C-scan and L-scan generated images of the concrete/GFRP composite interface

Glass Fiber Reinforced Plastics (GFRP) are fast becoming a viable new const ruction material. They are being used for rehabilitating old concrete struc tures-columns, beams, slabs and walls-by gluing the composite plate to the concrete surface. Proper attachment between the GFRP plate and the concrete surface is necessary for efficient use of GFRP composites to increase the strength of the rehabilitated structures. Delamination between the rehabili tated structure and the GFRP plate significantly reduces the strength of th e reinforced structure. Hence, delamination defects, if present at the inte rface, should be detected as soon as possible. In this paper, two ultrasoni c techniques to detect delamination defects between the GFRP plate and the concrete surface ape presented. One technique uses longitudinal waves or P- waves and the second technique uses Lamb waves. It is found that both techn iques can detect the defect when used properly. However, Lamb waves give a better image quality of the defect than longitudinal waves. (C) 1998 Elsevi er Science Ltd. All rights reserved.