1,721,083 research outputs found
Mixture Proportioning for Durable Concrete: Challenges and Changes
No full textNumerous changes and innovations have occurred in concrete materials and technology during the last century. These changes have provided engineers with many advantages in design and construction of concrete structures. At the same time, however, the application of the new developments and changes in concrete mixture proportions have also generated new durability problems.This article is published as Shah, Surendra P., Kejin Wang, and W. Jason Weiss. "Mixture proportioning for durable concrete: challenges and changes." Concrete International 22, no. 9 (2000): 73-78. Copyright 2000, American Concrete Institute. Posted with permission
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
Hydration, microstructure, transport properties and durability of self-compacting concrete
Full text linkBecause of the different mix design in comparison with traditional concrete and the abscence of vibration, different characteritics can be expected for self-compacting concrete (SCC). The degradation mechanisms of a cementitious material are greatly influenced by the permeability of the material for potentially aggressive substances. As the pore structure is different for SCC in comparison with traditional vibrated concrete, some changes in durability can be noticed.
This paper is first giving an overview of hydration, microstructure and transport mechanisms of self-compacting concrete. Afterwards, available durability results are summarzied in general. In this way some more general view on durability of Self-Compacting Concrete is obtained
Full scale pumping tests on SCC: test description and results
Full text linkPumping of concrete is a daily applied process, providing the possibility of continuously filling a formwork. Reports have been created dealing with the composition and the workability of the concrete, with the maximal discharge and pressures, with the characteristics of pumps and pipes, ... On the other hand, only a very few fundamental scientific studies on this topic are available.
In case of self compacting concrete (SCC), the same rules, valid for traditional concrete (TC), are applied. On the other hand, the verification of these rules, or new rules, are not reported (yet). SCC is considered as a special case of TC, having an advantageous composition for the pumping process, which should simplify the pumping and reduce the problems.
This paper shows the results from a series of pumping tests. After a description of the equipment is provided, a set of surprising results is presented : SCC causes higher pressure losses, compared to TC. Further results will prove the existence of a less viscous layer near the wall, a temperature increase inside the concrete equivalent to the pressure loss and the importance of thixotropy
Bond strength of reinforcing bars in self-compacting concrete: experimental determination
Full text linkIn reinforced concrete structures, understanding the bond mechanism is of great importance for the design (anchorage lengths, load bearing capacity, crack width, ...). Therefore this phenomenon has widely been studied for conventional vibrated concrete. For self-compacting concrete (SCC) however few test results are available and in practice the standards for conventional vibrated concrete (CVC) are applied to self-compacting concrete as well.
To fill in this lack of knowledge and to develop adapted standards for predicting the bond of reinforcement in SCC, an experimental program has been set up. The bond strength of reinforcement bars with different diameters has been tested for 1 conventional vibrated concrete and 2 self-compacting concretes. The testing method, by means of "beam-test" specimen, was based on RILEM RC6 part 1. During testing the free end slip of the bars and the applied load were recorded. The bar diameters ranged from 12 mm tot 40 mm.
From the test results it can be seen that the maximum and characteristic bond strength of self-compacting concrete is as high as for conventional vibrated concrete, or even slightly higher. The bond strength decreases however for increasing bar diameters, and the decrease seems to be a little larger for specimen made of SCC. The slip corresponding with the maximum bond strength increases for increasing bar diameters
Influence of demoulding oil on the rheological properties of fresh SCC
Full text linkIn concrete research centers, the determination of the rheological properties of concrete is becoming a daily business, easy to perform when the proper apparatus (and staff) are available. On the building site, rheometers are still absent, although some portable rheometers have been developed. Instead, the slump (flow) test is the only one performed to characterize the "workability" of the concrete. On the other hand, the rheological properties are very important on site, especially in case of self compacting concrete (SCC), in order to know whether the concrete can provide proper filling of the formwork, which pumping pressures will be needed, how long the concrete can wait before placement, ...
The difference between laboratories and building sites is not only noticeable by the test equipment, there is also another mentality and way of thinking. In a laboratory, the scientist tries to eliminate every disturbing factor as much as possible. On site, workmen prefer to work more easily, and if necessary, they apply some "tools" to ease their jobs, sometimes not being aware of the negative consequences.
Specifically in the domain of rheological characterization of concrete and its application, there is a large difference between lab and building site. In the lab, thorough cleaning of the testing materials is obtained by washing with water, but on site, as the water availability is restricted, releasing agents are applied so that the concrete does not stick to the equipment. Although these releasing agents are applied daily, very few scientific reports have been made on their influence on the rheological properties.
This paper describes the influence of one type of demoulding oil on the rheological properties of SCC. No research has been performed on the causes of the differences between SCC with or without oil, so the only purpose of this paper is to show the resulting differences. Secondly, the results have been obtained in steady state, thixotropy and loss of workability have not been investigated explicitly
Full scale pumping tests on SCC: application of the modified Hattori-Izumi theory
Full text linkStudying the flow of fresh concrete is influenced by time dependency of the rheological properties of the concrete. This time dependency can be divided into two parts : the non-reversible part, being loss of workability and the reversible part, called thixotropy. Loss of workability can be neglected in some cases, when comparing with the effect of thixotropy, but it is advised to keep track of it, especially in case of SCC for precast industry.
Several attempts have been made to characterize the thixotropic properties of concrete, but no general test procedure is known at this moment to universally describe thixotropy. In most cases, the study of the thixotropic properties is restricted to the area of interest of the authors, mostly the variation of static yield stress. Only one theory takes into account the influence of thixotropy on both viscosity and yield stress : the Hattori-Izumi theory, modified by J.E. Wallevik. This theory will be used to provide a qualitative description of the observed phenomena occurring during pumping of SCC, but due to the large complexity of both the theory and the practical application, a quantitative approach is beyond the scope of this study
Variations 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
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe 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
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