Study On The Flexural Properties Steel-Polypropylene Hybrid Fiber Reinforced Concrete

For two centuries,concrete has been one of the most widely used materials in civil engineering.However,its use is limited due to its many disadvantages such as low tensile strength,brittleness,and easy to crack.In order to improve the tensile strength and shear strength of concrete,enhance the toughness and impact resistance of concrete,and improve durability such as crack resistance and impermeability,many scholars at home and abroad explore the way to improve the concrete performance and develop the new materials continuously and expand its application range.The addition of fiber in concrete is a composite technology developed rapidly since 1970s.Fiber reinforced concrete has been widely used in civil engineering such as tunnels,highway pavements,bridges,industrial floors,and airport runways since its inception.In these projects,the flexural performance of fiber reinforced concrete is an important indicator of structural design and quality control.Therefore,the study on flexural performance of concrete is very important to theoretical research and engineering application of concrete.At present,the research results for flexural behavior of plain concrete and single fiber concrete has been abundant,but the report on the flexural behavior of hybrid fiber concrete is still lacking.In view of this,this paper systematic studied the flexural properties of steel-polypropylene hydrid fiber reinforced concrete through four-point bending test.The main work and results are as follows:(1)Considering the four major factors of the volume fraction of steel fiber,the volume fraction of polypropylene fiber,the aspect ratio of steel fiber and the steel fiber types,45 steel-polypropylene hybrid fiber reinforced concrete specimens were designed and produced.Based on the experimental results,the bending process of hybrid fiber reinforced concrete were analyzed.The results showed that:the flexural failure process of steel-polypropylene fiber reinforced concrete is slow and steady,showing obvious plastic characteristics,which is ductile failure;the enhancement of the steel-polypropylene hybrid fiber can be divided into four stages:elastic stage,stable development of micro cracks,the propagation of macro crack and fracture stage.(2)Based on experimental results,the effects of steel fiber volume fraction,polypropylene fiber volume fraction,steel fiber aspect ratio and steel fiber type on the flexural strengths,deflection and toughness were quantitatively analyzed.The results showed that:the increasing of steel fiber content.polypropylene fiber content or steel fiber aspect ratio can improve flexural strength?deflection and toughness,especially can improve post-peak flexural properties;between all factors,the steel fiber volume fraction plays the most import role in improving the flexural properties of hybrid fiber reinforced concrete;while the steel fiber volume fraction is beyond 1.5%,continue increasing the steel fiber volume fraction can improve the flexural properties of hybrid fiber reinforced concrete,but the degree of improvement is not significant;For the hybrid fiber reinforcement with different steel fibers,the specimens with hooked-end steel fibers exhibit the best flexural properties,while the specimens with straight steel fibers exhibit the worst flexural properties.(3)Based on the experimental measured load-deflection curves,the load-deflection curve equation was proposed.And it was verified that the theoretical curve agrees well with the experimental load-deflection curve.Finally,based on the research contents,some suggestions for further research is proposed.