Mechanical Properties Of Carbon Fiber Concrete And Its Application In Shield Tunnel

With the rapid development of China's economy,more and more cities have put more funds into the construction of subway projects in order to facilitate transportation.As the permanent lining of shield tunnel construction,the quality of pipe slice is directly related to the safety and durability of the whole tunnel.Now the main material of shield lining segments in subway engineering is based on the ordinary reinforced concrete is given priority to,but because of ordinary concrete belongs to brittle material,tensile performance is weaker,in the process of transportation and production are prone to missing Angle,the phenomenon such as crack,damage,will not only reduce the efficiency of construction,but also unfavorable influence on the service life of the whole tunnel.In view of the deficiency of ordinary concrete pipe slice,it is proposed that carbon fiber concrete is adopted to replace ordinary concrete material,which can improve the defects of ordinary concrete pipe slice.Carbon fiber has the advantages of cracking resistance,toughening and durability,which can provide effective help for improving the safety of subway tunnel.In this paper,the performance test of carbon fiber concrete was carried out,and the cube compression resistance,axial compression resistance,fracture resistance,tensile resistance and uniaxial cycle test were performed on the concrete,aiming to study the improvement of mechanical properties of concrete by adding carbon fiber.The simulation results show that carbon fiber concrete has a good effect on improving the defects of ordinary concrete pipe slices.Finally,the feasibility of carbon fiber pipe slices in practical application is verified.The main work is as follows:(1)The carbon fiber concrete test block with the length of 5mm,10 mm,20 mm and the contentof 0.08%,0.16%,0.24%,0.32% was prepared and tested for compression,tensile,flexural and axial compression.Study the difference of failure mode and the improvement effect of concrete performance,find out the optimal fiber content and length;draw the stress-strain curve of concrete according to the data,study the characteristics of curve change and analyze the influence of different content and length on the characteristic points of the curve;study the compressive toughness of concrete according to the axial compression curve,the results show that fiber can improve the mixing performance The peak stress and ultimate strain of the concrete can also effectively improve its toughness.According to the test data,the function of peak strain,fiber content and compressive strength is fitted.According to the previous research,the most consistent constitutive model is found,the curve parameters are calculated and the physical meaning is explained.At the same time,the relationship between fiber content and curve parameters is also fitted,and the limiting conditions of the constitutive model are proposed.(2)The concrete was tested in uniaxial compression cycle,and its stress-strain curve was analyzed to study its mechanical behavior.The results show that the concrete specimens mixed with carbon fiber not only show obvious ductile failure characteristics,but also can significantly improve the cyclic compressive behavior of concrete,which is mainly manifested in the increase of peak stress,post peak ductility and hysteretic energy consumption capacity,as well as the reduction of stiffness degradation and plastic strain accumulation.(3)According to the mechanical property test of carbon fiber concrete,the best mixing amount and length of carbon fiber are obtained,and C50 concrete test block is prepared with the best mixing amount and length.It is found that the effect of carbon fiber in high-strength concrete is better.The material parameters obtained on this basis carry out numerical simulation Research on segment,and the maximum combined internal force is obtained through the research and analysis of segment internal forceThe combination of internal forces optimizes the reinforcement of segments.It is found that the carbon fiber reinforced concrete segment can optimize the reinforcement by saving the amount of reinforcement and reducing the number and diameter of reinforcement,which also meets the economic requirements.Finally,the bending resistance of the carbon fiber segment is analyzed to verify the safety and rationality of the carbon fiber segment.Adding carbon fiber into the segment can improve the ability of crack resistance and deformation resistance of the segment.