Study On The Effect Of Graded Basalt Fiber On The Mechanical Properties Of Rubber Concrete

As a high molecular organic material,waste rubber is difficult to be harmless through natural degradation.In order to achieve harmless treatment and secondary utilization of waste rubber,some scholars have processed it into particles of aggregate size and added them to concrete,reducing the weight of concrete while improving its durability.However,the addition of rubber particles also weakens the mechanical properties of concrete.Basalt fiber,as a silicate fiber,has good compatibility with cement matrix,high tensile strength,and large elastic modulus,making it an ideal reinforcement and toughening material.Therefore,in this paper,basalt fiber with excellent mechanical properties is incorporated into the matrix to improve the mechanical properties of rubber concrete.The experiment took the collocation of fibers with different lengths as variables to explore their impact on the mechanical properties and microstructure of rubber concrete.At the same time,combined with the Abaqus finite element model,it revealed the crack evolution process and the crack resistance mechanism of graded fibers from microscopic perspective.The main research contents and results are as follows:(1)Basalt fiber has improved the mechanical properties of rubber concrete,compared to rubber concrete,when a single length fiber is added,the compressive strength increases by2.57% to 13.34%,the splitting tensile strength increases by 4.87% to 13.31%,and the flexural strength increases by 21.17% to 39.42%.Moreover,the mechanical strength first increases and then decreases with the increase of fiber length,reaching the maximum value at 12 mm.There is no connection between the elastic modulus and fiber length,and the elastic modulus increases by 4.51% to 7.33%.(2)The improvement effect of graded basalt fibers on rubber concrete varies depending on the fiber length collocation,and two types of fiber length group exhibits better mechanical properties than other groups.Compared with the three fibers and four fibers groups,the double fibers group showed an increase of 3.58% and 8.00% in compressive strength,11.41% and 13.16% in splitting tensile strength,5.27% and 8.32% in elastic modulus,and 4.51 and 22.39% in flexural strength.The above experimental data demonstrate the importance of improving the mechanical properties of the long fiber mass ratio when mixed with multiple lengths of fibers,and the synergistic effect between fibers can be better exerted by the combination of 12 mm and 18 mm fibers to enhance the strength of the matrix.(3)The microstructure and pore structure of the interface transition zone(ITZ)of each component of the matrix were analyzed by SEM and CT.The results shows that the main hydration products of rubber-matrix ITZ is hexagonal and lamellar CH.The rubber-matrix CS-H gel is less,and the ITZ strength is low,leading to the reduction of mechanical properties of rubber concrete.There are a large number of flocculent and granular C-S-H gel at sandmatrix ITZ and fiber-matrix ITZ.The hydration products on the basalt fiber surface fill the pores,improving the compactness of the matrix,and fiber also forms a three-dimensional network structure in concrete,preventing the settlement aggregates and the floating of rubber particles,optimizing the pore structure and improving the mechanical properties of the matrix.(4)Using Abaqus to establish a compressive model and a flexural model,and comparing the experimental results with the simulation results,it is shown that cracks first appear in aggregate dense areas,and long fibers are mostly distributed near the aggregate due to the sidewall effect,which can participate more in the stress than short fiber.When cracks occur,the stress in the concrete redistributes,and the tensile stress at the crack tip increases.The fiber across the cracks and play a bridging role in participating in the stress,absorbing energy during the pull-out or fracture process,and improving the mechanical properties of the matrix.