| In this dissertation, the overseas and domestic investigations about nondestructive testof concrete structures were summarized first. Based on these investigations and stresswave propagation theory, the impact echo scanning technology was used to study onthe testing and recognition of defects in the concrete structure, estimating the damagedegree of concrete, multi-layer structures, and the technology was used to estimatethe thickness of tunnel concrete lining.(1)The transmission patter of stress wave in concrete was discussed, including thereflection stress wave at different interface in concrete. A method used to recognizethe right thickness frequency in the spectrum was proposed.(2)The defects in the real concrete structures were simulated by putting differentmaterial in concrete sample manually. The impact echo scanning technology was usedto detect these defects. The spectrum analysis, 2-D and 3 D scanning method wereused to have qualitative and quantitative analysis.(3)Based on the stress wave propagation principle and the development of mechanicalproperty of concrete after compress load, the stress wave method was used to estimatethe damage degree of concrete caused by compressive load. The relationship betweendamage degree of concrete and stress wave speed, spectrum of reflect wave wasestablished.(4)Multi-layer structure composites were studied using impact echo scanning method.Thickness of multi-layers with good bond condition was tested by single point and2-D impact echo method. A theory method was proposed in order to improve theprecision of test result when the multi-layers were made of layers with differentmaterial. These methods then were used to evaluate the pavement structure of a highway.(5)After these theoretical and experimental studies, the impact echo scanningtechnique was used to in-situ test of a tunnel lining. The thickness of tunnel lining canbe rapidly and exactly estimated through spectrum, 2-D and 3-D Scanning analysis.
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