Comparison of Flatbed Scanner and RapidAir 457 System for Determining Air Void System Parameters of Hardened Concrete

Over the past 30 years, a great deal of research has been performed to develop an automated system to perform ASTM C 457, the standard test method for microscopical determination of parameters of the air void system in hardened concrete. The method presented here utilizes contrastenhanced images created by filling the voids white and coloring the remainder of the hardened concrete surface black. The images were collected with a standard desktop flatbed scanner with an advertised optical resolution capability of 4,800 4,800 dpi (~5.3 5.3 micron). Each image took approximately 10 min to collect. The 'black and white' contrast-enhanced images were used in conjunction with knowledge of either the mix design or batch weights to perform the calculations set forth in ASTM C 457. Each analysis was accomplished in about 15 to 20 min using a computer script program on a standard personal computer. The same prepared surfaces were also analyzed with a commercially available air void system analyzer. The data collected from the commercial system correlated well with that from the flatbed scanner.