Concrete mix with ground rice husk for 3D printing

Abstract

FIELD: building materials industry.SUBSTANCE: invention can be used for the manufacture of building products and structures in additive manufacturing technology by layer-by-layer extrusion (3D printing) of a raw mixture based on Portland cement, sand, ground rice husk, a finely ground pozzolanic component, a superplasticizer and sodium methyl siliconate. The concrete mix for 3D printing includes Portland cement, sand with 12% moisture content, lignosulfonate-based superplasticizer, finely ground pozzolanic component and water. In this case, Portland cement of the “ЦЕМ 1 42.5Н” brand is used, containing, wt.%: tricalcium silicate 59.7, tricalcium aluminate 8.0, dicalcium silicate 14.4, tetracalcium aluminoferrite 12.9, quartz sand with a fineness modulus of 3.5, "MasterPozzolith 55" is used as a superplasticizer based on linsulfonates, and as a finely ground pozzolanic component - waste ash from thermal power plants with a specific surface area of 230 m2 / kg, containing, wt.%: silicon dioxide 57.03, aluminium oxide 31.71 and additionally the raw mix contains sodium methylsiliconate "ГКЖ-11Н" and ground rice husk with a bulk density of 338 kg / m3 at a certain ratio of components.EFFECT: reduction in the thermal conductivity coefficient, reduction in the average density of structural heat-insulating concrete, and ensuring the mouldability of the mixture using 3D printing.1 cl, 2 tbl

Description

[0001] The invention relates to the field of the building materials industry and can be used for the manufacture of building products and structures in additive manufacturing technology by layer-by-layer extrusion (3D printing) of a raw mixture based on Portland cement, sand, ground rice husk, finely ground pozzolanic component, superplasticizer and sodium methyl siliconate.

[0002] A cement-based raw material mixture for construction 3D printing is known, 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, PCE superplasticizer produced by Shandong Hongyi Technology Co., Ltd - 1.5-2.5% of the cement weight, sodium tetraborate setting retarder and tartaric acid in a ratio of 1: (1-1.5) - 0.01-0.2% of the cement weight, while the 10-minute settlement 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 in the mixture, increased consumption of the components of the mixture and an increase in its cost caused by the use of fast-hardening sulfoaluminate cement and a setting retarder.

[0003] A highly thixotropic raw material mixture for construction 3D printing is known, which includes, in 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 a decrease in the physical and mechanical properties of the composite at temperatures above 140 0 C, caused by melting of polypropylene fiber.

[0004] A modified polymer-cement composite material for 3D printing is known, comprising, in 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, phloroglucinol furfural modifier 0.05-0.07, water is the rest [3]. The disadvantages of this invention are short setting time - up to 45-70 min, which causes difficulty in transporting the raw mix from the plant to the construction site, low compressive and bending strength at the age of 28 days, increased water absorption.

[0005] A device and method for producing heat-insulating walls from polystyrene concrete using a 3D printer are known, which includes feeding a binder from an extruder, preheated in it, through a nozzle to form the structural and heat-insulating part of the wall, polystyrene concrete with unfoamed polystyrene is used as a binder, which is extruded through a nozzle onto the surface of a previously laid layer over its entire width, after which it is heated by an electric current penetrating it, supplied to the side spatula-electrodes to the foaming temperature of the polystyrene and formed into a new layer using an upper pressing spatula and spatula-electrodes [4]. A disadvantage of this invention is the difficulty of uniformly distributing the filler, since the polystyrene foam granules have a low density and are prone to segregation (stratification) in the concrete mixture during its transportation and printing.This leads to structural inhomogeneity in the finished structure, localized reductions in strength and thermal insulation properties. Another drawback is reduced adhesion between the printed layers, as the surface of the polystyrene foam granules is hydrophobic, which impairs adhesion to the cement paste, reducing the integrity and strength of the material.

[0006] A modified fine-grained concrete mixture for 3D printing in construction is known, comprising, by weight: Portland cement 6, gypsum binder 22.8, metakaolin 1.2, quartz sand 60, superplasticizer "Glenium Ace 430" 0.2, copolymer based on carboxylic acid esters with the addition of a phosphate component "Best-TB" 0.3, a homogeneous mixture of oligoethoxysiloxanes "Ethyl silicate-40" 0.02, water - the rest [5]. The disadvantages of this invention are a decrease in the physical and mechanical properties of the composite when used in a humid environment, caused by softening of the binder.

[0007] The closest solution to the proposed invention is a raw mix for extrusion on a 3D printer, comprising, wt. %: Portland cement containing, wt. %: tricalcium silicate 68.1, tricalcium aluminate 7.2, 20.0-23.0, quartz sand with a fineness modulus of 2.2-2.4 and a moisture content of 1-2% 62.44-65.84, superplasticizer "MasterGlenium 430" based on polycarboxylate esters 0.20-0.23, finely ground pozzolanic component - biosilica with a hydraulic activity of at least 1400 mg / g, a degree of grinding of at least 1100 m 2 / kg 2.0-2.3, methylsilanetriol potassium salt "GKZh-11K" 0.010-0.012, water 11.950-12.018 [6].

[0008] The disadvantages of this invention include the low thermal insulation properties of hardened concrete due to its high density and thermal conductivity, which leads to the need for additional thermal insulation layers, and the high content of tricalcium silicate in Portland cement (68.1 wt.%), which requires high energy consumption due to the high firing temperature and raw materials. Another disadvantage of the invention is the use of biosilica with a high specific surface area (at least 1100 m) as a finely ground pozzolanic component. 2 / kg) limits the raw material base and increases the cost of finished products.

[0009] The objective of the proposed invention is to create a structural heat-insulating concrete that meets the average density, compressive strength and thermal conductivity requirements of GOST 25820-2021, molded using the 3D printing method, with improved thermal insulation properties, reduced average density indicators with reduced requirements for raw materials - the possibility of using Portland cement with a smaller amount of tricalcium silicate and the use of waste from the production of thermal power plant ash as a pozzolanic component while ensuring moldability using the 3D printing method.

[0010] The technical result of the proposed solution is a reduction in the thermal conductivity coefficient, a reduction in the average density of structural heat-insulating concrete, and ensuring the moldability of the mixture using 3D printing.

[0011] The stated objective is achieved in that the concrete mixture for 3D printing, including Portland cement, sand with a moisture content of 12%, a superplasticizer based on lignosulfonates, a finely ground pozzolanic component and water, is characterized by the fact that they use Portland cement grade CEM 1 42.5N, containing, by weight. %: tricalcium silicate 59.7, tricalcium aluminate 8.0, dicalcium silicate 14.4, tetracalcium aluminoferrite 12.9, quartz sand with a fineness modulus of 3.5, as a superplasticizer based on lignosulfonates they use "MasterPozzolith 55", as a finely ground pozzolanic component - waste ash from thermal power plants with a specific surface of 230 m 2 / kg, containing, wt. %: silicon dioxide 57.03, aluminum oxide 31.71 and additionally the raw material mixture contains sodium methylsiliconate "GKZh-11N" and ground rice husk with a bulk density of 338 kg / m3 3 with the following ratio of components, wt. %:

[0012] The specified Portland cement 23,389-27,331 Quartz sand with a moisture content of 1-2% and fineness modulus 3.5 35,084-40,997 The specified superplasticizer 0,21-0,245 The specified waste ash from thermal power plants 2,339-2,733 Sodium methyl siliconate "GKZh-11N" 0,012-0,014 Ground rice husks 12,436-21,284 Water 16,244-17,682

[0013] The following materials were used to produce the raw material mixture for extrusion on a 3D printer:

[0014] Portland cement CEM I 42.5N produced by OJSC Magnitogorsk Cement and Refractory Plant (GOST 31108-2020) with the following mineralogical composition: C3S - 59.7%, C2S - 14.4%, C3A - 8.0%, C4AF - 12.9%;

[0015] Quartz sand from the Kamsko-Ustinskoye deposit in the Republic of Tatarstan with a fineness modulus of 3.5 and a moisture content of 1-2% (GOST 8736-2014). Sand with a fineness modulus of 3.5 and a moisture content of 1.6% was used to prepare the samples;

[0016] Superplasticizer based on lignosulfonates "MasterPozzolith 55" produced by BASF Construction Systems LLC, which is a dark-brown liquid with a density of 1.15 g / cm at 20 °C 3 , pH - 4.5;

[0017] Finely ground pozzolanic component - waste ash from thermal power plant-2 (Almaty, Republic of Kazakhstan), specific surface area 230 m 2 / kg. Content of main components, wt. %: silicon dioxide 57.03, aluminum oxide 31.71;

[0018] Sodium methyl siliconate "GKZh-11N" produced by PJSC "Khimprom", which is a dark brown liquid with a density of 1.15 g / cm 3 at 20°C;

[0019] Milled rice husk from the Kyzylorda rice mill of the Republic of Kazakhstan, bulk density of 338 kg / m3 3 ;

[0020] Tap drinking water that meets the requirements of GOST 23732.

[0021] The proposed invention is implemented as follows: ground rice husks are pre-soaked in water for 24 hours, followed by pressing to a moisture content of 120%. Pre-measured dry components of the raw mix—Portland cement, sand, thermal power plant waste ash, and ground rice husks—are loaded into a working mixer and mixed until a homogeneous mass is obtained. Next, water, MasterPozzolith 55 superplasticizer, and sodium methylsiliconate are dosed by weight, mixed until a homogeneous solution is obtained, and gradually added to the thoroughly mixed solid components, stirring the mixture until a homogeneous mass with a mobility of Pk⋅3 (according to GOST 28013-98) is obtained at an immersion depth of the reference cone of 9-9.5 cm. The next step is to prepare the 3D printer: the inner surface of the removable storage bin is moistened with tap drinking water or a release agent.Next, the removable storage hopper of the construction 3D printer is filled with the prepared raw mix and a test extrusion is performed until the resulting extrudate is homogeneous. The raw mix is ​​then formed using layer-by-layer extrusion (3D printing) on ​​a construction 3D printer (e.g., the AMT S-6044 from SPETSAVIA LLC) in accordance with a pre-prepared 3D digital model. The 3D digital model of the samples is a 40 cm long strip with a layer height of 20 mm. The raw mix is ​​printed using the following adjustable printing parameters, set in the Mach3 software package (Artsoft founder Art Fenerty): spindle speed is 2000-5000 rpm, feed rate is 3000-6000 rpm.

[0022] Tests of prototype samples were also carried out.

[0023] After 28 days of normal curing, test specimens formed using layer-by-layer extrusion (3D printing) were prepared by cutting them into prisms measuring 40x40x160 mm. Thermal conductivity was determined according to GOST 25380-2014. Average density was determined according to GOST 12730.1-78. The formability of the mixture was assessed based on the criteria for achieving homogeneity and solidity of the layers printed on a construction 3D printer.

[0024] The compressive strength of the hardened composite was determined on halves of beam specimens measuring 40x40x160 mm in accordance with GOST 5802-86. "Construction Mortars. Test Methods" using a TP-1-1000 testing machine.

[0025] The compositions of the raw mixtures for extrusion on a 3D printer are given in Table 1, the physical and mechanical properties of the compositions are given in Table 2.

[0026] Table 1

[0027] Components Compositions of raw material mixtures for extrusion on a 3D printer, wt.% 1 2 3 4 5 6 (prototype) Portland cement 32,877 30 27,331 25,491 23,389 20,0 Sand 49,315 45 40,997 38,236 35,084 65,84 Superplasticizer "MasterGlenium 430" 0,2 Superplasticizer "MasterPozzolith 55" 0,3 0,27 0,245 0,23 0,21 Biosilica 2,0 Waste ash from thermal power plants 3,288 3 2,733 2,549 2,339 Methylsilanetriol potassium salt "GKZh-11K" 0,01 Sodium methyl siliconate "GKZh-11N" 0,016 0,015 0,014 0,013 0,012 Ground rice husks 6,825 12,436 17,387 21,284 Water 14,204 14,89 16,244 16,094 17,682 11,950

[0028] Table 2

[0029] Properties Physical and mechanical properties of the compositions 1 2 3 4 5 6 (prototype) Thermal conductivity coefficient, W / (m K) 0,82 0,57 0,45 0,37 0,31 0,84 Average density, kg / m3 2025 1815 1700 1570 1430 2040 Compressive strength at 28 days, MPa 41,1 18,6 11,9 8,3 3,5 10,4 Ensuring the moldability of the mixture using 3D printing Yes Yes Yes Yes Yes Yes

[0030] From the given data it follows that the optimal values ​​of the thermal conductivity coefficient, average density, compressive strength, satisfying the requirements for structural heat-insulating concrete according to GOST 25820-2021, are achieved for compositions No. 3-5, characterized by a Portland cement content of 23.389-27.331 wt. %, sand - 35.084-40.997 wt. %, superplasticizer "MasterPozzolith 55" - 0.21-0.245 wt. %, finely ground pozzolanic component - ash from thermal power plant waste - 2.339-2.733 wt. %, sodium methyl siliconeate "GKZh-11N" - 0.012-0.014 wt. %, ground rice husk - 12.436-21.284 wt. %, water - 16.244-17.682 wt. %.

[0031] When adding ground rice husk in an amount of 0-6.825 wt.% (compositions No. 1, 2) less than that specified in composition No. 3, a discrepancy is observed in the set of properties that meet the requirements for structural heat-insulating concrete according to GOST 25820-2021: an insufficient reduction in the thermal conductivity coefficient, average density, and compressive strength.

[0032] Concrete mix compositions No. 1-6 can be molded using 3D printing.

[0033] The concrete mixture with ground rice husk for 3D printing, obtained according to the proposed invention, satisfies the requirements of GOST 25820-2021 in terms of average density, compressive strength and thermal conductivity coefficient, moldable by 3D printing with improved thermal insulation properties, reduced average density indicators with reduced requirements for raw materials - the possibility of using Portland cement with a smaller amount of tricalcium silicate and the use of waste from the production of thermal power plant ash as a pozzolanic component while ensuring moldability by 3D printing.

[0034] The use of ground rice husk in an amount of 12.436-21.284 wt.% allows for a reduction in the thermal conductivity coefficient, average density, and compressive strength of concrete, meeting the requirements for structural and thermal insulation concrete according to GOST 25820-2021, while simultaneously ensuring formability using 3D printing and achieving the required properties.

[0035] Thus, the proposed solution allows for the production of a concrete mixture with ground rice husk for 3D printing, which meets the requirements of GOST 25820-2021 for this type of concrete with improved thermal insulation properties, reduced average density indicators with reduced requirements for raw materials - the possibility of using Portland cement with a lower amount of tricalcium silicate and the use of waste from thermal power plant ash as a pozzolanic component while ensuring formability using the 3D printing method.

[0036] Sources of information:

[0037] 1. Patent CN 105753404A, B33Y70 / 00, Cement-based material used for building 3D (three-dimensional) printing, filed February 13, 2016, published July 13, 2016.

[0038] 2. Patent CN 108715531A, C04B28 / 02, A kind of high thixotropic 3D printing concrete and preparation method thereof, application. 06 / 12 / 2018, publ. 08 / 28 / 2020.

[0039] 3. Patent, RU 2 661 970, C04B 28 / 04, C04B 14 / 02, C04B 22 / 08, C04B 26 / 00, C04B2111 / 20, C04B2111 / 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”, declared 31.07.2017, published 23.07.2018, bulletin No. 21.

[0040] 4. Patent, RU 2 739 244, B29C 64 / 106, B29C 64 / 20, E04B 2 / 02, B33Y 10 / 00, B33Y 30 / 00, Device and method for manufacturing heat-insulating walls from polystyrene concrete using a 3D printer, Molodin V.V., Vasenkov E.V., patent holder Federal State Budgetary Educational Institution of Higher Education “Novosibirsk State University of Architecture and Civil Engineering”, declared 16.10.2020, published 22.12.2020, bulletin No. 36.

[0041] 5. Mukhametrahimov, R. Kh. Fundamentals of additive 3D printing technology in construction: monograph / R. Kh. Mukhametrahimov, R. Z. Rakhimov, L. V. Ziganshina. - Kazan: Publishing house of Kazan. state. university of architecture and civil engineering, 2026. - 332 p. - ISBN 978-5-7829-0621-4.

[0042] 6. Patent, RU 2 786198, C04B 28 / 04, C04B 2111 / 20, B33Y 70 / 00, Raw material mixture for extrusion on a 3D printer, Mukhametrahimov R.Kh., Ziganshina L.V., patent holder Federal State Budgetary Educational Institution of Higher Education "Kazan State University of Architecture and Civil Engineering", declared 30.12.2021, published 19.12.2022, bulletin No. 35.

Claims

A concrete mixture for 3D printing, including Portland cement, sand with a moisture content of 12%, a lignosulfonate-based superplasticizer, a finely ground pozzolanic component and water, characterized in that Portland cement grade CEM 1 42.5N is used, containing, by weight %: tricalcium silicate 59.7, tricalcium aluminate 8.0, dicalcium silicate 14.4, tetracalcium aluminoferrite 12.9, quartz sand with a fineness modulus of 3.5, "MasterPozzolith 55" is used as a lignosulfonate-based superplasticizer, and waste ash from thermal power plants with a specific surface area of ​​230 m is used as a finely ground pozzolanic component. 2 / kg, containing, wt. %: silicon dioxide 57.03, aluminum oxide 31.71 and additionally the raw material mixture contains sodium methylsiliconate "GKZh-11N" and ground rice husk with a bulk density of 338 kg / m3 3 with the following ratio of components, wt. %: The specified Portland cement 23,389-27,331 Quartz sand with a moisture content of 1-2% and fineness modulus 3.5 35,084-40,997 The specified superplasticizer 0,21-0,245 The specified waste ash from thermal power plants 2,339-2,733 Sodium methyl siliconate "GKZh-11N" 0,012-0,014 Ground rice husks 12,436-21,284 Water 16,244-17,682