Research On The Interaction Between Liquid And Powder Based On Powder-based 3D Printing Technology

Concrete 3D printing technology has characteristics of free structural design,efficient construction,and labor saving.It has attracted more and more attention in the construction field and has become one of the key future directions of construction industrialization.Preliminary applications of 3D printing techniques in practical engineering have been achieved.Yet,basic research on powder-based 3D printing technology is not complete to date.Systematic approach to design materials of powder-based material is missing.These reasons limit the development of powder-based 3D printing technology.Therefore,the indicators characterizing the results of interaction between liquid and powder were established and interaction mechanism of liquid and powder in powder-based 3D printing technology was investigated in this thesis.In the current study,a one-dimensional penetration experiment was performed to investigate the penetration process and mechanism.The droplet penetration experiment was used to explore the results of interaction between liquid and powder.The performances of printed samples were studied by using a 3D printer.The results show that:(1)The penetration of liquid in cement and plaster is a physical penetration process,which is mainly controlled by capillary suction and viscous drag.The penetration process is divided into two stages,i.e.saturated penetration stage and unsaturated penetration stage.The saturated penetration stage conforms to the Washburn model,in which penetration depth of the liquid is proportional to the square root of time.In the range studied,the powder porosity and the hydration have a little effect on the liquid penetration behavior,while improving the liquid quality increases the penetration depth,but keeps the same penetration rate.Incorporating powdery thickener into cement is one of the effective ways to improve liquid penetration behavior.The addition of the thickener significantly increases the yield stress and viscosity of the liquid,thus reduces its penetration depth and penetration rate.The interaction mechanism of the liquid and thickener is key to affect the penetration process and result of the liquid in the mixed powder.(2)The powder reacts with the droplets and forms a solidified sample.These solidified samples can be quantified by the three indicators,i.e.thickness,volume and saturation level.Liquid viscosity is the most important factor affecting above mentioned three indicators.The higher viscosity leads to the higher saturation level and the reduced thickness and volume of the solidified sample.The effect of the powder porosity,the quality of the liquid and the surface tension on the indicators of different types of solidified samples are universal.Within the range studied,the decrease in the powder porosity or liquid surface tension increases the saturation level of the solidified samples.The increase in the mass of the droplets increases the thickness,volume and saturation of the solidified samples.(3)The strength of the 3D printing plaster samples is affected by saturation level and powder packing density.Higher saturation level or higher powder packing density is beneficial for the strength of printed samples.Drying post-processing is one of the effective ways to improve the strength of the printing plaster samples.The dimensional accuracy of the printed sample is slightly affected by the saturation level,but hardly affected by the powder packing density.The established indicators and revealed penetration mechanism in this thesis provide theoretical and technical support for the further improvement of powder-based 3D printing technology and particularly for designing powder-based 3D printing materials.