NONDESTRUCTIVE EVALUATION OF CONCRETE WITH IMPACT-ECHO AND PULSE-VELOCITY TECHNIQUES

The paper describes the applications of two nondestructive techniques, impact echo and pulse velocity, to evaluate the condition of concrete structures. The power plant case histories describe the evaluation of a concrete foundation, a tunnel slab, and turbine pedestal columns. In the impact-echo method, the response of a concrete structure to mechanical impact is monitored and analyzed. The impact induces longitudinal, shear, and surface waves that reflect off internal discontinuities as well as the backs and sides of the concrete members. These reflections, or echoes, can be analyzed with a fast-Fourier transform (FFT) analyzer to determine the condition of the concrete. The pulse-velocity method involves measurement of transit time of an acoustic wave through a concrete structure. Significant changes in transit time are associated with the internal makeup of the structure. This method can be used to determine uniformity of concrete and to detect internal faults such as cracks, voids, or honeycombing.