Test method for determination of air content of hardened concrete
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Insinööritieteiden korkeakoulu |
Master's thesis
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Authors
Date
2018-12-10
Department
Major/Subject
Concrete Technology
Mcode
ENG27
Degree programme
Master's Programme in Building Technology (CIV)
Language
en
Pages
65+22
Series
Abstract
Increased air content has been reported from drilled samples in the frost resistance concrete throughout Finland. Elevated air content has been measured at up to 15 percent which has resulted in inadequate compressive strength in various structures. However, the test method which is used to determine the air content in hardened concrete is not standardized. This thesis presents the results of measurements of air content in fresh and hardened concrete by using different methods and techniques. However, the absolute or true air content in concrete is always unknown. Therefore, the results do not show the correctness of measurement but the correlations between them. This thesis focuses on the measurement of air content in hardened concrete with different methods. The aim of this study was to draw a correlation between the methods and evaluate the performance of each method compared to a standardized method. A research was carried out in the Literature Review, which consisted of the hypothesis of air voids, the influence of air content, factors affecting the air content, and the methods for measurement of air content in hardened concrete. The Laboratory Work comprised of the preparation of nine different concretes in three groups of water-cement ratios and different air contents ranging from 2% to 10% by volume. A total of sixteen cores were drilled from each cast block. Their densities were measured. From the theoretical density and measured density, the Calculated method was conducted to measure air contents. A total of 65 cores, from the nine concrete, were examined with the Pressure Saturation method. A Thin Section round robin test was organised for 54 samples from the middle of the blocks. Based on the results, the Calculated method has good correlation with fresh concrete 0.98 R2 with ± 1.4% of error from the average within a standard deviation of nine blocks. However, this method is giving a false result if the concrete is inhomogeneous and cannot be used in in-situ cases since the mix-design of the concrete is not necessarily known. The Pressure Saturation method had a good correlation with fresh concrete and Calculated method with R2 of 0.96 and 0.98. The standard deviation of the method shows that the maximum error which was conducted is ± 1.2% from the mean value. Thin Section within a round robin test analysis proved that the results are unreliable due to problems with a relatively large variation of results regarding total air content. This is due to the high coefficient of variation of entrapped air (27% to 129%) in certain concretes. However, the average total air content results of Thin Section have a good correlation between the fresh concrete air content and Pressure Saturation.Description
Supervisor
Punkki, JouniThesis advisor
Al-Neshawy, FahimKeywords
air content, air voids, thin section, pressure saturation, calculated method