Characterization of entrained air voids in cement paste with scattered ultrasound

This research develops a technique that uses the attenuation of ultrasonic waves to characterize the average size and volume fraction of entrained air voids in hardened cement paste. Quantitative knowledge of entrained air void size and distribution helps ensure that an adequate design strength is developed, while maintaining resistance to freeze-thaw damage in cement-based materials. Ultrasonic attenuation coefficients obtained from pulse-burst signals are measured in the frequency range of 500 kHz-5 MHz. From these parameters, the average size and the volume fraction of the entrained air voids are determined using a combination of an ultrasonic scattering model and an inversion algorithm. Experiments are performed on specimens produced with and without entrained air voids. There is a good agreement between the model prediction and the experiments in these systems that contained < 10 % by volume of entrained air voids.