The Effect of Freezing and Thawing on the Permeability of Fly Ash PDF Download
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Author: Carlton S. Serrette
Publisher:
ISBN:
Category :
Languages : en
Pages : 114
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Author: Carlton S. Serrette
Publisher:
ISBN:
Category :
Languages : en
Pages : 114
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Author: Maria G. Rosa
Publisher:
ISBN:
Category :
Languages : en
Pages : 384
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Author:
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ISBN:
Category : Fly ash
Languages : en
Pages : 52
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Author: Yancy Schrader
Publisher:
ISBN:
Category :
Languages : en
Pages : 64
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Air is purposefully entrained into concrete primarily to improve resistance to freeze-thaw deterioration while saturated with water. Air entraining admixtures (AEAs) are chemical admixtures designed to entrain air into the concrete to provide adequate resistance to the effects of freezing and thawing. One of the challenges associated with air entrainment in concrete is the interaction of an AEA with supplementary cementitious materials present in the concrete, particularly fly ash. Fly ash is a by-product of the coal fired electrical generation industry, and often contains residual unburned carbon and other components that can increase the AEA demand of a particular concrete mix. Properly estimating the amount of AEA required to reach the specified air content in a concrete containing fly ash is of utmost importance to the ready mix concrete supplier, as an insufficient air content may lead to job site rejection and the resultant monetary losses. This study aimed to better relate fly ash and concrete properties obtainable prior to final concrete placement, to direct measures of concrete durability obtainable only after the concrete has set and been put into service. A new device known as the Super Air Meter (SAM) was studied concurrently to better examine the relationship between its System Air Metric number (SAM number) and hardened concrete durability properties. Generally, fly ashes with higher foam index values and surface areas required higher dosages of AEAs to reach a specified air content value. No such relationship could be determined with the more commonly available loss on ignition percentage of the fly ash. The SAM number correctly predicted an acceptable spacing factor in 9 out of 12 different concretes tested, although all of the concretes tested displayed poor performance in freeze-thaw durability. These results demonstrate that air content testing alone is not necessarily sufficient to ensure high quality, durable concrete structures.
Author: Kurt F. von Fay
Publisher:
ISBN:
Category : Concrete
Languages : en
Pages : 68
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Author: E.J. CHAMBERLAIN
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Author: BW. Langan
Publisher:
ISBN:
Category : Concrete
Languages : en
Pages : 4
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This investigation studied the effect of interrupted testing combined with prolonged freezing on the freeze-thaw resistance of concretes containing fly ash as part of the cementitious fraction, using ASTM Test Method for Resistance of Concrete to Rapid Freezing and Thawing (C 666-84, Method A). Also studied was the effect of "marginal" air contents on the above test parameters. Test results indicate that for fly ash concretes with air contents in excess of 5%, interrupted and/or prolonged periods of freezing do not affect the freeze-thaw resistance of the concrete. Early age freezing (14 days) of fly ash concretes did not appear to be detrimental to the performance of the fly ash concretes tested.
Author: Kejin Wang
Publisher:
ISBN:
Category : Concrete
Languages : en
Pages : 52
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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: Thomas Duane Larson
Publisher:
ISBN:
Category : Concrete
Languages : en
Pages : 416
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Author: Randolph Jay Allenstein
Publisher:
ISBN:
Category :
Languages : en
Pages : 134
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