Research On Low-cycle Compressive Fatigue Properties Of C60 Concrete Based On Microstructure Analysis After Exposure To High Temperatures

For engineering structures,such as the Television Cultural Centre,using high strength concrete materials,the most intractable problem encountered in the research process of structural assessment and reinforcement after fire is difficult to determine the temperature history and mechanical performance parameters of materials by nondestructive or micro-damage detection means,including the fatigue performance parameters.In view of the above engineering problems,this paper puts forward the scientific research on the relationship between the temperature history of high-strength concrete,the low-cycle compression fatigue damage and the microstructure evolution mechanism.The low-cycle compression fatigue test of C60 concrete after high temperature of 200,400,600,800℃ was carried out.Three microscopic detection methods,which are microhardness testing,mercury intrusion porosimetry and ultrasonic testing,were used to analyze microstructure evolution mechanism during fatigue damage of high-strength concrete at 0.8,0.85 and 0.9stress level respectively.By measuring parameters such as ultrasonic velocity,microhardness,most suitable pore size and pore size distribution,scientifically select reasonable key microscopic features and parameters based on grey theory,establish a fatigue damage model based on microstructure,and analysis the relationship between microscopic parameters and fatigue behaviors.The low-cycle compression fatigue cumulative damage model of high-strength concrete after high temperature is obtained.This model can not only qualitatively describe the microstructure characteristics of materials under the coupling of high temperature temperature history and low-cycle compression fatigue damage.but also accurately quantify the relationship between the microstructure parameters and the high temperature history and low-cycle compression fatigue damage.The research results are expected to benefit non-destructive testing,damage analysis and structural evaluation of concrete structures subjected to fire or other high temperature history,and even to determine reinforcement schemes.