Study On Mechanical Properties And Microstructure Of Steel Fiber Manufactured Sand Concrete After High Temperature

In the field of civil engineering,concrete,as an essential building material for infrastructure construction,is widely used in various engineering construction.With the increasing demand for concrete,the natural river sand as concrete aggregate has been nearly exhausted;As a new environmental protection building material that can replace natural river sand,machine-made sand has a good application prospect in both economic and environmental aspects;However,with the wide use of manufactured sand,the possibility of fire in buildings with manufactured sand concrete as the main building material is also increasing year by year.How to improve the high temperature resistance of manufactured sand concrete buildings is a hot research field nowadays,and the fire resistance of structures is often directly related to the composition of concrete structures.A large number of studies have found that,Adding fiber into mortar can improve the fire resistance of concrete structure.In order to study the change law of mechanical properties of steel fiber manufactured sand concrete after high temperature,a series of experimental studies were carried out with the volume ratio of steel fiber and the fire temperature as variables.The main research contents and results are as follows:(1)The phenomenon of high temperature test,mass loss rate,compressive and splitting tensile strength of 192 steel fiber reinforced concrete cube specimens were studied after batch high temperature test.The results show that:(1)The apparent color of steel fiber reinforced sand concrete changes from dark to light at different temperatures,and finally turns to gray at 800℃;(2)The mass loss rate of steel fiber reinforced sand concrete specimens increases with increasing temperature;(3)The addition of steel fiber has a significant effect on improving the strength value of machine-made sand concrete at both room temperature and high temperature.(4)The compressive and splitting tensile strength of concrete specimens generally decreases with the increase of fire temperature.Based on the test results,a deterioration model of strength of steel fiber reinforced sand concrete specimens subjected to high temperature was established.(2)The influence of fire temperature on the constitutive relationship of 60 prismatic specimens subjected to high temperature was studied by uniaxial compression test;The results show that the failure modes of mechanical sand concrete specimens are different with different steel fiber content.When the volume ratio of steel fiber is 1.0%,the peak stress reaches the maximum value.The peak strain increases gradually when the volume ratio of steel fiber increases from 0% to 1.5%.Based on the experimental data,zhenhai segmented model and Sargin model were used for fitting analysis,and it was found that Sargin model had better fitting degree.(3)to select the right amount of compression of concrete specimen damaged small block,electron microscope scanning and X ray diffraction experiment to study the temperature on the micro structure change of the sand mechanism of steel fiber concrete,the test results show that: under normal temperature condition,sand mechanism of steel fiber concrete hydration degree of cement mortar,tightly bound between hydration products;As the temperature increases,the number of pores and cracks in the matrix increases.When the temperature reaches 700℃,the number of pores in the matrix increases,and the structure becomes loose,which shows that the macroscopic mechanical properties decrease rapidly.