Research On Microstructural Evolutionary Mechanism During Compressive Fatigue Process Of High-Strength Concrete After High Temperature

High-strength concrete(HSC)structures might suffer from high temperature processes caused by fire or other factors.HSC structures subjected to high temperature may suffer from earthquakes or other cyclic loads.It can be seen that HSC may suffer from comprehensive conditions of high temperature and fatigue,which will cause damage to structures.The damage is not only at the macroscopic level but also at the microstructure and microstructural damage is the root cause of macroscopic damage.Therefore,it is necessary to study the changes in the microstructure during compression fatigue process of HSC after high temperature.In this paper,the microstructure during uniaxial compression fatigue process of HSC after high temperature was tested by using ultrasonic,micro-hardness test,mercury intrusion porosimetry(MIP),scanning electron microscopy(SEM)and X ray diffraction(XRD).By measuring the parameters of sonic time,microhardness and pore size distribution and the development and change of the cement paste,crystalline phase and microcracks,the variation of microstructure during fatigue process was respectively compared and analyzed from the qualitative and quantitative aspects.The correlation between the microstructural parameters and the number of cycles during fatigue process was analyzed.Based on the good correlation,the relationship models between fatigue damage and the microstructural parameters were established.Combined with the existing research,the relationship models of temperature history,fatigue damage and microstructural parameters were established.Both the dynamic evolution process and damage mechanism of microstructure of HSC under the condition of high temperature and fatigue were further revealed.This work form a scientific method to study the relationship between temperature history,fatigue damage and microstructure of concrete,which could be used as a reference for nondestructive testing,fatigue damage analysis and structure assessment of concrete suffering from fire or other high temperature process.