Non-destructive evaluation is widely applied in science and technology field to acquire the properties of materials and structures without damaging their integrity. The unique advantage of non-destructive evaluation methods made them strong candidates for health monitoring of concrete materials and structures....[ Read more ]

Non-destructive evaluation is widely applied in science and technology field to acquire the properties of materials and structures without damaging their integrity. The unique advantage of non-destructive evaluation methods made them strong candidates for health monitoring of concrete materials and structures.

In this study, two home-programmed automatic monitoring systems DEcLIN and FEbLIN had been developed and applied for such purposes based on the principle of AE and ultrasonic method. The two monitoring systems all utilize a brand new cement-based piezoelectric sensor as sensing element. The performance of cement-based piezoelectric sensors in detecting propagated mechanical wave is greatly enhanced when they are embedded in concrete materials or structures. Hence, it is quite suitable for evaluation of concrete fracture processes or hydration processes. Firstly, the fracture processes of concrete under static loading conditions were investigated using DEcLIN acoustic emission (AE) monitoring systems. Both parameter-based AE analysis and signal-based AE analysis were used to reveal the temporal status of concrete materials during various fracture stages. Based on the comparisons between different fracture processes, the characteristics of concrete fracture processes could be interpreted by parameter–based AE analysis. And frequency domain boundary of P-wave and S-wave could be clearly figured out by signal-based analysis to study the micro-crack behaviors during fracture processes. Secondly, the study on the fracture processes of concrete structures and dynamic response under earthquake loadings was carried out. Major frequency components correspond to AE and dynamic vibration in detected signals were filtered out to evaluate the dynamic behavior of concrete structures and damage processes, respectively. A damage indicator was defined to effectively reveal the temporal damage level of concrete structures under earthquake loadings. Thirdly, an investigation on the corrosion processes of reinforced concrete beams was conducted. AE monitoring method with embedded cement-based piezoelectric sensor was employed to distinguish various corrosion stages. Fourthly, a special study on the relationship between AE energy and fracture energy was carried out with concrete prism compression test. It was verified that there existed a close correlation between energy consumed for crack propagation and corresponding AE energy detected by cement-based piezoelectric sensor. Finally, hydration processes of concrete materials were comprehensively monitored and studied by FEbLIN systems using active ultrasonic principle. Based on the information revealed from the evolution trend of ultrasound parameters, hydration processes of concrete materials up to age of 1 day were divided into four major stages. The ultrasonic experimental results were compared with that of non-contact resistivity monitoring method. It is revealed that both methods can distinguish individual hydration stage and characteristic microstructure developments. However, ultrasonic is more sensitive to solid while non-contact resistivity method is prone to liquid phase development.

Inspired by all the experimental results, a prospective of civil infrastructure connected internet of things based on the cement-based piezoelectric sensors and assorted monitoring system was proposed. It is expected that human society will be changed for better from the proposed civil infrastructure connected internet of things.

The major contributions of this overall study are:

1. First time to use cement-based piezoelectric sensor as AE transducer for nondestructive testing in concrete materials and structures.

2. The board band feature of cement-based piezoelectric sensor is adequately used for signal-based analysis of AE from concrete crack and damage.

3. Corrosion process of concrete beams under single effect and coupling effect can be distinguished by AE analysis based on embedded cement-based piezoelectric sensor.

4. Fracture energy and AE energy are correlated in this study using cement-based piezoelectric. It is verified that AE energy can be used to quantitatively evaluate the fracture process of concrete.

5. This study provides a feasible way for concrete structure hydration monitoring from fresh stage to mature stage based on active ultrasonic principle.