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Author:
Publisher:
ISBN:
Category : Concrete
Languages : en
Pages : 102
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Book Description
Since air-void analyzer (AVA) was introduced in the 1990s, various studies have been conducted in the United States to apply this technology. Many concerns are raised on (a) the variation of the AVA tests, (b) the relationship between AVA and other standard measurements, and (c) AVA specification limits. The application of AVA tests in concrete practice is therefore very challenging. The goals of the present research project are to reduce variability and improve precision of AVA test results and to develop rational specification limits for controlling concrete freezing and thawing (F-T) damage using the AVA test parameters. The project consists of three phases: Phase 1 -- Literature search and analysis of existing AVA data (June 2007-August 2008), Phase 2 -- AVA testing procedures and specification modification and Phase 3 -- Field study of AVA and specification refinement. In the present research report, the major activities and findings of the Phase 1 study are presented, and the major tasks for the Phase 2 study are recommended. The major activities of the Phase 1 study included the following: performing a literature search, collecting and reviewing available AVA data, completing a statistical analysis on collected AVA data, and carrying out some AVA trial tests in lab. The results indicate that AVA is a time- and cost-effective tool for concrete quality control. However, robustness of the AVA equipment, test procedures, and resulting interoperations need further improvement for a proper implementation of the AVA technology in concrete practice.
Author:
Publisher:
ISBN:
Category : Concrete
Languages : en
Pages : 102
Get Book Here
Book Description
Since air-void analyzer (AVA) was introduced in the 1990s, various studies have been conducted in the United States to apply this technology. Many concerns are raised on (a) the variation of the AVA tests, (b) the relationship between AVA and other standard measurements, and (c) AVA specification limits. The application of AVA tests in concrete practice is therefore very challenging. The goals of the present research project are to reduce variability and improve precision of AVA test results and to develop rational specification limits for controlling concrete freezing and thawing (F-T) damage using the AVA test parameters. The project consists of three phases: Phase 1 -- Literature search and analysis of existing AVA data (June 2007-August 2008), Phase 2 -- AVA testing procedures and specification modification and Phase 3 -- Field study of AVA and specification refinement. In the present research report, the major activities and findings of the Phase 1 study are presented, and the major tasks for the Phase 2 study are recommended. The major activities of the Phase 1 study included the following: performing a literature search, collecting and reviewing available AVA data, completing a statistical analysis on collected AVA data, and carrying out some AVA trial tests in lab. The results indicate that AVA is a time- and cost-effective tool for concrete quality control. However, robustness of the AVA equipment, test procedures, and resulting interoperations need further improvement for a proper implementation of the AVA technology in concrete practice.
Author: Kejin Wang
Publisher:
ISBN:
Category : Concrete
Languages : en
Pages : 52
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Book Description
The aim of the present study is to investigate the effect of low-permeability concrete, made with reduced water-to-binder ratios (w/b) and/or supplementary cementitious materials (SCMs), on the need for air entrainment to achieve freezing-thawing (F-T) durability. In the present study, concrete mixes were made with different types of cement (Type I and IP), with or without fly ash replacement (15%), with different water-to-binder ratios (w/b=0.25, 0.35, 0.45 and 0.55), and with or without air entraining agent (AEA). All concrete mixtures were controlled to have a similar slump by using different dosages of superplasticizer. The rapid chloride permeability and F-T durability of the concrete samples were determined according to ASTM C1202 and ASTM C666A, respectively. The air void structure of the concrete was studied using the Air Void Analyzer, Rapid Air, and porosity tests (ASTM C642). In addition, the general concrete properties, such as slump, air content, unit weight, and 28-day compressive strength, were evaluated. The results indicate that all concrete mixes with proper air entrainment (ASTM C23 air content greater than or equal to 6%) showed good F-T resistance (durability factor greater than or equal to 86%). All concrete mixes without AEA showed poor F-T resistance (durability factor less than 40%), except for one mix that had very low permeability and high strength. This was the concrete made with Type IP cement and with a w/b of 0.25, which had a permeability of 520 coulombs and a compressive strength of 12,760 psi (88 MPa). There were clear relationships between the F-T durability and hardened concrete properties of non-air entrained concrete. However, such relationships did not exist in concrete with AEA. For concrete with AEA, good F-T durability was associated with an air void spacing factor less than or equal to 0.28 mm (by AVA) or less than or equal to 0.22 mm (by RapidAir).
Author: National Academies of Sciences, Engineering, and Medicine
Publisher: National Academies Press
ISBN: 0309388805
Category : Science
Languages : en
Pages : 351
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Book Description
As the nation's economic activities, security concerns, and stewardship of natural resources become increasingly complex and globally interrelated, they become ever more sensitive to adverse impacts from weather, climate, and other natural phenomena. For several decades, forecasts with lead times of a few days for weather and other environmental phenomena have yielded valuable information to improve decision-making across all sectors of society. Developing the capability to forecast environmental conditions and disruptive events several weeks and months in advance could dramatically increase the value and benefit of environmental predictions, saving lives, protecting property, increasing economic vitality, protecting the environment, and informing policy choices. Over the past decade, the ability to forecast weather and climate conditions on subseasonal to seasonal (S2S) timescales, i.e., two to fifty-two weeks in advance, has improved substantially. Although significant progress has been made, much work remains to make S2S predictions skillful enough, as well as optimally tailored and communicated, to enable widespread use. Next Generation Earth System Predictions presents a ten-year U.S. research agenda that increases the nation's S2S research and modeling capability, advances S2S forecasting, and aids in decision making at medium and extended lead times.
Author: Craig Larman
Publisher: Pearson Education India
ISBN: 9788131762363
Category :
Languages : en
Pages : 748
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Book Description
Author: Pierre-Claude Aïtcin
Publisher: Woodhead Publishing
ISBN: 0081006969
Category : Technology & Engineering
Languages : en
Pages : 668
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Book Description
Science and Technology of Concrete Admixtures presents admixtures from both a theoretical and practical point-of-view. The authors emphasize key concepts that can be used to better understand the working mechanisms of these products by presenting a concise overview on the fundamental behavior of Portland cement and hydraulic binders as well as their chemical admixtures, also discussing recent effects in concrete in terms of rheology, mechanics, durability, and sustainability, but never forgetting the fundamental role played by the water/binder ratio and proper curing in concrete technology. Part One presents basic knowledge on Portland cement and concrete, while Part Two deals with the chemical and physical background needed to better understand what admixtures are chemically, and through which mechanism they modify the properties of the fresh and hardened concrete. Subsequent sections present discussions on admixtures technology and two particular types of concrete, self-consolidating and ultra-high strength concretes, with final remarks on their future. - Combines the knowledge of two leading authors to present both the scientific and technology of admixtures - Explains what admixtures are from a chemical point-of-view and illustrates by which mechanisms they modify the properties of fresh and hardened concrete - Presents a fundamental, practical, and innovative reference book on the topic - Contains three detailed appendices that can be used to learn how to use admixtures more efficiently
Author: Richard R. Nelson
Publisher: Harvard University Press
ISBN: 9780674041431
Category : Business & Economics
Languages : en
Pages : 456
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Book Description
This book contains the most sustained and serious attack on mainstream, neoclassical economics in more than forty years. Nelson and Winter focus their critique on the basic question of how firms and industries change overtime. They marshal significant objections to the fundamental neoclassical assumptions of profit maximization and market equilibrium, which they find ineffective in the analysis of technological innovation and the dynamics of competition among firms. To replace these assumptions, they borrow from biology the concept of natural selection to construct a precise and detailed evolutionary theory of business behavior. They grant that films are motivated by profit and engage in search for ways of improving profits, but they do not consider them to be profit maximizing. Likewise, they emphasize the tendency for the more profitable firms to drive the less profitable ones out of business, but they do not focus their analysis on hypothetical states of industry equilibrium. The results of their new paradigm and analytical framework are impressive. Not only have they been able to develop more coherent and powerful models of competitive firm dynamics under conditions of growth and technological change, but their approach is compatible with findings in psychology and other social sciences. Finally, their work has important implications for welfare economics and for government policy toward industry.
Author: Péter Hardi
Publisher: International Institute for Sustainable Development = Institut international du développement durable
ISBN:
Category : Business & Economics
Languages : en
Pages : 184
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Book Description
Author: Nigel H. Banks
Publisher: Academic Press
ISBN: 0080920780
Category : Technology & Engineering
Languages : en
Pages : 637
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Book Description
Consideration of the interactions between decisions made at one point in the supply chain and its effects on the subsequent stages is the core concept of a systems approach. Postharvest Handling is unique in its application of this systems approach to the handling of fruits and vegetables, exploring multiple aspects of this important process through chapters written by experts from a variety of backgrounds.Newly updated and revised, this second edition includes coverage of the logistics of fresh produce from multiple perspectives, postharvest handing under varying weather conditions, quality control, changes in consumer eating habits and other factors key to successful postharvest handling.The ideal book for understanding the economic as well as physical impacts of postharvest handling decisions.Key Features:*Features contributions from leading experts providing a variety of perspectives*Updated with 12 new chapters*Focuses on application-based information for practical implementation*System approach is unique in the handling of fruits and vegetables
Author: Robert L. Ebel
Publisher: Prentice Hall
ISBN:
Category : Education
Languages : en
Pages : 648
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Book Description
Author:
Publisher:
ISBN:
Category : Concrete
Languages : en
Pages : 230
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Book Description
This study evaluated the impacts of construction on the air content and air-void system structure of Portland cement concrete pavements. The primary intent was to quantify the air content of fresh concrete before and after it has gone through the slipform paver. The air-void system parameters of hardened concrete were then assessed using cast and extracted core specimens. The results of the air content testing on fresh concrete and the concrete cylinder specimens cast in the field suggested that there is some loss of air as the concrete passes through the paver. Laboratory testing performed on cores extracted from the pavement did not provide any conclusive evidence that entrained air is lost during the slipform paving process. In fact, many of the extracted cores had measured air content values that were much higher than the specification requirement. If excessive, this could result in increased permeability and low-strength related issues. Although a rigorous statistical analysis was not performed, the results suggest that the air content testing on fresh concrete is not capturing the true air content of the concrete placed with a slipform paver. The fresh concrete air content is generally lower than the air content measured in the cores.
