Development of an Acoustic Method for Rapid Assessment of Air Void System in Fresh Concrete

Air parameters such as specific surface (SS) and spacing factor (SF) are essential in evaluating Freeze-Thaw (F-T) durability in fresh concrete. Currently there is no method or device that can accurately meet such requirements. We propose to develop an acoustic air void measurement system that can be used in the field to measure in near real time air void distributions in fresh concrete. The proposed solution is based on the fact that air bubbles are very sensitive to acoustic excitation. The instrument will measure as functions of frequency the properties of the acoustic propagation in terms of sound speed and attenuation, which change with the void distribution. Using mathematical relationships between the acoustic properties of the fresh concrete and the size distributions of air voids, an inversion procedure extracts the bubble size distribution. From this the specific surface and spacing factor of the air void system in fresh concrete that are important to determine the concrete’s F-T durability will be deduced. The instrument will provide rapid and accurate assessment of these parameters and will be easy to operate.