The Early-age Strength And Damage Monitoring Of The Recycled Aggregate Concrete Using The Piezoelectric EMI Method

With the city urbanization rapidly progressing,numerous reinforced concrete buildings have to be dismantled,which yields a great deal of waste concrete and pollutes the environment.On the other hand,a huge amount of concrete for construction is consumed every year,so the mining of stones leads to the disappearance of many mountains,destroying vegetation and biodiversity.For solving these problems,some scholars propose to crush the waste concrete into recycled coarse aggregate(RCA)to further produce recycled aggregate concrete(RAC).This environment-friendly technology has attracted both the research and engineering community,as well as the government.However,due to the flaw of RCA,the RAC is more prone to crack and lack of adequate strength,which will turn into a safety hazard.This paper focuses on the early-age strength and damage monitoring of the RAC utilizing self-made piezoelectric transducers by electromechanical impedance(EMI)method,with emphasis laid on investigating the impact of the recycled coarse aggregate replacement ratio.The main contents are as follows:(1)RAC specimens with five different RCA replacement ratios were cast and conducted both the compressive test and the EMI monitoring test utilizing the self-made embedded piezoelectric smart aggregate(SA)transducers at five different ages.According to the results,the early-age strength evaluating model of RAC considering the RCA replacement ratio and the EMI theoretical model of SA transducer were proposed,as well as the linear correlation of early-age strength and the increment rate of the conductance resonant frequency(CRF).(2)The crack depth development test and the EMI monitoring test were carried out on the RAC specimens afterwards.The results show that the embedded SA transducer can monitor the crack depth development more effectively than the externally bonded piezoelectric patch transducer,and the statistic Correlation Coefficient Deviation(CCD)index for crack depth evaluation has higher accuracy.(3)The loading damage test and the EMI monitoring test were carried out on the RAC specimens as well.The results show that the damage of RAC occurs at plastic stage,when the degradation percentage of secant modulus and CRF has a high linear correlation.In addition,the greater the RCA replacement ratio,the greater the decrease rate of the secant modulus and CRF at the end of the plastic stage of RAC compared to the elastic stage.