Research On Compressive Strength And Microstructure Of High Strength Concrete With Polypropylene Fiber Subjected To High Temperature

In recent years, China, as a developing country, has been developing rapidly. Because of large population and small per capita area, the land for construction is becoming less and less. Therefore, many high-rise and underground buildings become popular. Because of its advantages such as high strength, high capacity, high durability, high strength concrete has been widely used nowadays. However, high strength concrete is always dense, it will burst when suffering from fire disaster.When the environment temperatures is high, the strength indicators of concrete will decrease significantly, resulting in the decrease of carrying capacity of components, which will seriously affect the safety and economy. Research showed it had significant effects on burst when mixed with appropriate polypropylene fiber in high strength concrete. So it is of great significance researching various performance of high strength concrete with polypropylene fiber (PPHSC) concrete after subjected to fire.Funded by the National Natural Science Foundation (51278325) and the Natural Science Foundation of Shanxi Province (2011011024-2), in this paper, corresponding high-temperature experiments of C60 PPHSC specimens was designed, and the compressive strength test was conducted. Analyzing the trend of mechanical properties and micro-structure of HSC after exposed to different high temperatures. At the same time, the X-ray test and CT scan test had been done to analyze the internal microstructure from the perspective of qualitative and quantitative. Infrared thermal image test and mercury test had been done. Analyzing the changes of pore structure of concrete after exposed to high temperature. Using fractal theory to calculate and compare fractal dimension of concrete after high temperature. In addition, variation of concrete porosity, average pore size, pore surface area, fractal dimension, compressive strength at different high temperatures had been analyzed.This article carried out the research from following points:(1) Studying the phenomenon of high-temperature experiments, mass loss, compressive mechanical properties of C60 PPHSC at room temperature, 300℃-800℃ (temperature intervals is 100℃), analyzing the variation of mass loss and compressive strength with high temperature.(2) Studying the CT images of C60 PPHSC from the perspective of qualitative and quantitative, and describing the internal microstructure of concrete at different high temperatures. Analyzing the defect rate of each layer from the 300 layer to the 1200 layer (layer intervals is 100 layers) at different temperature based on the Image-Pro Plus software, and analyzing the relationship between defect rate, compressive strength and mass loss.(3) Describing the internal pore of C60 PPHSC, and guided by the.fractal theory and fractal characteristics of concrete. Studying the fractal dimension of pore structure using the fractal theory after exposed to room temperature,300℃, 500℃ and 700℃. Analyzing the change of concret eporosity, average pore size, pore surface area, fractal dimension, compressive strength at different high temperatures.(4) Based on the principle of infrared thermal imaging,detecting the infrared thermal imaging of C60 PPHSC under 300℃-800℃ (temperature interval is 100℃).Establishing the regression equation between infrared temperature average temperature rise, and analyzing the damage.of concrete after fire.