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Self-Diagnosis of Hybrid CFRP Rods and As-Strengthened Concrete Structures

A literature survey reveals that extensive studies have been published on the hybridization of composite and self-diagnosis of carbon fiber reinforced polymer (CFRP) composites. In these researches, not more than one type of carbon fibers or powders is used as active materials. This article addresses a new class of smart hybrid CFRP (HCFRP) rods consisting of at least two types of carbon fibers of different strength and moduli as active materials and their applications to concrete structures. The carbon fibers function as both structural and sensing materials by virtue of their good mechanical properties, electrical conductivity, and piezoresistivity. The hybridization focuses on two aspects: to better the electrical behavior of the HCFRP rods in order to obtain a stage-based sensing function, and to upgrade their mechanical properties. The self-diagnosis and damage detection functions of the HCFRP rods and/or the as-strengthened concrete structures are realized through measuring the change in electrical resistance. The sensing principles are based on the electrical resistance change with the strain change and sudden jumps in electrical resistance due to the gradual fractures of different types of carbon fibers. The results show that the electrical resistance of the HCFRP rods changes with strain in a stepwise manner. The sudden jumps in electrical resistance at different strain amplitudes are associated with the ruptures of different types of carbon fibers. Thus, the step-based sensing of HCFRP rods-selves or strengthened structures is realized. Moreover, the initiation and propagation of cracks in the HCFRP rod-strengthened concrete beams are also measured by means of clip gages and distributed fiber optic sensors (FOS).