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Abstract
Regular safety inspections in a timely manner are required for safety management and maintenance of structures in order to avoid accidents of the structure. As a way to inspect whether a structure is safe, non-destructive testing method has been widely used for the internal inspection of concrete structure. In spite of several previous studies on non-destructive testing techniques for concrete structures, there is still lack of scientific approaches and experimental validation of non-destructive testing for recycled coarse aggregate concrete hollow columns that are currently widely used in concrete structures, but need for accurate and efficient inspection methods. To address this issue, this study attempts to estimate and verify the thickness of concrete hollow columns using the impact-echo method. To achieve this goal, 40 MPa of mixed design strength according to four replacement ratios of recycled coarse aggregate was used to build an experimental specimen that has a rectangular hollow. The main findings of this study represent that average thickness values were 106, 152 and 207 mm, while average real thickness values were 99, 150 and 199 mm, which means that the average error rates between actual and the estimated values of thickness were 7·2, 1·1 and 4·1%, respectively. Applying impact-echo method based on the ultrasonic pulse velocity method to inspect internal defects would contribute to improving the accuracy of diagnosing other concrete structural members that consist of recycled coarse aggregate.