The Study On High Performance Of The Basalt Fibers Reinforced Cement-Based Materials And Its Composite Beams

The corrosion of steel bars in traditional steel reinforced concrete structures is easy to be caused after the cracking of concrete because of long-term use or extreme environments such as alpine regions,oceans,islands and reefs,which will seriously affects the usability and durability of structures.Fiber reinforced polymer bars(FRP bars)have many advantages such as light weight,high strength,corrosion resistance and self-recovery.The application of FRP bars can effectively solve the corrosion problem of steel bars,improve the durability and realize the long life of the structure.FRP bars have been applied more and more in the field of civil engineering.In order to solve the problems of excessive crack width and large deflection of FRP reinforced concrete structure subjected to load,improving the properties of cement-based materials is one of the ways.Cement-based materials are one of the most widely used materials in the world.Fiber composite design is the core idea to enhance the performance of cement-based materials.Combining fibers reinforced cement-based materials with FRP bars can form a composite beam with good crack resistance.To explore the influence of basalt fibers-which have the same raw materials with BFRP bars-on mechanical properties of the cement-based materials and composite beams,in this paper,mechanical properties test,bond slip test and composite beam bending test of basalt fibers reinforced cement-based materials are carried out.The theory of bending resistance of composite beams is systematically summarized.The main research is as follows:(1)The compressive,flexural and tensile properties of basalt fibers reinforced cement-based materials are studied under different factors such as fiber content,fiber length and water cement ratio.The enhancement effect of basalt fibers was evaluated comprehensively.It is found that the existence of fibers will reduce the compressive strength of materials,but can greatly increase the flexural strength and tensile strength.The maximum tensile strain of basalt fibers reinforced cement-based materials is about 0.03%,so the effect is not obvious.Fibers with different lengths will affect the tensile modulus of elasticity of materials.(2)In this paper,the bond behavior of basalt fiber reinforced cement-based material-BFRP bars is studied.It is found that the bond strength of basalt fiber reinforced cement-based material-BFRP bar is about 20 MPa,which is nearly equivalent to that of concrete-BFRP bars.When the peak bonding stress is reached,the slip of BFRP bars in basalt fiber reinforced cement-based material is greater than that of concrete.In the slipping process,the surface of bars is less worn by basalt fiber reinforced cement-based materials.In the bond slip curve,the trend of circulation attenuation of the residual curve is slower after the peak stress is reached.The retention of the mechanical properties of the BFRP bars is more significant.(3)When basalt fibers reinforced cement-based material is used to replace some concrete in the tensile zone of BFRP bars reinforcement beam,it is found that the composite beam satisfies the plane section assumption along the beam height direction,and the interface has good deformation compatibility.The load displacement curve of the composite beam is similar to that of the contrast group,and the number of cracks develops and the width of cracks decreases slightly.Based on the experiment,the stress calculation theory of composite beams with BFRP bars is established.Through trial calculation,it is found that if the ductile material is used to replace some concrete in the tensile zone,the rigidity and flexural ultimate bearing capacity of the girder can be increased.