Experimental Study On Cracking Resistance Of Recycled Concrete Beams With Waste Polypropylene Hybrid Fiber

With the development of society,a large number of old buildings have been unable to meet people’s requirements for production and life,so a large number of buildings have been abandoned and demolished,resulting in a large number of abandoned concrete.At the same time,the reconstruction or construction of a large number of buildings will consume a lot of cement resources.Apart from bulk transportation,the rest are all packed in bags.The cement packaging bags produced in China are mainly made of polypropylene(PP).As polypropylene is a hard to decompose material,it will have a serious impact on the environment.It is of great significance for sustainable green development to recycle waste cement bags reasonably.In this experiment,different proportion combinations of waste polypropylene fiber(RPP)and basalt fiber(BF)in recycled concrete under fixed mixing amount and different mixing amount under fixed proportion are adjusted,and the properties of test block and test beam under these two conditions are explored,and the following conclusion is obtained:After mixed fiber is mixed in recycled concrete with different mixing rate combination,from the analysis of load deflection curve,maximum deflection,crack development,characteristic load and reinforcement strain load curve,it can be seen that the improvement of crack resistance effect of sample beam comes from the addition of mixed fiber in recycled concrete.Among them,the performance of B60P40 group(3:2 mixing volume ratio,BF:RPP)test beam is superior to other groups in all loading periods,and it is the best mixing experimental group for crack resistance under this experimental condition.Based on the above test results,further study to change the different mixing rate of hybrid fiber can be found that the mixing of hybrid fiber can slightly improve the basic mechanical properties of the concrete matrix.Through futher study of the crack resistance of the sample beam components,C0.5 group beam has better crack resistance effect.Based on the above analysis,.it can be concluded that C0.5 test group(0.5%of the fixed proportion incorporation rate)is the best test group in this paper.Combined with the existing technical specifications of fiber reinforced concrete,the corresponding calculation formulas are derived by adjusting the influence coefficients β1 and β2 of the corresponding fiber on the crack width and the influence coefficients βB1 and βB2 of the short-term stiffness,and the test results and the calculation results are compared.The finite element software(ANSYS)is used to simulate the same size structure of the test beam.The stress nephogram of the concrete and the reinforcement and the crack development of the simulated specimen are analyzed.Compared with the actual test,it is found that the changes of the two are basically the same.The test values of deflection,initial cracking load and yield load of each group of test beams are compared with the simulation values.Although there are some differences between them,they are close to each other as a whole.