Experimental Study On The Effect Of High Temperature On The Mechanical And Impermeability Of Basalt Polypropylene Fiber Reinforced UHPC

Ultra high performance concrete(UHPC)is one of the most innovative engineering materials in recent 30 years,with ultra-high strength and durability.With the development of science and technology and the continuous improvement of building function,modeling and environmental protection requirements,the demand for UHPC application is becoming more and more urgent.The research on the performance of UHPC has become very important.At present,the research on UHPC is mostly about its performance at room temperature,but there is relatively little research on its performance after high temperature.This paper takes UHPC mixed with basalt fiber and polypropylene fiber as the research object,and explores its high-temperature burst resistance and mechanical and impermeability after high temperature through experiments,so as to provide reference for engineering application.Firstly,the basic mechanical properties of UHPC with different content of basalt fiber and polypropylene fiber are tested.The test results show that the single content of basalt fiber can improve the compressive and flexural strength of UHPC,and the effect is the best when the volume content of fiber is 0.12%.The single addition of polypropylene fiber has a negative effect on the compressive strength of UHPC,while the flexural strength has a strong improvement.At room temperature,the mixing of two fibers can improve the strength of UHPC to a certain extent,but the effect is not very significant.The research results of high temperature burst and mechanical properties after high temperature show that the addition of polypropylene fiber can improve the burst resistance of UHPC,and the effect is the best when the volume content of basalt and polypropylene fiber is0.06% and 0.2% respectively.The compressive and flexural strength of UHPC increased first and then decreased with the increase of temperature,reaching the peak at 350 ℃ and 200 ℃respectively.The mechanical properties of UHPC mixed with basalt fiber and polypropylene fiber at high temperature are better than those of single fiber.The results of impermeability test show that high temperature and fiber have no significant effect on UHPC flux before 200 ℃.As the temperature rises to 300 ℃,the electric flux increases obviously,and the greater the content of polypropylene fiber,the greater the electric flux,but it is still at a very low level on the whole.The effect of fiber and high temperature on the capillary water absorption of UHPC surface is different from the electric flux.The higher the fiber content,the greater the water absorption of UHPC.The 9h water absorption of UHPC increased significantly with the increase of temperature without fiber and basalt fiber.The water absorption of UHPC decreased at 200 ℃ and increased significantly at 300 ℃.In UHPC mixed with fiber,polypropylene fiber has a great influence on its water absorption,which is similar to that of single polypropylene fiber,and basalt fiber has a relatively small influence on its water absorption.