Preparation And Properties Of 3D Printed White Portland Cement-based Materials

With the rapid development of the social economy and the increasing improvement of living standards,people have put forward higher requirements for the aesthetic design and artistry of modern architecture,decoration,or landscape components.At present,the construction or molding method in the field of architectural decoration has a serious waste of resources and a long construction cycle,which seriously restricts the technological innovation and development of decorative products.Introducing 3D printing technology into the field of architectural decoration can solve the problems of traditional construction techniques such as complex construction,low efficiency,low precision,and high energy consumption,and provide broader freedom for construction in the field of architectural decoration.As a very special kind of Portland cement,white Portland cement is white and easy to be dyed.It is the most widely used material in the field of architectural decoration.At present,white Portland cement-based materials have many problems,such as long setting time,low early strength,poor interlayer bonding performance,and difficulty to regulate the rheological properties,etc.Hence,it is difficult to be directly applied in the field of 3D printed building materials.Therefore,because of the above problems,this paper adjusts the rheological properties and printable properties of white cement-based 3D printing materials and the mechanical properties of their products through the aspects of compound optimization of admixtures,nano modification,fiber reinforcement,and pigment coloring.The main research conclusions are as follows:(1)The basic composition of 3D printed white Portland cement-based materials was determined.Admixtures such as hydroxypropyl methylcellulose ether,calcium formate,and redispersible rubber powder were introduced to regulate the rheological properties,mechanical properties,and the stability of the printing structure of 3D printed white Portland cement-based materials,and the influence rule of rheological properties on printable properties was determined.Besides,the rheological and mechanical properties of 3D printed white cement-based materials were synergically controlled by additive compound optimization based on response surface methodology.The results show that to ensure the establishment of slurry printing structure,the plastic viscosity of white cement-based 3D printing material should be controlled in the range of 3.2 ～ 5.6 Pa·s,the dynamic yield stress should be controlled in the range of 250 ～ 480 Pa,and the static yield stress should not be less than 420 ～ 550 Pa.The optimal dosage ranges of cellulose ether,calcium formate,and rubber powder were determined by response surface methodology to be 0.40 ～ 0.45%,1.50 ～ 2.00%,and 1.25 ～ 1.50%,respectively.At this point,the deformation rate of white cement-based 3D printing can be controlled at 15%,and the 3D compressive strength is more than 37 MPa.(2)Nanomaterials were introduced to solve the problems of high viscosity,low mechanical properties and excessively high deformation rate in the printing process of admixture-modified 3D printed white Portland cement-based materials,the introduction of nanomaterials can further regulate the rheological properties,structural stability,and mechanical properties of 3D printed white Portland cement-based materials.The influences of the nanomaterials on the rheological properties and mechanical properties were determined by studying the rotation mode and vibration mode,and the key rheological parameters affecting the printable properties were also determined.The results show that the introduction of nanomaterials can significantly improve the mechanical properties of the slurry.When the content of nano-silica and nano calcium carbonate reaches 0.5% and 5.0%,respectively,the3 D compressive strength of white cement-based 3D printing material increases by 29% and38%,and the 3D flexural strength increases by 61% and 100%,respectively.The introduction of nanomaterials can also improve the stacking performance of 3D printed white Portland cement-based materials.When the nano-silica content is 0.5%,the deformation rate of the printed structure is only 4.31%.At the same time,the extrudable performance of the slurry can be improved when the dosage of nanomaterials is low.When the dosage of nanomaterials is 2%,the optimal extrudable pressure is only 0.10 MPa.(3)Short-cut fibers were introduced to solve the problems of poor extrusion performance and toughness during the printing process of nano-modified 3D printed white Portland cement-based materials,and the deformation mechanism of the slurry structure under gravity was simulated by creep mode.The results show that when the content of PVA fiber is less than 1%,the yield stress,zero shear viscosity,elastic modulus and thixotropy of the white cement-based 3D printing material can be significantly increased.At this time,the deformation rate of the printed structure reaches the lowest value of 3.38%,and the extrusion pressure reaches the maximum value of 0.17 MPa.When the content of PVA fiber is 1.25%,the flexural strength can reach 7.65 MPa,which is 148% higher than that of the blank group.Besides,the yield stress,zero shear viscosity,elastic modulus,and thixotropy of the 3D printed white Portland cement-based materials decreased first,then increased,and finally decreased with the increase of the polypropylene fiber content.When the polypropylene fiber content was 1%,the deformation rate reached the lowest value of 4.69%,and the optimal extrusion pressure reached 0.16 MPa.At the same time,the flexural strength reached5.85 MPa,which was 90.2% higher than that of the blank group.(4)By studying the influence of inorganic pigments and composite pigments on the color difference of 3D printed white Portland cement-based materials,the color control of color decorative printing components was realized.At the same time,the influences of inorganic pigments and composite pigments on the rheological properties,printability,and mechanical properties of cement-based 3D printing materials were also determined.The results show that the deformation rate of 3D printed white Portland cement-based materials decreases with the increase of the content of inorganic pigments,and increases first and then decreases with the increase of the content of composite pigments.Among them,iron oxide yellow pigments have the most obvious improvement in buildability.When the content of iron oxide yellow pigments is 4%,the deformation rate reaches the lowest value of 3.15%.At the same time,both inorganic pigments and composite pigments can improve the extrudability of slurry when the content of inorganic pigments is lower.When the iron oxide yellow pigment content is 2%,the optimal extrusion pressure reaches the lowest value of 0.10 MPa.Except for the blue composite pigment,which can greatly reduce the mechanical properties of the printing components,the other three pigments can improve the mechanical properties of the printing materials to a certain extent.When the iron oxide green pigment is mixed with 4%,the compressive strength and flexural strength can reach 50.31 MPa and 5.38 MPa,respectively.