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Superabsorbent polymers and nanosilica for mitigation of autogenous shrinkage and promotion of self-healing of cementitious materials
No full textContinuously rising demands for more durable and robust materials
require the adaptation of the construction industry. Moreover, the
increasing concern about global warming results in challenges regarding
the extensive use of Portland cement, being the source of around 8% of
the world’s carbon dioxide emissions. Over the last years, a shift towards
the use of (ultra)-high-performance concrete is noticed, combining an
improved mechanical performance and higher durability, which allows
to extend a structure’s lifetime and to reduce the amount of repairs
needed. These types of concrete are characterized by a low waterto-
cement ratio, meaning that complete hydration of cement particles
is unfeasible. As hydration proceeds, the limited amount of water
present in these cementitious mixtures induces self-desiccation, leading
to autogenous shrinkage. When this shrinkage is restrained, tensile
stresses develop inside the material. As autogenous shrinkage occurs
at early age and the tensile strength of concrete is relatively low, the
risk of cracking is strongly increased compared to conventional concrete,
which may reduce the durability and compromise the future mechanical
performance.
To reduce autogenous shrinkage and limit the risk of shrinkage cracking,
an internal curing mechanism was introduced inside the cementitious
mixtures by means of superabsorbent polymers (SAPs). SAPs are
able to absorb and retain large amounts of water. When included
during mixing, they absorb part of the available water. When selfdesiccation
occurs, associated with a decrease in relative humidity and
rising capillary pressure, the stored water is released by the SAPs. This
internal curing eect limits the drop in relative humidity and induces
continued hydration, mitigating autogenous shrinkage. Within this
research, mortar and concrete mixtures with a water-to-binder ratio of
0.35 were examined. To obtain internal curing, a quantity of 0.2% of
SAPs by weight of the binder was included, together with an additional
amount of 26 grams of water per gram of SAP. The internal curing
efficiency of the SAPs was evaluated by means of restrained shrinkage
ring tests. The set-up allowed for a comparison between various mixtures
of both the shrinkage strains and the age of cracking. Results showed
that upon addition of SAPs to mortar and concrete blends shrinkage
could be reduced up to 70% when comparing identical curing ages. Also,
no visible fracture was observed during at least one month of curing in
SAP mixtures, whereas fracture occurred within two weeks of curing for
mortars without SAP addition.
Despite the beneficial effect of SAP addition for mitigation of autogenous
shrinkage, the release of their absorbed water creates macropores
inside the hardened cementitious matrix, which negatively influence
the mechanical properties. For this reason, it was chosen to partially
substitute cement by a nanomaterial, which would counterbalance the
lowered mechanical performance. Astudy on different nanoparticles was
performed and demonstrated the benefits of incorporating nanosilica,
acting as nucleation sites for the hydration products and showing an early
pozzolanic reaction. Aprofound characterization of various cementitious
mixtures was carried out and revealed the eects of nanosilica and SAPs
on the micro- and macrostructural properties. The addition of 0.2%
of SAPs largely increased the pore volume and decreased the density
of the cementitious material. Caused by the presence of macropores,
the compressive strength reduced up to 15% in comparison to the
reference material. On the contrary, the substitution of 2% of cement by
nanosilica generated a pore refinement as well as an improvement of the
compressive strength by 12%. By combining both SAPs and nanosilica,
a similar compressive strength of the mortar was obtained with respect
to the reference material. Additionally, the development of autogenous
shrinkage in these mixtures was reduced in comparison to the reference
material, similar to the addition of SAPs solely.
In case cracking does occur, due to shrinkage or other causes, the presence
of SAPs inside the cracks promotes the self-sealing and self-healing
ability of the cementitious material. By absorption of moisture from
the environment, the swelling of the SAPs blocks the cracks, meaning
that aggressive substances are no longer able to enter the material.
The subsequent release of water promotes the further hydration of
unhydrated cement particles inside the cracks and the crystallization
of calcium carbonate. The self-sealing and self-healing efficiency were
evaluated by means of water permeability experiments and mechanical
loading and reloading, respectively. During the water permeability
tests, an immediate sealing effect was noticed upon the inclusion of
SAPs. Furthermore, a decrease in water permeability was noticed
over time as specimens were cured in wet-dry cycles, signifying crack
closure. The latter was confirmed by microscopic analysis, showing
up to 100% closure of crack widths below 150 m after 28 days of wetdry
curing. Regarding the assessment of the mechanical restoration,
only a minimal effect of SAP addition was noticed after 14 days of
wet-dry curing. The inclusion of nanosilica to SAP mixtures did however
show an additional improvement of the crack closure over time, caused
by the pozzolanic nature of the nanoparticles. Therefore, it could be
concluded that a cementitious mixture was designed that benefitted
from the SAPs’ internal curing action and improvement of self-healing,
without a reduction of the mechanical performance.
The results obtained throughout this research demonstrated the internal
curing by the SAPs, leading to the mitigation of autogenous shrinkage,
and the promotion of crack closure, based on various measuring techniques.
In order to characterize the curing and healing processes and
gain a better understanding and real time information of the mechanism,
elastic wave set-ups were implemented, based both on passive (acoustic
emission) and active (ultrasound) monitoring. The internal curing
action induced by the SAPs, releasing their absorbed water upon selfdesiccation,
was revealed by the use of acoustic emission. As the moment
of water release is highly important to effectively reduce autogenous
shrinkage, the use of acoustic emission paves the way for reliable, noninvasive
and easily applicable monitoring of this delicate microstructural
process. Additionally, the improved self-sealing and self-healing ability
of mixtures with SAPs was examined by ultrasound measurements. The
adopted technique for the monitoring of the crack openings confirmed the
closure of cracks by the restoration of the wave velocity and attenuation
over time and provided a non-destructive measuring method for selfhealing
evaluation, closely related to the crack closure data
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
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
Author Under Sail The Imagination of Jack London, 1893-1902
No full textIn Author Under Sail, Jay Williams offers the first complete literary biography of Jack London as a professional writer engaged in the labor of writing. It examines the authorial imagination in London's work, the use of imagination in both his fiction and nonfiction, and the ways he defined imagination in the creative process in his business dealings with his publishers, editors, and agents. In this first volume of a two-volume biography, Williams traverses the years 1893 to 1902, from London's "Story of a Typhoon" to The People of the Abyss. The Jack London who emerges in the pages of Author Under Sail is a writer whose partnership with publishers, most notably his productive alliance with George Brett of Macmillan, was one of the most formative in American literary history. London pioneered many author models during the heyday of realism and naturalism, blurring the boundaries of these popular genres by focusing on absorption and theatricality and the representation of the seen and unseen. London created an impassioned, sincere, and extremely personal realism unlike that of other American writers of the time. Author Under Sail is a literary tour de force that reveals the full range of London as writer, creative citizen, and entrepreneur at the same time it sheds light on the maverick side of machine-age literature.Intro -- Title Page -- Copyright Page -- Dedication -- Contents -- Acknowledgments -- Introduction -- 1. Spirit Truth -- 2. From Absorption to Theatricality and Back Again -- 3. "I Will Build a New Present" -- 4. Sons as Authors -- 5. Fathers as Publishers -- 6. The Daughter as Author -- 7. Lovers as Authors -- 8. At Sea with the Family -- 9. Yellow News, Yellow Stories -- 10. The Return Home -- Notes -- Bibliography -- Index -- About Jay WilliamsIn Author Under Sail, Jay Williams offers the first complete literary biography of Jack London as a professional writer engaged in the labor of writing. It examines the authorial imagination in London's work, the use of imagination in both his fiction and nonfiction, and the ways he defined imagination in the creative process in his business dealings with his publishers, editors, and agents. In this first volume of a two-volume biography, Williams traverses the years 1893 to 1902, from London's "Story of a Typhoon" to The People of the Abyss. The Jack London who emerges in the pages of Author Under Sail is a writer whose partnership with publishers, most notably his productive alliance with George Brett of Macmillan, was one of the most formative in American literary history. London pioneered many author models during the heyday of realism and naturalism, blurring the boundaries of these popular genres by focusing on absorption and theatricality and the representation of the seen and unseen. London created an impassioned, sincere, and extremely personal realism unlike that of other American writers of the time. Author Under Sail is a literary tour de force that reveals the full range of London as writer, creative citizen, and entrepreneur at the same time it sheds light on the maverick side of machine-age literature.Description based on publisher supplied metadata and other sources.Electronic reproduction. Ann Arbor, Michigan : ProQuest Ebook Central, YYYY. Available via World Wide Web. Access may be limited to ProQuest Ebook Central affiliated libraries
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