Research On Concrete Carbonation Depth Identification Based On Piezoelectric Ceramics

In recent years,scholars have made continuous progress in the research of piezoelectric ceramic sensors,which has attracted attention and achieved good results in structural health monitoring and damage assessment of concrete structures.The existence of carbonation of concrete greatly shortens the service life of concrete structures.In order to identify the degree of carbonation of concrete,some destructive methods are often used.The limitations of destructive detection methods make non-destructive testing technology(NDT)evaluate the degree of carbonation of concrete or determine the depth of carbonation of concrete.It is of great significance.Based on the piezoelectric ceramic sensor,this paper designs an active monitoring system and identifies the carbonization of concrete structures:(1)Three kinds of concrete test blocks with different mix ratios of 0.37,0.45 and 0.53 and a size of 100 mm×100 mm×100 mm were designed.After the concrete test blocks were naturally cured in the curing room for 28 days,they were placed in the concrete accelerated carbonation box for accelerated carbonation for 3 days,7 days,14 days and 28 days respectively.The material properties such as density and porosity of concrete were measured.The detection system based on piezoelectric ceramics was used to measure and record the signals of excitation signals passing through each specimen with different mix ratios and different carbonation degrees,and each signal was analyzed at the same time.The carbonization depth was measured by phenolphthalein indicator method.The carbonization depth of specimens with different proportions and different carbonization degrees was analyzed.The microstructure of concrete before and after carbonization was observed,and the influence of carbonization on the microstructure of concrete was analyzed.The results show that carbonization has a great influence on the microstructure of concrete.The signal characteristics of the signals collected by the detection system based on piezoelectric ceramics have obvious changes with the increase of concrete carbonization time.(2)The time-frequency curves of the stress wave signals propagating in concrete with different water-cement ratios and different carbonation degrees detected by the detection system based on piezoelectric ceramics were drawn.By changing the frequency and type of the incident signal,the maximum time-domain amplitude,the maximum frequency-domain amplitude and the wavelet packet energy value of the received signal were calculated.The variation of the signal eigenvalues of the specimens with different mix ratios collected by the piezoelectric ceramics with the carbonation depth was analyzed.The experimental data are analyzed,the damage index is defined,and different types of functions are used to fit the damage index with the carbonation degree of concrete,and the fitting accuracy is compared.The results show that for the same test block,the amplitude of the received signal decreases with the increase of the incident signal frequency.The signal amplitude and wavelet packet energy increase first and then decrease with the increase of concrete carbonization time and are positively correlated with the density of concrete and negatively correlated with the porosity of concrete.The relative energy value RE of concrete with different mix ratios has unity with the change of carbonization depth.When the carbonization degree of concrete test block and RE value are fitted by cubic function,the error is the smallest and the accuracy is the highest.(3)The finite element software ABAQUS was used to establish the electromechanical coupling model of piezoelectric ceramics and concrete before and after carbonization.By studying the propagation process of stress wave in concrete,the mechanism of concrete carbonization identified by active monitoring method based on piezoelectric ceramics was analyzed.The finite element calculation results of the established electromechanical physical field coupling model are compared with the experimental results to verify the effectiveness of the established model for the identification of concrete carbonation based on piezoelectric ceramics.The results show that in concrete,with the excitation source as the center,the longitudinal and transverse waves propagate diffusely around,while the Rayleigh wave propagates rollingly from the excitation source to both ends on the surface of the medium.In the finite element model,the porosity is negatively correlated with the signal amplitude of the stress wave,which is in good agreement with the experimental results,which verifies the validity and reliability of the established model for the identification of concrete carbonation based on piezoelectric ceramics.In summary,it is feasible to apply the piezoelectric ceramic carbonization identification system established based on the active monitoring technology of piezoelectric ceramics to the carbonization identification of concrete.Based on this method,the carbonization status and carbonization degree of concrete structures can be effectively detected.