Compression-shear Mechanical Properties And Particle Flow Simulation Of Carbon Fiber Recycled Concrete

Recycled concrete is made by partially or completely replacing natural aggregate with recycled aggregate and mixing sand,water and cement.It meets the goals of’carbon peak’and’carbon neutrality’and can promote the green and high-quality development of the construction industry.In this paper,in order to study the influence of carbon fiber on the compression-shear performance of recycled concrete under the combined action of compression and shear,the fiber length,content and normal stress are taken as variables,and the compression-shear test is carried out.The contribution degree of different variables to shear strength and the compression-shear failure characteristics of specimens are analyzed.The indoor compression-shear test is simulated by particle flow software PFC^2D,and the following conclusions are obtained.（1）Adding carbon fiber to the specimen has a certain improvement effect on the compressive strength,and the effect of fiber content on the compressive strength of the specimen is greater than that of fiber length.With the increase of fiber length,the tensile strength of the specimen increases first and then decreases.When the fiber length is 9 mm,the tensile strength of the specimen reaches the peak.After the fiber is added,the crack width produced by the compression failure of the specimen is significantly smaller than that of the undoped fiber specimen,and even no macroscopic cracks appear in some positions.The upper part of the specimen is not completely split when the splitting failure occurs,and the have a certain fluctuation compared with the vertical line.（2）With the increase of fiber length,the shear strength of the specimen increases first and then decreases,and the optimum fiber length is 6 mm.With the increase of fiber content and normal stress,the shear strength of the specimen increases,and the shear strength of the specimen increases with the increase of normal stress.The increase rate of shear strength decreases with the increase of normal stress.The addition of fiber only increases the shear strength of the specimen,and does not affect the change law of shear strength.Among the three variables,the normal stress has the greatest influence on the shear strength.With the increase of the normal stress of the specimen,the failure mode of the specimen shows the change rule of shear failure→compression-shear composite failure→compression failure,and the number and angle of inclined long cracks also increase.After the addition of carbon fiber,the bridging effect of the fiber enhances the integrity of the recycled concrete,resulting in a smaller diagonal crack angle and failure area than the undoped fiber specimen,and the skin drop is better than the undoped fiber specimen.The transformation of the failure mode is slower than that of the undoped fiber specimen,but the failure mode is basically the same as that of the undoped fiber specimen.（3）With the increase of normal stress,the total number of micro-cracks in the stable stage of the specimen gradually increases.After the fiber is added,the fiber plays a role in crack resistance in the specimen,effectively preventing the initiation and development of micro-cracks.With the increase of normal stress and fiber content,the shear strength of the specimen also increases gradually,and the normal stress has a linear relationship with the shear strength of the specimen.The crack initiation stress,peak stress and residual stress of the specimen increase monotonously with the increase of the normal stress of the specimen.The crack initiation stress,crack initiation strain,peak stress and peak strain of the specimen after adding fiber are greater than those of the specimen R-0-0,while the residual stress and residual strain of the specimen after adding fiber show no obvious increase or decrease.