The Effect Of Hybrid Fiber On The Durability Of Recycled Concrete Under The Coupling Action Of Loading And Corrosion Freeze-thaw

Because of the defects of recycled aggregate itself,the durability of recycled concrete is lower than that of ordinary concrete with the same proportion,which has become one of the problems to be solved in the promotion and application of recycled concrete technology.Therefore,using fiber reinforced recycled aggregate concrete(RAC)is one of the important ways to realize the modification of recycled concrete.In this paper,1kg/m~3 polypropylene(PP)fiber and glass fiber are used to prepare fiber reinforced RAC with the same type of fiber with different sizes and two types of fibers.The content of polypropylene fiber in polypropylene fiber recycled concrete is 1kg/m~3.Considering the length(19mm)and length(3mm)of PP fiber,the mass ratio of 1:0,7:3,5:5,3:7,0:1 is mixed,and the fiber content in RAC is 1kg/m 3.Considering the length(19mm)and length(6mm)of glass fiber,the mass ratio of 1:0,7:3,5:5,3:7 and 0:1 is mixed,and the fiber content in RAC is also 1kg/m~3.For PP-glass hybrid fiber,the size of both PP fiber and glass fiber is 19mm,the content of hybrid fiber in RAC is also 1kg/m~3,considering the mass ratio of PP fiber and glass fiber is 7:3,5:5,3:7.Based on the macro performance,the influence of fiber on the durability of RAC under the coupling action of load,corrosion and freeze-thaw cycles was studied,and the strengthening mechanism of recycled concrete was discussed from the micro level combining with ESEM analysis.The main research contents and results are as follows:(1)The 28d compressive strength of different hybrid fiber reinforced recycled concrete is compared and analyzed.The definition of hybrid effect coefficient of mechanical properties of fiber reinforced RAC is put forward,and the effect analysis is carried out in combination with the coefficient,and the mechanism of efficiency enhancement is analyzed.The results show that the addition of hybrid fiber can make the failure of RAC change from brittle failure to plastic failure.When PP fiber,glass fiber and hybrid PP-glass fiber are added into RAC,the compressive strength of RAC is lower than that of reference concrete.However,the hybrid effect coefficient of most RAC reinforced with hybrid fiber is greater than zero,which shows better performance than that of single fiber.(2)Based on the comparative analysis of the compressive strength and loss rate of compressive strength of different hybrid fiber reinforced RAC after 50 times of corrosion and freeze-thaw,the definition of hybrid effect coefficient of frost resistance and durability of fiber reinforced RAC is put forward,and the effect analysis is carried out in combination with the coefficient,and the mechanism of efficiency enhancement is analyzed.The results show that adding polypropylene fiber,glass fiber and hybrid PP-glass fiber can improve the frost resistance of RAC.The same type and different size of fibers show positive hybrid effect,which is better than single size fiber.Hybrid PP-glass fiber shows positive hybrid effect,which is better than single size fiber.(3)The load mechanism of repeated load and corrosion freeze-thaw alternation is used to simulate the complex environment of load and freeze-thaw coupling of RAC.The compressive strength and loss rate of compressive strength of different hybrid fiber reinforced RAC under the multi factor coupling action are studied.The definition of hybrid effect coefficient of multi factor coupling durability of fiber reinforced RAC is put forward and the effect is combined with the coefficient,and the mechanism of efficiency enhancement is analyzed.The results show that the durability of RAC can be improved by adding PP fiber,glass fiber and hybrid PP-glass fiber.The same type of fiber with different size shows positive hybrid effect,which is better than single size fiber.Hybrid PP-glass fiber has positive hybrid effect,which is better than single size fiber.(4)The changes of hydration products of recycled concrete before and after the coupling action of load,corrosion and freeze-thaw cycles,and the influence of the interaction of freeze-thaw and load on the microstructure of RAC and the interface transition zone between fiber and matrix were studied by ESEM.The hybrid mechanism of durability of hybrid fiber reinforced RAC is explained from the micro level.