Effect Of Hybrid Coarse Polypropylene-basalt Fiber On Bearing Capacity Of Concrete Pipe

Concrete pipes have been widely used in various municipal projects,such as water pipe and sewage pipe.As is well-known,concrete is a typical brittle material with the characteristics of easy cracking and poor ductility.The incorporation of fibers can play a good role in strengthening and toughening,but there are few reports on the mechanical properties of fiber concrete pipe.On the other hand,coarse polypropylene fiber and basalt fiber have attracted extensive attention of scholars at home and abroad in recent years.Among them,coarse polypropylene fiber is considered as a potential substitute for steel fiber.However,the current research on coarse polypropylene-basalt mixed fiber concrete mainly focuses on specimens,few attentions is pay on the performance of tubular members.Based on the current research status,three-point tests of ordinary reinforced / non-reinforced concrete pipe and polypropylene-basalt fiber reinforced / non-reinforced concrete pipe are completed in laboratory,combine with numerical simulation and theoretical analysis,the influence of different fiber incorporation on the bearing capacity of concrete pipe joints is compared、verified and expanded by ABAQUS.The main research contents and results are as follows:(1)Under the condition of non-reinforced concrete,the influence of coarse polypropylene-basalt fiber on the axial compressive bearing capacity of non-reinforced concrete were studied through the bearing capacity test.The results show that the non-reinforced concrete pipe B0P0 reaches the peak value and then rapidly fails.When mixed with coarse polypropylene-basalt fiber reinforced concrete pipe B2P4,it can maintain good integrity,and the bearing capacity which increased by 46.26 % compared with B0P0 is highest.The failure mode of all pipe are bending failure,that is,four main cracks will be formed in the inner side of the top and bottom of the segment,the outer side of the left and the outer side of the right.(2)Under the condition of reinforced concrete,the effect of coarse polypropylene-basalt fiber on the bearing capacity of reinforced concrete under axial compression was studied by bearing capacity test.The results show that the spalling between concrete and steel bars in reinforced concrete pipe RB0P0 is serious,and the spalling block is large.However,there is no obvious spalling in reinforced concrete pipe RB2P4 mixed with coarse polypropylene-basalt fiber,which shows the characteristics of cracking but not spalling.Compared with RB0P0,the bearing capacity of RB2P4 increases by 30.19 %,which is lower than that of B2P4 compared to B0P0.(3)ABAQUS was used for numerical simulation.Combined with the three-point test data of pipe,the model of non-reinforced / reinforced concrete pipe was established.ABAQUS was used to simulate the influence of fiber content ratios on the bearing capacity of non-reinforced / reinforced concrete pipe,and the influence of changing the circumferential and longitudinal reinforcement on the bearing capacity of coarse polypropylene-basalt fiber reinforced concrete pipe.The results show that the influence order of different fiber content ratio on the bearing capacity of reinforced concrete pipe is B2P4> B1.2P4.8> B0P6> B4P2> B3P3> B4.8P1.2> B6P0.The influence order of different fiber content ratio on the bearing capacity of reinforced concrete pipe is: RB2P4 > RB1.2P4.8 > RB0P6> RB3P3> RB4P2> RB4.8P1.2> RB6P0.(4)Based on the analysis of the stress of the control section of the pipe and the experimental data,the corresponding strengthening coefficient of the flexural capacity of the reinforced concrete pipe with different fiber content ratio is proposed by using the data obtained from the simulation of the reinforced concrete pipe.The results show that the top section is only in the bending state,and the lateral section is under the axial force and bending moment state,during the stress analysis of the whole section.The flexural capacity enhancement coefficients of RB0P6,RB6P0,RB1.2P4.8,RB2P4,RB3P3,RB4P2 and RB4.8P1.2 are 1.27,1.1,1.29,1.37,1.24,1.16 and 1.18,respectively.