Experimental Research On The Damage And The Nonlinear Creep Interaction Of Concrete

In this paper,considering the concrete structure in the casting molding defects inevitably exist in the process of micro first injury,studied under uniaxial compressive load inside the concrete damage evolution rule,and then from the damage of concrete and the interaction of nonlinear creep,initial damage under sustained load is studied on the influence of nonlinear creep and nonlinear creep damage in the process of evolution.It provides a theoretical basis for predicting the damage evolution and creep development of concrete structures in practical engineering.The main research contents and results of this paper are as follows:(1)This paper discusses the application of impact echo method in concrete damage detection and the feasibility of impact echo method and acoustic emission in detecting internal damage changes of concrete under continuous load.The results show that the increase of the number of main peaks and the increase of the period of reflection signals on the bottom boundary surface can be used as the basis to identify the damage.The elastic wave velocity has a good correlation with the degree of damage inside concrete.There is a linear correlation between the decrease of elastic wave velocity and the deterioration of compressive strength.Under sustained load,because the damage of concrete internal development is small,in the case of the Dutch time is shorter,the cumulative development of damage value is less than the error values of the shock echo method,in comparison,the change of the acoustic emission parameters change in the unloading process for a better regularity,therefore,under sustained load damage appropriate USES acoustic emission testing.(2)The effects of initial damage on mechanical properties of concrete specimens,evolution of internal damage and Felicity effect of concrete during uniaxial compression were studied.The results show that the mechanical properties such as compressive strength and elastic modulus are deteriorated by the addition of air entraining agent,that is,initial damage is introduced to a certain extent to concrete specimens,and the greater the initial damage is,the longer the initial damage is,the greater the internal damage of concrete in the stage of compression and elastic change;the damage of concrete specimens mainly occurs in plasticity.Deformation and post-peak failure are two stages.The initial damage of concrete has a great influence on the stress upper limit level of Felicity ratio and Kaiser effect.The larger the initial damage of concrete,the smaller the Felicity ratio and the lower the stress upper limit level of Kaiser effect under the same load grade.(3)The concrete specimens with different degrees of initial damage were subjected to a30-day continuous load.The creep strain and acoustic emission parameters of concrete during loading were collected.The influence of initial damage on the non-linear creep of concrete and the development law of damage in the process of non-linear creep were studied by analyzing the changes of acoustic emission parameters.The results show that the concrete undergoes two stages: attenuation creep and steady creep during the 30-day load holding period.Initial damage promoted creep,and the higher the load holding level,the stronger the effect.The greater the initial damage is,the more severe the damage will be in the process of load holding.In the process of load holding,the counting rate,energy rate and creep rate of ae ringing have similar changing rules.They all go through a rapid changing stage and then gradually become stable.In the attenuation creep stage,higher strain energy is released.In the stable creep stage,the strain energy presents a process of aggregation and release,which reflects that the internal failure of concrete is periodic.