| As an indispensable structural material in modern engineering construction,concrete is affected by construction technology,curing conditions,environmental temperature and humidity during pouring and coagulation molding.As an indispensable structural material in modern engineering buildings,concrete is affected by construction technology,curing conditions,environmental temperature and humidity during the process of pouring and setting,and some initial imperfections such as pores and micro-cracks will produce.These initial imperfections are external to the load.Under the influence of factors,it will further develop and cross,which will affect the macroscopic mechanical properties and failure modes of concrete.Engineering practice shows that the instability failure of concrete structures is closely related to the initiation,expansion,coalescence and penetration of initial imperfection cracks.Therefore,it is of great significance to carry out research on the deformation characteristics and failure modes of concrete considering the influence of initial imperfections.In this paper,uniaxial compression tests are carried out on concrete specimens with initial imperfections,and their deformation characteristics and failure modes are studied in combination with acoustic emission technology and high-speed photography.The main research contents and conclusions are as follows:(1)Experimental design of concrete failure considering the effects of initial imperfections.According to the purpose of the test,the raw materials and their proportions of the test pieces were determined.The mica sheets with a thickness of0.15 mm were used to simulate the internal initial imperfection of different sizes and inclinations,and the overall test arrangement of test loading and control,acoustic emission,high-speed photography equipment and the test plan was determined.(2)Study on the deformation characteristics of concrete considering the effects of initial imperfections.Through the uniaxial compression test of concrete specimens with internal initial imperfection,the effects of initial internal imperfection of concrete with different sizes and different inclination angles on the strength and deformation characteristics of the specimens were studied.The results show that the peak stress of concrete specimens with internal initial imperfection is lower than that of the complete specimens,and it increases with the increase of the inclination angle of the imperfection,and then increases the "V" shape.When the inclination angle is 45 °,the peak value The tendency is minimal and the tendency to decrease as the size increases is more pronounced.At 90°,the peak stress is the largest;compared with the stress-strain curve of the complete specimen,the loading section of the specimen containing the imperfection exhibits a certain hardening tendency,the unloading section is more gradual,but the residual strength is basically the same,and the more obvious this trend when the inclination angle is closer to 45°.when the imperfection size is less than 30×30mm,it has little effect on the mechanical properties of the test piece.(3)Study on the failure modes of concrete considering the effects of initial imperfections.Real-time dynamic detection of imperfectionive concrete specimens was carried out by using acoustic emission technology and high-speed camera technology.The parameters such as accumulated AE events and AE energy values were used to describe and analyze the failure process of concrete specimens with imperfection.The results show that the failure process of concrete specimens with internal initial imperfection is divided into four stages: crack initiation,expansion,coalescence and penetration failure.The failure mode of the specimen with the initial imperfection inclination angle of 0° and 90° is similar to that of the complete specimen,mainly due to tensile failure.The specimens with inclination angles of 30°,45° and 60° are mainly damaged by shear along the initial imperfection. |
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