Research On Basic Mechanical Performance Of Hybrid Fiber Recycled Concrete

Hybrid fiber recycled concrete,as the name suggests is a new type of ecological materials in the production of recycled concrete by adding different kinds of fibers in a certain proportion.The addition of hybrid fiber improves the ductility of the traditional recycled concrete,overcomes the defect of easy cracking,and improves the performance of recycled concrete,which has a good engineering and practical value.The research contents and conclusions of this paper are as follows:(1)The gradation,crushing index,moisture content and bulk density of recycled coarse aggregate were tested.Test results show that the recycled coarse aggregate has a high water absorption and crushing index,which belongs to a third grade aggregate;the aggregate gradation used in the experiment can basically meet the requirements of the concrete;and the small packing density of recycled coarse aggregate indicates it’s advantages in the lightweight concrete.(2)The cube compressive strength and cube splitting tensile strength of hybrid fiber recycled concrete were tested by using orthogonal test method.The influence of the ratio of recycled concrete and recycled brick,the ratio of glass fiber and polypropylene fiber,content of air entrained water reducing agent on the strength of recycled concrete was studied.Test results show that the proportion of glass fiber and polypropylene fiber,content of air entrained water reducing agent on hybrid fiber recycled concrete compressive strength and splitting tensile strength has no significant effect;the proportion of recycled concrete and recycled brick of hybrid fiber recycled concrete compressive strength and splitting tensile strength has a significant impact.(3)Single factor test was used to study the hybrid fiber recycled concrete by two single factor change parameters: the ratio of recycled concrete and recycled brick,the ratio of glass fiber and polypropylene fiber.The mechanical properties and the constitutive curves of two kinds of hybrid fiber recycled concrete were obtained respectively.The influence of the mechanical property indexes with the changing parameters was studied.Test results show that:With the ratio of recycled concrete aggregate and recycled brick aggregate increase,hybrid fiber recycled concrete cube compressive strength,splitting tensile strength,axial compressive strength,elastic modulus,toughness index,ratio of axial compressive strength and compressive strength shows upward trend,the ratio of splitting tensile strength and cube compressive strength and Poisson’s ratio show no obvious regularity,but the peak strain and ultimate strain of hybrid fiber recycled concrete are generally decreased.With the increase of the ratio of glass fiber and polypropylene fiber,cube compressive strength,splitting tensile strength,axial compressive strength,Poisson’s ratio,the ratio of axial compressive strength and cube compressive strength did not show significant changes in the trend,elastic modulus,the peak strain and the ultimate strain increased,the toughness index,the ratio of splitting tensile strength and compressive strength showed a decreasing trend.The composition of coarse aggregate has a great influence on the slope of the rise of the curve,and the fiber composition has a great influence on the ductility and deformation of recycled concrete after the peak strain.(4)The application of digital image processing technology to complete the real concrete section model;the failure mechanism of old interface is analyzed by establishing a model of concrete.The analysis results show that the application of digital image technology can build a two-dimensional real section model of concrete,which provides the basis for the simulation of the real stress state of the recycled concrete;interface is the weak part of recycled concrete prone to damage,which has a great influence on the mechanical properties of recycled concrete.