The Experts below are selected from a list of 18924 Experts worldwide ranked by ideXlab platform
Kyong-ku Yun - One of the best experts on this subject based on the ideXlab platform.
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air void structure strength and permeability of wet mix shotcrete before and after shotcreting operation the influences of silica fume and air entraining agent
Cement & Concrete Composites, 2016Co-Authors: Pangil Choi, Jung Heum Yeon, Kyong-ku YunAbstract:Abstract It is well known that the air-void structure of hardened concrete has substantial effects on the mechanical properties and durability of concrete. In this study, laboratory evaluations were conducted to quantify the effects of air-entraining agent (AEA) and silica fume on the air-void characteristics of wet-mix shotcrete (WMS) before and after shotcreting process. For this purpose, a high-resolution image analyzer capturing elaborate graphical layouts of air-void structure using the linear transverse method was employed. Also, this study examined the effects of air-void characteristics, such as air content and Spacing Factor, on the strength and permeability of WMS. Based on the findings of this study, it can be concluded that: (1) shotcreting process considerably reduces overall air contents in WMS; (2) incorporating AEA with a 4.5% silica fume replacement ensures both satisFactory Spacing Factor and good retention of small entrained air bubbles even after shotcreting, which may improve the freeze-thaw and scaling resistance; (3) the compressive and flexural strengths of WMS were reduced as the air content increased and average Spacing Factor decreased; and (4) the air content affected the permeability of WMS, but no consistent correlation was found between Spacing Factor and permeability.
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durability assessment for crushed sand wet mix shotcrete mixed with mineral admixtures
Journal of The Korea Concrete Institute, 2014Co-Authors: Kyeore Lee, Seungyeon Han, Kyeong Nam Gung, Kyong-ku YunAbstract:The purpose of this dissertation was to investigate the effect of mineral admixtures, such as fly ash, blast furnace slag powder, meta kaolin and silica fume, on the basic properties and durability of crushed sand shotcrete, selecting a series of shotcrete mixtures with a variable admixture. Compressive strength increased as the content of mineral admixtures increased, specially it was the most effective when using meta kaolin both at sample specimen and core after shotcreting. Rapid chloride ion permeability test and sulfuric acid resistance test showed that both durability increased as the substitute rate of mineral admixture increased. In air void analysis with image analysis, the targeted the Spacing Factor and specific surface were not satisfied because air-entrained agent was not used.
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estimation of air void system and permeability of latex modified concretes by image analysis method
Journal of The Korea Concrete Institute, 2005Co-Authors: Won-kyong Jeong, Kyong-ku Yun, Seungho HongAbstract:Addition of latex to concrete is known to increase its durability and permeability. The purpose of this study is to analyze air void systems in latex-modified concretes using a reasonable and objective method of image analysis with such experimental variables as water-cement (w/c) ratios, latex contents (0%, 15%) and cement types (ordinary portland cement (OPC), high-early strength (HES) cement and very-early strength (VES) cement). The results are analyzed by Spacing Factor, air volume (content) after hardening, air void distribution and structure. Additionally, air void systems and permeability of latex-modified concrete (LMC) are compared by a correlation analysis. The results are as follows. The LMC of the same w/c ratio showed better air entraining (AE) effect than OPC with AE water reducer. The VES-LMC showed that the quantity of entrained air below increased more than four times. For the case of HES-LMC, microscopic entrained air between the range of 50 to increased greater than 7 times even in the absence of anti-foamer. Although Spacing Factor was measured rather low, the permeability of latex-modified concrete was good. It is construed that air void system does not have a considerable effect on the property of latex-modified concrete, but latex film (membrane) has a definite influence on the durability of LMC.
S. Chatterji - One of the best experts on this subject based on the ideXlab platform.
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Freezing of air-entrained cement-based materials and specific actions of air-entraining agents
Cement & Concrete Composites, 2003Co-Authors: S. ChatterjiAbstract:Abstract The freeze–thaw resistance of all cement-based materials is improved by incorporating a fine air bubble system in them. For acceptable life expectancy, incorporated air bubble volume should be about 25% of the cement paste. The specific surface of the air bubble system need to be above 25 mm2/mm3 and a Spacing Factor below about 0.16 mm. Powers explained these on the basis of his saturated flow hydraulic pressure mechanism. According to Powers’ mechanism, the chemical nature of the air-entraining agent has no part in this improvement in performance. Helmuth, one of the principal co-workers of Powers, has questioned a number of assumptions of Powers’ mechanism. Most importantly, Helmuth showed that ice penetrates concrete as dendritic crystals. Furthermore, a number of workers have shown that the chemical nature of the air-entraining agent affects the freeze–thaw resistance of cement-based materials. Some air-entraining agents do not improve the freeze–thaw resistance even though they entrain air of the required characteristics. In this paper, a modified and expanded version of Helmuth’s model of ice penetration in concrete is utilised to explain the action of air bubbles. All air bubbles contain a layer of water on their inner surfaces. Surface tension spreads out water in the air bubbles as annular layers. Air-entraining agents may form or precipitate hydrophobic layers on air bubble surfaces. When an ice dendrite reaches an air bubble, the annular water layer freezes to an annular layer of ice. The hydrophobic layer on the air bubble surface reduces the ice–paste bond. Under this circumstance, the ice layer within the air bubble grows. During this growth, water is withdrawn from the surrounding by suction. A water movement under suction does not produce any expansive pressure. Withdrawal of water to the air bubbles explains the beneficial action of air entrainment. The specific efficiency of air-entraining agents is explained by the different degree of hydrophobicity produced by air-entraining agents.
Jie Yuan - One of the best experts on this subject based on the ideXlab platform.
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freezing thawing resistance evaluations of concrete pavements with deicing salts based on various surfaces and air void parameters
Construction and Building Materials, 2019Co-Authors: Jie Yuan, Feipeng XiaoAbstract:Abstract The interaction of deicing chemicals and freezing-thawing cycles produces serious scaling damage of airport concrete pavement. The indoor test of freezing-thawing resistance with deicing salts of concrete is still open to the question, and the indirect evaluation method has inherent disadvantages. In this study, the damage process of different surfaces of concrete when immersed into deicing salt solution was compared and analyzed. Roughness growth ratio (RGR) was proposed to quantify the degree of pockmark caused by salt freeze damage. Industrial computer tomography (CT) technology was used to scan the hardened cement concrete specimens to obtain the bubble structure distribution information. The void-to-void distance as a Factor was proposed to evaluate the freezing-thawing resistance with deicing salts performance of the cement concrete, and compared with the Power’s Spacing Factor of the salt resistance performance of the hardened cement concrete in the existing specification. The results revealed that the molded surface showed the worst resistance to the salt frost action, followed by the molded side, and the sawed side was the best. It was found that there was a good correspondence between the air content of concrete test surface and the mass loss during freezing-thawing cycles. Powers’ Spacing Factor was found to underestimate the resistance potential to frost damage when compared to the void-to-void distance Factor d - , which had a good correlation with scaling mass at 28 freezing-thawing cycles. Thus, the freezing-thawing resistance with deicing salts of the cement concrete could lead to introduce the void-to-void distance Factor d - for characterization of hardened concrete.
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characterization of air voids and frost resistance of concrete based on industrial computerized tomographical technology
Construction and Building Materials, 2018Co-Authors: Jie Yuan, Jiake ZhangAbstract:Abstract Air voids structure is the key parameter that affects the frost resistance of concrete, but traditional approaches of measuring the air voids of concrete are all destructive. This work utilizes the industrial computerized tomography to visualize the microstructure change during cyclic freeze/thaw test. The results indicate that the combination of industrial computerized tomography with subsequent image processing program can precisely measure the morphology and position of air voids in concrete. The air content measured by computerized tomography is slightly higher than that of traditional pore structure analyzer. The air content and Spacing Factor increase after cyclic freeze-thaw for both air-entrained and non-air-entrained concrete, and the variation rate of non-air-entrained concrete is several times that of air-entrained concrete. Besides, it can be directly observed from the reconstruction model that he air voids in air-entrained concrete experience no obvious expansion after cyclic freeze/thaw test, which increases the frost resistance of concrete.
Pangil Choi - One of the best experts on this subject based on the ideXlab platform.
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air void structure strength and permeability of wet mix shotcrete before and after shotcreting operation the influences of silica fume and air entraining agent
Cement & Concrete Composites, 2016Co-Authors: Pangil Choi, Jung Heum Yeon, Kyong-ku YunAbstract:Abstract It is well known that the air-void structure of hardened concrete has substantial effects on the mechanical properties and durability of concrete. In this study, laboratory evaluations were conducted to quantify the effects of air-entraining agent (AEA) and silica fume on the air-void characteristics of wet-mix shotcrete (WMS) before and after shotcreting process. For this purpose, a high-resolution image analyzer capturing elaborate graphical layouts of air-void structure using the linear transverse method was employed. Also, this study examined the effects of air-void characteristics, such as air content and Spacing Factor, on the strength and permeability of WMS. Based on the findings of this study, it can be concluded that: (1) shotcreting process considerably reduces overall air contents in WMS; (2) incorporating AEA with a 4.5% silica fume replacement ensures both satisFactory Spacing Factor and good retention of small entrained air bubbles even after shotcreting, which may improve the freeze-thaw and scaling resistance; (3) the compressive and flexural strengths of WMS were reduced as the air content increased and average Spacing Factor decreased; and (4) the air content affected the permeability of WMS, but no consistent correlation was found between Spacing Factor and permeability.
Marek Zielinski - One of the best experts on this subject based on the ideXlab platform.
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air void system and frost salt scaling of concrete containing slag blended cement
Construction and Building Materials, 2009Co-Authors: Zbigniew Giergiczny, Michal A Glinicki, M Sokolowski, Marek ZielinskiAbstract:Abstract The experimental investigation on the frost-salt scaling resistance of air-entrained concrete containing CEM II/B-S 42.5N and CEM III/A 42.5N-HSR/NA slag-blended cements was performed. The air void system in concrete was evaluated in fresh concrete using AVA and in hardened concrete using an automated image analysis procedure. The mass of scaled material was increased for an increased slag content, in spite of increased compressive strength and flexural strength, decreased water absorption and decreased depth of water penetration of concrete. Increasing slag content resulted in a decrease of the total volume of air in hardened concrete and in a corruption of the air void system exhibited by a decrease of micropores content. The increase of mass of scaled material was proportional to the increase of the Spacing Factor of air voids, except for CEM III/A cement concrete exhibiting accelerated scaling.
