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 contrast-enhanced 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.