Abstract
The addition of short fibers in concrete mass offers a composite material with advanced properties, and fiber-reinforced concrete (FRC) is a promising alternative in civil engineering applications. Recently, structural health monitoring (SHM) and damage diagnosis of FRC has received increasing attention. In this work, the effectiveness of a wireless SHM system to detect damage due to cracking is addressed in FRC with synthetic fibers under compressive repeated load. In FRC structural members, cracking propagates in small and thin cracks due to the presence of the dispersed fibers and, therefore, the challenge of damage detection is increasing. An experimental investigation on standard 150 mm cubes made of FRC is applied at specific and loading levels where the cracks probably developed in the inner part of the specimens, whereas no visible cracks appeared on their surface. A network of small PZT patches, mounted to the surface of the FRC specimen, provides dual-sensing function. The remotely controlled monitoring system vibrates the PZT patches, acting as actuators by an amplified harmonic excitation voltage. Simultaneously, it monitors the signal of the same PZTs acting as sensors and, after processing the voltage frequency response of the PZTs, it transmits them wirelessly and in real time. FRC cracking due to repeated loading ad various compressive stress levels induces change in the mechanical impedance, causing a corresponding change on the signal of each PZT. The influence of the added synthetic fibers on the compressive behavior and the damage-detection procedure is examined and discussed. In addition, the effectiveness of the proposed damage-diagnosis approach for the prognosis of final cracking performance and failure is investigated. The objectives of the study also include the development of a reliable quantitative assessment of damage using the statistical index values at various points of PZT measurements.
Highlights
Fiber-reinforced concrete (FRC) with short discrete fibers as mass reinforcement is an efficient cement-based composite that can overcome, up to a point, the drawbacks of the quasi-brittleness of plain concrete [1,2,3]
Steel fibers have extensively been studied in small-sized concrete specimens under various loading conditions [4,5,6] and in large-scale reinforced concrete (RC) structural members subjected to monotonic [7,8,9,10] and, recently, to reverse cyclic deformations [11,12,13,14]
Test results of this study provide a valuable reference for future applications and design of FRC, with an emphasis on the quantification of the influence of the added synthetic fibers on the post-peak compressive behavior and damage assessment
Summary
Fiber-reinforced concrete (FRC) with short discrete fibers as mass reinforcement is an efficient cement-based composite that can overcome, up to a point, the drawbacks of the quasi-brittleness of plain concrete [1,2,3]. Fiber-optical sensors can be used in various in-situ and real-time surveillance applications in civil engineering structures, such as monitoring of strain, displacement, vibration, cracks, corrosion, and chloride-ion concentration They have high sensing capability, the ability to operate in harsh environments, and a large sensing scope. The applied step-by-step loading–unloading–reloading procedure includes compressive stresses within the elastic range, near the ultimate strength and in the post-peak response, in order to investigate for the first time the sensitivity of the PZTenabled EMA-based technique to diagnose damage at various levels when a specimen is unloaded to minimize the developed stress effect. A new and meticulous health-monitoring procedure is proposed that includes measuring and recording the frequency responses of the PZTs mounted to the FRC cube surface using dense mesh points of damage identification This way, the location, distance, direction, and width of the cracks can be evaluated accurately and verified by the experimental observations.
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