Numerical Analysis And Validation Of The Early Age Mechanical Buildability Of 3D Printing Concrete

3D concrete printing is a new type of intelligent construction technology,which has been applied in infrastructure fields such as pedestrian bridge,bus station,and architectural landscapes.The ultra-early mechanical behavior of concrete materials has an important impact on the 3D printing construction performance,structural stability and mechanical strength of concrete.As the early performance of concrete materials constantly changes with time and environment,it becomes a difficult problem for the stable stacking construction of modeless 3D printing.It is of great significance for the standardization and structural promotion of 3D printing to study the influence mechanism of the material’s ultra-early mechanical behavior on construction molding,quantify the range of material characteristic parameters that meet the printing requirements,and establish the prediction and evaluation method for constructability and stable forming.In this paper,the evaluation of 3D printing’s constructability is carried out by using the methods of rheological static yield stress and Mohr Coulomb criterion to judge the constructability collapse,as well as the method of overturning judgment based on the principle of compression bar.The 3D printing concrete materials were prepared and tested for early age parameters such as rheological properties,early stiffness,density,and setting time,and the effects of printing velocity and printing interval time on constructability were studied were studied.Meanwhile,with the help of numerical calculations,the effects of stiffness development,print velocity,print layer height,print interval time on collapse and dumping,as well as lateral deformation characteristics were analyzed,and and the material characteristics to meet the demand of stable printing and the optimization parameter range of printing process are identified.Finally,a large-scale 3D printing special-shaped arch as an example to verify the feasibility and effectiveness of the method used in this paper.The following test and analysis results were obtained: under the environment of relative humidity of 36%～40% and ambient temperature of 9～12 °C,the initial setting time of the printing material is about 200 minutes and the final setting time is about 260 minutes.The lateral deformation of 3D printing structures is not more than 1 mm before the structure is damaged.Under the conditions of high printing velocity,high printing layer height and short printing time interval,the printable height of the structure is lower,and the material is more prone to yield damage.As the printing velocity increases,the print layer height decreases,and the printing time interval increases,the printable height of the structure will increase,and the failure mode will gradually transition to the collapse failure.The mechanical properties of materials,printing process and geometric form and size of structures,all of which interact and interact with each other.Combined with the simulation analysis results,for small-size(taking a single-layer path of 0.5 m as an example)structures,the recommended range of printing velocity is(0,50] mm/s,the recommended range of printing layer height is(0,10]mm,and the recommended range of interval time is [15,+∞)s.For large-size(taking a singlelayer path of 21 m as an example)structures,the recommended range of printing velocity is(0,25] mm/s,the recommended range of printing layer height is(0,15] mm,and the recommended range of interval time is [120,+∞)s.Based on the applied calculation method,the printing design of large-scale special-shaped arch is pre-evaluated.Printing was performed at a printing velocity of 100 mm/s,a print layer height of 10 mm,and a time interval Δt = 630 s.The slump deformation was within 5 mm,completing the stable construction of large-sized structures.