The Influence Of Fiber On Tensile Mechanics And Permeability Properties Of Concrete

The shortcomings of concrete material are low tensile strength and brittleness.Concrete structures normally work with cracks.The anti-permeability of cracked concrete increases.Impermeability,as important factors of concrete durability,affects the safety and applicability of concrete structure.The fiber can not only improve the tensile property of concrete,but also improve the permeability resistance by improving the crack surface roughness.Therefore,it is of certain significance to study the influence of different types and content of fibers on the mechanical properties and permeability of concrete under uniaxial tensile load.This paper is based on the research direction of the National Natural Science Foundation of China(51578109).In this paper,the effects of fiber type,fiber content and layered thickness(for layered concrete)on the mechanical properties,permeability properties and crack surface morphology of concrete under uniaxial tensile load were studied.The main contents are as follows:(1)Based on uniaxial tensile tests,the effects of fiber types,fiber content and layering degree on the tensile properties of fiber reinforced concrete(FRC)were investigated.It is found that steel fiber can obviously improve uniaxial tensile toughness of concrete.The SF80PP2.3 specimen showed positive confounding effect on tensile strength.(2)The effect of steel fiber on salt-freezing damage and flexural property of concrete after salt freezing-thaw cycle was studied.The result shows that steel fiber significantly slowed down the declining trend of flexural strength of concrete specimens after salt freeze-thaw cycles.For the same number of salt freeze-thaw cycles,with the increase of fiber content,the flexural strength of concrete after salt freeze-thaw increased gradually.Therefore,steel fiber improved the effect of salt freeze-thaw cycle on the flexural strength of concrete specimens.(3)Combined with uniaxial tensile test,water permeability test and surface laser scan test of concrete are carried out.The influences of fiber types and content on permeability and crack surface roughness of FRC were analyzed.The result shows that steel fiber determines the permeability and surface morphology of concrete cracks.With the increase of fiber content,the permeability of concrete crack decreased gradually,but the roughness of crack surface increased.For the concrete with same fiber volume content,the higher the proportion of steel fiber was,the lower the crack permeability was.The SF80PP2.3 specimen of hybrid fiber concrete showed positive hybrid effect on anti-permeability.(4)The effect of steel fiber on the mechanical properties and permeability of layered concrete under uniaxial tensile load is studied.The results show that with the increase of steel fiber content or layer thickness,the uniaxial tensile toughness of concrete increased,and the crack permeability decreased.The fracture permeability parameter α decreased exponentially with the increase of fracture roughness parameter.Therefore,it is possible to predict the permeability of FRC by measuring the surface morphology of concrete cracks.