Embedded Piezoelectric Transducer And Its Application In Monitoring Cement Hydration

After mixing cement with water,cement clinker minerals are hydrated into hydrated calcium silicate,calcium hydroxide and hydrated calcium sulphoaluminate.As time goes on,the initial slurry gradually changes from plastic to solid stone body after setting and hardening.The ultrasonic method is developed in recent years,a kind of cement paste,mortar and concrete early hydration process monitoring method,which is based on principle of solid liquid gas velocity and material using ultrasonic in cement based materials in three-phase associated characteristics,get parameters of ultrasonic wave propagation in material in the evolution through experiments.The evolution laws of acoustic characteristic parameters of cement based materials,such as wave velocity,first wave amplitude and main frequency,are studied.The price of existing ultrasonic probe foe metal package is high,and is mainly used for the nondestructive testing of concrete,cement is suitable for embedded monitoring.To solve this problem,we put forward the development of embedded piezoelectric transducer to prepare the embedded piezoelectric transducer with good compatibility with cement.The piezoelectric ceramic transducer is composed of a piezoelectric element,a matching layer and a shielding layer.Lead Zirconate Titanate PZT4 is used as a emission transducer because of its good emission properties.Lead Zirconate Titanate PZT5 is used as the piezoelectric element of receiving transducer.The Al₂O₃ slice with thickness of 0.5mm is selected as the matching layer for protection,and the copper net acts as a shielding layer to reduce the clutter.The mixture of the epoxy resin:the curing agent:the mixture of tungsten powder ratio of 4:1:0.25 is used as the backing layer of transducer,which can effectively restrain the radial vibration and improve the acoustic attenuation performance of the transducer.The frequency bandwidth of the piezoelectric ultrasonic transducer is 20 kHz,and the signal-to-noise ratio is 47.56dB.In the stability test,the transducer has good compatibility with cement,it has uniformity,the response of launching and receiving is easy to observe,and it has good attenuation performance.It can be used to monitor the process of cement hydration.Before ultrasonic monitoring of cement hydration,it is necessary to determine the ultrasonic testing parameters in the process of cement hydration monitoring,including the pulse interval test,the distance between receiving transducer and the emission transducer,and the propagation time of ultrasonic wave in transducer.The short pulse interval is too short to cause the uncertainty of the first wave of ultrasonic test,and the time delay leads to too long.The distance between the receiver and receiving transducer is 4cm.Through the acquisition of the ultrasonic first wave time at 3 different distances,it is calculated that the propagation time of ultrasonic wave between the transmitting transducer and receiving transducer is 2.3×10^-6s?The piezoelectric transducers are used for the cement hydration monitoring to monitor the hydration process of water cement ratio with 0.3,0.4,0.5 ordinary Portland cement and sulphoaluminate cement.The time domain curve of the ultrasonic wave is obtained.The time domain curve is converted to the frequency domain by Fourier transform.The time and frequency of the time domain curve and the frequency domain curve are obtained.The ultrasonic testing results are combined with the strength,setting time,hydration heat curve,XRD and SEM in the hydration process of cement.The results show that the hydration process of sulphoaluminate cement is much faster than that of ordinary Portland cement.As the hydration reaction proceeds,the amplitude of the time domain curve first increases and then decreases,and the number of ultrasonic pulses cycle increases to a certain degree at about 1 days and then no longer increases.In the receiving wave spectrum of piezoelectric transducer,the frequency of main frequency increases first and then decreases.The ultrasonic wave and ultrasonic parameters received by the piezoelectric transducer can divide the hydration reaction of cement into different stages.Sulphoaluminate cement ultrasonic waveform began to appear much earlier than Portland cement,which is consistent with the setting time and strength test shows the law,comparative analysis of the microstructure can be obtained between ultrasonic parameters and the microstructure of cement paste.