Fatigue Damage And Micro-Structure Evolution Mechanism Of High-Strength Concrete Under Low Cycle Compression After High Temperatures

High-strength concrete structures subjected to fire may also suffer from low cyclic loading caused by earthquakes,etc.When evaluating the performance and determining the reinforcement plan of a disaster-affected project,it is necessary to know mechanical property parameters of the material for structural analysis,including fatigue property parameters.However,the assessment methods for residual seismic capacity of concrete structures after fire are incomplete currently,and it is difficult to determine the fatigue property parameters of the material after high temperatures through non-destructive or micro-damage testing methods.The fundamental reason behind this engineering problem lies in the lack of scientific research on the relationship between low-cycle fatigue damage and micro-structure evolution mechanism of high-strength concrete after high temperatures.In view of this,a research method combining experimental and theoretical analysis was adopted in this paper to study the low-cycle fatigue damage and its microscopic evolution mechanism of high-strength concrete under compression after high temperatures.An electro-hydraulic servo fatigue tester was used to perform uniaxial low-cycle fatigue tests,and analyze low-cycle uniaxial compressive fatigue performance parameters of high-strength concrete test blocks after different high temperature history,including residual fatigue life,deformation modulus and residual strain.The relationship between temperature history,loading cycles and fatigue performance parameters was studied.The degradation law of low-cycle fatigue performance of concrete was explored.Ultrasonic detector,micro-hardness tester,and scanning electron microscope were used to measure the changes of ultrasonic parameters,micro-hardness,and micro-structure of the interface transition zone during cyclic loading,and reveal the dynamic evolution mechanism of micro-structure.The comprehensive damage variable based on macro and micro parameters was defined,and a comprehensive fatigue damage accumulation model for high-strength concrete after high temperatures was further established.The research results can provide theoretical basis for non-destructive or micro-damage detection and fatigue damage assessment of concrete structures after fire or other high temperature process.