Acoustic impact-echo investigation of concrete delaminations using liquid droplet excitation

Impact-echo testing is an effective technique to map delaminations on concrete bridge decks. Non-contact acoustic measurement techniques are used to measure responses excited by a transient point load. Non-contact excitation using falling liquid droplets is demonstrated to excite the resonant modes associated with delamination defects. Slow and fast liquid flows produce large and small droplets with varying impact parameters. Spectrograms of acquired acoustic data demonstrate the effectiveness of the technique to detect concrete delaminations. Photography reveals the size differences of the droplets. Non-contact excitation and measurement can be deployed in situations where mechanical coupling to the material is undesirable.