Research On Preparation And Performance Of 3D Printing Lightweight Aggregate Concrete

3D printing concrete technology has attracted the attention of the academic and engineering circles due to its advantages of no formwork support,low labor cost and personalized customization.Most of the existing 3D printing concrete technologies are aimed at conventional density grades of concrete,and the research on 3D printing lightweight aggregate concrete is very limited.In view of the short printable time window of lightweight aggregate concrete and the difficulty of printing,this paper proposes a preparation technology of"surface shell",and successfully prepared 3D printed lightweight aggregate concrete with different density grades.The printing quality,mechanical properties and pore characteristics of printed lightweight aggregate concrete were explored.The main research contents and conclusions are as follows:（1）The rheological properties of freshly mixed lightweight aggregate concrete with different preparation processes were explored.On this basis,the relationship between the printable window time of freshly mixed lightweight aggregate concrete and its actual printing effect was studied.The research shows that the preparation process has a great influence on the rheological parameters and printing performance of 3D printed lightweight aggregate concrete.Compared with the traditional preparation method,the static yield stress growth rate of the lightweight aggregate concrete prepared by the"surface shelling"method is the lowest,and the printable window time of the prepared clay ceramsite concrete exceeds 30 min.Combined with the actual printing test,it is found that when the printable window time is greater than 30 min,the prepared lightweight aggregate concrete can successfully complete the printing of the entire building component.The higher the proportion of lightweight aggregate in the prepared 3D printed lightweight aggregate concrete,the higher the roughness of the upper surface of the printed specimen,but the reduction in the number of cracks on the side of the printed specimen.（2）The mechanical properties of the prepared 3D printed lightweight aggregate concrete were investigated.The study found that the flexural strength anisotropy of 3D printed lightweight aggregate concrete is:z>y>x;the compressive strength is:x>y>z.The coefficient of variation of the strength of 3D printed clay ceramsite concrete in all directions at7 days is lower than that of 3D printed ordinary concrete,but higher at 28 days;The coefficient of variation of the strength of 3D printed shale ceramsite concrete in all directions is lower than that of 3D printed ordinary concrete at 7 days and 28 days.The impact of the printing process on the strength of 3D printed lightweight aggregate concrete is lower than that of 3D printed ordinary concrete.Since 3D printing will increase the porosity of lightweight aggregate concrete,the dry density of the prepared 3D printed specimens is lower than that of the poured specimens.There is a good linear fitting relationship between the strength and dry density of the prepared lightweight aggregate concrete.（3）The pore characteristics of 3D printed lightweight aggregate concrete were analyzed by X-CT.The study found that the matrix porosity of the 3D printed specimens is higher than that of the poured specimens.The porosity of lightweight aggregate concrete matrix decreases with the increase of lightweight aggregate content.The relationship between the strength and porosity of lightweight aggregate concrete can be well represented by f=kln(_p^p0).The matrix pore shape of the lightweight aggregate concrete approaches the standard circle with the increase of the lightweight aggregate content in the concrete;the matrix pore shape of the 3D specimen is more irregular than that of the pouring specimen.