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Evaluation of bonding quality between concrete layers using Lamb waves

Concrete slabs such as bridge decks and parking garage slabs deteriorate and show signs of distress in the concrete cover when they are exposed to severe environmental conditions. Repair strategy consists of removing the deteriorated concrete and replacing it by a new layer. The success of this repair method is strongly dependent on the quality of bonding between the existing substrate and the overlay. Evaluation of bonding can be done by mechanically testing cores retrieved from the slab. However, this method is time-consuming, destructive, and the results represent only the locations where the cores were retrieved. GPR is a non-destructive method that may detect the interface between the substrate and the overlay. It permits inspection of large survey areas, but it is difficult to tell whether the two concrete layers have a good quality of bonding between each other. This paper presents an experimental study on the use of Lamb waves to evaluate the quality of bonding between concrete layers. Two planar cracks that simulate poor quality of bonding between concrete layers were created at different depths in a thick slab. Tests were carried-out at the surface of the slab and the acquired signals were processed using frequency-wavenumber analysis. Reliable results were obtained and the method was found to have high capability to detect planar cracks and thus evaluate the quality of bonding between concrete layers.