Effect Of Fibers On Permeability And Crack Geometry Of Cracked Concrete

Conrete material with brittleness is vulnerable to cracking.Reinforced concrete structures are usually cracked in service.After cracking,the permeability of concrete can be increased.This facilitates favorable paths of ingress for water,ions and other aggressive agents,which can initiate various deterioration processes such as carbonation,alkalis-aggregate-reaction,and corrosion of steel reinforcement.Thus the safty and serviceability of the structere can be affected and the costs of repair can be increased.With the inclusion of fibers in concrete,the material brittleness can be reduced and post crack toughness increased.Besides,the crack propagation can be limited and crack geometry can be modified which affects the durability such as permeability of concrete.So it is of significant importance to evaluate the influence of fiber type and fiber content on cracked concrete permeability and crack geometry.Corresponding to the project supported by National Natural Science Foundation of China(No.51578109),experimental study on influence of fiber type and fiber content on cracked concrete permeability with and without loading,crack recovery,flexural behavior of concrete notched beam and crack geometry were conducted.The main work is focused on such aspects as follows:(1)Cracks with various widths were induced by splitting test.Experimental study on the crack recovery and splitting toughness affected by steel fiber,macro polypropylene fiber and micro polypropylene fiber were performed.In permeability test,effect of fibers on water permeability of cracked concrete were evaluated.The results show that steel fiber and macro polypropylene fiber show positive effect on crack recovery,splitting toughness and watertightness of concrete,while micro polypropylene fiber has little effect on these behaviors.Hybrid use of fibers shows positive hybrid effect.(2)The workability,air content and compressive strength of concrete were studied in slump test,air content and axial compression test.In permeability test subjected to loading,the mass of water downstream and diameter variation values were acquired simultaneously during the loading process.Thus the effect of steel fiber and macro polypropylene fiber on cracked concrete subjected to loading can be evaluated.The results show that with the inclusion of fibers,the flowability of fresh concrete can be decreased and air content increased.Fibers effect on concrete compressive strength is not obvious.With the increase of fiber content,permeability of concrete can be decreased.Hybrid use of fibers shows positive hybrid effect on reduction of permeability.(3)Three-point bending test of notched beam was conducted to evaluate the effect of steel fiber and macro polypropylene fiber on beam flexural properties.The results show that with the increase of fiber content,flexural resistance of concrete beam can be improved.Hybrid use of fibers shows positive hybrid effect on reinforcement of concrete beam.(4)The visualization of 3D reconstruction for concrete fracture surface were presented by laser scanning test.The effect of steel fiber and macro polypropylene fiber on crack geometry were studied based on statistics method,analysis of crack profile tortuosity and fracture surface roughness and fractal geometry method.The results shows that the standard deviation of Z coordinates can be increased with the incorporation of fibers,but no obvious relationship between the standard deviation and fiber content is found.With the increase of fiber content,the crack profile tortuosity,fracture surface roughness and fractal dimension can be increased.Hybrid use of fibers shows positive hybrid effect on the increase of the above indexes.