Research On The Pivotal Technology Of 3D Printed Concrete Arch Bridge

As a method to generate structural model based on computer 3D data design,3D printing has been successfully applied in many fields especially in construction engineering because of its advantages of mould-free,rapid and fine forming.Due to the technical characteristics of 3D printing,the printing material must meet certain standards of buildability,transient plasticity,mechanical properties,long term performance and durability.The strength range of 3D printed concrete in the current study is generally between 40MPa and 60MPa,which is not suitable for the construction of long-span structures,such as bridges,factories,space grids.With the development of new construction technology,3D printing bridge has become one of the current research hotspots.3D printing technology is expected to break through the technical barriers in the current bridge construction and design,and efficiently complete the construction of new structures.In order to solve the above problems,this paper takes 3D printed arch bridge as the research target,develops new 3D printed high-strength concrete materials,and then,on the basis of the newly 3D printed concrete,further researches are carried out on the type design and force simulation of 3D printed bridge.The following work is carried out:(1)Based on the mix ratio design of 3D printed concrete,the effects of water-binder ratio,sand binder ratio,mineral powder content and fiber content on material properties were studied.The mix ratio optimization design of 3D printed concrete was carried out through mechanical properties and working performance.The new PVA fiber concrete has a 28-day compressive strength greater than 80MPa,a 28-day flexural strength greater than 13MPa,a fluidity between 160mm-170mm with good thixoelasticity and water retention,and can meet the requirements of 3D printing pumped extrusion and stacking molding.(2)Based on the optimization of the mix ratio of 3D printed concrete materials,the influence of printing direction and cascade effect on the mechanical properties of 3D printed structures was explored from aspects of mechanical properties and durability,and the internal mechanism of materials was explored with the help of computed tomography(CT).It was found that although 3D printing stacking molding reduced the large holes in the structure and made the matrix more compact,the interface defects presented anisotropy.The strip defects of 3D printed structures were larger than those of interlaminar defects,and all defects had a great impact on the mechanical properties and durability of 3D printed concrete structures.(3)The early performance of 3D printed concrete was improved by using carbon nanotubes,and the influence of different volume on the properties of the materials was investigated.The synergistic effect of macro fiber(PVA fiber)and micro fiber(carbon nanotube)was compared by scanning electron microscope(SEM).The experiment found that multi-walled carbon nanotubes have no adverse effect on the buildability of concrete,and can effectively improve the early strength of 3D printed concrete.Meanwhile,the dispersion effect of carbon nanotubes is essential for the effective bridging of micro-cracks,which will affect the improvement of concrete early strength.(4)The pedestrian bridge was constructed with 3D printed concrete.Based on numerical simulation,the simplified scale model was determined in this paper to carry out the static load test,in order to study the influence of printing layering and steel wire mesh reinforcement on the mechanical properties of the molding structure,and to make a comparative analysis with the concrete structure formed by the mold.The research can provide engineering reference for structure design,force analysis and failure form of printing structure.The results show that the 3D printed arch bridge model has good stiffness and superior bearing capacity,the steel wire mesh enhances the bearing capacity and deformation capacity of the arch bridge,and improves the brittle characteristics of the failure mode.In the case of similar reinforcement ratio,the stiffening effect of the dense steel mesh is better than that of the thin steel mesh.