Elastic wave propagation in complex systems - The interaction of waves with in-homogeneities in impact echo testing studied by modelling and by scanning laser vibrometry

Laser vibrometer based contactless measurements of elastic wave fields at the surface of a concrete block excited by a mechanical impact are presented. The interaction of the waves with a grouted duct is investigated. Numerical simulations of the same situation provide wavefront snapshots, which show similarities with the measurements concerning the primary wave field but also significant differences with regard to the wave-duct interaction. The latter result shows that the assumption of a perfectly bonded interface between duct wall and concrete matrix, as used in the simulation, is not realized in practice. It is assumed that this weak bonding significantly contributes to the detectability of grouted ducts and to the non-detectability of injection faults inside these ducts.