrvatskom šumarskom institutu načinjena je zbirka monolita najvažnijih šumskih tala. Zbirka je izrađena novom metodom pričvršćivanja pomoću epoksidne ...smole. Nakon što se iskopa pedološka jama, pripremi se čelo profila i načini se prizma tla dimenzije 20 cm X 100 cm i debljine 5 cm. Prizma se podijeli na razmake od po 10 cm. Podjela nam je potrebna zbog što vjernijeg prenošenja tla na podlogu načinjenu od vodootpornog drveta i ograničenu letvicama 2 X 3 cm. Oštrom alatkom se odvoji dio tla (oko 10 cm) i prenese u okvir koji mora biti položen horizontalno, a u njemu je premazan sloj epoksidne smole debljine do 1 cm. Nakon što se malo prosuši na zraku, monolit se učvršćuje s bezbojnim mat lakom i nakon toga se može prikazati u okomitom položaju ili objesiti na zid nekog izložbenog prostora. Nova metoda je jednostavnija i brža jer nije potreban masovni monolit u sanduku koji je teško ponekad transportirati do prve prometnice.
Compoziția este construită pe orizontală într-un desen liniar geometric și precis. Contrastul de luminozitate este evidențiat prin separarea celor două planuri ale imaginii. Inferior, într-un ...întuneric tenebros, este descrisă o suprafață ovoidală ce cuprinde forme antropo-zoo-morfe abia sugerate. Planul superior, pământean este luminat prin fundalul obținut prin linii orizontale, paralele, punctate. Planul oblic în perspectivă este cadrilat matematic. Pe acesta, în colțul din stânga este dispus un cap de monolit sculptural, imprimat cu negru-albăstrui. O construcție prismatică geometrică ocupă aproape întreaga suprafață supraterană. Aceasta își are originea în planul inferior unde este abia vizibil, în întuneric, restul formei. Cromatica este dominată de griuri neutre și negru. Compoziția este închisă dar are un caracter dinamic. Lucrarea este semnată și datată în partea dreaptă jos, cu creion: „Corina Beiu Angheluță 72”.
stânga jos, cu creion: Ex. artist Marile prefaceri II - gravură în metal color
semnătură
exemplar de artist
Pe orizontală, central este redat monolitic un pesonaj fără detalii anatomice. Brațul stâng este flexat și sprijinit de cap. Brațul drept este întins peste un element liniar sprijinit la nivelul ...solului. Desenul este realizat cu creionul și creion roșu, cu linii puține, modulate și vibrate și puțină estompă. Lucrarea nu este nici semnată și nici datată.
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