Resistance of CEM III/B based materials to acid attack

Cementni materijali u poljoprivrednim i drugim industrijskim objektima izloženi su dejstvu kiselina. Zbog toga vek konstrukcija zavisi od trajnosti maltera ili betonskih elemenata u agresivnoj sredini. U radu je predstavljena otpornost na koroziju koja je uzrokovana sulfatnom, nitratnom, ureom, mlečnom i sirćetnom kiselinom. Skenirajuća elektronska mikroskopija (SEM) korišćena je da se ispita efekat agresivnih rastvora na mikrostrukturu i mehaničke osobine maltera. Hemijska otpornost prizmi od maltera i dve vrste betona testirana je prema metodi Koch-Steinegger. Kako je uslov za otpornost na agresivne rastvore taj da zatezna čvrstoća maltera nije manja od 70% u odnosu na referentne prizme negovane u vodi, može se zaključiti da su malter i beton, napravljeni sa CEM III/B, u ovom istraživanju otporni na sve kiseline kojima su tretirani. .Cement based materials in the agricultural and other industrial structures are exposed to acid attack. That is the reason why the service life of structure depends on the durability of mortar or concrete elements in aggressive environment. Resistance to corrosion caused by sulphate, nitrate, carbamide, lactic acid and acetic acid was presented. Optical and scanning electron microscopy (SEM) was used to examine the effect of aggressive solutions on the microstructure and mechanical properties of mortar. The chemical resistance of mortar prisms and two types of concrete were tested according to the Koch-Steinegger method. As the condition for resistance in aggressive solution is that flexural strength of mortar prisms is no less than 70 % compared to referent prisms cured in water it can be concluded that mortar and concrete made with CEM III/B in this investigation are resistant to all treated acids

Concrete mix design for reconstruction of northwest breakwater in the Tripoli harbour - Libya

Reconstruction of Northwest breakwater in the Tripoli Harbour - Libya (about 4500 m long) required manufacture of various concrete elements (cubes and accropodes) in total amount of 550 000 m(3). Volumes of cubes were 6,3 m(3), 8,5 m(3) and 12,7 m(3), volumes of accropodes were 6,3 m(3) and 9,0 m(3). After preliminary trials and trial production, an optimum mix proportion was chosen, in compliance with technical specification requirements. One of the main causes for concrete blocks cracking is the temperature difference between core and external surface of the blocks, so new blocks with new mix proportions were made (three variations in cement content). Temperature was measured at three characteristic points: in the middle of the cube, in the middle of vertical outer surface and in the middle of horizontal upper edge. Finally, optimal proportions of the constituent materials were adopted

The estimation of compressive strength of normal and recycled aggregate concrete

Procena čvrstoće pri pritisku se postavlja kao važan zadatak proizvođačima betona, naročito pri projektovanju betonskih mešavina i obezbeđenju zahtevanog kvaliteta proizvedenog betona. U radu je prikazano poređenje eksperimentalnih rezultata čvrstoće pri pritisku betona sa prirodnim i recikliranim agregatom sa rezultatima dobijenim na osnovu jednačina prikazanih u tehničkoj regulativi. Prikazan je koeficijent determinacije eksperimentalnih podataka i rezultata dobijenih na osnovu preračuna prema jednačinama datim u EN 1992-1-1, ACI 209 i tabeli za preračun datoj u SRPS U.M1.048. Prikaz zavisnosti čvrstoće pri pritisku betona na osnovu jednačina datih u radu se odnosi na određivanje zavisnosti u odnosu na vrstu upotrebljenog cementa i starosti betona negovanog na konstantnoj temperaturi.Estimation of concrete strength is an important issue in ready-mixed concrete industry, especially, in proportioning new mixtures and for the quality assurance of the concrete produced. In this article, on the basis of the existing experimental data of compressive strength of normal and recycled aggregate concrete and equation for compressive strength calculating given in Technical regulation are compared. The accuracies of prediction by experimental data obtained in laboratory as well as by EN 1992-1-1, ACI 209 and SRPS U.M1.048 are compared on the basis of the coefficient of determination. The determination of the compressive strengths by the equation described here relies on determination of type of cement and age of concrete with the constant curing temperature

Frost resistance of concrete with crushed brick as aggregate

Predmet istraživanja su betoni spravljeni sa recikliranom opekom kao agregatom. Eksperimentalni rad je obuhvatio više vrsta betona spravljenih sa istom količinom cementa (385 kg/m3) i istom konzistencijom (sleganje oko 1 cm). Kao agregat je korišćena reciklirana opeka i kombinacija reciklirane opeke i prirodnog rečnog agregata. Posmatran je uticaj upotrebljenih frakcija drobljene opeke i njihovog procentualnog učešća na čvrstoću pri pritisku, upijanje vode i otpornost prema dejstvu mraza. Na osnovu rezultata eksperimentalnih istraživanja može se zaključiti da se primenom reciklirane opeke kao agregata dobija novi kompozitni materijal sa zadovoljavajućim fizičko - mehaničkim karakteristikama.The investigation included concrete made by using recycled brick as aggregate. Experimental work included several types of concrete made with the same cement content (385 kg/m3), and same consistency (slump about 1 cm). Recycled brick and combination of natural river aggregate and recycled brick were used as aggregates. The influence of percentage and grain size of crushed brick aggregate on concrete compressive strength, water absorption and frost resistance were observed. On the basis of the results obtained during experimental research, a general conclusion can be drawn that the application of recycled concrete as aggregate can lead to new composites with satisfactory physical-mechanical properties

Effect of nano-silica and aggregate type on properties of ultra high performance concrete

The aim of this investigation is to develop ultra high performance concrete (UHPC) for multipurpose - higher mechanical and ionizing radiation protection. The effect of nano-silica replacement (2 or 5%) on the properties of UHPC was compared with the referent concrete by testing compressive and flexural strength. As nano-silica influences cement hydration and modifies the pore structure, qualitative and quantitative analysis of pores was done using a device RapidAir 457. The second objective of this paper is to evaluate the influence of different aggregates on concrete properties. Two types of aggregate were used: quartz and barite. One of the most important characteristics of the concrete for protection against gamma and X radiation is its Total Attenuation Coefficient (µ/ρ)tot

Some properties of foam concrete

U svetskoj praksi primena peno - betona je veoma raširena, naročito za prekrivanje i termičku izolaciju industrijskih i komercijalnih zgrada. Ovim projektom hteli smo da približimo građevinskoj javnosti mogućnosti primene određenih materijala, njihovih svojstava, tehnike dobijanja peno - betona i adekvatne načine ugradnje. Naznačena su glavna svojstva peno - betona (zapreminska masa u suvom stanju, zapreminska masa u svežem stanju, pritisna čvrstoća, modul elastičnosti, skupljanje usled sušenja, termička ekspanzija termička provodljivost..). Takođe, ovde se daju mogućnosti primene peno betona u određenim delovima konstrukcije. Važno je napomenuti da je proizvodnja peno - betona u Evropi u ekspanziji, dok se peno - beton u Americi i Indoneziji koristi u značajnoj meri. Na osnovu toga jasno je da su i rezultati istraživanja na ovom polju u Americi na daleko višem nivou nego u Evropi.Foam-concrete has worldwide application, especially in covering and thermal isolation of industrial and commercial buildings. Our intention with this project was to clearly represent the possibilities of application of certain materials, their properties, production techniques and modalities of application, to engineering society. Main properties of foam-concrete were listed (such as: bulk density in dry density, bulk density of green concrete compressive strength, modulus of elasticity, thermal movement, thermal conductivity..). This project also is listing possibilities of foam-concrete application in different parts of building. It is important to emphasize that the production of foam concrete in Europe is in its expansion while the foam-concrete in USA and Indonesia is being widely used. Based on that, it is clear that the conclusion can be drawn that the research results in this field in USA are at a much higher level than in Europe

Izbor komponentnih materijala za beton sa aspekta trajnosti

Betonske konstrukcije su često u eksploataciji izložene spoljašnjim uticajima. Preporuke koje definiše evropski stan-dard SRPS EN 206 za korišćenje betona u pojedinim klasa-ma izloženosti nisu dovoljne i iz tog razloga je usvojen i standard SRPS U.M1.206 koji predstavlja nacionalni doda-tak za njegovu primenu. Dejstvo mraza značajno utiče na trajnost betonske konstrukcije jer može da dovede do raza-ranja strukture betona. Zaštita se postiže dodavanjem hemij-skih dodataka koji uvlače vazduh u svež beton. U radu je prikazana mogućnost primene novog dodatka Sika Aer Solid. Ispitivana je otpornost betona na dejstvo mraza, mraza u prisustvu soli za odmrzavanje, prodiranje vode pod pritiskom i koeficijent migracije hlorida u laboratorijskim uslovima i uzorcima izvađenim iz betonskih prefabrikovanih elemenata. Betoni sa Sika Aer Solid su za istu klasu konzistencije u odnosu na aerirane betone imali bolja svojstva i u svežem i u očvrslom stanju

Non-alcoholic fatty liver disease: a multidisciplinary clinical practice approach—the institutional adaptation to existing Clinical Practice Guidelines

Non-alcoholic fatty liver disease (NAFLD) is among the most frequently encountered chronic liver diseases in everyday clinical practice. It is considered the hepatic manifestation of metabolic syndrome. Today, liver biopsy is still the gold standard for NAFLD confirmation and assessing NAFLD's possible progression to non-alcoholic steatohepatitis, fibrosis, cirrhosis, and hepatocellular carcinoma. Because of the high prevalence of NAFLD and potential associated risks of invasive diagnostic procedures, it is of great interest to recruit the patients for liver biopsy. However, as the presence of liver fibrosis determines the further clinical course, liver biopsy is expectedly reserved for those with increased fibrosis risk. The quality of liver biopsy recruitment and patient monitoring could be significantly improved by using non-invasive tools to assess liver fibrosis presence and interactive collaboration between general practitioners, gastroenterologists, and endocrinologists. As a result, the quality of liver biopsy recruitment and patients monitoring could be significantly improved. Here, we proposed clinical practice guidelines that could be implemented for everyday clinical practice in NAFLD patients

Hepatitis C virus as cause of fulminant hepatitis-sequence analysis of the 5’ nontranslated region

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Some properties of foam concrete

U radu su navedeni materijali koji se mogu koristiti za spravljanje peno-betona. Prikazana su najvažnija svojstva peno-betona. Takođe, dati su i rezultati sopstvenih istraživanja.In this paper materials which can be ingredients for foam concrete are given The most important properties of foam concrete are presented. Also, the results of our own investigation are shown