Impact wave propagation mechanisms and response characteristics in defective concrete

Abstract Concrete structures are widely adopted in engineering construction. However, the combined effects of construction quality, load, and environmental factors can lead to well-concealed defects within concrete structures, e.g. holes and cracks, which seriously affect their long-term performance. Nondestructive testing is usually performed to test and diagnose internal defects in concrete, with the impact wave method being widely used due to its significant advantages. However, in-depth research on the impact wave propagation mechanisms and response characteristics in concrete is lacking, which limits the accuracy of impact wave detection and defect identification. Accordingly, this study first constructs finite element models of concrete without and with defects (holes, cracks, etc) for the numerical simulation of the dynamic impact wave propagation process. Further, impact wave testing is conducted on defective concrete to thoroughly analyze the time-frequency characteristics of the impact wave signal in defective concrete. Thus, the impact wave propagation mechanism and response characteristics in defective concrete structures can be clarified, the theory of impact wave detection can be improved, and the accuracy of impact wave-based concrete defect detection can be enhanced. The test results show that thickness frequency drifting toward the low-frequency direction is an important characteristic of defects in the concrete structure, and the drift is more prominent as the defect size increases. The horizontal reflective surface of a crack defect has a stronger reflection than the curved reflective surface of a hole defect. The effect and behavior of the impact wave in defective concrete structures show obvious propagation patterns and response characteristics, and each defect type corresponds well with specific spectral response characteristics. The research results can effectively improve the recognition efficiency of internal defect types of concrete structures and guide the actual engineering detection and repair.