2013 PCI • New Sensor for In-Mixer Air Volume Measurement
Introducing a New Sensor for In-Mixer Air Volume Measurement
It is well established that freeze-thaw durable concrete requires proper levels of entrained air. As an inexpensive mix component, entrained air can also improve concrete workability. Despite well over fifty years of commercial production of air entrained concrete, the high batch to batch variability of air content is one of the concrete industry’s most vexing quality control problems. A sensor has recently been developed that can accurately determine the air volume in concrete based on the impact that air bubbles have on the propagation of low-frequency acoustic waves. This sensor provides continuous, real-time air measurements during the entire mixing process for stationary wall mixers. Knowing the air content in each batch during the mixing process allows producers to adjust practices to dramatically reduce batch to batch air volume variability. This paper will present data developed in a laboratory environment as well as from several precast producers that document the correlation between the acoustically determined air content and that determined via the pressure method in fresh concrete per ASTM C231.