As nation's infrastructure is getting old, nondestructive evaluation of existing structures and construction quality control are getting important. In this thesis, flaw detection techniques of concrete members using impact echo and spectral analysis of surface waves (SASW) methods were introduced. Both techniques are based on stress wave propagation. Experimental tests were performed using three types of concrete members where voids, crack, and poor concrete were included at known locations. The first type member was designed to detect voids and vertical cracks, the second type was designed to determine the different thickness of member, and the third type was designed to detect the location and quality of poor concrete. Within reasonable accuracy, locations of voids and poor concrete, thickness, and quality of concrete were determined by impact echo method and the dynamic modulus of concrete were measured using SASW method. The proper selections of impact source, receiver coupling and frequency range were found to be important in the testing. Both NDT methods showed a feasibility for the implementation into quality evaluation of concrete members in practice.
