Study On Mechanical Properties Of Recycled Fiber Reinforced Concrete Beams

With the continuous development of the construction industry,more and more waste concrete and other construction wastes are produced.These construction wastes not only affect the living environment of human beings,but also cause great environmental pollution.The reuse of waste concrete can improve the environment.The research and application of recycled concrete mechanical properties can not only reduce the impact of construction waste on the environment,but also solve the contradiction between supply and demand of natural aggregate to a certain extent.Due to the defects of recycled concrete,its application scope is limited.In order to improve the performance of recycled concrete,various kinds of modified materials are added to recycled concrete,including fiber materials.The main work of this paper is as follows:The mechanical properties of recycled fiber reinforced concrete beams were studied by using 50%recycled aggregate to fix the broken waste concrete aggregate,including residue and powder.In the experiment,two kinds of fiber materials,polypropylene fiber and steel fiber,were selected to make recycled concrete beams with polypropylene fiber,steel fiber recycled concrete beams and recycled concrete beams without any fiber.The effects of polypropylene fiber and steel fiber on the cracking resistance,shear resistance of inclined section and bending resistance of normal section of recycled concrete beams were studied and analyzed And the fiber content under the best mechanical properties in the range of the addition was obtained.By introducing the fiber reinforced coefficient,the calculation formulas of the cracking resistance,bending resistance and cracking resistance of recycled concrete beams under different fiber output are put forward.The basic conclusions are as follows:1)The addition of polypropylene fiber and steel fiber improves the crack resistance,shear resistance of inclined section and bending resistance of normal section of recycled concrete beam,and improves the ductility of recycled concrete beam.2)Polypropylene fiber recycled concrete beam,in the fiber content of 0.6kg/m~3?1.4kg/m~3,with the increase of fiber content,the crack resistance shows a gradual upward trend,when the fiber content is 1.4kg/m~3?1.8kg/m~3,with the increase of fiber content,the crack resistance gradually decreases;steel fiber recycled concrete beam,in the fiber content of 30kg/m~3?90kg/m~3,with the increase of steel fiber content,the crack resistance gradually increases When the content of steel fiber is 90kg/m~3,the crack resistance is the best.3)With the increase of fiber content,the shear capacity of fiber recycled concrete beams increases first and then decreases.When the content of polypropylene fiber is 1.4kg/m~3,the shear capacity of inclined section is the best;when the content of steel fiber is 70kg/m~3,the shear capacity of inclined section is the best.4)When the content of polypropylene fiber is 0.6kg/m~3?1.4kg/m~3,the flexural capacity of normal section increases with the increase of fiber content.When the content of fiber is1.4kg/m~3?1.8kg/m~3,the bearing capacity decreases with the increase of fiber content.When the content of fiber is 1.4kg/m~3,the bearing capacity is the best.When the steel fiber content is30kg/m~3?70kg/m~3,the flexural capacity of the normal section increases gradually with the increase of the fiber content.When the fiber content is 70kg/m~3?90kg/m~3,the bearing capacity decreases gradually with the increase of the fiber content.When the steel fiber content is 70kg/m~3,the flexural capacity of the normal section reaches the best.5)According to the test results of recycled concrete beams,the fiber-reinforced coefficient is introduced,and combined with the code for design of concrete structures(GB 50010-2010),the calculation formulas of cracking load,maximum crack width,shear capacity of inclined section and bending capacity of normal section are put forward under the 50%replacement rate of recycled aggregate.