A Comparative Study of the Very Early Age Cement Hydration Monitoring Using Compressive and Shear Mode Smart Aggregates

The load-bearing capacity of concrete is highly influenced by the initial cement hydration process, especially in its very early age (0-48 h). Due to the rapid and intense chemical reactions between the cement and the water in the very early hydration process, it is still a challenge to monitor the cement hydration process in real time. In this paper, we investigated a stress wave-based active sensing method to monitor the cement hydration process using piezoceramic-based transducers, called smart aggregates. Using different types of the embedded piezoceramic patches, including d(33) and d(15) modes, smart aggregates can function as both the compressive and shear wave transmitters and receivers. In each mode of the smart aggregate, the active sensing approach that uses a pair of smart aggregates, one as a wave transmitter and the other one as a wave receiver, was employed. A comparative study was conducted to investigate the performance of monitoring the very early age cement hydration process by using compressive wave (P-wave) and shear wave (S-wave). A frequency domain analysis of the received signal was performed during the very early age cement hydration process. Experimental results reveal the differences of the received signal strength, valid monitoring period, and the effective frequency range by using both P-wave and S-wave.