The objective of the research presented in this paper is to develop a new nondestructive test method to determine the cover thickness of reinforcing bars in concrete structures that contain closely arranged reinforcing bars. Even though the commercial covermeters based on magnetic and electrical methods are widely used in the detection of the depth and location of reinforcing bars, they are not suitable in the case of bars with small spacing. The technique proposed in this paper for detection of the closely arranged reinforcing bars makes use of stress waves. The conception of the new test scheme originated from the fact that the propagation of stress waves follows the shortest travel path dominated by the reinforcing bar under the test point and is not affected by adjacent reinforcing bars. Numerical studies were performed to investigate how the travel time of a P-wave propagating through reinforcing bars is changed as the test line is moved away from the axis of the reinforcing bars. Experimental studies were performed on concrete specimens that contain reinforcing bars with close spacing. Results obtained from numerical analysis show that when the test point is not exactly above the steel bar the travel time for a P-wave is increased with an increase in distance from the test line to the reinforcing bar Experimental results show that no matter how close the reinforcing bars are placed in concrete specimens, the cover thickness of the bars can be still measured accurately
