Microwave NDE of RC beams strengthened with CFRP laminates containing surface defects and tested under cyclic loading

Abstract

Abstract: Carbon fiber reinforced polymer (CFRP) laminates are externally bonded to reinforced concrete (RC) members to provide additional strength such as flexural, shear, etc. However, the presence of defects in the form of delaminations between the CFRP laminate and concrete substrate may significantly affect the structural integrity and stiffness of the structural section. Microwave near-field nondestructive evaluation (NDE) techniques, utilizing open-ended rectangular waveguides, have the ability to detect these defects. This paper presents the results of an investigation on the influence of cyclic loading on delaminations in reinforced concrete beams fabricated and strengthened with CFRP laminates. The delaminations were formed in the beams by applying pressured air beneath CFRP sheets when epoxy was in fresh state. The beams were exposed to severe environmental conditionings and sustained load of 40 % of the ultimate moment capacity. All the beams were cycled under fatigue loading for 2-million cycles. A microwave reflectometer and an automated scanner were used in order to study the behaviour of the delaminations under cyclic loading. Introduction & Background: The development of new material systems like carbon fiber reinforced polymers (CFRP) used for strengthening and rehabilitation of existing structures are getting higher demands and wide range of applications in recent years. CFRP laminates gained importance over steel plate bonding because they offer superior performance such as resistance to corrosion, and high stiffness-to-weight ratio. Even though CFRP