Research on Ultrasonic Method for Detecting the Depth of Concrete Cracks

Cracks are one of the most common defects in concrete structures, and it is important to develop techniques for accurate measurement of crack depth. In this study, six concrete specimens with different crack depths and reinforcement distribution were designed. By analyzing the effects of these two factors on the detection of crack depth by ultrasonic method, and trying to use the impact echo method for comparative study. The results of the study show that when the measuring distance is approximately equal to two times the crack depth, the detection results are relatively accurate with an error of no more than ±2%. However, when the measurement distance is less than twice the crack depth, the larger the crack depth or the denser the spacing of rebar distribution, the more significant the adverse effect on the detection of crack depth, resulting in a gradual increase in the error. In addition, the more complex the direction of rebar distribution, the greater the error in the detection results. When the cracks are arranged next to the reinforcement, the detection error is generally greater than 10%, in which case the ultrasonic method is not recommended to detect the crack depth. At the same time, the impact echo method has a low frequency and the detection error is too large, so it is not recommended to be directly applied in the crack depth detection work. The crack depth and rebar distribution have a significant effect on the accuracy of the ultrasonic method in detecting crack depth. The ultrasonic method can provide more accurate results when the measurement distance is appropriate, but the error will increase significantly when the distribution of complex reinforcement or the crack depth is large. The impact echo method is not suitable for crack depth detection due to its excessive detection error.