Compressive Behavior Of Steel Fiber Reinforced Concrete With Fire Insulation After Elevated Temperatures

With the rapid development of social economy and the accelerating pace of urbanization, the city is full of skyscrapers and suffers from excessive population. The building damage and casualties caused by fire accidents often occurs. In order to prevent a fire hazard in the actual project, people often painted fire-resistant coating on the surface layer of concrete of public buildings & tunnels buildings. The high temperature mechanical properties of the concrete covered with a fire-resistant coating are different with that of the concrete without fire-resistant coating. This paper researched the high temperature mechanical properties of steel fiber concrete covered with a certain thickness of fire-resistant coating.Firstly, the influence of the target temperature, the thickness of fire-resistant coating and the content of steel fiber on the mechanical properties of steel fiber reinforced concrete after high temperature is studied. Then, the temperature stress and temperature field of concrete coated with fire resistant paint is simulated in the processes of heating, thermostats and cooling by finite element simulation. Finally, the microstructure of steel fiber reinforced concrete after high temperature are observed by scanning electron microscope (SEM) and probes high temperature damage of the internal structure and the variation with temperature of the interface region between steel fiber reinforced concrete and concrete matrix. The main findings are as follows:(1) At high temperatures, fire insulation can well isolate fiber reinforced concrete from heating by reducing the temperature of the concrete surface, thereby delaying and mitigating fire damage of the concrete structures. After a certain temperature conditioning, it can significantly reduce the risk of falling on the mechanical properties (compressive strength, splitting tensile strength, flexural strength) of the steel fiber reinforced concrete coated with fire insulation, and increases the value of the residual mechanical strength.(2) At a certain high temperature, with the thickness of fire insulation increasing, the compressive strength, splitting tensile strength and flexural strength of steel fiber reinforced concrete shows an increasing trend, and the impact of the fire insulation is the most significant at 800? high temperature conditions. With the thickness of fire insulation increasing, this positive effect begins to weaken, and the increase of the mechanical properties of steel fiber reinforced concrete became slow.(3) When the surface of steel fiber reinforced concrete is covering with a certain thickness of the fire-resistant coating, the reduction on mechanical properties of concrete in high temperature decreases with the increase of steel fiber content. When the target temperature conditions is consistent, the more the content of steel fiber is, the greater the mechanical strength of the concrete.(4) At a constant temperature stage, with the increase in holding time, the temperature difference between the centers of the specimen and the specimen surface decreases. In addition, the stress of constant temperature difference inside and outside of the concrete reduces. In the natural cool-down phase, the peak stress increases at first and then decreases, hence, it can be concluded that there is a certain degree of high temperature damage during the cooling stage. With the increase of the thickness of the coating and the increase of the content of steel fiber, the temperature difference between the surface and the center of the specimen decreases.(5) Increasing as the temperature, the internal structure of concrete gradually begins to deteriorate and hydration products gradually decompose. Compared with ordinary concrete at 800?, the extent of damage of the steel fiber concrete matrix covering by fire retardant coating reduces and cement stone shows small degree of deterioration. As the temperature increases, the cement stone at the interfacial region between steel fiber and cement concrete matrix gradually becomes powdery, so the adhesion between the concrete and steel fiber decreases. However, when the target temperature is the same, the degree of injury of cement stone at interface region on the concrete surface with fire retardant paint greatly reduced compared with concrete without fire insulation and the adhesion between the concrete and steel fiber is better.