Youyuan Lu

A new smart traffic monitoring method using embedded cement-based piezoelectric sensors

Cement-based piezoelectric composites are employed as the sensing elements of a new smart traffic monitoring system. The piezoelectricity of the cement-based piezoelectric sensors enables powerful and accurate real-time detection of the pressure induced by the traffic flow. To describe the mechanical-electrical conversion mechanism between traffic flow and the electrical output of the embedded piezoelectric sensors, a mathematical model is established based on Duhamels integral, the constitutive law and the charge-leakage characteristics of the piezoelectric composite. Laboratory tests show that the voltage magnitude of the sensor is linearly proportional to the applied pressure, which ensures the reliability of the cement-based piezoelectric sensors for traffic monitoring. A series of on-site road tests by a 10 tonne truck and a 6.8 tonne van show that vehicle weight-in-motion can be predicted based on the mechanical-electrical model by taking into account the vehicle speed and the charge-leakage property of the piezoelectric sensor. In the speed range from 20 km h−1 to 70 km h−1, the error of the repeated weigh-in-motion measurements of the 6.8 tonne van is less than 1 tonne. The results indicate that the embedded cement-based piezoelectric sensors and associated measurement setup have good capability of smart traffic monitoring, such as traffic flow detection, vehicle speed detection and weigh-in-motion measurement.

Ultrasonic monitoring of the early-age hydration of mineral admixtures incorporated concrete using cement-based piezoelectric composite sensors

The early-age hydration processes of concretes with mineral admixtures have been monitored and evaluated by a newly developed ultrasonic method based on embedded cement-based piezoelectric composite sensors. With the embedded ultrasonic (P-wave) measurement system, the waveform, wave velocity, attenuation coefficient index, and frequency-domain spectrum of detected ultrasonic waves during hydration can be recorded. The mineral admixtures examined include fly ash, slag, and silica fume, which replace part of the cement in concrete mixtures. It is found that the ultrasonic transmission parameters can be related to the microstructure changes of the concrete. Both the acceleration effects of silica fume and the retardation effects of fly ash and slag on the early hydration of concrete can be determined and explained through the analysis and comparison of the characteristics of the velocity curves. The attenuation coefficient index curve provides additional observation for the study of hydration kinetics. Moreover, the function of fresh concrete in filtering the high-frequency component of the wave varies with time, and concrete can be considered as low-pass frequency spectral filter. Frequency spectra analysis at different ages of fresh concrete provides useful information to reveal the early-age hydration process.

Signal-Based Acoustic Emission Monitoring on Mortar Using Cement-Based Piezoelectric Sensors

Signal-based acoustic emission (AE) monitoring on mortar was performed under 3 types of static loading patterns: cubic-splitting, direct-shear, and pullout. Each applied loading pattern was expected to produce a distinguished fracture process on mortar. This study was the first to combine a cement-based piezoelectric sensor (such as an AE transducer) and a home-programmed DEcLIN monitoring system for monitoring the concrete fracture process in mortar. It was found that the cement-based piezoelectric sensor has much better sensitivity and a much broader frequency domain response range as compared to traditional piezoelectric ceramic transducers after embedding into mortar specimens. The 3-D localization of AE sources and the signal-based AE energy index obtained by the DEcLIN system were used to explain and quantitatively evaluate the fracture processes of mortar specimens under various types of loadings. It was revealed that the fracture processes in mortar under the cubic-splitting and direct-shear loading patterns were evidently more brittle than that of the pullout test.

The application of 1–3 cement-based piezoelectric transducers in active and passive health monitoring for concrete structures

1–3 cement-based piezoelectric composite has been developed for health monitoring of concrete structures. Transducers made of this type of composite have broadband frequency response. Plain concrete and engineered cement composite (ECC) beams with embedded 1–3 cement-based piezoelectric transducers were prepared and tested. During experiments, the transducers were used to perform active and passive detection of the damage evolution of the beams. In active detection, a damage index based on the average energy of the received waves was proposed and used. In passive detection, acoustic emission (AE) events were recorded and the accumulated AE event number was analyzed with the loading history. Crack localization was also accomplished in the passive monitoring. The results of the two methods demonstrated similar trends in interpreting the damage evolution of the concrete beam. The results were also consistent with each materials characteristics.

Cement-based piezoelectric sensor for acoustic emission detection in concrete structures

In this study, brand new cement-based piezoelectric composite sensors have been developed for acoustic emission detection in a civil engineering structure. The new developed sensors have good compatibility with concrete, the most widely used construction material. Especially, the tuned acoustic impedance of the composite sensor is very close to that of concrete. Following different fabrication procedures, two kinds of sensors, sensor with 0-3 connectivity pattern or 1-3 connectivity pattern have been fabricated and characterized. The piezoelectric properties and sensitivity are investigated and analyzed using a Physical Acoustic Corporation data acquisition system. The properties are compared to that of the Physical Acoustic Corporation transducer (PAC). It is found that the cement-based piezoelectric sensor perform much better when embedded into the concrete structure. The sensor ability in detecting AE signals generated by formation of micro-cracks or dislocation in the concrete beams is improved dramatically. There is a great potential to use such type of sensor for health monitoring of civil structures.

Embedded Cement-Based Piezoelectric Sensors for Acoustic Emission Detection in Concrete

In this research, the feasibility of using embedded cement-based piezoelectric sensors to detect the acoustic emission (AE) activities in concrete has been studied. A sensor is presented that is made with the 0–3 cement-based piezoelectric composite as sensing element. The composite is formed by pressing mixed cement-piezoelectric powder into a penny-shaped thin plate. In the terminology of 0–3, 0 represents the dimension of the piezoelectric particle and 3 stands for the dimensions of the matrix. By adjusting the dosage of the piezoelectric ceramic powder, the properties of the composite can be tailored to suit designated applications. Sensors made of the composite (0–3 sensor) are able to be embedded into concrete and have broadband frequency response. It is shown by a four-point bending test on a concrete beam that the sensors have excellent ability in AE activity detection. High sensitivity is also observed for the embedded sensors.