Investigation of piezoelectric composite transducer in ultrasonic monitoring of cement hydration

Ultrasonic receiving transducers were fabricated by using 1–3 type cement/polymer based piezoelectric composites as sensing elements and a mixture of cement and epoxy resin as packaging material. An electromagnetic shielding coating material was used as a shielding layer. Based on the ultrasonic wave technique, the hydration reaction processes of Portland cement pastes with various water-to-cement ratios (w/c = 0·28, 0·40 and 0·50) were monitored by using the ultrasonic transducers. Performance analysis of the transducers showed that the shielded transducer has characteristics of a high signal-to-noise ratio, large head wave amplitude and a clear waveform. The head wave amplitude of the shielded transducer was 73% greater than that of the unshielded transducer, and the amplitude ratio of the head wave to the second wave of the shielded transducer was also increased (by 46%). The relationship between waveform and the wave parameters of the received ultrasonic wave and cement hydration reaction time was analysed. It was found that the cement hydration reaction process can be divided into different periods. The wave velocity in the cement paste is sensitive to w/c ratio, and increases with the progress of cement hydration reaction as well as the compressive strength. This was confirmed by the micro-morphology of the cement paste at various periods.