Ubiquitous Piezoelectric Sensor Network (UPSN)-Based Concrete Curing Monitoring for u-Construction

Recently, there has been increasing demand for high-rise buildings or wide-span bridges. These structures are constructed with a mount of mass concrete. However, the concrete might be susceptible to brittle fracture if the curing process is inadequate. Therefore, to prevent this drawback, it is essential to predict the strength development of concrete during the curing process. In addition, real-time monitoring of the curing strength is important for reducing the construction time and cost because it can determine the appropriate curing time to achieve sufficient strength to progress to the next phase safely. The in-situ strength of concrete structures can be determined with a high precision by performing the strength testing and/or material analysis on core samples removed from the structure (Irie et al., 2008). However, this method might destroy the concrete structure. Therefore, a range of methods based on the thermal, acoustical, electrical, magnetic, optical, radiographic, and mechanical properties of the test materials have been developed to monitor the strength development without damaging the host structures (ACI Committee 228, 2003; Lamind and Pielert, 2006; Metha and Monterio, 2005). These methods typically measure certain properties of concrete from which the strength and/or elastic constants can be estimated. Among these techniques, several methods using a Schmidt hammer or an integrated temperature have been normally used. However, these are unsuitable for use at construction sites because they do not allow real-time monitoring of the curing process of concrete structures at inaccessible places. The recent advent of smart materials, particularly piezoelectric materials, can provide a solution for the real-time monitoring for strength development. Electromechanical impedance techniques that employ piezoelectric materials have emerged as a potential tool for the implementation of a built-in monitoring system for civil infrastructures (Park G. et al., 2000, 2003; Park S. et al. 2005, 2006, 2011). This technique utilizes high-frequency structural excitation, which is typically > 20 kHz from surface-bonded PZT (Lead-ZirconateTitanate) patches, to sensitively monitor the changes in the mechanical impedance of the test structures. Furthermore, the recent advances in online monitoring, including actuation and sensing, on-board computing, and radio-frequency (RF) telemetry, have improved the