Study On Acoustic Emission Characteristics Of Concrete With Drop Of High Temperature Under Uniaxial Compression

In recent years,the problem of high ground temperature has attracted more and more scholars’ attention.Some underground caves and tunnels with high rock temperature will cause a sudden drop in high temperature of the lining concrete during initial water flow,and then form a temperature gradient state.The temperature stress caused by this huge temperature gradient has a great impact on the mechanical properties of the concrete lining structure,which has a certain effect on the stability of the project.It is of great practical significance to study the mechanical behavior of concrete bodies under temperature gradients.Acoustic emission is one of the non-destructive testing methods.The use of it to monitor concrete damage and stress has been recognized by many scholars.Acoustic emission parameters can provide certain theoretical criteria for concrete instability.Based on this engineering background,in this paper,the model of temperature drop in concrete under different high temperature conditions is established.The paper mainly studied the heat conduction law,mechanical property changes and failure modes of concrete under different temperature gradients are mainly studied.Then the basic parameters of acoustic emission and the size of acoustic emission damage are used to reflect the degree of concrete damage.The frequency spectrum of the concrete under the temperature gradient is analyzed,which provides a theoretical basis for the stability of the concrete under the temperature gradient of the actual project.The main research contents of this article are as follows:(1)The heat conduction law of the concrete is obtained by monitoring the formation process of the temperature gradient of the concrete.Through uniaxial compression tests of concrete under different temperature gradients,the mechanical properties and crack propagation laws of concrete are summarized.The results show that the greater the temperature gradient,the more severe the concrete degradation.(2)Through the analysis of acoustic emission impact count and energy count are closely related to micro-crack damage of concrete.The sudden increase of acoustic emission signals is a predictive feature of concrete damage.The damage of variable and temperature gradient compensation coefficient are introduced to establish the damage constitutive equation of concrete under temperature gradient.The damage stress variable to establish the theoretical stress-strain curve of concrete is consistent with the actual stress-strain curve.The damage factor can represent the amount of concrete damage.(3)It is making program the b-value algorithm for acoustic emission using MATLAB.The results show that the increase of b value can be used as a sign of small-scale crack growth of concrete,and the sudden decrease of b value is a prediction of the critical failure point of concrete.As the temperature gradient increases,the maximum value of b value increases.(4)The high frequency signal of acoustic emission frequency can be used as a sign of the deterioration of concrete.The high frequency signal is positively correlated with the small-scale expansion of cracks.As the temperature gradient increases,the proportion of high-frequency signals increases,and the corresponding dominant frequencies at low frequencies tend to decrease.As the temperature gradient increases,the main frequency ratio and amplitude ratio of concrete acoustic emission tend to decrease,and the frequency component types of the spectrum show a normalized trend.