NDE of concrete-FRP systems

Abstract

Engineering structures made of different materials have an ancient root in many engineering disciplines such as civil, mechanical, and aerospace engineering. Such structural systems or structures are commonly known as composite structures or composite systems. In civil engineering, reinforced concrete (RC), prestressed concrete (PC), and concrete-FRP (fiber reinforced plastic) systems are three well-known examples. Different from RC and PC structures, concrete-FRP systems are usually formed by using FRP sheets/plates/strips to externally bond to the surface of damaged concrete structures for retrofitting, repair, and strengthening. Externally bonded FRP sheets/plates/strips can provide additional tensile strength, or shear strength, or compressive strength (through the confinement effect) to existing concrete structures. However, air pockets and FRP delamination introduced during improper installation can lead to the brittle, immature failures of concrete-FRP systems. Furthermore, the surface information of concrete structures for condition assessment becomes unavailable after the installation of FRP. In this paper, a review of nondestructive evaluation (NDE) techniques for concrete-FRP systems is provided. Contact and non-contact NDE techniques are compared on their detection of subsurface anomaly inclusion/ delamination in concrete-FRP systems. An emphasis is placed on the recent development of remote NDE techniques such as laser Doppler vibrometer (LDV) and synthetic aperture radar (SAR). Challenges in the condition assessment of concrete-FRP systems in the field are also discussed for different NDE techniques.