Study On Acoustic Emission Characteristics And Assessment Of Recycled Concrete Compression Damage

As a new type of material,recycled concrete materials contribute a lot to environmental protection and resource recycling.However,its research has been slow due to the single progress of means and methods.As a new technology,acoustic emission technology has achieved good results in the application of ordinary concrete performance research,and it is an important means of research breakthrough in recycled concrete materials.However,the difference in the intrinsic composition of recycled concrete materials and ordinary concrete leads to different acoustic emission characteristics.There is almost no basic research on the acoustic emission of recycled concrete,which can’t provide enough theoretical support for applying acoustic emission technology to recycled concrete.Based on this,the key parameters of acoustic emission of recycled concrete materials under different design factors are taken as the research object.At the same time,the acoustic emission Kaiser effect under cyclic loading and unloading is carried out.Finally,the evaluation method of acoustic emission damage of recycled concrete structures under stress is proposed.The main research contents and achievements are as follows:The compressive failure test of recycled concrete with different loading rate,aggregate particle size and water-cement ratio was designed,and its mechanical properties and acoustic emission signals were collected simultaneously.Combined with the macroscopic performance and stress-strain curve,the compression of the recycled concrete is staged,and the cumulative analysis method of the acoustic emission stage is proposed.The basic characteristics and internal causes are studied by this method.The results show that: Compared with ordinary concrete,recycled concrete has more initial acoustic emission signals during loading;The loading rate increases,the acoustic emission signal increases due to the initial loading,but the pre-loading AE signal and mid-loading AE signal decreases;The increase of the diameter will cause the mid-loading AE signal increases;The water-cement ratio increases makes the increase of pre-loading AE signal,and it also leads to the reduction of mid-loading AE signal.The cumulative analysis method of the acoustic emission stage is effective for the degree and pattern of AE analysis.The acoustic emission law under cyclic loading and unloading is explored.It is found that the acoustic emission of recycled concrete material has a certain reversibility.Based on the experimental data,the Felicity’s ratio of acoustic emission is studied.The effective stress range of the recycled concrete Kaiser effect is 0% to the 86% peak stress.Under different factors,because the lower limit of material stress level depends on its own factors and the upper limit of stress level depends on the failure mechanism,only the upper limit of stress will change regularly.And the difference between the effective stress range and ordinary concrete was analyzed: the internal damage of the recycled aggregate is more,and the strength of the joint surface of the new mortar is greater,which together cause the difference of the damage process under the same stress level.This affects the irreversibility of acoustic emissions.The study of acoustic emission characteristics of regenerated concrete and its Kaiser effect provides a basis for damage assessment.To establish a damage assessment system,the acoustic emission parameter analysis method is used and the event,ringing and energy are used as research objects,based on the theory of acoustic emission rate process and The Dai Labuz model proposed a fourth-order polynomial model of acoustic emission cumulant-stress level of recycled concrete materials.The acoustic emission probability density function and damage model were obtained by fitting the experimental data.The model shows that the acoustic emission probability density of recycled concrete materials is relatively low at low level and decreases with stress.When the stress level is about 0.7,it bottoms out and rebounds rapidly until the peak stress,and the damage factor also shows a corresponding change.Based on the definition of material damage factor,the system summarizes the acoustic emission detection process of recycled concrete compression structure.This method can better evaluate structural damage and measure the history of structural stress.