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Detecting the concrete crack depth has always been a technical problem. The traditional detection methods，which are based on stress wave theory, have limitations such as low accuracy, complex operation, time-consuming and laborious procedures. This paper proposes a new method based on the combination of tracer and hand-held radar to better complete this task. Its main procedures include firstly spreading tracer diffusion to the bottom of the crack propagation, and then mapping the location of the air-tracer interface by radar waves, thus visualising the crack depth information. This paper elaborates the detection principle of this new method, carried out the feasibility numerical analysis and simulation verification. Also, the concrete standard crack specimens were made, together with relevant experimental researches. As to the feasibility of the method, it is verified by using common distilled water and saturated sodium chloride solution as tracers. The detection effects of these two tracers are compared and analysed by comparing the test data with the actual depth of the specimen. This research innovatively applies tracers to actively improve the electrical ability of concrete cracks, and then uses radar to detect the electrical distribution of cracks, realising the visual detection of crack depth. [ABSTRACT FROM AUTHOR]

The cracks with a width of more than 0.3 mm can seriously affect the safety and stability of concrete structures. Presently, there are many techniques for measuring the crack depth, each with its own advantages and disadvantages. However, due to the technical limitations and different applicability of each method, their accuracy in actual crack detection is often insufficient. In this article, to improve the detection accuracy in technological applications, the mature concrete crack depth detection technologies are summarised. The currently popular non-destructive testing technologies are divided into two categories: stress wave detection technology and electromagnetic wave detection technology. The specific detection methods and development status of the two technologies are discussed. Further, based on the detection principles, the advantages and disadvantages of various detection methods are systematically compared. The application conditions of each detection method are explored, and their feasibility for different forms of cracks are comprehensively analysed. A set of optimal methods for crack depth detection is proposed. Besides, the key points for the accurate measurement of concrete crack depth are discussed. [ABSTRACT FROM AUTHOR]