Experimental Study On Mechanical Performance Of New Fiber Composite Truss Reinforced BFRPC Ballastless Track Slab

The ballastless track structure of high-speed railway has been widely used and developed in China and many other countries because of its good stability,strong durability and small maintenance.As an important part of ballastless track structure,ballastless track slab generally adopts reinforced concrete structure.However,due to the low tensile strength and poor durability of ordinary concrete,the development of ballastless track structure is greatly affected.Reactive powder concrete（RPC）is a new type of high-performance concrete material with high strength and high toughness,and RPC has high compactness,so its durability and corrosion resistance are also better than ordinary concrete.However,steel fiber commonly used in RPC are prone to corrosion in extreme environments such as ocean or salt freezing.At the same time,the addition of steel fiber may also have an impact on the track circuit system of high-speed railway.Using basalt fiber（BF）with higher tensile strength,better insulation and durability instead of steel fiber to make reactive powder concrete can effectively avoid the impact of fiber materials on structural durability in harsh environment.Fiber reinforced polymer（FRP）bars has been widely used in concrete structures because of its high strength,light weight,electrical insulation（except carbon fiber）,corrosion resistance and other advantages.Steel-fiber reinforced polymer composite bars（SFCBs）not only has the advantages of pure FRP bars,but also has higher stiffness.Combining these two kinds of fiber composite reinforcement with BFRPC,a new type of fiber composite truss reinforced BFRPC ballastless track slab is designed,which is expected to further improve the rigidity,bearing capacity and durability of ballastless track slab on the basis of solving the insulation problem of ballastless track slab,so as to meet the service life requirements of ballastless track structure.Based on the above ideas,this paper studies the mechanical properties of BFRPC and the static properties of new type of fiber composite truss reinforced BFRPC ballastless track slab.The main work and conclusions are as follows:（1）The mix proportion optimization of BFRPC materials required for the test was studied.Based on the influence parameters such as basalt fiber content and water to binder ratio,a kind of RPC material with strength grade of RPC 100-RPC120 and good workability is designed by single-factor analysis method.The research shows that among many influencing parameters,the water to binder ratio has the largest influence on coefficient.Within a certain range,with the decrease of water binder ratio,the compressive strength of BFRPC gradually increases,but at the same time,the fluidity of the mixture also decreases.The test results show that when the water binder ratio of BFRPC is 0.15,the volume content of fiber is 0.2%,and the cementitious material accounts for 51%,the cubic compressive strength of bfrpc is the highest,which is 113.9MPa.（2）On the basis of obtaining the best mix proportion,the basic mechanical properties of BFRPC are tested and studied.Test the cube compressive strength,axial compressive strength,splitting strength,axial tensile strength,flexural strength,elastic modulus,Poisson’s ratio,and uniaxial compressive stress-strain curve of BFRPC.The research shows that the cube compressive strength and axial compressive strength of BFRPC are 113.2MPa and 88.9MPa respectively,the axial tensile strength is 6.83MPa,the flexural strength is 18.52MPa,the splitting tensile strength is 4.5MPa,the elastic modulus is 38.3GPa,and the Poisson’s ratio is 0.22,which meets the mechanical property requirements of RPC in GB/T31387-2015 reactive powder concrete.According to the stress-strain constitutive model equation under uniaxial compression,the experimental curve is fitted with the theoretical curve,and the modified formula of the complete stress-strain curve under uniaxial compression is proposed.（3）Experimental study on static performance of ballastless track slab.Three full-size ballastless track slabs were prepared in the test,including one steel truss reinforced BFRPC ballastless track slab and two new fiber composite truss reinforced BFRPC ballastless track slabs.The results show that the failure mode of BFRPC ballastless track slab reinforced by steel truss is tension fracture of truss bottom chord;The failure mode of two new fiber composite truss reinforced BFRPC ballastless track slabs is inclined section bending shear failure.The ballastless track slabs reinforced by BFRPC meet the requirements of bearing capacity,and have obvious advantages over ordinary concrete ballastless track slabs reinforced by trusses of the same type in limiting mid span deflection and crack development.In addition,BFRPC ballastless track slab is superior to ordinary concrete ballastless track slab in ductility and energy consumption.On the basis of the test,the shear capacity and deflection of the ballastless track slab are calculated and compared,which provides a theoretical basis for the follow-up study.（4）Based on the static load test data of three full-size ballastless track slabs,the finite element model of ballastless track slab is established.The development of its failure mode,bearing capacity and deflection is studied through nonlinear analysis method and compared with the test results to verify the reliability of the model.On this basis,by changing the concrete strength and reinforcement ratio,the change law of stiffness and bearing capacity of ballastless track slab under static load is explored.