Concrete early-age strength monitoring using embedded piezoelectric transducers

Abstract

At early ages of concrete structures, strength monitoring is important to determine thestructures’ readiness for service. Piezoelectric-based strength monitoring methods providean innovative experimental approach to conduct concrete strength monitoring at early ages.In this paper, piezoelectric transducers in the form of ‘smart aggregates’ are embedded intothe concrete specimen during casting. Piezoceramic materials can be used as actuators togenerate high frequency vibrating waves, which propagate within concrete structures;meanwhile, they can also be used as sensors to detect the waves. The smart aggregate isa one cubic inch, pre-cast concrete block with a wired, embedded PZT (leadzirconate titanate, a type of piezoceramic) patch. The strength development ofconcrete structures is monitored by observing the development of harmonic responseamplitude from the embedded piezoelectric sensor at early ages. From experimentalresults, the amplitude of the harmonic response decreases with increasing concretestrength. The concrete strength increases at a fast rate during the first few daysand at a decreasing rate after the first week. Concordantly, the amplitude of theharmonic response from the piezoelectric sensor drops rapidly for the first week andcontinues to drop slowly as hydration proceeds, matching the development of theconcrete strength at early ages. Concrete is heterogeneous and anisotropic, whichmakes it difficult to analyze mathematically. Fuzzy logic has the advantage ofconducting analysis without requiring a mathematical model. In this paper, a fuzzylogic system is trained to correlate the harmonic amplitude with the concretestrength based on the experimental data. The experimental results show that theconcrete strength estimated by the trained fuzzy correlation system matches theexperimental strength data. The proposed piezoelectric-based monitoring method has thepotential to be applied to strength monitoring of concrete structures at early ages.