| Reinforced concrete structure is very important in civil engineering. It is widely used in modern construction, bridge, infrastructures and so on. However, reinforced concrete structure tends to suffer from serious environmental conditions and the durability is a severe problem.One of the main causes of durability for reinforced concrete structures is reinforcement corrosion. Therefore, monitoring steel corrosion becomes a hot topic in the field of health monitoring of civil engineering in recent years. Nowadays, researchers have developed a variety of relatively mature methods of nondestructive testing. However, these methods have usually hysteresis, inaccuracy, less sensitivity and so on. Ultrasonic guided wave monitoring is a dynamic non-destructive testing technology. The advantages of ultrasonic guided wave monitoring for reinforcement corrosion are real-time, online and continuous. In addition, it can judge the different stages of steel bar corrosion. It is the ultimate purpose of non-destructive detection.This paper researched the reinforcement corrosion using ultrasonic guided wave monitoring including :(1) Piezoelectric sensors were fabricated used in ultrasonic guided wave monitoring.Ultrasonic guided wave propagation rules were studied in the steel. The different packaged areas and frequencies influenced ultrasonic guided wave propagation in steel. The results showed that with the increasing of frequency, amplitude decreased obviously. As packaged area increased, the amplitude of ultrasonic guided wave attenuated seriously.(2) The reinforcement corrosion was monitored using ultrasonic guided wave. The amplitude of ultrasonic guided wave could response the degree of reinforcement corrosion.The results showed that the amplitude of ultrasonic guided wave signal decreased in the first stage and increased in the second stage. In the first stage, the interface of concrete and steel bar was filled with the corrosion produces gradually. When the ultrasonic guided wave amplitude value became minimum, cracks started emerging in concrete. In the second stage,cracks developed in concrete. When cracks emerged in surface of concrete specimen, the amplitude of ultrasonic guided wave tended towards stability.(3) Swept-frequency signal of different steel bar corrosion stage were handled usingwavelet packet signal processing methods. Energy of the wavelet packet were calculated. The total energies and each frequency band energies were analyzed by wavelet packet signal. The energy of ultrasonic guided wave swept-frequency signal increased after decreasing. In addition, the energy of ultrasonic guided wave signal in various frequency bands was more and more dispersed and caused the change of the energy spectrum.(4) The interface of reinforcement and concrete were observed by scanning electron microscope. The results showed that the interface was loose weak area before reinforcement corrosion. When reinforcement corroded, the interface was filled with rust produces. The interface became dense area. Besides, Rust layer after concrete appearing cracks was thicker than its before concrete appearing cracks.In this paper, the experimental results indicate that ultrasonic guided wave could monitor reinforcement corrosion in steel concrete structure real-timely and online. It could reflect the degree of reinforcement corrosion effectively. |
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