RU2762841C1 - Mixture for producing decorative composite in predetermined colour scheme in construction 3d printing technology and method for production thereof - Google Patents

Abstract

FIELD: additive manufacturing technology.

SUBSTANCE: invention relates to the field of production of building materials adapted to the technology of construction 3D printing and exhibiting architectural expressiveness. The mixture for producing a decorative 3D-printing composite consists of dry components and a liquid grouting agent at the ratio thereof of 7.54 to 7.58:1, the ratio of the dry components of the mixture (% wt.): portland cement CEM I 42.5 N – 43.10 to 43.48, sand with a fineness modulus Mf ≤ 1.25 – 53.35 to 53.89, metakaolin with a content of SiO₂ of no less than 53% and Al₂O₃ of no less than 47 % – 0.855 to 0.866, red powder pigment based on Fe₂O₃ with a content thereof of no less than 96.1%, or green based on Cr₂O₃∙2H₂O + Fe₂O₃ with a content of Fe₂O₃ of no less than 26.1 % – 1.304 to 2.155. The liquid grouting agent comprises the following components at the mass ratio thereof (%): water – 95 to 95.2, superplasticiser based on polycarboxylate esters – 3.2 to 3.3, polypropylene fibre – 1.6 to 1.7. The method for producing a decorative mixture consists in the fact that the components of the solution are mixed together in predetermined ratios and in a certain sequence, first, dry components are mixed in a high-speed rotary mixer for 1 to 2 minutes: portland cement, fractionated filling aggregate (quartz sand), a viscosity modifier additive – metakaolin; simultaneously, the liquid grouting agent is prepared – water is mixed with a superplasticiser based on polycarboxylate ether in a separate container, introduced whereto directly prior to application is the reinforcing component – polypropylene fibre; the solution is added to the dry components, the resulting mixture is mixed by a high-speed rotary mixer for 3 to 5 minutes. In order to produce an item in a predetermined colour scheme, two methods for introducing a pigment are possible: the first method – the powder pigment of a certain color is introduced into the mixture of dry components to produce a composite coloured uniformly throughout the volume; the second method – the powder pigment is introduced directly into the mixer 10 to 15 seconds prior to the end of mixing to produce a composite coloured differentially throughout the volume.

EFFECT: production of a 3D-printing mixture for a decorative volume-coloured composite in a predetermined colour scheme with high operational characteristics, exhibiting plasticity and shape stability.

2 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 classical concrete mixes and mortars in 3D printing technology is difficult, since their rheological properties are not adapted to the printing process. In particular, such mixtures do not possess the plasticity required for extrusion, the dimensional stability that ensures the perception of the load during layer-by-layer printing without formwork, they have late setting times, and delayed hardening. In addition, concretes and mortars based on gray cement do not have architectural expressiveness and aesthetic appeal.

A known method of manufacturing decorative concrete products, which is as follows. The main components of the mixture (Portland cement, crushed stone, dye (soot - technical carbon P-803), water) are thoroughly mixed and then polyvinyl acetate is added to it, after which mixing is also carried out until a homogeneous mass is obtained, from which the product is molded by casting. After curing and stripping, the product undergoes additional processing - its surface is polished and treated first with a solution of printing ink in an organic solvent, and then with a solution of organic glass in acetone. After that, the surface of the product is again polished until a deep mirror shine appears / Patent, Method for the manufacture of decorative concrete products, RU 2 017 703 C1, publ. 15.08.1994 /.

The disadvantage of this technical solution is the use of a coarse aggregate (crushed stone), which will complicate the passage of the mixture through the print head of the construction printer. At the same time, the high water-cement ratio of the mixture determines its high mobility and fluidity, which excludes the possibility of using such a mixture in the technology of form-less construction 3D printing. In addition, to obtain the decorative texture of the product, its stripping requires additional labor and energy-intensive processing of its surface, which significantly increases its cost and contradicts the principle of robotic construction 3D printing technology.

An analogue of the proposed technical solution is a mixture for the preparation of concrete "Kremnegranit", which includes Portland cement, crushed stone, sand, plasticizer MDF, water and pigment (TiO ₂ ). In this case, the method of obtaining a concrete mixture is as follows: dry components are mixed in a mixer for 3 minutes, after which water with a plasticizer dissolved in it is gradually added to them. In this case, pellets are formed, the core of which is crushed stone, and the shell consists of a moistened mixture of Portland cement and sand. Pigment is added to the concrete mixture after the pellets are formed. The resulting mixture is unloaded into a mold and subjected to vibration / Patent, Method for making concrete "Kremnegranit", RU 2 348 598 C2, publ. 10.03.2009, bul. No. 7 /.

The disadvantage of this technical solution is the use of crushed stone as a large aggregate, which will not allow the mixture to pass through the print head of the construction printer. In addition, the resulting mixture does not have viscous-plastic properties and is too rigid, which will not allow its use in 3D printing technology.

Closest to the proposed invention, taken as a prototype, is a method of making a decorative concrete mixture, which consists in mixing white Portland cement, filler, plasticizer and bleaching additives, and white Portland cement is preliminarily subjected to mechanical activation by joint grinding with superplasticizer C-3 for
30-40 minutes. 12-15 minutes before the end of activation, a bleaching additive is introduced into this mixture in the form of a shell pigment, which is titanium dioxide on calcite or microcalcite. The mixing of mechanically activated cement and aggregate is carried out within 5 - 7 minutes after preparation of the dough with a water-cement ratio of 0.30 - 0.33 / Patent, Method for making decorative concrete mixture, RU 2 133 724 C1, publ. 07/27/1999 /.

Similar features of the prototype and the proposed technical solution are a low water-cement ratio, the use of a superplasticizer, a pigmented additive in the mixture, as well as a step-by-step preparation of the mixture.

The disadvantage of this technical solution is the lack of data on the rheological properties of the mixture. However, it is indicated that the products are manufactured using traditional injection molding technology, which suggests that the mixture has high mobility and fluidity, therefore, its use in the technology of non-form construction 3D printing is not possible.

The technical result of the claimed invention is aimed at increasing the versatility and expanding the scope of 3D-additive building technologies by obtaining a mixture for a volumetric-colored composite with the required technological parameters for the printing process and physical and mechanical properties of the material, and at the same time possessing aesthetic appeal and architectural expressiveness, for the achievement of which does not require the finishing of products. The technological parameters of the mixture include its rheological characteristics: plasticity, ensuring 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 and characteristics of the durability of the composite include: compressive strength; compressive strength when splitting layers; density; water absorption, frost resistance, drying shrinkage.

Comparative analysis with the prototype shows that the inventive mixture for a decorative volumetric-colored composite of a given color and the method for its production differs in that specially selected components are used to obtain it, which are mixed with each other in specified ratios and in a certain sequence, which ensures plasticity and dimensional stability mixtures required in the technology of formwork 3D printing and variable color of the resulting composite.

To obtain a 3D-printed mixture, the following dry components are used with their mass ratio (%): Portland cement CEM I 42.5 N - 43.10 - 43.48, sand with a fineness modulus Mk ≤ 1.25 - 53.35 - 53, 89, metakaolin with at least 53% _{SiO 2 and at least 47% Al 2} O ₃ - 0.855 - 0.866, red powder pigment based on Fe ₂ O ₃ with its content at least 96.1% or green based on Cr ₂ O ₃ ⋅2H ₂ O + Fe ₂ O ₃ with a Fe ₂ O ₃ content of at least 26.1% - 1.304 - 2.155. A liquid grout is a solution that contains the following components at their mass ratio (%): water - 95 - 95.2, superplasticizer based on polycarboxylate ethers - 3.2 - 3.3, polypropylene fiber - 1.6 - 1.7 ...

The method for producing a mixture for 3D-printed volumetric-colored composite is as follows. In a high-speed rotary mixer, dry components are mixed for 1 - 2 minutes: Portland cement, quartz sand, metakaolin. At the same time, a liquid grout is being prepared - water is mixed with a superplasticizer. A reinforcing component - polypropylene fiber is introduced into the resulting solution immediately before use. The grout is added to the dry components, the resulting mixture is mixed in a high-speed rotary mixer for 3 - 5 minutes. In order to obtain a product of a given color, two methods of pigment introduction are possible. In the first method, the pigment is introduced into a mixture of dry components, which contributes to obtaining a composite that is uniformly colored throughout the volume. In the second method, the pigment is introduced directly into the mixer 10 - 15 seconds before the end of mixing. In this case, a composite is obtained that has a differentiated color by volume. Thus, the claimed solution meets the criterion of the invention "novelty".

The technical result of the proposed invention is to obtain a decorative volumetric-colored composite for construction 3D printing of a given color.

The mixture for obtaining a decorative volumetric-colored composite can be used for printing construction objects, architectural forms, facade decor elements 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 original components:

1. Portland cement CEM I 42.5 N (grade M500 D0) in accordance with GOST 31108-2016 “Cements for general construction. Specifications "(mineralogical composition C ₃ S - 60.85%, C ₂ S - 13.38%, C ₃ A - 7.42%, C ₄ AF - 11.23%).

2. Fractionated aggregate - quartz sand with Mk ≤ 1.25 in accordance with GOST 8736-2014 “Sand for construction work. Technical conditions ".

3. Metakaolin grade "VMK-45" with SiO ₂ content not less than 53% and Al ₂ O ₃ not less than 47% according to TU 23.99.19-004-34556001-2017.

5. Red powder pigment based on Fe ₂ O ₃ with its content not less than 96.1% or green based on Cr ₂ O ₃ ⋅2H ₂ O + Fe ₂ O ₃ with Fe ₂ O ₃ content not less than 26.1 %.

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

7. Superplasticizer based on polycarboxylate esters. Density
1.055 - 1.065 kg / dm3, pH = 4.0 - 5.5.

8. Polypropylene fiber for concrete and mortar, produced in accordance with ISO 9001: 2008 and meets European standard EN 14889-2: 2008. Fiber length 12mm, diameter
22 - 34 microns, density 0.91 kg / dm ³ , tensile strength 300 - 400 N / mm ² .

To obtain a 3D-printed mixture, the following dry components are used with their mass ratio (%): Portland cement CEM I 42.5 N - 43.10 - 43.48, sand with a fineness modulus Mk ≤ 1.25 - 53.35 - 53, 89, metakaolin with at least 53% _{SiO 2 and at least 47% Al 2} O ₃ - 0.855 - 0.866, red powder pigment based on Fe ₂ O ₃ with its content at least 96.1% or green based on Cr ₂ O ₃ ⋅2H ₂ O + Fe ₂ O ₃ with a Fe ₂ O ₃ content of at least 26.1% - 1.304 - 2.155. A liquid grout is a solution that contains the following components at their mass ratio (%): water - 95 - 95.2, superplasticizer based on polycarboxylate ethers - 3.2 - 3.3, polypropylene fiber - 1.6 - 1.7 ...

The method for producing a mixture for 3D-printed volumetric-colored composite is as follows. In a high-speed rotary mixer, dry components are mixed for 1 - 2 minutes: Portland cement, quartz sand, metakaolin. At the same time, a liquid grout is being prepared - water is mixed with a superplasticizer in a separate container. A reinforcing component - polypropylene fiber is introduced into the resulting solution immediately before use. The grout is added to the dry components, the resulting mixture is mixed in a high-speed rotary mixer for 3 - 5 minutes. In order to obtain a product of a given color, two methods of pigment introduction are possible. In the first method, the pigment is introduced into a mixture of dry components, which contributes to the formation of a composite that is uniformly colored throughout the volume. In the second method, the pigment is introduced directly into the raw mixture 10 - 15 seconds before the end of mixing. In this case, a composite is obtained that is differentially colored in terms of volume.

To assess the plasticity and extrusion capacity of the viscous-plastic mixture, the compressive yield strength was determined immediately after its manufacture. For this, a squeezing test was carried out with a constant deformation rate of 5 mm / s, since at this 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 carried out 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 Criteria Evaluation of the Rheological Behavior of Mixtures for Construction 3D Printing // Building Materials. - 2018. - No. 12. - P. 30-35 /.

To determine the physical and mechanical properties of a composite material for construction 3D printing, samples are prepared in the form of a cube with an edge length of 50 × 50 × 50 mm and are tested for compression in accordance with GOST 10180-2012, determination of density and water absorption in accordance with GOST 12730.3-78.

To determine the adhesion strength of the layers of the freshly laid mixture, a series of layered cube specimens with the rib length of 50 × 50 × 50 mm was made from the viscous-plastic mixture, the production of which was carried out in two stages. First, samples of 50 × 50 × 25 mm were made, which after 5 minutes were combined into a single sample with dimensions of 50 × 50 × 50 mm. After 28 days of hardening, the samples were tested for tensile splitting, the load was applied along the adhesion seam of the samples in accordance with GOST 10180-2012. The formation of a seam between two fresh surfaces most reliably makes it possible to evaluate 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 frost resistance grade of the obtained composite material was determined according to GOST 10060-2012.

Determination of shrinkage deformations during drying of a decorative volume-colored composite was carried out under dehydration conditions that simulate the development of shrinkage in thin-layer printed structures. For this, specimen-plates with dimensions of 10 × 40 × 160 mm were made, the dehydration of which was carried out at a given temperature (t) and humidity of the environment (W) until a constant mass and size was achieved. To create a temperature and humidity regime, the plate samples were placed in a desiccator over a CaCl ₂ ⋅6H ₂ O solution (modeling the operating conditions of drying, t = 21 º С, W = 30%), and then dehydrated over dry CaCl ₂ matter (modeling the conditions of complete dehydration, t = 21 º С, W = 5%). Sample measurements and processing of the results were carried out in accordance with GOST 25485 - 2019.

The properties of the viscous-plastic mixture and the physical and mechanical properties of the composite for construction 3D printing are presented in table. one.

Table 1

Rheological properties of a viscous-plastic mixture and physical and mechanical properties of a volumetric-colored decorative composite for construction 3D printing

Parameter name Meaning Compressive yield strength, kPa 3.90 - 5.09 Structural strength of a viscous-plastic mixture, kPa 1.91 - 5.22 Plastic strength viscous-plastic mixture, kPa 32.13 - 44.90 Relative deformation of the layer of the viscous-plastic mixture before the onset of destruction, mm / mm 0.03 - 0.04 Setting start, min 120 - 135 Compressive strength of composite material at the age of 24 hours, MPa 30.7 - 40.6 Compressive strength of composite material at the age of 28 days, MPa 69.5 - 83.0 Density of the composite material, kg / m ³ 2.08 - 2.27 Water absorption of composite material,% 7 Bond strength of composite layers (ultimate tensile strength during splitting), MPa 2.6 - 3.2 Frost resistance grade F200 Drying shrinkage, mm / m humidity of the environment 30% 1.1 - 1.2 humidity of the environment 5% 0.7 - 0.8

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

The use of a pigment of a given color, in a certain dosage and with a certain method of its introduction into the mixture helps to obtain a decorative, volumetric-colored composite of a given color. There are two ways to introduce the pigment. In the first case, when the powder pigment is introduced directly into the mixture of dry components, followed by the introduction of a liquid grout, the effect of uniform volumetric coloration of the composite is achieved. In the second case, when the pigment is introduced into the viscous-plastic mixture 10 - 15 seconds before the end of mixing, it is possible to obtain a composite having a differentiated color by volume. Thus, the aesthetic effect and architectural expressiveness of the resulting products are achieved.

In addition, pigments based on Fe ₂ O ₃ can act as a seed during crystallization (accelerate hardening processes), reduce the setting time of the binder (improve the dimensional stability of the system), and also interact, due to their amphotericity, with various components of the cement system, providing the system with additional neoplasms.

The introduction of metakaolin makes it possible to regulate the structural and mechanical properties of the cement system due to a similar crystal chemical structure. Due to the developed and active surface, metakaolin exhibits the ability to form polymolecular layers of adsorbed water on the surface, which contributes to an increase in the aggregate stability and structural strength of the cement system. At the same time, a decrease in the interaction of cement particles due to the presence of particles coated with polymolecular layers of adsorbed water in the intergranular volume contributes to an increase in the plasticity of the system with an optimized metakaolin content.

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

The use of a superplasticizer based on polycarboxylate esters in an optimal concentration is a factor in changing the properties of the liquid phase and makes it possible to effectively control the plasticity of the mixture.

The achievement of the required technical result in the implementation of the invention is that the use of a pigment of a given color range and its introduction into the cement mixture in various ways provides various options for volumetric coloring, which gives the resulting products an aesthetic effect and architectural expressiveness. In addition, the components that make up the mixture for a decorative volumetric-colored composite for 3D printing are set in a certain ratio, at a given percentage of the components in these phases, interacting to provide plasticity that affects extrusion; the dimensional stability required for layer-by-layer laying of the mixture without deformation of the layer during its subsequent loading; the established setting time, determined on the basis of the technology of layer-by-layer three-dimensional printing; compressive strength, density, water absorption, frost resistance and shrinkage, providing high performance characteristics of the composite.

Claims (6)

1. A mixture for obtaining a decorative volumetric-colored composite for construction 3D printing, characterized in that dry components and a liquid grout with polypropylene fibers distributed in it are used, the ratio between dry components and a liquid grout is 7.54 - 7, 58: 1; dry components: Portland cement CEM I 42.5 N, quartz sand with M _c ≤ 1.25, metakaolin with a SiO ₂ content of at least 53% and Al ₂ O ₃ at least 47%, a red powder pigment based on Fe ₂ O ₃ with its content of at least 96.1% or green based on Cr ₂ O ₃ ⋅2H ₂ O + Fe ₂ O ₃ with a Fe ₂ O ₃ content of at least 26.1%, the mass ratio of the components of the solid phase (%): Portland cement 43.10 - 43.48 quartz sand 53.35 - 53.89 metakaolin 0.855 - 0.866 powder pigment 1.304 - 2.155 liquid grout: water, superplasticizer based on polycarboxylate ethers, polypropylene fiber, mass ratio of components in the liquid phase (%): water 95 - 95.2 superplasticizer 3.2 - 3.3 polypropylene fiber 1.6 - 1.7 2. A method of obtaining a 3D-printed mixture according to claim 1 for a decorative volume-colored composite, consisting in the following: at the first stage, Portland cement, sand, metakaolin are mixed in a high-speed rotary mixer for 1 - 2 minutes, at the same time a liquid grout is obtained - in a separate container, water is mixed with a superplasticizer based on polycarboxylate ethers, immediately before use, polypropylene fiber is introduced into the resulting solution with vigorous stirring, the resulting grout is introduced into a mixture of dry components, the resulting mixture is mixed with a high-speed rotary mixer for 3 - 5 minutes, in order to obtain products of a given color, two methods of pigment introduction are possible: in the first method, to obtain a composite uniformly colored throughout the volume, a powder pigment of a certain color is introduced into a mixture of dry components; In the second method, to obtain a composite, differentially colored by volume, the pigment is introduced directly into the mixer 10 - 15 seconds before the end of mixing the mixture.