1,720,987 research outputs found
A new setup for rapid durabiity screening of new blended cements
Full text linkIn 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 inhibitors for steel in concrete – an update
Full text link16 anni fa un primo stato dell’ arte “Inibitori di corrosione per il calcestruzzo armato” è stato pubblicato come EFC numero 35. Gli inibitori di corrosione vengono utilizzati maggiormente come tecnica preventive, dunque aggiunti durante l’impasto del calcestruzzo. In questo caso i risultati di prove in laboratorio ed il comportamento in pratica indicano che il tempo di innesco di corrosione viene prolungato da un fattore di circa due. La riduzione della velocità di corrosione invece non è significativo. Inibitori applicati sul calcestruzzo indurito come sistema di ripristino hanno mostrato risultati positivi solamente a tenori di cloruro bassi e quando la corrosione è in fase iniziale.16 years ago a first state of the art report “Corrosion Inhibitors for Steel in Concrete” has been published as EFC publication No. 35. Industry continued to develop and improve admixtures that can be added to the fresh concrete (preventative) or systems that can be used as surface applied inhibitors (curative). This paper presents an update on the state of the art on corrosion inhibitors, with particular emphasis on long-term and especially field studies. There is a general agreement from both laboratory and field studies that mixed-in corrosion inhibitors can delay the onset of chloride-induced corrosion in good quality concrete by a factor of about 2. The reduction of the corrosion rate once corrosion has initiated appears to be much less significant. Surface applied inhibitors can show positive results only at low chloride concentrations and with beginning corrosion
Corrosion rates in carbonated low clinker cements: are the new binders really sustainable?
Full text linkLowering 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
Monitoring pH in corrosion engineering by means of thermally-produced iridium oxide electrodes
Full text linkA pH sensor to be used in highly alkaline media under continuous long-term immersion conditions is crucial in various engineering applications. This work develops the production protocol and posterior conditioning of thermally oxidized iridium (IrOx) electrodes to be used as potentiometric pH sensors embedded in highly alkaline environments such as concrete or cathodically protected steel in soil. The main investigated aspects for the desired applications are the potential-pH response, its reproducibility, accuracy, and oxygen dependency. The stability during long-term immersion is also studied in detail. The studied IrOx electrodes responded to pH changes with slopes between -50 and -68 mV/pH unit, even after continuous immersion in alkaline solutions for almost 2 years. Additionally, the electrodes response did not show oxygen dependency. Our results highlight the importance of sufficient conditioning in alkaline media prior to use. When properly produced, conditioned, and pre-calibrated the electrodes reproducibly permit measuring the pH with a maximum error of 0.5 pH units over a range of at least pH 9 to 13.5. Preliminary results show that the studied electrodes are promising sensors for monitoring pH changes in concrete
Relative importance of corrosion rate and exposure condition on the practical use of new environmentlally friendly binders
Full text linkLowering 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
Full text linkThe 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
A discussion of the paper “Influence of surface charge on ingress of chloride ion in hardened pastes” by Y. Elakneswaran, T. Nawa, and K. Kurumisawa
Full text linkA discussion of the paper “Influence of surface charge on ingress of chloride ion in hardened pastes” by Y. Elakneswaran, T. Nawa, and K. Kurumisawa
No full textVariations on the Author
Full text link“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
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