Abstract: An apparatus for non-destructively testing concrete comprises a tri-wheel platform having a transducer mounted adjacent each wheel and mechanically coupled to the concrete to be responsive to vibration. An aperture is formed in the center of the platform equispaced from the three transducers. Vibrations are imparted to the concrete that emanate outwardly toward the transducers by manually striking the concrete through the center aperture with a rubber tipped impact rod. The transducers generate electrical signals responsive to the amplitudes of detected vibrations which are a function of the structural continuity of the concrete. Electronic circuitry monitors the outputs of the transducers and makes comparisons of the signals to determine whether a flaw exists in the concrete within the region bounded by the three transducers.