Automated air void analysis of hardened concrete — a Round Robin study

The RapidAir is an automatic system for analysing the air void content of hardened concrete. The analysis requires polishing of the concrete surface as described in ASTM C 457 as well as a contrast enhancement of the surface. The system can automatically analyse the air void system according to the ASTM C 457 and EN 480-11 standards. The sample preparation includes contrast enhancement steps ensuring white air voids in black concrete (aggregate and paste). For a well-lapped sample of good quality concrete the contrast enhancement procedure requires approximately 5–10 min to perform. The air content can be analysed in less than 15 min traversing 2413 mm (95 in.) — a significant improvement compared to several hours normally required to perform a manual linear traverse analysis. This paper describes the method and technique required for automatic analysis using the RapidAir system as well as data from a Round Robin study. Three samples were circulated to 7 different laboratories for automatic air void analysis. Prior to the automatic analysis the samples were analysed manually using linear traverse and point counting methods. The results of the Round Robin study showed very good repeatability and reproducibility of the RapidAir system but large variations when using manually performed analysis.