An electromechanical impedance measurement-based solution for monitoring fresh concrete maturity

This paper proposes an electromechanical impedance measurement (EIM)-based solution for monitoring concrete maturity that refers to concrete strength development at the early stage. A smart aggregate (SMA) that consists of a waterproofed piezoelectric patch is developed. The working principle is explained based on the impedance theory of an electromechanically coupled system. A finite element (FE) model of the EIM-SMA unit is established. The stiffness of the applied spring foundation is varied to emulate the concrete hardening process. The simulation results reveal that a peak located between 60 and 70 kHz in the impedance plot could be used as an indication to reflect the stiffness variation of the spring foundation. A 3D-printed mold is designed for rapid production of the EIM-SMA units. In the experiment, two sample EIM-SMA units are used to monitor fresh concrete maturity in the first 6 h after casting. The results of the two sample EIM-SMA units agreed well. The experimental results matched the simulation prediction. Compared to a bar-dropping test that is widely adopted at construction sites, the impedance evolution of an EIM-SMA unit is much smoother and has better monotonicity. In general, the proposed method has been proven to be a reliable solution to monitor the maturity development of concrete.