RU2775135C1 - Concrete mixture for 3d printing - Google Patents

Abstract

FIELD: building materials.

SUBSTANCE: invention relates to the building materials industry and can be used for the manufacture of building products and structures in the additive manufacturing technology by layer-by-layer extrusion (3D printing) of a concrete mixture based on Portland cement, sand, finely ground pozzolanic component and superplasticizer. The 3D printed concrete mix includes Portland cement, sand, superplasticizer and water. Portland cement contains 68.1 wt.% tricalcium silicate and 7.2 wt.% tricalcium aluminate, quartz sand with a fineness modulus of 2.2-2.4 and a moisture content of 1-2% is used as sand, and additionally, the concrete mixture contains finely ground pozzolanic component - biosilica with a specific surface area of ​​at least 1100 m2/kg and hydraulic activity of at least 1400 mg/g, and "Relamix PK" is used as a superplasticizer - a copolymer based on polyoxyethylene derivatives of unsaturated carboxylic acids with the following content of components, wt.%: Portland cement - 20.0-23.0, sand - 63.99-67.48, superplasticizer "Relamix PC "- 0.20-0.23, finely ground pozzolanic component - biosilica - 2.0-2.3, water - 10.32-10.48.

EFFECT: reducing the consumption of Portland cement and superplasticizer in the concrete mixture, increasing the dimensional stability and ensuring the absence of defects in the form of ruptures of printed layers from the concrete mixture with the possibility of its extrusion on building 3D printers that implement the layer-by-layer extrusion method, reducing shrinkage deformations, water absorption, increasing the flexural strength of the hardened composites printed on a 3D printer (without the use of molds).

1 cl, 2 tbl

Description

The invention relates to the building materials industry and can be used for the manufacture of building products and structures in the additive manufacturing technology by layer-by-layer extrusion (3D printing) of a concrete mixture based on Portland cement, sand, finely ground pozzolanic component and superplasticizer.

Known raw material mixture based on cement for building 3D printing, including sulfoaluminate cement - 150-400 kg, ash - 0-250 kg, sand with a particle diameter of 0.075-5 mm, polypropylene fiber with a length of 3-6 mm, superplasticizer PCE manufactured by Shandong Hongyi Technology Co., Ltd - 1.5-2.5% by weight of cement, retarder sodium tetraborate and tartaric acid in a ratio of 1: (1-1.5) - 0.01-0.2% by weight of cement, while the 10-minute draft of the proposed cement-based material is 90-110 mm, the beginning of setting is 15-80 minutes, the end of setting is 30-100 minutes [1]. The disadvantages of this invention are the presence of a large number of components of the mixture, the increased consumption of the components of the mixture and the increase in its cost caused by the use of fast-hardening sulfoaluminate cement and retarder.

A highly thixotropic raw material mixture for construction 3D printing is known, including, wt %: a special thixotropic agent 1.0-3.0, cement 35-40, a superplasticizer based on polycarboxylate esters 0.1-0.4, polypropylene fiber 0 ,1-0.4, water 12.5-14.5, sand - the rest [2]. The disadvantages of this invention are the reduction of the physico-mechanical characteristics of the composite at temperatures above 140 ⁰ C, caused by the melting of polypropylene fiber.

A modified polymer-cement composite material for 3D printing is known, including, wt %: Portland cement 24.37-34.16, polyvinyl acetate dispersion 2.44-2.56, sand 50.74-61.38, liquid glass 1.70- 2.44, polypropylene fiber 0.02-0.03, phloroglucinfurfural modifier 0.05-0.07, water - the rest [3]. The disadvantages of this invention are the low setting start time - up to 45-70 minutes, which makes it difficult to transport the raw mix from the plant to the construction site, low compressive strength and bending at the age of 28 days, increased water absorption.

The closest solution to the proposed invention is a two-phase mixture based on cement for composites in building 3D printing technology, phase 1 of which contains components in the following mass ratio of the solid phase,%: 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 contains components in the following mass ratio of the liquid phase, %: superplasticizer 4.1-4.6, water 95.4-95.9 [4].

The disadvantages of this invention are the increased consumption of Portland cement and superplasticizer (1.2-1.4% by weight of Portland cement), low dimensional stability of the printed layers from the raw mix, high shrinkage deformation of the hardened composite due to increased consumption of Portland cement and the use of sand belonging to the group "very fine » (according to GOST 8736-2014), high water absorption, low flexural strength of the hardened composite, decrease in the physical and mechanical characteristics of the composite at temperatures above 140 ⁰ C, caused by the melting of polypropylene fiber, the use of tetrapotassium pyrophosphate and xanthan gum as viscosity modifiers intended for use as additives for concretes and mortars (according to GOST 24211-2008). Also, the disadvantage of the invention is the lack of data on the moisture content of the components of the raw mixture, which affect the rheological and physico-mechanical properties of the composites, as well as the lack of data on the implementation of this invention on a 3D printer that implements the method of layer-by-layer extrusion and the quality of the products obtained. In addition, the disadvantage is the method used in the invention for preparing samples, which consists in their manufacture in the forms of 70x70x70 mm, 70x70x280 mm, while the construction 3D printing technology excludes the use of forms, which leads to a change in the pore structure of the composite and a distortion in obtaining reliable results. physical and mechanical properties (compressive and tensile strength, density, water absorption, etc.).

The objective of the invention is to reduce the consumption of Portland cement, a superplasticizer in a concrete mixture for building 3D printing, to increase dimensional stability and ensure the absence of defects in the form of breaks in printed layers from a concrete mixture with the possibility of its extrusion on building 3D printers that implement the method of layer-by-layer extrusion, to reduce shrinkage deformations , water absorption, increased flexural strength of hardened composites printed on a 3D printer (without the use of molds).

The technical result of the proposed solution is to reduce the consumption of Portland cement and superplasticizer in the concrete mixture, increase dimensional stability and ensure the absence of defects in the form of breaks in the printed layers of the concrete mixture with the possibility of its extrusion on building 3D printers that implement the method of layer-by-layer extrusion, reduce shrinkage deformations, water absorption, increase flexural strength of hardened composites printed on a 3D printer (without the use of molds).

The task is achieved in that the concrete mixture for 3D printing, including Portland cement, sand, superplasticizer and water, is characterized in that Portland cement contains 68.1 wt.% tricalcium silicate and 7.2 wt.% tricalcium aluminate, as sand quartz sand with a fineness modulus of 2.2-2.4 and a moisture content of 1-2% is used, and additionally, the concrete mixture contains a finely ground pozzolanic component - biosilica with a specific surface area of at least 1100 m ² /kg and a hydraulic activity of at least 1400 mg / g, and Relamix PK is used as a superplasticizer - a copolymer based on polyoxyethylene derivatives of unsaturated carboxylic acids with the following content of components, wt.%:

Portland cement
Sand
Superplasticizer "Relamix PK"
Finely ground pozzolanic component - biosilica
Water 20.0-23.0
63.99-67.48
0.20-0.23
2.0-2.3
10.32-10.48

For the manufacture of concrete mix for 3D printing, the following materials were used:

Portland cement CEM I 42.5N produced by Asia Cement LLC (GOST 31108-2016) with the following mineralogical composition: C ₃ S - 68.1%, C ₂ S - 9.4%, C ₃ A - 7.2%, C ₄ AF - 11%;

Quartz sand of the Kamsko-Ustyinsky deposit of the Republic of Tatarstan with a fineness modulus of 2.2-2.4, moisture content of 1-2% (GOST 8736-2014). To prepare the samples, sand with a fineness modulus of 2.3 and a moisture content of 1.5% was used;

Superplasticizer in the form of a copolymer based on polyoxyethylene derivatives of unsaturated carboxylic acids "Relamix PK" manufactured by Poliplast Kazan LLC, which is a light brown liquid, density at 20 ⁰ C 1.04 g/cm ³ , pH - 5;

The finely ground pozzolanic component is biosilica with a hydraulic activity of at least 1400 mg/g, a grinding degree of at least 1100 m ² /kg (STO 23998461-020-2018). Samples were prepared using biosilica with a hydraulic activity of 1443 mg/g, a grinding degree of 1186 m ² /kg;

Tap drinking water that meets the requirements of GOST 23732.

The proposed invention is carried out as follows: pre-metered dry components of the concrete mix - Portland cement, sand, biosilica - are loaded into a working mixer and mixed until a homogeneous mass is obtained. Then, dosing is carried out by weight of water, superplasticizer "Relamix PK", they are mixed until a homogeneous solution is obtained and it is gradually added to thoroughly mixed dry components, mixing the mixture until a homogeneous mass with PK 2 mobility (according to GOST 28013-98) is obtained at a depth immersion of the reference cone 7-8 cm. At the next stage, the 3D printer is prepared: the inner surface of the removable storage bin is moistened with drinking tap water or release agent. Next, the removable storage bin of the construction 3D printer is filled with the prepared concrete mixture and test extrusion is carried out until the resulting extrudate is homogeneous. Then, the concrete mixture is molded by layer-by-layer extrusion (3D printing) on a construction 3D printer (for example, AMT S-6044 of SPETSAVIA LLC) in accordance with a pre-prepared three-dimensional digital model. The three-dimensional digital model of the samples is a strip 40 cm long, with a single layer height of 20 mm. The concrete mixture is printed with the following adjustable printing parameters set in the Mach3 software package (Artsoft founder Art Fenerty): the spindle speed is 3000-5000 units, the feed rate is 4000-6000 units/min.

The shape stability of the printed layers of the concrete mixture was evaluated by the ability of the mixture to maintain its position in space under the influence of technological factors, namely, by the maximum height of the printed sample without technological interruptions until it reaches a critical state - loss of stability as a whole, characterized by its overturning or loss of stability of the sample shape with displacement printed layers.

Samples were also tested according to the prototype using Portland cement CEM I 42.5N according to GOST 31108-2016, sand with a fineness modulus less than or equal to 1.25 according to GOST 8736-2014, xanthan gum containing (C ₃₅ H ₄₉ O ₂₉ ) _n not less than 91%, technical tetrapotassium pyrophosphate with a content of K ₄ P ₂ O ₅ not less than 98%, polypropylene fiber 12 mm long, superplasticizer based on polycarboxylate ethers, water.

After 28 days of normal hardening, samples were prepared for testing, molded by layer-by-layer extrusion (3D printing), by sawing them into 40x40x160 mm prisms. The water absorption of the hardened composite was determined according to GOST 12730.3-78 “Concrete. Method for determining water absorption. The flexural strength of the hardened composite was determined on beam specimens 40x40x160 mm in size according to GOST 5802-86. "Construction solutions. Test Methods” using the MII-100 testing machine. Shrinkage deformations were assessed by the presence of shrinkage cracks on the hardened composites, the presence of defects in the form of ruptures in the printed layers of the concrete mix was carried out by a visual-instrumental method using a measuring metal ruler according to GOST 427-75 and a measuring magnifier with illumination according to GOST 25706-83.

The compositions of concrete mixtures for 3D printing are shown in Table 1, the physical and mechanical parameters for the compositions are given in Table 2.

Table 1

Components Compositions of concrete mixtures for 3D printing, wt. % one 2 3 four 5 6 7 8 (prototype) Portland cement 18.0 21.5 21.5 20.0 21.5 23.0 25.0 37.85 Sand 68.95 68.35 63.35 67.48 65.73 63.99 60.85 48.80 Superplasticizer "Relamix PK" 0.15 0.215 0.20 0.22 0.23 0.25 Biosilica 1.5 2.15 2.0 2.15 2.3 2.5 xanthan gum 0.07 Tetrapotassium pyrophosphate technical 0.07 Polypropylene fiber 1.72 Superplasticizer based on polycarboxylate esters 0.47 Water 11.4 9.935 13.0 10.32 10.40 10.48 11.4 11.02

table 2

Properties Physical and mechanical parameters for compositions one 2 3 four 5 6 7 8 (prototype) Dimensional stability of printed layers of concrete mixture (product height obtained by 3D printing without technological interruptions), cm fifteen fourteen eleven twenty 23 22 16 ten Bending strength for 28 days, MPa 7.2 8.8 8.5 8.4 8.8 9.2 7.4 4.0 Water absorption, % 8.4 7.0 8.9 5.3 5.1 5.0 5.0 7.5 Shrinkage deformations (presence of shrinkage cracks - yes / no) Yes Yes Yes No No No No Yes Defects in the form of gaps (yes / no) No Yes No No No No No Yes

It follows from the given data that the maximum values of the dimensional stability of the printed layers from the concrete mix, the flexural strength, the water absorption of the hardened composites are achieved when the content of Portland cement in the concrete mixture is 20.0-23.0% of the total mass of the composition, sand - 63, 99-67.48%, Relamix PK superplasticizer - 0.20-0.23%, finely ground pozzolanic component - biosilica - 2.0-2.3%, water - 10.32-10.48%. With the introduction of Portland cement, superplasticizer "Relamix PK", finely ground pozzolanic component - biosilica, in an amount less than those indicated in table 1 (composition 4), there is a decrease in the studied properties compared to the claimed limits. With their introduction, in an amount greater than those indicated in Table 1 (composition 6), the studied properties of the compositions printed on a 3D printer are reduced. There are no shrinkage cracks in the compositions of concrete mixes for construction 3D printing (compositions 4-7), in compositions 1, 3-7 there are no defects in the form of gaps.

The concrete mixture for 3D printing, obtained according to the proposed invention, has a reduced consumption of Portland cement and superplasticizer, increased dimensional stability and the absence of defects in the form of ruptures in the printed layers of the concrete mixture with the possibility of its extrusion on building 3D printers that implement the method of layer-by-layer extrusion, products - high strength characteristics in bending, absence of shrinkage cracks, low water absorption.

The use of sand of medium size with a fineness modulus of 2.2-2.4 in combination with a reduced cement-sand ratio makes it possible to reduce the development of shrinkage deformations of the composite molded by layer-by-layer extrusion (3D printing). In addition, a reduced cement-sand ratio makes it possible to reduce the consumption of Portland cement in the concrete mixture while ensuring formability on a 3D printer and physical and mechanical properties.

The use of Relamix PK superplasticizer (a copolymer based on polyoxyethylene derivatives of unsaturated carboxylic acids) in an amount of 0.20-0.23 wt.% makes it possible to reduce the amount of mixing water, increase the dimensional stability and density of the mixture, and the physical and mechanical characteristics of the hardened composite while ensuring optimal rheotechnological properties of the concrete mixture for its layer-by-layer extrusion.

The introduction of a finely milled pozzolanic component - biosilica with a grinding degree of at least 1100 m ² /kg, hydraulic activity of at least 1400 mg / g can improve the formability of the concrete mix by providing cohesion, uniformity and plasticity, which contributes to the production of hardened composites printed on a 3D printer , with reduced shrinkage deformations and the absence of defects on them.

Joint use of superplasticizer "Relamix PK" in the amount of 0.20-0.23 wt.% and biosilica with a grinding degree of at least 1100 m ² /kg, hydraulic activity of at least 1400 mg/g in the amount of 2.0-2.3 wt .% contributes to giving the concrete mixture optimal rheotechnological properties, increasing the dimensional stability of the printed layers from the concrete mixture, and the physical and mechanical properties (increasing the flexural strength, reducing water absorption) of hardened composites printed on a 3D printer.

Thus, the proposed solution makes it possible to obtain a concrete mixture for 3D printing with a reduced consumption of Portland cement and superplasticizer, which has high dimensional stability, and products based on it with high bending strength characteristics, low water absorption, reduced shrinkage deformations and the absence of defects on them.

Sources of information:

1. Patent CN 105753404A, B33Y70/00, Cement-based material used for building 3D (three-dimensional) printing, Appl. 02/13/2016, publ. 07/13/2016.

2. Patent CN 108715531A, C04B28/02, A kind of high thixotropic 3D printing concrete and preparation method thereof, Appl. 06/12/2018, publ. 08/28/2020.

3. Patent, RU 2 661 970, С04В 28/04, С04В 14/02, С04В 22/08, С04В 26/00, С04В2111/20, С04В2111/343, Modified polymer-cement composite material for 3D printing, Poluektova V.A. ., Shapovalov N.A., Chernikov R.O., Evtushenko E.I., patentee Federal State Budgetary Educational Institution of Higher Education "Belgorod State Technological University". , bid. 07/31/2017, publ. 07/23/2018, bul. No. 21.

4. Patent, RU 2 729 086, С04В 28/04, Two-phase mixture based on cement for composites in the technology of construction 3D printing, Slavcheva G.S., Aratmonova O.V., Shvedova M.A., Britvina E.A. ., patentee Federal State Budgetary Educational Institution of Higher Education "Voronezh State Technical University"., Appl. 10/21/2019, publ. 08/04/2020, bul. No. 22.

Claims (2)

Concrete mixture for 3D printing, including Portland cement, sand, superplasticizer and water, characterized in that Portland cement contains 68.1 wt.% tricalcium silicate and 7.2 wt.% tricalcium aluminate, quartz sand with a particle size modulus of 2 is used as sand ,2-2.4 and humidity of 1-2%, and additionally the concrete mixture contains a finely ground pozzolanic component - biosilica with a specific surface area of at least 1100 m ² / kg and a hydraulic activity of at least 1400 mg / g, and "Relamix" is used as a superplasticizer PC" is a copolymer based on polyoxyethylene derivatives of unsaturated carboxylic acids with the following content of components, wt.%: Portland cement
Sand
Superplasticizer "Relamix PK"
Finely ground pozzolanic component - biosilica
Water 20.0-23.0
63.99-67.48
0.20-0.23
2.0-2.3
10.32-10.48