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RapidAir 457 - Air void analyzer - linear traverse and modified point count! |
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Concrete
Experts International has developed and is marketing the
RapidAir 457, Air
void analyzer capable of performing an ASTM C
457 or EN 480-11 conforming analysis in
less than 15 minutes.
Concrete Experts International offers highly specialized technical equipment to determine the distribution of air voids in hardened concrete. The RapidAir 457 Automated-Air-Void-Analyzer instrument is an automated measuring system for analyzing the air content, and distribution in hardened concrete, which is of importance when evaluating the freeze-thaw resistance of concrete. The system can replace the manual tests performed as described in the ASTM designation C 457: “Standard Test Method for Microscopical Determination of Parameters of the Air-Void System in Hardened Concrete, procedures A and B”, or the test performed according to EN 480-11 “Determination of air void characteristics in hardened concrete”. Both methods include specifications for grinding, and polishing a plane section of concrete, and for measuring the air void distribution with the use of a microscope according to the linear traverse method. A standard manual test will normally require 4-6 hours for a trained technician operating the microscope. The analysis time required with RapidAir 457 Automated-Air-Void-Analyzer is 15 minutes for the linear traverse analysis, 30 minutes for the modified point count and is performed automatically with no operator interference. The RapidAir 457 Automated-Air-Void-Analyzer test equipment comprises a computerized control unit (PC) with a 20.1’’ LCD color monitor, a video camera, and a microscope objective mounted on a moving stage, and a user-friendly analysis software operating in MS-Windows environment designed to guide the user smoothly through the test. Following the traditional grinding, and polishing steps of ASTM C 457, a contrast enhancing technique (described in EN 480-11) is used to obtain a surface of the concrete plane section where air voids are bright white, and the rest of the surface is black. Such a surface facilitates maximum precision, and identification of all air voids present in the concrete. The time needed to perform a contrast enhancement is usually not longer than 5 minutes and maximum 30 minutes. Another advantage of the RapidAir 457 Automated-Air-Void-Analyzer instrument is that it eliminates the need for “split second” human judgment during the analysis since all preparation defects are considered during the contrast enhancement procedure. Following the contrast enhancement, the plane section is mounted onto the moving stage placed under the video camera. The control unit now moves the stage automatically, and the air void distribution is determined from a scan of typically 1870 areas located throughout the plane section. After scanning, the air void parameters are immediately calculated by the software, and a test report (view report example 500 kb) with information of air content, specific surface area, and spacing factor can be printed using the software’s report generator. The raw data can also be saved in a file, and subsequently imported into spreadsheet software to perform additional user-specific analysis. In order to document the RapidAir 457 system samples of nine concretes that had previously been analyzed by thirteen European laboratories were obtain. The nine concrete samples were each measured 4 times by the RapidAir 457 system. Between each measurement the sample was rotated 90 degrees. The investigated area was 80 x 80 mm and the total traversed length was 2413 mm in all the measurements. A good agreement has been found to exist between the average values of air content measured by the RapidAir 457 system, and the average values of the thirteen European laboratories. Likewise, a good agreement also exists between the values of specific surface area measured by RapidAir 457, and the values measured by the thirteen European laboratories. The
repeatability (within-laboratory precision) of the parameters “air
content”, “specific surface area”, and “spacing factor” obtained with
the RapidAir 457 system compares favorably to the repeatability values
provided in ASTM C 457. The RapidAir 457 system has a standard deviation
of 0.37 on measurement of air content, whereas ASTM, citing two studies,
provides standard deviation values 0.29 and 0.57 respectively for
measurement of air content.
RapidAir 457 Case Story 01 References: ASTM C 457: “Standard Test Method for Microscopical Determination of Parameters of the Air-Void System in Hardened Concrete”. EN 480-11: “Admixtures for concrete, mortar and grout – test methods – Part 11: Determination of air void characteristics in hardened concrete”. Pade, C., Jakobsen, U.H., Elsen, J.: ” A New Automatic Analysis System for Analyzing the Air Void System in Hardened Concrete”, Proceedings of the International Cement Microscopy Association, ed. Jany, L, and Nisperos, A., San Diego, 2002, pp. 204-213. Jakobsen, U.H., Pade, C., Thaulow, N., Brown, D., Sahu, S., Magnusson, O., De Buck, S. and De Schutter, G. 2006: Automated air void analysis of hardened concrete - a Round Robin study. Cement and Concrete Research, vol 36, 8, pp. 1444-1452
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The RapidAir 457 system is currently in daily operation in more than 35 companies and universities around the world. |
 The RapidAir 457, Automated Air Void Analyzer system. |
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 The polished contrast enhan-ced concrete plane section under the objective. |
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 Surface of an approximately 100 x 100 mm polished section after contrast enhancement. |
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 Nine different concretes tested for total air content by the RapidAir 457 Automated-Air-Void-Analyzer system vs. the average measured air content of thirteen European laboratories. |
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 Nine different concretes tested for specific surface area by the RapidAir 457 Automated-Air-Void-Analyzer system vs. the average measured specific surface area of thirteen European laboratories. |
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 RapidAir 457 standard deviations of parameters “air content”, “specific surface area”, and “spacing factor”. |
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