Download or read book Investigation of the Cause and Effect of Air Void Coalescence on Air Entrained Concrete Mixes written by and published by . This book was released on 2004 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Air entraining admixtures (vinsol or non-vinsol) are used in concrete mixes that will be exposed to freeze-thaw cycles or sulfate attack. Entrained air is intended to improve the durability and resistance of hardened concrete to freeze-thaw cycles. However in many instances a significant loss of compressive strength has been observed in concrete mixes containing non-vinsol admixtures. Mixture forensic analysis has determined air void coalescing to be the main factor in observed low compressive strengths. The result of air void coalescing is the over design of compressive strength to account for the possible lower strengths and decreased confidence in the compressive strengths obtained during the quality control/assurance process.

Download or read book Investigation of the Cause and Effect of Air Void Coalescence in Air entrianed Concrete Mixes written by Gabriel Rene Camposagrado and published by . This book was released on 2004 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Air entraining admixtures (vinsol or non-vinsol) are used in concrete mixes that will be exposed to freeze-thaw cycles or sulfate attack. Entrained air is intended to improve the durability and resistance of hardened concrete to freeze-thaw cycles. However in many instances a significant loss of compressive strength has been observed in concrete mixes containing non-vinsol admixtures. Mixture forensic analysis has determined air void coalescing to be the main factor in observed low compressive strengths. The result of air void coalescing is the over design of compressive strength to account for the possible lower strengths and decreased confidence in the compressive strengths obtained during the quality control/assurance process.

Download or read book The Effect of Air Entrainment Upon Compressive Strength of Concrete written by Kent Albert Allemeier and published by . This book was released on 1948 with total page 66 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Evaluating Air entraining Admixtures for Highway Concrete written by Mohamad Nagi and published by Transportation Research Board. This book was released on 2007 with total page 60 pages. Available in PDF, EPUB and Kindle. Book excerpt: "This report presents a recommended procedure for evaluating air-entraining admixtures used in highway concrete. The procedure involves the testing of non-air-entrained concrete and concrete containing the air-entraining admixture under simulated field conditions. Criteria are proposed for acceptance of admixtures for use in either highway pavements or structures. The recommended procedure and acceptance criteria will guide materials engineers in evaluating and selecting air-entraining admixtures that should contribute to appropriate freeze-thaw durability and thus to good performance and long service life. The content of the report will be of immediate interest to materials engineers, researchers, and others concerned with the design of concrete mixtures for use in highway pavements and structures."--taken from Foreword, page [v].

Download or read book Properties of Air Bubbles in Air Entrained Concrete written by Le Tuan Pham and published by . This book was released on 2019 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: It is widely accepted that air entrainment, a purposeful introduction of small air bubbles in concrete, is critical to the long-term durability of concrete in freeze-thaw environments. Air entraining admixtures (AEA) are added to the mixture to stabilize air bubbles created during mixing, ensuring a proper air void system in the hardened concrete. Despite the complexity of creating a suitable air void system in concrete, previous study and experience established the reliability and robustness of such systems under a variety of conditions through use of neutralized vinsol resin (NVR) AEA products. In recent years, synthetic AEAs have been used more frequently due to limited supply of NVR to the concrete industry. With the use of synthetic AEAs, there are more reports of new problems including difficulties in accurately measuring the air content. This study was conducted to find the root cause of the increasing difficulties in controlling the air contents in portland cement concrete associated with synthetic AEAs. Main challenges included the lack of existing techniques to evaluate AEAs and air bubbles in concrete, and lack of data to help identify causes. Given these challenges, a multi-scale experimental study that included testing of field and laboratory concrete, and testing of foam and individual air bubbles was undertaken. The results indicate that the disparity between QC test results and the actual air contents in concrete pavements associated with the use of synthetic AEAs could be attributed to less robust air bubbles stabilized with synthetic AEAs compared to those entrained with NVR and the resulting increased loss of these air bubbles during concrete sampling. The cause of this decreased robustness and resulting air loss was traced directly to the properties of the bubble shells. The shells of air bubbles in concrete entrained with synthetic AEAs were thinner and less stiff than those associated with an NVR AEA. Through this research new test protocols were developed to measure stiffness and thickness of the shell of air bubbles extracted from cement paste and to quantify stability of foams of AEAs in a cementitious environment. These tests could be used by researchers and practitioners who are interested in developing new admixtures and/or identifying admixtures with undesirable performance.

Download or read book Control of Air Content in Concrete written by David Whiting and published by Transportation Research Board National Research. This book was released on 1983 with total page 96 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Effect of Vibration on the Air Void Parameters and Freezing thawing Resistance of Air entrained Concrete written by J. E. Backstrom and published by . This book was released on 1957 with total page 44 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Air Void Clustering written by Kyle Riding and published by . This book was released on 2015 with total page 205 pages. Available in PDF, EPUB and Kindle. Book excerpt: Air void clustering around coarse aggregate in concrete has been identified as a potential source of low strengths in concrete mixes by several Departments of Transportation around the country. Research was carried out to (1) develop a quantitative measure of air void clustering around aggregates; (2) investigate whether air void clustering can be reproduced in a laboratory environment; (3) determine if air void clustering contributes to lower compressive strengths in concrete mixes; and (4) identify potential factors that may cause clustering. Five types of coarse aggregate and five different air entraining agents were included in the laboratory study to determine if aggregate type or chemical composition of the air entraining agent directly relates to air void clustering. A total of 65 mixes were made, implementing the frequently used technique of retempering that has been previously associated with air void clustering around aggregates. Cylinders for compressive strength testing as well as samples for total air void analysis in the hardened concrete were made. Compressive strength at 7 and 28 days was determined, and automated testing for total air void analysis (including a new method of clustering evaluation) was performed on all mixes. This study found that it is possible to reproduce air void clustering in laboratory conditions. However, the results have shown that retempering does not always cause air void clustering. It was also observed that air void clustering is not responsible for a decrease in compressive strength of retempered concrete, as neither aggregate type nor chemical composition of the air entraining agent had a significant impact on severity of void clustering around coarse aggregate particles. It was found that the total air content and an inhomogeneous microstructure of the cement paste, not air void clustering, were responsible for lower strengths.

Download or read book An Investigation of the Effect of Fly Ash on the Entrained air void System in Concrete Using a Newly Developed Image Analysis System microform written by Barbara Yvette Hughes and published by National Library of Canada. This book was released on 1989 with total page 338 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Challenges Opportunities and Solutions in Structural Engineering and Construction written by Nader Ghafoori and published by CRC Press. This book was released on 2009-10-29 with total page 1890 pages. Available in PDF, EPUB and Kindle. Book excerpt: Challenges, Opportunities and Solutions in Structural Engineering and Construction addresses the latest developments in innovative and integrative technologies and solutions in structural engineering and construction, including: Concrete, masonry, steel and composite structures; Dynamic impact and earthquake engineering; Bridges and

Download or read book A Laboratory Investigation of the Effect of Pumping on Entrained Air Voids in Concrete written by William Elkey and published by . This book was released on 1995 with total page 436 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Factors Affecting the Origin of Air void Clustering written by Ronald L. Kozikowski and published by . This book was released on 2005 with total page 20 pages. Available in PDF, EPUB and Kindle. Book excerpt: Air-void clustering is a phenomenon in which entrained air-voids abnormally cluster around coarse aggregate particles. Numerous cases of low strength concrete have been attributed to this phenomenon and this study investigated the possible causes of the problem. There are many opinions as to why air void clustering occurs, but to our knowledge, no study has ever been conducted and published to determine the specific cause(s) of the phenomenon. Therefore, various parameters were obtained through a literature search and interviews with industry experts to evaluate their potential influence on air-void clustering. A visual petrographic rating system was developed to establish a standardized method for determining the severity of clustering. A correlation was found between this rating system and compressive strength loss and was used to evaluate which parameters had the most influence on air-void clustering. Problematic air-void clustering was found to coincide with late additions of water to the concrete mixture. The type of air-entraining admixture used in the concrete was found to have a major influence on clustering. It was noted that longer mixing times exacerbated the condition and that air-void clustering tended to occur in relatively finer air-void systems.

Download or read book Clustering of Air Voids Around Aggregates in Air Entrained Concrete written by Andy Naranjo and published by . This book was released on 2007 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Air Void Clustering in Concrete written by Jan Vosahlik and published by . This book was released on 2014 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Air void clustering around coarse aggregate in concrete has been identified as a potential source of low strengths in concrete mixes by several Departments of Transportation around the country. Research was carried out to (1) develop a quantitative measure of air void clustering around aggregates, (2) investigate whether air void clustering can be reproduced in a laboratory environment, (3) determine if air void clustering can blamed for lower compressive strengths in concrete mixes, (4) and identify potential factors that may cause clustering. Five types of coarse aggregate and five different air entraining agents were included in the laboratory study to see if aggregate type or chemical composition of air entraining agent directly relates to air void clustering. A total of 65 mixes were made, implementing the frequently used technique of retempering that has been previously associated with air void clustering around aggregates. Compressive strength specimens as well as samples for hardened void analysis were made. Compressive strength at 7 and 28 days was determined and the automated hardened void analysis (including a new method of clustering evaluation) was performed on all samples. It was found that it is possible to reproduce air void clustering in laboratory conditions. However, the results have shown that retempering does not always cause air void clustering. It was also observed that air void clustering is not responsible for a decrease in compressive strength of retempered concrete as neither aggregate type nor chemical composition of air entraining agent had a significant impact on severity of void clustering around coarse aggregate particles. It was also found that the total air content and an inhomogeneous microstructure and not air void clustering were responsible for lower strengths.

Download or read book Effect of Vibration Time Upon Loss of Entrained Air from Concrete Mixes written by and published by . This book was released on 1949 with total page 34 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Theory of Air Entrainment written by Abdul Hameed Khan and published by . This book was released on 1949 with total page 156 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Field Study of Air Content Stability in the Slipform Paving Process written by and published by . This book was released on 2012 with total page 230 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.