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The piezoelectric-based electromechanical impedance (EMI) and wave propagation (WP) techniques have been widely used to monitor homogeneous and non-homogeneous materials in laboratory conditions. However, there have been limited studies investigating the use of these techniques for monitoring construction materials. This study therefore considers two commonly used construction materials, namely, structural adhesive (homogeneous) and concrete (non-homogeneous). Both of these materials develop stiffness and strength upon mixing and subsequent curing. Monitoring such properties is desirable to ensure timely decisions can be made, such as formwork removal and load application. The WP technique is a well-established and reliable monitoring technique that requires multiple lead zirconate titanate (PZT) transducers. It was previously proven to effectively monitor the curing process of adhesive and concrete materials. On the other hand, the EMI technique, which is more sensitive than the WP technique and requires only a single PZT transducer, has had limited application to adhesive and concrete. This thesis reports an investigation on the feasibility of the EMI technique for monitoring structural adhesive and in-situ concrete. The study is divided into three stages, namely (I) proof-of-technique experimental study for monitoring adhesive curing in laboratory conditions with the EMI technique (with verification via the WP technique), (II) analytical and numerical modelling studies of adhesive curing in laboratory conditions using the EMI and WP techniques, and (III) application of the EMI and WP techniques for monitoring in-situ concrete curing. In Stage I, the EMI technique was employed for monitoring adhesive curing in laboratory conditions. The WP technique was simultaneously employed to verify the EMI-acquired outcomes using the same set of PZT transducers. The measured results were acquired as electrical signatures, and were compared and correlated to tensile strength tests. In Stage II, analytical and numerical modelling studies were conducted to investigate the interaction between the PZT transducer and adhesive substrate. Semi-analytical and semi-numerical models were developed by simulating, verifying and correlating the electrical signatures with destructive tests. These resulting models can quantitatively determine the elastic modulus and tensile strength of structural adhesive at various curing durations. Following Stages I and II, the EMI and WP techniques were then employed to monitor in-situ concrete curing at a construction site subjected to external interferences. The measured results were comparable to ultrasonic pulse velocity (UPV) tests and showed a close relationship to compression tests. These promising results show the potential use of the EMI and WP techniques in practical applications. |
