A Study of the Air-void Characteristics of Hardened Concrete PDF Download
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Author: Fulton Keller Fears
Publisher:
ISBN:
Category : Concrete
Languages : en
Pages : 206
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Book Description
Author: Fulton Keller Fears
Publisher:
ISBN:
Category : Concrete
Languages : en
Pages : 206
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Book Description
Author:
Publisher:
ISBN:
Category : Concrete
Languages : en
Pages : 19
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Book Description
Observations at the Research Council, coupled with the national interest in possible changes in the air void characteristics of air-entrained concretes because of the wide use of admixtures and changes in cement properties, raised a question as to whether or not there was a progressive increase over the years in the size of air voids being incorporated in concrete. Thus, the main objective of the study reported here was to evaluate the changes in air void characteristics of hardened concrete as determined by ASTM C457 and by other means for concrete produced in Virginia from 1945 to 1980. Air void parameters including the air content, specific surface, and spacing factor --were determined on 630 concretes. The results did not indicate an overall significant increase in the size of air voids; however, it was observed that, in general, they did show that the average size and the distribution of the voids were marginal compared to generally accepted values. While this finding indicates that air voids may not be as small as optimum, the freeze-thaw performance of air-entrained concretes in Virginia supplied under the present specifications generally has been satisfactory.
Author: Handi Celik Ozyildirim
Publisher:
ISBN:
Category : Concrete
Languages : en
Pages : 19
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Author: Hamdi Celik Ozyildirim
Publisher:
ISBN:
Category : Concrete
Languages : en
Pages : 36
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This study was intended to evaluate the air void characteristics of concrete in an attempt to identify, quantitatively or semi-quantitatively, different types of voids and to predict their influence on strength and durability. At the outset, it was anticipated that total air contents and water-- cement ratios of concrete mixtures would reflect the presence of excess water or air voids. However, because it is difficult to determine the water-cement ratio of hardened concrete, an attempt was made to relate the water-cement ratio and the air content, taken as independent variables, to the parameters of the void system that are .readily determined from the hardened concrete. The parameters of the void system considered were 1. The specific surface and the spacing factor calculated from linear traverse data. 2. The constants of a continuous chord frequency distribution curve derived from a probability density function. 3. The mean diameters and the number of bubbles per unit volume determined by a graphical method. The concrete samples were prepared in the laboratory, and the variables included the amount of air entrainment, the water cement ratio, the mixing time, and the mixture temperature. The data on the void system were obtained by utilizing the chord lengths of voids determined by the linear traverse analysis of concrete specimens. Within the framework of the study it was not possible to correlate the combined effect of water and air content with the above mentioned void parameters. A good correlation was obtained between the air contents of fresh and hardened concretes that were properly measured. Satisfactory relationships were established between the measures of resistance to freezing and thawing (weight loss, relative dynamic modulus of elasticity, and the surface rating), and certain parameters-of the void system (the spacing factor, the specific surface, and the diameter of the bubbles).
Author: Duane E. Amsler
Publisher:
ISBN:
Category : Concrete
Languages : en
Pages : 48
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Author: Ryan David Foley
Publisher:
ISBN:
Category :
Languages : en
Pages : 282
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Author: R. Pleau
Publisher:
ISBN:
Category : Air voids
Languages : en
Pages : 9
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Book Description
Many parameters affecting the quality of the air void characteristics measurement are reviewed and discussed. The difficulties more frequently encountered during the measurement process are described, and some simple rules are proposed in order to increase, as much as possible, the accuracy and reproducibility of the test. The influence of the sampling size is studied, and the variability of air content, specific surface, and spacing factor is estimated from a statistical analysis of about 600 different concrete mixtures. The influence of the operator's subjectivity is also investigated, and the effect produced by large air voids on the computation of the spacing factor is discussed.
Author: National Research Council (U.S.). Highway Research Board
Publisher:
ISBN:
Category : Air-entrained concrete
Languages : en
Pages : 34
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Paper 1: A method was developed which makes it possible to determine the characteristics of the entrained air voids in concrete. Briefly, the procedure consisted of cutting and polishing a section of concrete to expose the distributed voids. Paper 2: The performance record is described of 14 concrete test roads in five northeastern states. Built 10 to 14 years ago with a wide range of variables, these roads provide an opportunity to compare the performance of air-entrained concrete with adjacent sections of the same construction but without air entrainment.
Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 11
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Since 1993, the Quebec Department of Transportation requires all its concrete suppliers to demonstrate that their concrete satisfies the requirements of the CSA A23.1 standard as regards the maximum spacing factor of the air void system. This new requirement raises questions about the reproducibility of the ASTM C 457 test method. An interlaboratory study was carried out to verify if the variability of the test method is sufficiently low to allow reliable decisions on the acceptance or rejection of in-place hardened concrete. A total of 18 operators from 13 different laboratories microscopically examined the six concrete slabs used for the study. It is concluded that the average reproducibility coefficient of variation is 14.4 % for the total air content measurement and 14.2 % for the spacing factor measurement. Considering these results, the probability that the measured value of the spacing factor exceeds the mandatory limit of 230 um on a concrete production containing an air void system with a spacing factor of 170 um (the target value proposed in the CSA A23.1 M-94 standard is less than 0.7 % (a propability of error of about 1 %, 5 %, or 10 % is typical of most quality control test methods).
Author:
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ISBN:
Category :
Languages : en
Pages :
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