Research On The Crack Resistance Mechanism Of Flexible Fiber Reinforced Concrete And Its Application In Continuous Rigid Frame Bridge

Flexible fiber reinforced concrete is a cement based composite material with flexible fiber as reinforcement.By adopting the combination of theoretical analysis,experimental research and finite element numerical simulation,this paper studies the crack resistance mechanism of flexible fiber reinforced concrete,the crack resistance effect of flexible fiber and the influence factors on the effect.Relying on a practical engineering,the paper also studies the crack resistance effect of flexible fiber on early crack of mass concrete.Through the above research work,further improvement on the crack resistance mechanism of flexible fiber reinforced concrete can be expected,which may of some guidance to the engineering application of flexible fiber reinforced concrete.The paper further proposes the crack resistance mechanism of flexible fiber reinforced concrete based on energy balance theory.Analysis shows that: fibers can improve the fracture toughness of the material or reduce the crack extension force to resist crack by means of energy consumption;at the instant when a crack tip cross through a fiber,the energy consumption of the single fiber is huge,and the sum of energy consumption of a series of fibers across the crack without being pulled out or pulled off is also huge;and the energy consumption of fibers is related to such influence factors as the length,content,diameter and interface specific surface energy(bonding strength)of fiber and so on,and the longer the fiber length,the higher the fiber content,the smaller the fiber diameter and the greater the interface specific surface energy(bonding strength),the more the fiber energy consumption and the better the crack resistance effect.Through flexure test,plastic shrinkage test,fracture toughness and fracture energy test,and pendulum impact test,the paper studies the influencing degree and law of the fiber length and fiber content on the flexural strength,plastic shrinkage resistance crack,fracture toughness and fracture energy,and impact fracture energy.Polyester fiber has a limited influence on the flexural strength,relatively large influence on fracture toughness and impact fracture energy,and great influence on fracture energy,and can improve the early plastic shrinkage crack resistance performance of cement matrix;overall,with the increase of length and content of the fibers,the crack resistance and reinforcement effect of fiber are improved.Through the establishment of a plane stress finite element model with a central through crack,and based on the crack tip stress and stress intensity factor of crack tip along the crack line direction,the crack resistance effect of flexible fibers are illustrated,which shows the longer the fiber length and the higher the fiber content,the better the crack resistance effect.In this paper,the test results and the finite element analysis results are consistent with the crack resistance mechanism of the flexible fiber reinforced concrete based on the energy balance theory,which verifies the rationality of the crack resistance mechanism proposed in the paper.Relying on a continuous rigid frame bridge in the highway from Nanchuan of Chongqing to Daozhen of Guizhou,the paper studies the crack resistance effect of flexible fibers on the early crack of mass concrete,and comparatively analyzes the effect of flexible fibers on the shrinkage crack of No.0 block by establishing the No.0 block model.Results shows that flexible fibers can improve the anti-cracking performance of mass concrete against early crack,and the number of the cracks is less and their development degree are lower at the beam segment reinforced by polyester fibers compared with conventional beam segments without fibers in continuous rigid frame bridge;in the finite element analysis,the shrinkage cracks of No.0 block is mainly distributed in the bottom slab and the web of box girder,and the number of cracking unit of the concrete reinforced by polyester fibers is less than that of ordinary concrete.However,the crack resistance effect obtained through the finite element results is inferior to that in practical application.