尾波干涉法检测混凝土受压状态试验研究

Experimental study on detecting compressive state of concrete by coda wave interferometry

弹性波波速变化能够反映混凝土内部裂缝和应力的变化,其关键是对受压状态下的混凝土进行高精度检测。通过对4种不同强度等级的混凝土试块进行受压状态下的尾波干涉试验,分析混凝土内部微裂缝引起的多次散射波(尾波)的特性,将尾波波形与直达波波形进行对比性分析,并对尾波波速变化率随应力的变化规律及尾波传播的影响因素进行分析。结果表明:尾波波形具有一定的时间延迟,尾波相较于直达波传播的路径更长,对于混凝土内部损伤微变化更加敏感;随着应力的增加尾波波速变化率逐渐增大,当应力达到极限荷载的60%左右时,波速变化率增长到最大值随后开始减少,波速变化率趋势与混凝土损伤状态具有高度的相关性,利用超声波尾波波速变化检测混凝土的损伤状态效果更好。

The change of elastic wave velocity can reflect the change of cracks and stress in concrete. The key is to detect the concrete under compression with high precision. Through the coda interference test of four concrete specimens with different strength grades under compression, the characteristics of multiple scattered waves(coda) caused by micro cracks in concrete are analyzed, the coda waveform is compared with the direct wave shape, and the variation law of coda velocity with stress and the influencing factors of coda propagation are analyzed.The results show that the coda wave has a certain time delay, the propagation path of coda wave is longer than that of direct wave, and it is more sensitive to the micro change of internal damage in concrete;With the increase of stress, the coda velocity change rate gradually increases. When the stress reaches about 60% of the ultimate load, the wave velocity change rate increases to the maximum value and then begins to decrease. The trend of wave velocity change rate has a high correlation with the damage state of concrete. The effect of detecting the damage state of concrete by ultrasonic coda velocity change is better.