Monitoring the curing process of in-situ concrete with piezoelectric-based techniques – A practical application

The stiffness and strength properties of freshly poured concrete develop over time as the concrete hardens due to curing. The monitoring of such properties therefore enables timely construction decisions such as formwork removal. Traditional point-in-time destructive tests can be cumbersome, while continuous non-destructive testing is desirable. Piezoelectric-based electromechanical impedance (EMI) and wave propagation (WP) techniques fall into the latter, and they have been verified for monitoring concrete properties during curing in the laboratory. This paper reports the first field application of the EMI and WP techniques for monitoring concrete curing, where smart aggregate (SA) sensors are embedded into concrete pour strips of a multi-storey residential building during construction. For comparison and verification purposes, destructive compression and non-destructive ultrasonic pulse velocity (UPV) tests were conducted. Results obtained from both EMI and WP techniques were consistent and repeatable. They were also comparable to the UPV result, and they showed a close correlation to the compressive strength tests. The current study has also revealed that the electrical signatures acquired from the EMI and WP techniques have a linear relationship. EMI-based and WP-based semi-analytical models (and their derivations) that can quantify the compressive strength and modulus of elasticity of concrete at various curing durations are also presented. This reported study ultimately demonstrates the applicability and practical application of the EMI and WP techniques for real-time measurements, bridging the gap between laboratory-based studies and field applications.