L.H.S. Forever!

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Case Study on Early Age Shrinkage of Cement-based Composites

The aim of this paper was to study the behaviour of new high-performance fibre-reinforced cement composite materials (FRCC) that are reinforced with polyvinyl alcohol (PVA) fibres. The shrinkage deformations at early age, the compressive strength and modulus of elasticity of the new compositions had been determined. Test results shows that the addition of PVA fiber 1.10% and 0.55% by weight of the cement has negligible influence on concrete drying shrinkage, however, it is affect the concrete plastic and autogenous shrinkage. The results of the experiments permitted the prediction of long-term deformations of the concrete. Wider use of this material permit the construction of sustainable next generation structures with thin walls and large spans that cannot be built using the traditional concrete

Specific Challenges of Adopting Eurocodes in Latvia

AbstractThis paper provides an overview of the history and current situation of implementation of Eurocodes in Latvia. The specific challenges of using Eurocodes in the structural design industry and academic education are highlighted in the work. Based on examples of application of Eurocodes, some essential differences are analysed that have to be considered by the National Technical Committee during the National Annexes development process. The procedures established to support further maintenance of the Eurocodes are explained and the plans for future Eurocode development are described

Creep Behaviour of Concrete With Glass Waste Microfiller

Every year there are several hundred tons of waste glass produced in Latvia. Glass can be re-used as a fine raw material and it presents a possibility to save natural, non-renewable materials. The use of glass powder in concrete production can make the construction industry more environmentally friendly. This paper examines the possibility of using glass powder as cement replacement in a new type of concrete. In the experiment, cement was partially (20% and 40%) replaced with glass powder. The long-term deformation (creep) of this new concrete was monitored. Three different concrete mixtures were batched. Specimens of 20% and 40% cement replacement were compared with the specimens made of standard concrete. The samples were tested in two extreme conditions: in one case they were kept in 100% humidity ensured by preventing the desiccation of the concrete, and in the other case samples were air-dried by preventing them from becoming wet. Compression strength and modulus of elasticity of 7 and 28 days old cubic samples was determined

Crack Development Research in Extra Fine Aggregate Cement Composites

The cracking properties in cement-based composites widely influences mechanical behavior of construction structures. The challenge of present investigation is to evaluate the crack propagation near the crack tip. During experiments the tension strength and crack mouth opening displacement of several types of concrete compositions was determined. For each composition the Compact Tension (CT) specimens were prepared with dimensions 150x150x12mm. Specimens were subjected to a tensile load. Deformations and crack mouth opening displacement were measured with extensometers. Cracks initiation and propagation were analyzed using a digital image analysis technique. The formation and propagation of the tensile cracks was traced on the surface of the specimens using a high resolution digital camera with 60 mm focal length. Images were captured during testing with a time interval of one second. The obtained experimental curve shows the stages of crack development

Učestalost subjektivnih simptoma i nekih objektivnih nalaza u radnika zaposlenih na preradi krutog otpada u sekundarni otpad

We conducted this study to address concerns regarding a perceived increase in bronchitis, skin rashes, and diarrhea and long term health effects in workers at two Refuse Derived Fuel (RDF) processing plants. We abstracted medical records to assess symptom occurrence, and to identify spirometry and lab abnormalities overall FEV, and FVC showed no decrease over time for workers with more than five years of exposure. The primary self reported symptoms were low back pain and headaches followed by skin rashes, colds, \u27flu\u27, hay fever and ear problems. Conclusions from this analysis are limited by lack of standardized protocols or a control group. However, results from this analysis pointed out potential occupational health problems among RDF workers for future epidemiological and environmental studies.Istratraživanje je provedeno u dva pogona za preradu krutog otpada, prikupljanog iz velikog urbanog područja, u sekundarni otpad. U pogonu koji je u funkciji od 1988. poroizvodi se 400-500 tona, a u nešto starijem (u funkciji od 1986.) 800-900 tona takvog otpada na dan. U otpadu za preradu, sastav kojeg varira ovisno o tome što se odlaže, dominiraju papir i kartonski proizvodi. Ti materijali uz druge organske materijale poput dvorišnog otpada, predmeta od plastike i ostataka hrane čine energetsku vrijednost proizvedenog sekundarnog otpada. Pregledom koji je bio usmjeren na respiratorne smetnje, kožne iritacije, probavne poremećaje te neke moguće kronične učinke obuhvaćena su 92 radnika koji su se odazvali ispitivanju (od ukupno 108 zaposlenih). Forsirani respiratorni volumeni (FEV, i FVK) u radnika s pet i više godina izloženosti nisu pokazali tendenciju smanjenja u odnosu na očekivane vrijednosti. Među registriranim smetnjama izdvajaju se bol u križima, glavobolje, slijede zatim kožni osipi, prehlade, influenca, hunjavica. Autori ističu da je mogućnost sigurnijeg zaključivanja o zdravstvenim rizicima bila ograničena činjenicom da ispitivanje nije provedeno uporabom standardiziranog protokola te da je nedostajala kontrolna skupina. Rezultati ipak upućuju na to da ovoj vrsti profesionalne aktivnosti treba obratiti potrebnu pozornost kako u ocjeni izloženosti tako i u epidemiološkim istraživanjima

Chiasma

Newspaper reporting on events at the Boston University School of Medicine in the 1960s

PLAIN AND PVA FIBRE-REINFORCED GEOPOLYMER COMPACT TENSION SPECIMEN CRITICAL AREA SURFACE COMPOSITION ASSESSMENT

For more than 40 years, low calcium alkali-activated cement composite, or in other words, geopolymer, has been around. In recent years there has been increased interest in this material and its properties. It is mainly due to the claim that geopolymer is the cement of the future. This claim is based on environmental factors. For instance, the CO2 emissions for geopolymer binder can be up to 6 less than for Portland cement binder. Most of the researches regarding geopolymer composite properties examine only mechanical and long-term properties in compression. There has been a lack of long-term tests in tension due to difficulties in performing them. As the tensile stresses are an essential part of structure assessment, it is necessary to evaluate new material properties as thoroughly as possible. Due to the nature of geopolymer specimen hardening (polymerisation), there is a difference in modulus of elasticity development and shrinkage caused by binding that could have factors that regular Portland cement specimens do not.This article aims to evaluate the surface composition of plain and 1% PVA reinforced geopolymer compact tension specimens that have been subjected to creep and shrinkage tests. Specimen cross-section images were acquired using the scanning electron microscope (SEM). Using the quantitative image analysis method, amounts of cross-section composition elements are determined. Furthermore, the amount of cracks is determined and compared between plain and PVA fiber-reinforced specimens.It has been determined that even though 1% of PVA fibre-reinforced specimens have lower tensile strength, their creep and shrinkage strains are lower, and the number of microcracks at the notch base of the specimen. Still, it has to be acknowledged that the amount of air voids in all analysed specimens is relatively high.

COMPARISON OF THE LONG-TERM PROPERTIES IN COMPRESSION OF DIFFERENT SIZE FOAMED CONCRETE

Foamed concrete has been used as a building material since the early 1920s. In the beginning, it was used as an insulation material with very low density. Since then there have been attempts to make this material more load-bearing and structural. In the present-day foamed concrete is being used in soil reinforcement, manufacturing of building blocks and other sorts of construction materials. [1] The aim of this article is to determine long-term properties and strength of foamed concrete specimens as well as compare the results between two differently sized foamed concrete specimens. The size of creep and shrinkage specimens were Ø46x190 mm and Ø75x180 mm. The creep properties of the specimens were determined by loading them with 20% of the ultimate stress value. [2] The compressive strength, creep and specific creep of specimens were determined as well as specimen size factor to creep deformations

Advances in Identifying Beryllium Sensitization and Disease

Beryllium is a lightweight metal with unique qualities related to stiffness, corrosion resistance, and conductivity. While there are many useful applications, researchers in the 1930s and l940s linked beryllium exposure to a progressive occupational lung disease. Acute beryllium disease is a pulmonary irritant response to high exposure levels, whereas chronic beryllium disease (CBD) typically results from a hypersensitivity response to lower exposure levels. A blood test, the beryllium lymphocyte proliferation test (BeLPT), was an important advance in identifying individuals who are sensitized to beryllium (BeS) and thus at risk for developing CBD. While there is no true “gold standard” for BeS, basic epidemiologic concepts have been used to advance our understanding of the different screening algorithms