Smart aggregates: multi-functional sensors for concrete structures—a tutorial and areview

Abstract

This paper summarizes the authors’ recent pioneering research work in piezoceramic-basedsmart aggregates and their innovative applications in concrete civil structures. The basicoperating principle of smart aggregates is first introduced. The proposed smart aggregate isformed by embedding a waterproof piezoelectric patch with lead wires into a smallconcrete block. The proposed smart aggregates are multi-functional and can performthree major tasks: early-age concrete strength monitoring, impact detection andstructural health monitoring. The proposed smart aggregates are embedded into thedesired location before the casting of the concrete structure. The concrete strengthdevelopment is monitored by observing the high frequency harmonic wave response ofthe smart aggregate. Impact on the concrete structure is detected by observingthe open-circuit voltage of the piezoceramic patch in the smart aggregate. Forstructural health monitoring purposes, a smart aggregate-based active sensingsystem is designed for the concrete structure. Wavelet packet analysis is used as asignal-processing tool to analyze the sensor signal. A damage index based onthe wavelet packet analysis is used to determine the structural health status. Tobetter describe the time-history and location information of damage, two types ofdamage index matrices are proposed: a sensor-history damage index matrix and anactuator–sensor damage index matrix. To demonstrate the multi-functionality ofthe proposed smart aggregates, different types of concrete structures have beenused as test objects, including concrete bridge bent-caps, concrete cylinders anda concrete frame. Experimental results have verified the effectiveness and themulti-functionality of the proposed smart aggregates. The multi-functional smartaggregates have the potential to be applied to the comprehensive monitoringof concrete structures from their earliest stages and throughout their lifetime.