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Civil Engineering Graduate Seminar
Speaker: Shuaicheng (Sam) Guo, PhD candidate
The entrained air voids can improve the concrete freeze-thaw durability with satisfactory spacing factors or size distribution. Therefore, it is important to measure air void size distribution for quality control of concrete construction. This paper aims to develop nondestructive ultrasonic scattering methods to measure air void distribution evolution at both early-age and hardened stages. In the theoretical evaluation of ultrasonic attenuation, the combined normal and log-normal distribution were used to describe small-size and large-size air void size distribution, respectively. The experimental attenuation was measured by using the wave spectral ratio between the first and the second transmission waves in frequency domain. With optimized inverse analysis, the air void size distribution parameters were obtained by achieving the minimum error between experimental and theoretical attenuation. Four samples with different contents of air entrainment agent were particularly prepared for ultrasonic scattering measurement. The early-stage sample measurement showed that the whole air content slightly decreases with curing time. The air void size distribution of hardened samples (at 28-day age) were compared with ASTM C 457 imaging test results. The air void size distribution of different types of samples was favorably compared, especially in the small size range (< 1 mm). The results indicated that this developed ultrasonic scattering technique has promises in air void size distribution measurement of both early-age and hardened concrete samples.
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