Research On Forming Accuracy And Mechanical Properties Of Concrete 3D Printed Components

Concrete 3D printing technology is a new type of additive manufacturing and intelligent construction technology,unique construction molding method gradually by domestic and foreign experts and scholars attention and research.With the continuous research on the printability of concrete 3D printing materials,a major breakthrough has been achieved in printability,but there is little research on the accuracy of 3D printing components and no corresponding evaluation criteria.Therefore,based on the existing research,this paper investigates the forming accuracy and mechanical properties of 3D printed components.(1)In order to ensure the working and mechanical properties of the printable cementitious materials,this paper optimises the design of the mix ratio by means of sieving tests,mechanical tests,setting tests and flowability tests.The test results show that the setting time,flow rate and mechanical properties of the cementitious materials are better when the admixtures of cement,sand,fly ash,silica fume,water reducing agent,retarder and water are 1%,1.12%,0.09%,0.03%,0.04%,0.06%and 0.32%respectively,therefore this paper is extended with this ratio.(2)In order to investigate the forming accuracy and constructability of concrete 3D printed components,this paper investigates the forming accuracy and constructability of printed components using ICP algorithms and tilt-photometry.The results show that the best forming accuracy is achieved when the extrusion speed is 138mm/s,and the best printing speed V_dand extrusion speed V_jare achieved at this time;the buildability is analysed by the boundary deviation between the base model and the 3D reconstruction model,and it is found that the buildability is reduced due to the large compression deformation of the 4th layer,which affects the forming accuracy.(3)In order to investigate the influence of the printing path on the mechanical properties of 3D printed components,mechanical tests were carried out using three printing paths and anisotropy coefficients were proposed to characterise the mechanical anisotropy under different printing paths;the influence of microstructure and chemical product distribution at the interlayer interface on the mechanical properties was analysed using electron microscopy scanning technology.The test results show that the best force direction for all three printing paths is the Z-direction;the interlayer interface is not fully filled with hydration products,and there are defects such as voids,bubbles and cracks,which reduce the mechanical properties of the printed components.(4)In order to study the influence of flexible fibers on the mechanical properties of cement based 3D printing components,the mechanism of flexible fibers in the bearing capacity of cement based 3D printing components was studied through material mechanics tests and electron microscope scanning technology.The test results show that the mechanical properties of printed components can be improved by adding proper amount of PP fiber and PVA fiber,and the improvement effect of PP fiber is more obvious than that of PVA fiber;The mechanical properties of the printing component will be reduced when the amount of both is too much.The PP fiber at the interlayer interface is stretched,which can alleviate the damage of the component.The PVA fiber is directly pulled off without obvious deformation,which has no obvious effect on delaying the development of cracks.