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The interaction between calcium lignosulfonate and cement
Get PDFModern concrete applications intensify the need for highly-flowable concretes, which are at the same time durable and possess good mechanical properties. The addition of plasticizers to the concrete mix allows obtaining highly workable concretes maintaining low water-to-binder ratios, which is beneficial for compressive strength and durability.
However, the addition of plasticizer can cause retardation in the setting time of concrete, which limits the dosage of plasticizer usable in practice. In addition, incompatibility issues can exist between plasticizer and cement, possibly leading to higher LSs dosage needed to reach a given workability, severe setting retardation, rapid set, and sudden slump loss.
In this PhD thesis, a sugar-reduced softwood calcium lignosulfonate (LSs) was used as plasticizer. The LSs was used in pastes of two Portland cements with different chemical composition and specific surface area: a CEM I 52.5 N (ANL) and a CEM I 52.5 R (CX), as defined by the European Standard EN197-1:2011.
The first objective of this PhD thesis is to understand the mechanisms behind the interaction between lignosulfonate and cement. This is important to foresee the effects of the plasticizer on workability and setting time of cement, avoiding any possible incompatibility issue.
In light of the mechanisms of consumption of LSs by the cement paste, the impact of the LSs on the rheology and setting time of the cement paste was studied. This represented the second objective of this PhD thesis.
The investigations in this first phase of the PhD project brought in light that the amount and morphology of the ettringite formed in the cement paste played a major role in the rheological and setting behaviour of the cement pastes investigated. For this reason, the third objective of this PhD thesis was to investigate more deeply the impact of the LSs on ettringite.
The investigations undertaken in this PhD thesis highlighted that, when added immediately with the mixing water (immediate addition, IA), the LSs led to an increased formation of ettringite after 30 minutes of hydration, especially for the high-C3A cement (CX). No increase in the ettringite formed was detected when the LSs was added after 10 minutes of hydration (delayed addition, DA). The ettringite had cubic or rectangular prism shape and length between 0.1 and 0.4 µm. The ettringite morphology appeared unaltered when observed after 6 hours of hydration. Therefore, the LSs was found not to change the morphology of ettringite in the systems analysed in this PhD thesis.
The large amount of ettringite formed provided additional surface area, which increased the LSs consumption for monolayer surface adsorption. This was found to be the main mechanism of LSs consumption for CX cement both for IA and for DA. Monolayer surface adsorption was also found to be the main mechanism of LSs adsorption for ANL cement for DA, while other mechanisms, still to be determined, appeared to play a role for ANL cement for IA. For both cements, calcium complexation, multilayer adsorption and intercalation in AFm were considered unlikely.
The large amount of ettringite formed appeared to decrease the workability of cement paste, leading to early stiffening and, in some cases, to rapid set. The workability of cement paste with LSs also seemed directly correlated to the degree of LSs coverage of the available surface for adsorption. A sudden drop in yield stress and viscosity was measured for the cement pastes that reached an adsorption plateau (DA). Samples which did not reach surface saturation (IA) showed a more gradual increase in workability, requiring higher LSs dosages when compared to those needed for DA. However, for DA, both cement pastes were found to be very sensitive to variations in LSs dosage: even a small increase from the optimal LSs dosage could lead to sudden slump loss.
As to the impact of LSs on setting time, the setting retardation was found to be directly correlated to the amount of free LSs in the pore solution. The DA of LSs was found to lead to higher setting retardation, because of the lower LSs consumption by the cement paste compared to when the LSs was added with IA. This led to a higher amount of free LSs available to retard C3S hydration. In the samples where the highest amount of ettringite was formed, the increased LSs adsorption caused by the additional surface area reduced the amount of free LSs in the pores solution. This was reflected in lower setting retardation, which was measured with isothermal calorimetry. In addition, increasing LSs dosages led to larger retardation of the silicate peak compared to the aluminate one, causing the two peaks to merge. This can potentially lead to poisoning of C3S hydration and severe delay of setting, causing incompatibility between plasticizer and cement.
In conclusion, the use of the LSs studied in this PhD thesis in combination with cement characterized by high C3A content and fineness appears critical, as possibly leading to incompatibility issues such as higher LSs dosage needed to reach a given workability, severe setting retardation, rapid set, and sudden slump loss. Therefore, before using LSs in the concrete practice, special attention should be paid to the combination between the LSs and the cement chosen
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
Crosslinking UV-curable polymers with organic dyes for highly stable, multifunctional, light-harvesting luminescent solar concentrators
No full textA multifunctional luminescent system characterized by outstanding durability is presented in this work as polymeric matrix for luminescent solar concentrators (LSCs). Such coating was fabricated by embedding a modified perylene-based organic dye in a fluorinated matrix consisting in a blend of photo-curable fluorinated polymers. The coating can easily crosslink when exposed to UV-light. The presence of lateral double bonds in the organic dye molecule enables its co-crosslinking with the acrylate fluorinated matrix. Multifunctionality is granted to the coating by remarkably high water contact angle values, slightly exceeding 120°, which impart easy cleaning properties to the LSC device. Accelerated weathering tests (800 h) showed the outstanding stability of LSCs prepared using the fluorinated matrix co-crosslinked with the modified perylene presented here. These devices retained their initial optical efficiency during the intense weathering test. On the contrary, devices fabricated with the same fluorinated polymers, but incorporating a similar dye with the same chemical structure except for the lateral double bonds enabling co-crosslinking with the polymeric matrix, exhibited a 10% efficiency loss over the testing time. The increased stability can be explained by taking into account the effect of the linkage between the organic dye and the host matrix. The fast and easy preparation process presented in this work represents a scalable approach to remarkably stable and truly multifunctional LSCs
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
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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