RU2729086C1 - Two-phase mixture based on cement for composites in construction 3d printing technology - Google Patents

Abstract

FIELD: construction.SUBSTANCE: invention relates to construction materials adapted to 3D construction printing modes. Invention includes a two-phase mixture based on cement for composites in construction 3D printing technology. Two-phase mixture contains two phases: solid (phase 1) - mixture of dry components, and liquid (phase 2) - aqueous solution. Ratio of the two phases is equal to 7.6–7.8:1. Phase 1 includes Portland cement CEM I 42.5 H, sand with fineness modulus Mk≤1.25, xanthan gum with content (CHO)of not less than 91 %, technical tetrapotassium pyrophosphate with content of KPOnot less than 98 %, polypropylene fibre with length of 12 mm. Components of solid phase are in mass ratio, %: portland cement - 44.1–44.5; sand - 55.14–55.4; xanthum gum - 0.08–0.1; technical tetrapotassium pyrophosphate - 0.08–0.1; polypropylene fibre - 0.2–0.3. Phase 2 contains water and superplasticizer based on polycarboxylate esters. Weight ratio of components of liquid phase is, %: superplasticizer - 4.1–4.6; water 95.4–95.9.EFFECT: technical result is increased plasticity, shape stability, compression strength, bending tensile strength, adhesion strength of composite layers.1 cl, 1 tbl

Description

The invention relates to building materials that are used for 3D-additive building technologies of three-dimensional printing (3D printing).

The use of classic cement mixtures for 3D printing is difficult due to the fact that traditional mixtures in their parameters are not adapted to 3D printing modes in terms of rheological characteristics, namely, they do not have the plasticity required for extrusion, dimensional stability, which ensures the perception of the load during layer-by-layer printing. without formwork, have late setting times, delayed hardening.

Known material for construction 3D printing, consisting of the following components and parts by weight: cement - 100, active additives - 0-80, superplasticizer - 0.01-5, hardening accelerator - 0.01-10, coagulant - 0.01- 5, fillers - 0.1-25, binder - 0-5, air-entraining additive - 0-1, plasticizer 0.01-25, water repellent - 0-5, starch ether - 0-2, fiber - 0.01-0 , 5, powdery filler - 0-150, fine aggregate - 50-300, coarse aggregate (gravel or pebbles) - 0-400 / Patent, CN, 3D printing cement-based material and preparation method thereof 104891891, publ. 09.15.2015 /. The disadvantage of this technical solution is that the mixture does not meet the required rheological characteristics for construction 3D printing, namely, it has a rapid loss of plasticity, which negatively affects the extrusion process during printing. In addition, the use of a large number of different components significantly complicates the manufacturing technology and increases the cost of the composite material.

Known composite material for construction 3D printing obtained from the following raw materials in percentage by weight: cement - 33% -40%, inorganic powder - 0% -8%, sand - 32% -38%, polymer binder - 2.5 % -3%, compound coagulant - 0.2% -1% (accelerator: lithium carbonate - 0.05% -0.01%; moderators: sodium tetraborate - 0.05% -0.35%, sodium gluconate - 0 % -0.05%), stabilizer - 1% -2%, thixotropic agent - 0.5% -1.5%, superplasticizer - 0.1% -0.5% and mixing water - 16.7% -20 % / Patent, CN, Cement-based composite material used for 3D printing technology as well as preparation method and application thereof 104310918, publ. 28.01.2015 /. The lack of data on the rheological characteristics of the mixture does not allow making a conclusion about its suitability for three-dimensional construction printing. The most characteristic properties for mixtures during 3D printing have not been determined: plasticity, which is responsible for the normal extrusion of the mixture, and resistance to load perception during layer-by-layer printing of a structure without formwork.

An analogue of the claimed invention is a two-component composite material based on cement / Patent, CN, Bi-component cement based composite material for 3D printing as well as preparation method and application thereof 105384416, publ. 09.03.2016 /. The material is obtained by mixing two components in a ratio of 10 (15): 1. Composition of the first component: cement - 34% -40%, inorganic powder - 0% -6%, sand - 40% -44%, polymer binder - 2.5 % -3%, retarder - 0.3% -1%, superplasticizer - 5% -15%, volume stabilizer - 1% -2%, defoamer - 0.05% -0.1%, mixing water - 12% - 13.4%. The composition of the second component: cement accelerator - 2% -3%, thixotropic agent - 3% -4%, antifoam - 1% -1.5%, mixing water - 91.5% -94%.

The disadvantage of this technical solution is that each component of the material has a limited shelf life of properties that affect the structure of the resulting material, and the start time of the mixture setting is less than 15 minutes, in all examples given in the patent, which will negatively affect the adhesion strength of the composite layers. Also, the lack of requirements for the rheological properties of the mixture does not allow judging the possibility of its use for 3D printing.

Closest to the proposed invention, taken as a prototype is a modified polymer composite material for 3D printing / Patent RU 2 661970 C1, Modified polymer composite material for 3D printing. Cl. С04В 28/04, С04В 14/02, С04В 22/08, С04В 26/00, С04В 111/20, publ. 07/23/2018 /. The composition of the composite material in the following mass ratios,%: Portland cement - 24.37-34.16, polyvinyl acetate dispersion - 2.44-2.56, sand - 50.74-61.38, water glass - 1.70-2, 44, polypropylene fiber - 0.02-0.03, phloroglucinofurfural modifier - 0.05-0.07, water - the rest. The disadvantage of the technical solution is the low compressive strength at the age of 28 days and low tensile strength, in all the presented compositions the compressive strength does not exceed 27.4 MPa, the tensile strength is less than 1.3 MPa. Also, the patent does not contain data on evaluating the rheological properties of a fresh mixture, which are criterion for construction 3D printing: plasticity and dimensional stability.

The technical result of the claimed invention is aimed at increasing the versatility and expanding the field of application of 3D-additive building technologies by obtaining a mixture based on cement, consisting of solid and liquid phases, with the required technological parameters for the printing process and the physical and mechanical properties of the material. The technological parameters of the mixture include its rheological characteristics: plasticity, which ensures extrusion; dimensional stability, providing layer-by-layer laying of the mixture without deformation of the layer during its subsequent loading; setting time. The physical and mechanical properties of the material include: compressive strength, flexural tensile strength, water absorption, adhesion strength of the composite layers.

Comparative analysis with the prototype shows that the claimed two-phase mixture based on cement for construction 3D printing, including Portland cement, sand and fiberglass, differs in that two phases are used to obtain it: phase 1 - solid, a mixture of dry components, and phase 2 - liquid , an aqueous solution, in a ratio of 7.6-7.8: 1. A mixture of dry components (phase 1): Portland cement CEM I 42.5 N, sand with a fineness modulus Mk≤1.25, xanthan gum, containing (C ₃₅ H ₄₉ O ₂₉ ) _n at least 91%, technical tetrapotassium pyrophosphate, with a K ₄ P ₂ O ₅ content of at least 98%, polypropylene fiber 12 mm long. Mass ratio of components: Portland cement - 44.10-44.50%, sand - 55.14-55.40%, xanthan gum - 0.08-0.10%, technical tetrapotassium pyrophosphate - 0.08-0.10% , polypropylene fiber - 0.2-0.3%. Aqueous solution (phase 2): water and superplasticizer based on polycarboxylate esters, mass ratio of components: water - 95.4-95.8%, superplasticizer - 4.1-4.6%. Thus, the claimed solution meets the criterion of the invention "novelty".

The composition of the two-phase mixture can be used to obtain innovative materials for printing construction objects using 3D additive technologies.

Comparison of the proposed solution not only with the prototype, but also with other known technical solutions in this field of technology did not reveal the presence of signs in them that coincide with the proposed technical solution, or signs that affect the achievement of the required technical result. This makes it possible to conclude that the invention meets the "inventive step" criterion.

Characteristics of the starting components:

1. Portland cement CEM I 42.5 N (grade M500) in accordance with GOST 31108-2016 "Cements for general construction. Technical conditions ". Mineralogical composition: C ₃ S - 62%, C ₂ S - 13%, C ₃ A - 7.5%, C ₄ AF - 11.5%;

2. Sand with a fineness module Mk≤1.25 in accordance with GOST 8736-2014 “Sand for construction work. Technical conditions ".;

3. Xanthan gum, containing (C ₃₅ H ₄₉ O ₂₉ ) _n not less than 91%. It is a viscosity modifier - a thickener that increases the dimensional stability of the mixture, necessary for layering the mixture without deformation of the underlying layers when printing without formwork;

4. Technical tetrapotassium pyrophosphate, with a K ₄ P ₂ O ₅ content of at least 98%. It is an accelerator and viscosity modifier that regulates the plasticity of the mixture, ensuring the extrusion of the mixture during printing;

5. Polypropylene fiber for concrete and mortar, manufactured in accordance with ISO 9001: 2008 and meets European standard EN 14889-2: 2008. Fiber length 12 mm, diameter 22-34 microns, density 0.91 kg / dm, tensile strength 300-400 N / mm ² ;

6. Superplasticizer based on polycarboxylate esters. Density 1.055-1.065 kg / dm ³ , pH = 4.0-5.5;

7. Water - complies with GOST 23732-79 “Water for concrete and mortars. Technical conditions ".

A technology for producing a two-phase mixture for construction 3D printing.

At the first stage, phase 1 is obtained, which consists of dry components: Portland cement CEM I 42.5 N, sand with a size modulus of Mk≤1.25, xanthan gum, with a content (C ₃₅ H ₄₉ O ₂₉ ) _{n of} at least 91%, technical tetrapotassium pyrophosphate, with a K ₄ P ₂ O ₅ content of at least 98%, polypropylene fiber 12 mm long. Mass ratio of components: Portland cement - 44.10-44.50%, sand - 55.14-55.40%, xanthan gum - 0.08-0.10%, technical tetrapotassium pyrophosphate - 0.08-0.10% , polypropylene fiber - 0.2-0.3%. The components of the solid phase are loaded into the mixer and mixed for 4-5 minutes until all components are evenly distributed in the volume of the mixture.

The second stage consists in obtaining liquid phase 2, an aqueous solution consisting of water - 95.4-95.9%, a superplasticizer based on polycarboxylate esters - 4.1-4.6%. The superplasticizer is added to the water with vigorous stirring.

Next, a two-phase cement mixture is prepared for construction 3D printing as follows: liquid phase 2 is introduced into the finished solid phase 1 in a ratio of 7.6-7.8: 1 and the mixture is intensively stirred for 3-5 minutes until a homogeneous mass is obtained.

To assess the plasticity and extrusion capacity of the viscous-plastic mixture, the compressive yield stress was determined immediately after its manufacture. For this, a squeezing test was performed with a constant strain rate of 5 mm / s, since at a given test rate the behavior of the system during extrusion is most adequately modeled / Toutou Z., Roussel N., Lanos, C. The squeezing test: A tool to identify firm cement-based material's rheological behavior and evaluate their extrusion ability // Cement and Concrete Research. - 2005. - No 35 (10). - P. 1891-1899./.

To assess the dimensional stability immediately after the manufacture of the mixture, the following characteristics were determined:

- structural strength, which characterizes the ability of a viscous-plastic mixture to take a load without deforming the printed layer,

- plastic strength, which characterizes the ability of a viscoplastic mixture to take a load without cracking;

- the relative deformation of the layer of the visco-plastic mixture before the beginning of the formation of cracks.

To assess the characteristics of dimensional stability, a compressive test was performed at a constant loading rate of 0.5 N / s (corresponds to the speed when printing construction objects with industrially produced printers), which simulates the effect of the load from the overlying layers on the initially laid layers / Slavcheva G.S., Shvedova M. A., Babenko D.S., Analysis and criterional assessment of the rheological behavior of mixtures for construction 3D printing. - 2018. - No. 12. - S. 30-35./.

To determine the physical and mechanical properties of a composite material for construction 3D printing based on a cement mixture, samples are prepared in the form of a cube with an edge length of 70 × 70 × 70 mm and in the form of square prisms 70 × 70 × 280 mm and tests for compression and tension according to GOST 10180-2012, determination of density and water absorption according to GOST 12730.3-78.

To determine the adhesion strength of the layers of the freshly laid mixture, two series of samples 140 × 70 × 20 mm in size were made from the viscous-plastic mixture. The production of samples was carried out in two stages, first, samples of 70 × 70 × 20 mm were made, which were combined into a single sample with dimensions of 140 × 70 × 20 mm after 5 minutes for the first series, and after 15 minutes for the second series. Specimens of two series after 28 days of hardening were tested for three-point bending, the load was applied along the adhesion seam of the specimens. The formation of a seam between two fresh surfaces most reliably makes it possible to assess the bond of layers during printing, in contrast to standard methods that determine the strength of an adhesive seam, in which a viscous-plastic mixture is placed on a hardened sample, which does not correspond to the conditions of 3D printing.

The properties of a two-phase viscous-plastic mixture and the physical and mechanical properties of a composite based on a two-phase mixture for construction 3D printing are presented in table. 1.

The main parameter influencing the rheological characteristics of a visco-plastic mixture, which are criterion for the process of construction 3D printing, is the ratio of the solid and liquid phases in the mixture. The technologically necessary plasticity, aggregate stability and structural strength of mixtures are achieved by optimizing the phase ratio.

The use of sand as a filler makes it possible to influence the visco-plastic properties of the mixture and its structural strength by changing the spatial packing of the solid phase particles. The two-phase cement mixture has the ability to flow viscous-plastic without destruction of the structure during extrusion and sufficient structural strength to ensure dimensional stability with an optimized sand dosage.

Polypropylene fiber 12 mm long increases crack resistance, increases tensile flexural strength.

The introduction of tetrapotassium pyrophosphate, which is an accelerator and viscosity modifier that regulates the plasticity of the mixture, makes it possible to increase the density and stability of the mixture by interacting with ions of the liquid phase; on the other hand, the interaction products deposited on the grains of binders in the form of films of different density and permeability retain their properties (shape), but under the action of an external load, the films are capable of collapsing, water again flows to the particles of the mixture, thereby the mixture becomes plastic and exhibits fluidity ...

As a viscosity modifier - a thickener, xanthan gum acts, which is chemically inert with respect to the minerals of the mixture, but changes the density and viscosity of the mixture, increasing the structural strength of the system, which, as a result, increases the dimensional stability of the mixture, which is necessary for layering the mixture without deforming the underlying layers when printing without formwork. On the other hand, due to the structuring of the liquid phase, the setting and hardening process is regulated, the amount of active water required for cement hydration changes.

The introduction of a superplasticizer based on polycarboxylate ethers in an optimal concentration is a factor in changing the properties of the liquid phase and allows you to effectively control the plasticity, structural and plastic strength of the mixture.

Achieving the required technical result in the implementation of the invention consists in the fact that the two phases included in the composition of the mixture based on cement for 3D printing are set in a certain ratio, at given percentages of the components in these phases, when interacting, providing plasticity that affects extrusion, dimensional stability required for layer-by-layer laying of the mixture without deformation of the layer during its subsequent loading, certain setting times required based on the technology of layer-by-layer three-dimensional printing, compressive strength, tensile strength of the material in bending, water absorption, adhesion strength of composite layers.

Claims (5)

A two-phase cement-based mixture for composites in construction 3D printing technology, including Portland cement, sand and fiberglass, characterized in that it contains two phases, a solid (phase 1) - a mixture of dry components, and a liquid (phase 2) - an aqueous solution, in the ratio of 7.6-7.8: 1; Phase 1: Portland cement CEM I 42.5 N, sand with a fineness modulus Mk≤1.25, xanthan gum with a (C ₃₅ H ₄₉ O ₂₉ ) _n content of at least 91%, technical tetrapotassium pyrophosphate with a K ₄ P ₂ O ₅ content not less than 98%, polypropylene fiber 12 mm long in the following mass ratio of solid phase components,%: Portland cement 44.1-44.5 sand 55.14-55.4 xanthan gum 0.08-0.1 technical tetrapotassium pyrophosphate 0.08-0.1 polypropylene fiber 0.2-0.3 phase 2: water and superplasticizer based on polycarboxylate ethers, mass ratio of components of the liquid phase,%: superplasticizer 4.1-4.6 water 95.4-95.9