Three Seismic Nondestructive Methods Used to Monitor Concrete Slab Injection Tests

A long term research program to determine the effectiveness of cement grouts injected in concrete dams was initiated by the Institute of Research in Electricity of Hydro-Quebec (IREQ) in 1986. To investigate the effectiveness of the grouts, three nondestructive methods based on seismic wave propagation were recently applied to various concrete slabs. The Impact-Echo method was used to determine the crack profile before the injection process began in one of the slabs. This method was used successfully and the detected internal crack depths agreed well with crack depths measured on the sides of the concrete slab. Acoustic Emission was used to monitor the penetration of the grout inside the crack. This method also allowed the researchers to determine at which moment, during the injection test, the cement grout mixture needed to be changed. Sonic Tomography was used to produce a tomographic image of the internal seismic wave velocities which traveled through the slab before and after the injection tests. Two different transmitter and receiver arrangements were used to determine the best measurement configuration. This paper illustrates the usefulness of combining various seismic wave based nondestructive methods to obtain a better knowledge of fracture detection and cement grout propagation, which can eventually lead to practical applications on concrete structures and hence on concrete dams.