Vapor Pressure And SEM Microstructure Analysis Of C60 High Performance Concrete At Elevated Temperature

HPC has better performance than conventional concrete,so it is easier to split at high temperature(fire)because of its dense structure and low permeability.The vapor pressure theory explains the cause of the concrete splitting.Due to the complexity of the vapor pressure test,the test data are scarcity in the reference.Therefore it is significant to explore vapor pressure and micro structure changes of HPC at high temperature,to provide experimental basis for the vapor pressure theory and prevent the HPC cracking.Based on the National Natural Science Foundation of China(51478290),the C60 HPC specimens without fiber and polypropylene fiber were studied in this research.The main research is as follows:1.Through the test of splitting tensile strength of HPC at different temperature,the relationship between splitting tensile strength and splitting tensile strength loss rate and temperature was analyzed.600 ? and 500 ? are threshold temperature for the non-doped fiber and fiber-doped specimen,splitting tensile strength loss rate was 57.88% and 63.71%,respectively.2.The variation law of the vapor pressure versus time and the temperature at different depths of the none reinforced concrete small slab(none fiber and 0.1%,0.2%,0.3% polypropylene fiber)and reinforced concrete small slab(none fiber and 0.2% polypropylene fiber)under the high temperature resistance furnace were analyzed.It is shown that the polypropylene fiber can significantly reduce the vapor pressure and 0.2% is the optimum content of polypropylene fiber.3.The vapor pressure of high performance concrete large slab(none fiber and 0.2% polypropylene fiber)under fire and load coupling at different internal measuring points is studied with the change of time and temperature of the measuring point.It is shown that the incorporation of polypropylene fibers under the combination of open flame and load also suppresses the internal vapor pressure of the concrete and the value is larger at 50 mm point.4.The comparison of vapor pressure at the same measuring point under the high temperature resistance furnace,fire and load coupling shows that the vapor pressure increases with the coupling of fire and load,and the inhibition effect of polypropylene fiber on the vapor pressure is reduced.Based on the theory of thin-walled ball,the contact between vapor pressure and splitting tensile strength was established.The possible burst position of the fiber specimen was calculated,and the fact that the polypropylene fiber specimen was not exploded was verified.5.The effect of temperature on the microstructure of high performance concrete was discussed.The microscopic images of the channels of the slurry,the interface transition zone,the pore structure and the polypropylene fiber after high temperature were observed by scanning electron microscopy(SEM).The qualitative analysis was carried out on the without fiber and 0.2% polypropylene fiber specimen.The results show that the high-performance concrete at room temperature is more compact at 155?,and degrades at 300? and 500?.The quantitative analysis of the porosity of high-performance concrete decreases first and then increases using the IPP software.The results show that the porosity of the polypropylene fiber specimen is lower than that of the none fiber specimen after 300 ?,and the curve of porosity and the vapor pressure at different temperatures were fitted.