The Corrosion Monitoring Of Steel Bar In Reinforced Concrete Based On Piezoelectric Sensor

With the increasing application of reinforced concrete in tunnels, buildings and bridges and other infrastructures, it has become one of the main materials in architecture engineering. Real-time online structural health monitoring is of great importance as the security and durability of reinforced concrete structures have become a threat to the life and property of human. In recent years, the rapid development of intelligent materials provides a new way for structural health monitoring technology. Piezoelectric ceramic has been widely studied and applied as its functions of sensing concurrently with actuating, as well as broadband frequency, quick response, low price, etc. Based on the above background, this paper studied the corrosion monitoring of steel bar in reinforced concrete based on piezoelectric sensor under the support of the National Natural Science Foundation of China (No.51272090). The main research works and results are as follows:(1) Embedded electrical impedance sensor and ultrasonic sensor were developed for health monitoring according to the characteristics of concrete structures. PZT-5 was used as sensing element and cement/epoxy was used as waterproof material to fabricate electrical impedance sensor. The results indicate that the mixture of cement, epoxy and resin with the ratio of 1:1:0.25 has an excellent waterproofness. Piezoelectric impedance analysis of sensors bonded on steel bars in reinforced concrete is able to monitor corrosion via the electromechanical impedance technique. PZT-5 piezoelectric ceramic and 1-3 piezoelectric composites were used as sensing element to fabricate receiving type ultrasonic sensor, while PZT-4 piezoelectric ceramic was used as actuating element to fabricate emission type ultrasonic sensor. The results show that receiving type ultrasonic sensor has advantages of single resonance peak, low resonance frequency, good compatibility with concrete and excellent receiving property. Corrosion monitoring can be achieved by analysis of the received waves through reinforced concrete with different corrosion rates.(2) Based on the electromechanical impedance technique, a corrosion identification test was carried out on specimens of reinforced concretes with different corrosion rates. The result showed that the electrical impedance sensor with a larger electromechanical coupling coefficient is more suitable for steel corrosion monitoring. The magnitude and the frequency of the impedance signature of the electrical impedance sensor bonded to the reinforced concrete shifted after corrosion. The resonance peaks’ values of the resistance/reactance signature increased during the corrosion process, while the frequency corresponding to the resonance peaks of the resistance/reactance signature shifted left. The difference values of resistance/reactance signature at the same frequency between health state and corrosion states increased with corrosion damage rate. To quantify damage, root mean square deviation (RMAD) and mean absolute percentage deviation (MAPD) were used as damage index. RMSD and MAPD were suitable to quantify corrosion and progressive severity. The damage indexes of resistance were larger than the reactance’s, which indicated that the resistance was more sensitive to corrosion damage. The RMSD values of resistance at 100～150 kHz exhibited a linear trend with corrosion damage rate, while MAPD was at 150～200 kHz.(3) Based on the e ultrasonic testing technique, a corrosion identification test was carried out on specimens of reinforced concretes with different corrosion rates. The results showed that, compared to the PZT-5 type receiver type ultrasonic sensor,1-3 piezoelectric composite sensor was more suitable for monitoring corrosion of reinforced concrete structure, with the advantages of single dominant frequency, significantly peak value and better resolution. The receiving ultrasonic waves had irregular waveform, and there were several continuous wave packets. The wave velocity, amplitude, dominant frequency’s amplitude of receiving ultrasonic waves had obvious relation to steel corrosion rate. When the corrosion rate was at 0% to 2%, the wave velocity, amplitude, dominant frequency’s amplitude of receiving ultrasonic waves decreased rapidly with the increase of the corrosion rate. When the corrosion rate was at 2% to 6%, the wave velocity, amplitude, dominant frequency’s amplitude also decreased while with a decrescent range. When the corrosion rate was more than 6%, the wave velocity, amplitude, dominant frequency’s amplitude did not changed basically. The dominant frequency decreased with the increase of the corrosion rate, but this change was not obvious in the initial stage of corrosion. The ultrasonic parameters of velocity, amplitude and dominant frequency’s amplitude can be used as characteristic parameters to monitor the corrosion sate of reinforced concrete.