Study On Critical Failure Characteristics Of Concrete With Initial Defects And Constitutive Model Of Uniaxial Compression Damage

Concrete is the main force of the construction industry.With the shortage of original resources and the requirement of sustainable development,the recycling of construction waste has entered a new stage,and recycled concrete is one of the main actors.Recycled concrete is more complex than ordinary concrete,and the amount of recycled concrete will bring inevitable initial defects.It is better to study the influence of initial defects on the damage evolution and instability of concrete by defining different degrees of initial defects with different replacement rates of recycled coarse aggregate.In order to develop the engineering application of recycled concrete better,the research method is also the most important.The research on the damage mechanism and instability characteristics of brittle materials should start from the inside of materials,and the nondestructive and real-time characteristics of acoustic emission technology are the core characteristics of this study.In this paper,the experiment of concrete prism with different replacement rate of recycled coarse aggregate is the main research objects.Based on the acoustic emission technology,the damage characteristics and failure characteristics of prisms under monotonous and cyclic compression are analyzed.In this paper,the critical characteristics of acoustic emission of recycled concrete with different initial defects are discussed,and the damage constitutive model of concrete considering the influence of replacement rate of recycled coarse aggregate is established by using the content of acoustic emission characteristics as damage variable.The main research contents are as follows:(1)The basic mechanical properties of concrete specimens with different replacement rate of recycled coarse aggregate and the lead breaking test of acoustic emission are tested to study the change trend of basic mechanical properties with different initial defects;the research shows that there is no definite relationship between the lead breaking parameters of acoustic emission and the initial defects of concrete;the attenuation curve of the amplitude of acoustic emission is drawn to prepare for the study of acoustic emission.(2)The monotonic compression test was carried out on concrete prisms with different replacement rate of recycled coarse aggregate.The accelerated release process of acoustic emission energy in the process of failure was fitted.The accelerated release degree of acoustic emission energy in the process of failure of concrete with different replacement rate of recycled coarse aggregate was judged by the change of parameters after fitting,and the critical failure characteristics of concrete specimens under compression were analyzed.(3)Based on acoustic emission technology,cyclic loading and unloading test is carried out.Combined with Kaiser effect theory,fractal theory and response ratio theory,the acoustic emission signal in the process of concrete failure is analyzed.The results show that the change of Felicity ratio,fractal dimension and response ratio Y can characterize the critical characteristics of concrete failure.(4)Based on the analysis of stress-strain curve of prism specimen under uniaxial compression,combined with the characteristics of stress-strain curve,the appropriate acoustic emission characteristic parameters are selected as damage variables,the regeneration parameters are introduced,the initial defect degree of concrete with different replacement rate of recycled coarse aggregate is considered,and the damage constitutive model is established by using Weibull statistical method and damage theory.It is proved that the model has high fitting degree and conforms to the damage rule of concrete with different replacement rate of recycled coarse aggregate.