1,720,965 research outputs found
Hydration kinetics and thermomechanics of blended cement systems.
No full textDuring hydration, thermal, autogeneous, and drying deformations are responsible for driving early age stress development, that often leads to concrete cracking at early ages. Early age stress development is also controlled by aging viscoelastic properties like creep and relaxation. Five major features of hydrating blended cements including hydration kinetics, evolution of microstructure, development of mechanical properties, autogeneous deformation, and early age stress development are investigated in this research. Hydration kinetics, considered the primary source of age-dependent behavior, is analyzed experimentally and analytically. The implications of hydration on the macroscopic behavior are also studied. Properties such as, compressive strength, tensile strength, Young's modulus, fracture energy, creep compliance, and autogeneous deformation are shown to be tied strongly to hydration level. Two methods are employed to determine the degree of hydration of blended cements and the degree of reaction of pozzolans: isothermal calorimetry and differential thermal analysis (DTA). The analysis indicates that heat of hydration can be higher in blended cement systems, and that pozzolan reactions are slower than the cement reaction. Then, microstructural characteristics of blended cements as influenced by hydration and the presence of pozzolans, are investigated using sorption techniques. The results provide an estimate on the surface area of different hydration products and information on the pore structure of hydration products/gel. These results together with a micromechanics-based model prove to be significant in describing the humidity-driven shrinkage in cement paste. Predictions based on this model are made and verified from drying shrinkage and autogeneous shrinkage results. A new method for predicting the degree or heat of hydration and property development under nonisothermal conditions is proposed. A comprehensive stress calculation procedure that uses the relations between the properties and hydration level, and the method for predicting hydration is developed to predict the early age stress development. The new procedure uses heat of hydration as a measure of aging. Incorporation of temperature effects on properties is taken care through the calculation of heat of hydration. The prediction results are accurately verified by experiments. A significant improvement from the classical procedure can be achieved by the new procedure.PhDApplied SciencesCivil engineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/128400/2/3029410.pd
Kekuatan Riset Multiskala dalam Membentuk Teknologi Infrastruktur Masa Depan
Get PDFAbstrak. Riset multiskala adalah bidang riset yang mengeksploitasi beragam fenomena fisika dan kimia yang terjadi pada berbagai skala observasi. Yang menjadi perhatian utama dalam riset ini adalah skala observasi berpengaruh terhadap tingkat pemahaman mengenai suatu fenomena fisika atau kimia. Pemahaman yang mendalam biasanya didapat setelah observasi pada skala yang lebih kecil (mikron- maupun nano-meter) yang dapat dilakukan pada suatu bahan/sistem buatan manusia maupun bahan/sistem di alam. Riset multiskala dikenal menghasilkan terobosan-terobosan dalam bidang iptek. Contoh yang sangat nyata adalah pelapis anti basah yang dihasilkan dari rekayasa struktur permukaan sehingga butiran cairan membentuk sudut kontak < 900 (non wetting), jenis pelapis yang tahan terhadap suhu sangat tinggi yang disebut pelapis pelindung panas (thermal barrier coating), dan semen pemakan polutan yang mengandung titanium dioksida yang dapat mempermudah proses dekomposisi polutan di udara. Contoh-contoh ini setidaknya ini dapat mengilhami kita akan potensi dari riset multiskala pada aplikasi teknologi infrastruktur. Tulisan ini mengetengahkan hasil riset multiskala terutama yang erat hubungannya dengan perkembangan teknologi infrastruktur. Diharapkan apa yang disajikan dapat dikembangkan lebih lanjut di lingkungan ITB.Abstract. Multiscale research is a subject that exploits various physical and chemical phenomena at different observation scales. In this research, the emphasis is that the observation scale influences our level of understanding regarding a physical or chemical phenomenon. A deeper understanding is usually acquired by making observations at smaller scales (micon- or nano-meter) that can be done towards man-made or natural materials/systems. Multiscale research is known to produce breakthrough inventions in science and technology. Some real examples include the non wetting coating that is developed by engineering a surface that allows for the liquid contact angle to be less than 900 (non wetting), the thermal barrier coating which can withstand exposures tovery high temperature environment, and the pollutant consuming cement containing titanium oxide which allows for decomposition of pollutants in air. These examples can inspire the development of multiscale research for infrastructure technology. This paper highlights the results of multiscale research, especially those that is relevant to the development of infrastructure technology. It is desired that what is presented can be developed further at ITB
Role of plasticity on indentation behavior: Relations between surface and subsurface responses
No full textAbstractSurface and subsurface responses during frictionless indentation of elasto-plastic solids are investigated. Cases of monotonic and repeated loading are considered. It is shown that the role of plasticity parameters on indentation behavior cannot be well described in terms of surface response alone. It must be tied with subsurface response. In particular, the difference between the materials exhibiting isotropic hardening and that exhibiting kinematic hardening is less apparent when the force-displacement response and the deformed surface from the two are compared. Yet, it is quite apparent when subsurface response such as plastic strain, residual stress and plastic zone dimension are compared. An attempt has been made to characterize such surface and subsurface responses, for different plastic behavior, and to compare them with estimations obtained from analytical solutions
A Study on Effects of Creep and Shrinkage in High Strength Concrete Bridges
No full textAbstractThe last three decades have been marked by remarkable growth of high strength concrete applications in building and bridges. Both types of construction will benefit from the positif effetcs such as reductions in member sizes and amount of reinforcement, when using high strength concrete. However, bridges are often made with long spans resulting in significant dead weight which combined with the creep and shrinkage properties of concrete, leads to significant deformation and loss of prestressing force in the long term. In this study, the effects of creep and shrinkage of high strength concrete used for prestressed concrete bridge girder is investigated. The aim is to quantify the loss of prestress in high strength concrete bridge and to find justfications on increasing usage of high strength concrete for bridges. A continuous-span bridge built using span by span method (movable scaffold system) is chosen as a case study. Three grades of concrete strength are investigated, 40MPa, 80MPa, and 100MPa, each representing normal, moderately high and high strength concrete. These are grades that can be routinely produced by concrete industry without significant alteration in current production/process technology. As part of this study, a literature survey has also been conducted. It suggests that high strength concrete requires modification of current creep and shrinkage code (applicable only for normal concrete). Thus, the initial part of this study deals with determination of proper creep and shrinkage code. Then, a finite element analysis of the bridge case is performed. The result indicates that reduction in girder size and amount of prestressing is not simply governed by concrete strength, but by the comlplex effects of strength, creep and shrinkage behavior of high strength concrete
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
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