RU2780314C1 - Modified cement-based construction mix for 3d printing - Google Patents

Abstract

FIELD: construction materials.

SUBSTANCE: invention relates to the field of construction materials industry and can be used for the manufacture of building products and structures in additive manufacturing technology using layer-by-layer extrusion (3D printing) of a modified construction mixture based on Portland cement, sand, finely ground pozzolan component, superplasticizer and methylsilantriol potassium salt. The modified cement-based construction mix for 3D printing, including Portland cement, sand, superplasticizer and water, characterized in that Portland cement contains, wt. %: 68.1 tricalcium silicate, 7.2 tricalcium aluminate, quartz sand with a grain size of 2.2-2.4 and a moisture content of 1-2, MasterPozzolith 55 based on lignosulfonates is used as a superplasticizer, and additionally modified construction mixture contains methylsilantriol potassium salt ”GKZH-11K”, a binary mixture of finely ground pozzolan component: bio-silica with a grinding degree of at least 1100 m²/kg and a hydraulic activity of at least 1400 mg/g and kaolin with a grinding degree of at least 1800 m²/kg and a hydraulic activity of kaolin 600 mg/g with the following component content, wt. %: specified Portland cement 20.0–23.0, specified quartz sand 59.20-62.85, superplasticizer MasterPozzolith 55 0.20-0.23, finely ground pozzolan component: biosilicon 2.0-2.3, finely ground component: kaolin 2.0-2.3, methylsilantriol potassium salt “GKZH-11K” 0.010-0.012, water 12.940-12.958.

EFFECT: reducing the consumption of Portland cement and superplasticizer in the modified construction mixture, increasing the shape stability and ensuring the absence of defects in the form of ruptures of printed layers from the modified construction mixture with the possibility of its extrusion on construction 3D printers implementing the method for layer-by-layer extrusion, reducing shrinkage deformations, water absorption, increasing the bending strength of hardened composites printed on 3D printer (without using forms).

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 modified building mixture based on Portland cement, sand, finely ground pozzolanic component, superplasticizer and methylsilanetriol potassium salt.

Known raw material mixture based on cement for construction 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 decrease in the physical and 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 the 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, reduction in the physico-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 layer-by-layer extrusion method 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 distortion of 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 modified building mix for 3D printing, increase dimensional stability and ensure the absence of defects in the form of breaks in printed layers from a modified building mix with the possibility of extruding it on building 3D printers that implement the method of layer-by-layer extrusion, reducing 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 modified building mixture, increase dimensional stability and ensure the absence of defects in the form of ruptures in printed layers from the modified building mixture with the possibility of extruding it on building 3D printers that implement the method of layer-by-layer extrusion, reducing shrinkage deformations, water absorption , increasing the flexural strength of hardened composites printed on a 3D printer (without the use of molds).

The task is achieved in that the modified mortar based on cement for 3D printing, including Portland cement, sand, superplasticizer and water, is characterized in that Portland cement contains 68.1 wt.% tricalcium silicate, 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 wt.%, "MasterPozzolith 55" based on lignosulfonates is used as a superplasticizer, and an additionally modified building mixture contains methylsilanetriol potassium salt "GKZH-11K ”, a binary mixture of finely ground pozzolanic component - biosilica with a grinding degree of at least 1100 m ² / kg and a hydraulic activity of at least 1400 mg / g and kaolin with a grinding degree of at least 1800 m ² / kg of kaolin hydraulic activity of 600 mg / g with the following component content , wt.%:

Specified Portland cement
Specified quartz sand
Superplasticizer "MasterPozzolith 55"
Finely ground pozzolanic component - biosilica
Finely ground component - kaolin
Methylsilanetriol potassium salt "GKZH-11K"
Water 20.0-23.0
59.20-62.85
0.20-0.23
2.0-2.3
2.0-2.3
0.010-0.012
12.940-12.958

The following materials were used to manufacture a modified cement-based mortar for 3D printing:

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%, With 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 based on lignosulfonates, "MasterPozzolith 55" manufactured by BASF Building Systems LLC, which is a dark brown liquid, density at 20 °C 1.15 g/cm ³ , pH 4.5.

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 produced by Diamix LLC (STO 23998461-020-2018). Biosilica with a hydraulic activity of 1443 mg/g and a grinding degree of 1186 m ² /kg was used to prepare the samples.

The finely ground pozzolanic component is kaolin with a hydraulic activity of at least 600 mg/g, a grinding degree of at least 1800 m ² /kg (TU 5729-016-48174985-2003). For the preparation of samples used kaolin with a hydraulic activity of 627.3 mg/g, a grinding degree of 1859 m ² /kg;

Methylsilanetriol potassium salt "GKZH-11K" produced by PJSC "Khimprom", which is a dark brown liquid with a density of 1.34 g / cm ³ at 20 ° C;

Tap drinking water that meets the requirements of GOST 23732.

The proposed invention is carried out as follows: pre-dosed dry components of the modified building mix - Portland cement, sand, biosilica, kaolin are loaded into the working mixer and mixed until a homogeneous mass is obtained. Then, dosing is carried out by weight of water, superplasticizer "MasterPozzolith 55", methylsilanetriol potassium salt, they are mixed until a homogeneous solution is obtained and it is gradually added to the thoroughly mixed dry components, stirring the mixture until a homogeneous mass with a mobility of Pk 2 is obtained (according to GOST 28013- 98) at an immersion depth of the reference cone of 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 a release agent. Next, the removable storage hopper of the construction 3D printer is filled with the prepared modified construction mixture and test extrusion is carried out until the resulting extrudate is homogeneous. Then, the modified building 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. Printing of the modified building mixture is carried out 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 from the modified building 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 offset 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 printed layers from a modified building mixture 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 modified building mixtures based on cement for 3D printing are shown in Table 1, the physical and mechanical parameters for the compositions are shown in Table 2.

Table 1

Components Compositions of modified building mixtures based on cement for 3D printing, wt. % one 2 3 four 5 6 7 eight 9 (prototype) Portland cement 18.0 21.0 21.0 21.0 20.0 21.5 23.0 24.5 37.85 Sand 65.632 61.58 60.97 58.34 62.85 61.02 59.20 57.727 48.80 Superplasticizer "MasterPozzolith 55" 0.15 0.20 0.215 0.23 0.25 Biosilica 1.5 2.3 2.3 2.0 2.15 2.3 2.5 Kaolin 1.5 2.3 2.3 2.0 2.15 2.3 2.5 Methylsilanetriol potassium salt "GKZH-11K" 0.008 0.010 0.010 0.010 0.011 0.012 0.013 xanthan gum 0.07 Tetrapotassium pyrophosphate technical 0.07 Polypropylene fiber 1.72 Superplasticizer based on polycarboxylate esters 0.47 Water 13.21 15.12 15.72 16.05 12,940 12.954 12.958 12.51 11.02

table 2

Properties Physical and mechanical parameters for compositions one 2 3 four 5 6 7 eight 9 (prototype) Form stability of printed layers from a modified building mixture (product height obtained by 3D printing without technological interruptions), cm fourteen fifteen 13 eighteen 19 21 22 fifteen ten Bending strength for 28 days, MPa 9.9 9.3 10.9 10.8 11.5 11.9 11.0 9.0 4.0 Water absorption, % 8.4 9.1 7.5 8.7 7.2 7.3 7.2 7.1 7.5 Shrinkage deformations (presence of shrinkage cracks - yes / no) No No No Yes No No No No Yes Defects in the form of gaps (yes / no) Yes Yes Yes No No No No No Yes

It follows from the given data that the maximum dimensional stability of the printed layers from the modified building mixture, the ultimate strength in bending of hardened composites are achieved when the content of Portland cement in the composition of the modified building mixture is 20.0-23.0% of the total mass of the composition, sand is 59.20 -62.85%, MasterPozzolith 55 superplasticizer - 0.20-0.23%, finely ground pozzolanic component - biosilica - 2.0-2.3%, finely ground pozzolanic component - kaolin - 2.0-2.3% , methylsilanetriol of potassium salt "GKZH-11K" - 0.010-0.012%, water - 12.940-12.958%. With the introduction of Portland cement, superplasticizer "MasterPozzolith 55", finely ground pozzolanic component - biosilica, finely ground pozzolanic component - kaolin, methylsilanetriol of potassium salt "GKZH-11K", in an amount less than those indicated in Table 1 (composition 5), there is a decrease in the parameters of the studied properties compared to with the stated limits. With their introduction, in an amount greater than those indicated in Table 1 (composition 7), the studied properties of the compositions printed on a 3D printer decrease or increase slightly. There are no shrinkage cracks in the compositions of modified building mixtures based on cement for 3D printing (compositions 1-3, 5-8), in compositions 4-8 there are no defects in the form of gaps.

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

The use of medium-sized sand 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 a modified building mix while ensuring formability on a 3D printer and physical and mechanical properties.

The use of "MasterPozzolith 55" superplasticizer based on lignosulfonates in the amount of 0.20-0.23 wt.% makes it possible to reduce the amount of mixing water, increase the density of the mixture and the physical and mechanical characteristics of the hardened composite, while ensuring optimal rheotechnological properties of the modified building mixture for its layer-by-layer extrusion , which also provide high dimensional stability of the printed layers from the modified building mix.

The introduction of a finely milled pozzolanic component - biosilica with a grinding degree of at least 1100 m ² /kg, a hydraulic activity of at least 1400 mg / g can improve the dimensional stability of printed layers from a modified building mixture by improving its uniformity, cohesion and plasticity during layer-by-layer extrusion (3D printing ).

The introduction of a finely ground pozzolanic component - kaolin with a grinding degree of at least 1800 m ² /kg, a hydraulic activity of at least 600 mg / g, makes it possible to increase the flexural strength of hardened composites due to interaction with portlandite formed during the hydration of Portland cement, and an increase in the number of neoplasms from low-basic calcium hydrosilicates.

The use of a binary mixture of biosilica with a grinding degree of at least 1100 m ² /kg, a hydraulic activity of at least 1400 mg/g and kaolin with a grinding degree of at least 1800 m ² /kg, a hydraulic activity of at least 600 mg/g allows to achieve a synergistic effect, expressed in increasing the dimensional stability of printed layers from a modified building mixture with the possibility of extruding it on construction 3D printers that implement the layer-by-layer extrusion method, by improving its uniformity, coherence and plasticity during layer-by-layer extrusion (3D printing), which makes it possible to obtain products on a 3D printer without defects in the form of gaps, increasing the flexural strength of the hardened composite, printed on a 3D printer.

The use of methylsilanetriol potassium salt "GKZH-11K" in the amount of 0.010-0.012 wt.% allows to reduce the water absorption of hardened composites printed on a 3D printer (without using forms), by making the walls of capillaries and pores water-repellent.

Joint use of the superplasticizer "MasterPozzolith 55" in the amount of 0.20-0.23 wt.%, a binary mixture of biosilica with a grinding degree of at least 1100 m ² /kg, a hydraulic activity of at least 1400 mg/g and kaolin with a grinding degree of at least 1800 m ² /kg, hydraulic activity of at least 600 mg/g in the amount of 4.0-4.6 wt.% and methylsilanetriol of potassium salt "GKZH-11K" in the amount of 0.010-0.012 wt.% contributes to giving the modified building mixture optimal rheotechnological properties , increasing the dimensional stability of printed layers from a modified building mixture, physical and mechanical indicators (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 modified mortar based on cement for 3D printing by layer-by-layer extrusion with a reduced consumption of Portland cement and superplasticizer, which has high dimensional stability, and products based on it with high flexural strength characteristics, low water absorption, reduced shrinkage deformations and their absence of defects.

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., Patent holder Federal State Budgetary Educational Institution of Higher Education "Belgorod State Technological University". 07/31/2017, publ. 07/23/2018, bul. No. 21.

Patent, RU 2 729 086, С04В 28/04, Two-phase mixture based on cement for composites in the technology of building 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". 10/21/2019, publ. 08/04/2020, bul. No. 22.

Claims (2)

Modified mortar based on cement for 3D printing, including Portland cement, sand, superplasticizer and water, characterized in that Portland cement contains 68.1 wt.% tricalcium silicate, 7.2 wt.% tricalcium aluminate, sand - quartz sand with a fineness modulus of 2.2-2.4 and a moisture content of 1-2 wt.%, "MasterPozzolith 55" based on lignosulfonates is used as a superplasticizer, and an additionally modified building mixture contains methylsilanetriol potassium salt "GKZH-11K", a binary mixture of finely ground pozzolanic component - biosilica with a grinding degree of at least 1100 m ² /kg and a hydraulic activity of at least 1400 mg/g and kaolin with a grinding degree of at least 1800 m ² /kg and a hydraulic activity of kaolin of 600 mg/g with the following content of components, wt.% : Specified Portland cement 20.0-23.0 Specified quartz sand 59.20-62.85 Superplasticizer "MasterPozzolith 55" 0.20-0.23 Finely ground pozzolanic component - biosilica 2.0-2.3 Finely ground component - kaolin 2.0-2.3 Methylsilanetriol potassium salt "GKZH-11K" 0.010-0.012 Water 12.940-12.958