1,720,962 research outputs found
A new setup for rapid durabiity screening of new blended cements
Get PDFIn order to reduce CO2 emission and energy consumption of cement production substantially, the clinker content in the cements must be reduced. Blended cements, with high clinker substitution by a large variety of supplementary cementitious materials (SCMs), are appearing on the market. Today’s performance tests are time consuming, focus on transport properties for service-life modeling and neglect factors directly playing a role in corrosion (pH of the pore solution, alkalinity reserve). Thus a new way of testing blended cements that is both rapid and relevant for assessing corrosion performance is needed.
We propose a new test setup that consists of small (8 x 8 cm2) and thin (6 mm) mortar samples instrumented with reference electrode, 5 steel wire electrodes and a stainless steel grid counter electrode, allowing performing both traditional and sophisticated electrical and electro¬chemical measurements. This innovative setup can be used to test any cement blend, w/c ratio and admixture content. Durability testing including the transport properties of the mortar and corrosion behavior of the steel can be performed both for chloride or carbonation induced corrosion. Specific applications that are envisaged are:
- Fast durability screening of new blended cements in standard conditions;
- Durability testing of already established blended cements in a variety of environmental conditions or testing of mixes for specific structures or environments;
- Research on the mechanisms and controlling factors of steel corrosion in concrete.
The users are cement producers, test laboratories, research institutions, standardization bodies, owners of new structures etc. The potential for application world¬wide is huge, especially because cement producers and users are still local and many different new blends have to be tested. The setup contributes to tackle the main future challenge of the building industry: to guarantee long-term durability of reinforced concrete infrastructure with minimum amount of clinker in the cement
Corrosion rates in carbonated low clinker cements: are the new binders really sustainable?
Get PDFLowering the clinker content of concrete using SCMs can contribute significantly to reduce the en-ergy consumption and the CO2 emissions of building materials. Substitution of clinker up to 65% is now possible according to European and Swiss standards. Uncertainty about durability, especially carbonation induced corrosion, is the main factor limiting the practical use of these blended ce-ments: containing less CaO they have less capacity to neutralize CO2 and thus higher carbonation rate, which may lead to premature corrosion of steel reinforcement. Results in literature on the corrosion rate in carbonated concrete are rare and refer to ordinary Port-land cement only. For service life prediction of concrete structures with new, blended cements, cor-rosion rate data are urgently needed because the so-called “corrosion propagation stage” might be a significant part of the total service life of the structure. To be able to collect data of corrosion propagation rates in a reasonable time a new experimental set up has been designed. Parameters that can be measured are electrical resistivity of the sample, cor-rosion potential and corrosion rate of the steel, oxygen diffusion and consumption rate; their evalua-tion should allow to investigate the protective nature of the low clinker material for steel in concrete and the mechanism, particularly the kinetics, of carbonation induced corrosion. The first results show that in certain environments blended cements could be more susceptible to corrosion
Relative importance of corrosion rate and exposure condition on the practical use of new environmentlally friendly binders
Get PDFLowering the clinker content of concrete using SCMs can contribute significantly to reduce the energy consumption and the CO2 emissions of building materials. Uncertainty about durability, especially carbonation induced corrosion, is the main factor limiting the practical use: containing less CaO they have less capacity to neutralize CO2 and thus higher carbonation rates, which may lead to premature corrosion of steel reinforcement. Results in literature concerning corrosion of steel in carbonated concrete are rare and refer mostly to ordinary Portland cement. Generally, a trend to higher corrosion rates at higher relative humidity was found. To estimate service life of concrete structures made with new blended cements corrosion rate data are urgently needed, because the so called “corrosion propagation stage” might significantly contribute to the total service life. Corrosion rate has to be measured for different blended cements, w/c ratios and exposure conditions. To collect data of corrosion propagation rates in a reasonable time, a new experimental set up has been designed. The new test setup consists of small (8 x 8 cm) and thin (6 mm) mortar samples instrumented with a reference electrode, 5 steel wire electrodes and a stainless steel grid counter electrode. The thin sample allows full carbonation within 1 week (4% CO2). Parameters that can be measured are electrical resistivity, corrosion potential and corrosion rate, oxygen diffusion. These results should allow to investigate the mechanism, particularly the kinetics, of carbonation induced corrosion. The first results show that new blended cements could be more susceptible to corrosion in certain exposure conditions. Depending on the environment the steel dissolution rate can vary of a factor of 200, from < 0.1 μm/year at 50% RH, to 20 μm/year in wet conditions. To define the application limits of new binders, the interaction with variable exposure conditions has to be carefully evaluated
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
- …
