Ultrasonic scattering measurement of air void size distribution in hardened concrete samples

• Favorably compare ultrasonic scattering measurement with ASTM C457 test results.
• Apply combined log-normal and normal distributions for improved measurement accuracy.
• Describe small-size and large-size air void distributions of air-entrained concrete.
• Ultrasonic air void measurement can help to evaluate freeze-thaw durability.

The size distribution of air voids in concrete has significant impacts on freeze-thaw damage. This study presented a non-destructive ultrasonic scattering technique to determine the air void size distribution in hardened concrete samples. The ultrasonic scattering theory was applied to calculate the theoretical attenuation of concrete by including the effects of the viscoelastic matrix and different sizes of air voids and aggregates. The air void size distribution was determined by using an inverse analysis to minimize the difference between theoretical and experimental attenuation of concrete. The logarithm normal distribution for large-size air voids and normal distribution for small-size air voids were selected to better represent the air void size distribution in concrete. Both the large-size range and small-size air void distributions were obtained with ultrasonic scattering techniques for hardened concrete specimens. These results were favorably compared with the petrography-based ASTM C 457 method. The comparisons indicated that the developed ultrasonic scattering technique can measure the size distribution of air voids in concrete for the evaluation of freeze-thaw durability.