RU2820187C1 - Modified fine-grained concrete mixture for construction 3d printing - Google Patents

Abstract

FIELD: construction materials science.

SUBSTANCE: invention can be used for 3D printing of various building structures, architectural and decorative elements and small architectural forms. Modified fine-grained concrete mixture for construction 3D printing contains the following, wt.%: portland cement “ЦЕМ” I 42.5 26.1–26.9, metakaolin BMK-45 with pozzolanic activity of at least 1,200 mg/g 3.04–3.24, quartz sand with fineness modulus of 1.8 39.1–40.7, cellulose microfiber with an average fiber length of 3.2 mm, an average diameter of 0.032 mm, obtained from recycled water from pulp and paper plants, 0.18–0.20, polycarboxylate-based hyperplasticiser 0.13–0.14, microcalcite 17.4–18.6, superabsorbent polymer—sodium polyacrylate 0.039–0.041, water 11.8–12.1.

EFFECT: high dimensional stability, reduced plastic shrinkage of the concrete mixture, high strength of the concrete while simultaneously reducing consumption of portland cement in the concrete mixture.

1 cl, 2 tbl

Description

The invention relates to building materials science, in particular to fine-grained concrete mixtures for additive technologies and can be used for 3D printing of various building structures, architectural and decorative elements and small architectural forms.

A known composite material for 3D printing consists of components in the following mass ratios, %: 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; phloroglucinolfurfural modifier 0.05-0.07; water - the rest [RU 2661970, С04В 28/04 Modified polymer-cement composite material for 3D printing, publ. 07/23/2018]. The disadvantage of the proposed composite material is its low strength.

A modified raw material mixture for construction 3D printing is also known, including the following components (wt.%): Portland cement 20.0-23.0; sand 62.7-66.2; superplasticizer “MasterGlenium 115” 0.20-0.23; diatomite 2.0-2.3; polyphenylethoxysiloxane "FES-50" 0.010-0.012; water 11.57-11.73 [RU 2777007, С04В 28/04. Modified raw material mixture for construction 3D printing in additive manufacturing technology, publ. 08/02/2022]. The disadvantages of the mixture are the lack of data on compressive strength, as well as the accepted methodology for determining flexural strength, which involves testing after 28 days of normal hardening, which does not correspond to the real conditions of hardening of materials in 3D printing technology.

A known concrete mixture for 3D printing is based on cement using expanded clay aggregate, containing the following components (parts by weight): fast-hardening sulfoaluminate cement 3.0-4.9; fly ash 0.75-1.15; microsilica 0.20-0.40; limestone flour 0.08-0.12; expanded clay 2.4-3.2; sand 5.0-6.0; NaOH 0.002-0.005; water 2.3-2.8; hydrophobic additive 0.040-0.052; PVA fibers 0.005-0.007; basalt fibers 0.005-0.007; hydroxypropyl methylcellulose 0.04-0.06 [CN 110078459A, 2019. A kind of novel 3D printing is crushed haydite concrete material and its preparation and application]. The disadvantage of this invention is the high energy intensity of the process of preparing the mixture due to the division of the components into 4 groups and the need for their parallel-sequential mixing.

The closest in technical essence and achieved result is a raw two-phase mixture based on cement, adopted as a prototype (RU 2729085, С04В 28/04 Two-phase mixture based on cement for composites in construction 3D printing technology, published 08/04/2020). It includes two phases. The first, solid phase, consists of the following components (wt.%): Portland cement 43.4-44.2; sand 54.8-55.3; metakaolin 0.8-1.0; polypropylene fiber 0.2-0.3. The liquid phase includes water and a superplasticizer based on polycarboxylate ethers in the following ratio (wt.%): superplasticizer 3.0-3.6; water 96.4-97.0. The disadvantage of the material is the high specific consumption of cement, exceeding 860 kg per 1 m ³ .

The specificity of construction three-dimensional printing lies in the large open surface area of printed products, which accelerates the evaporation of moisture from hardening concrete, causing the risk of cracking and a decrease in strength. The issue of the influence of temperature and humidity conditions of hardening on the physical and mechanical properties of concrete is covered in domestic and foreign literature [1, 2]. Studies [3, 4] show that the strength of concrete hardened under unfavorable conditions for 28 days is 40-70% lower than that of concrete under normal hardening conditions.

Traditional methods of caring for hardening concrete on a construction site (covering with insulating material, backfilling with wet sawdust and periodically moistening the exposed concrete surface) using 3D printing are labor-intensive and difficult to implement in practice. As a result, construction 3D printing technology can use internal care for hardening concrete. The implementation of the internal care method consists of introducing water-saturated components into the concrete composition - porous aggregates or superabsorbent polymers (SAP), which accumulate part of the process moisture, gradually releasing it later, thereby creating favorable conditions for concrete hardening. In addition, the introduction of SAP reduces the plastic shrinkage of concrete mixtures [5, 6].

There are three main methods of using superabsorbent polymers in concrete technology: the introduction of SAP, saturated with water, in the form of a hydrogel [7, 8]; introduction of SAP components with delayed polymerization [9]; introduction of dry SAP in the form of powder or granules [5, 10]. Each method has its own advantages and disadvantages. The optimal dosage of SAP depends on its water-holding capacity and for most substances is in the range of 0.05-2% by weight of cement. The dosage of sodium polyacrylate was chosen based on the results of experiments and amounted to 0.14-0.15% by weight of cement.

To increase the dimensional stability and cohesive strength of a concrete mixture during 3D printing, as well as the mechanical characteristics of the resulting concrete, it is rational to use microfiber. The developed mixture uses cellulose microfiber obtained from waste from pulp and paper mills. In addition, cellulose microfiber has significant water-holding capacity [11], which has a positive effect on the internal care mechanism.

The ratio of components of the developed mixture for 3D printing is, wt.%:

Table 1

Component Proposed composition Prototype Portland cement 26.1 - 26.9 38.3 - 39.0 Metakaolin 3.04 - 3.24 0.7 - 0.9 Microcalcite 17.4 - 18.6 - Sand 39.1 - 40.7 48.4 - 48.8 Cellulose microfiber 0.18 - 0.20 - GLANDERS 0.039 - 0.041 - Hyperplasticizer 0.13 - 0.14 0.35 - 0.42 Water 11.8 - 12.1 11.3 - 11.4 Polypropylene fiber - 0.2 - 0.3

The raw materials used have the following characteristics:

- Portland cement CEM I 42.5 produced by Asia Cement LLC (GOST 31108-2020) of the following mineralogical composition: C ₃ S - 67.3%, C ₂ S - 11.9%, C ₃ A - 6.7%, C ₄ AF - 11.9%;

- active mineral additive - metakaolin VMK-45 (GOST 59536-2021) (S _beat = 1700 m ² /kg) with pozzolanic activity 1250 mg/g;

- mineral filler - microcalcite MM-315 (S _beat = 230 m ² /kg);

- fine quartz sand with a particle size modulus of 1.8 (GOST 8736-2014);

- cellulose microfiber with an average fiber length of 3.2 mm, an average diameter of 0.032 mm, which is a waste of pulp and paper production, generated during local treatment of the mill's circulating water. The fibers are predominantly represented by unbleached sulphate cellulose with a tensile strength of 80-90 MPa.

- SAP - sodium polyacrylate with an absorption capacity of 220-250 g _H2O /g (average particle diameter 0.1-0.5 mm);

- powdered hyperplasticizer based on modified polycarboxylate esters “Sika ViscoCrete-226P”;

- water (GOST 23732-2011).

The process of preparing a concrete mixture is as follows. A solution for mixing the concrete mixture is pre-made. To do this, the specified amounts of SAP, water and hyperplasticizer are mixed in accordance with the recipe, and the resulting mixture is kept for 2 hours at room temperature.

Dry components are loaded into the concrete mixer: cement, microcalcite, metakaolin, sand, cellulose microfiber. The dry mixture is mixed until the color is uniform and the cellulose fibers are evenly distributed. Next, the previously prepared mixing solution is dosed into the concrete mixer and mixed for 3-5 minutes. In the experiments, a turbulent concrete mixer (v=600 rpm) was used; the mixing duration was 5 minutes. The plastic strength of the concrete mixture was determined using a conical plastometer within 10 minutes after mixing. Dimensional stability was determined as the ratio of the maximum height of the extrudate column to its average diameter at the moment of rupture or loss of stability when the operating extruder moves upward at a speed of 200 mm/min, with an optimally set flow value. Experimental samples were molded by extrusion and left to harden in air (T=23-25°C, ϕ=55-65%). The strength of the interlayer seam was determined using a universal tensile testing machine equipped with special grips. The strength of the seam was determined after 1 day of hardening under the specified conditions. The interlayer holding time was 10 minutes. The strength of the samples was determined at the age of 1 and 28 days. Before testing, the supporting faces of the samples were leveled by grinding. Table 2 shows the rheotechnological characteristics of the developed concrete mixture and the physical and mechanical properties of the modified fine-grained concrete.

table 2

Characteristic Developed mixture Prototype Plastic strength of concrete mixture, kPa 28-35 35-37 Dimensional stability of concrete mixture using 3D printing 6-9 n/a Ultimate compressive strength (after 1 day), MPa 27-30 43-45* Compressive strength (after 28 days), MPa 52-57 60-63* Ultimate bending strength (after 28 days), MPa 5-6 3.9-4* Peel strength of the adhesive seam, MPa 2.1-2.5 2.5-4.3 Density of concrete, kg/m ³ 2210-2250 2200-2300 Specific consumption of cement, kg per 1 m ³ 579-596 850-870

* data for hardening under normal conditions (GOST 10180-2012)

The introduction of sodium polyacrylate and cellulose microfiber improves the hardening conditions of cement stone, increases the cohesiveness and cohesive strength of the concrete mixture, and improves the dimensional stability characteristics of the printing masses. In addition, cellulose microfiber prevents the formation of cracks caused by shrinkage deformations. Thanks to the use of chemical and mineral modifiers in the composition of a fine-grained concrete mixture, the amount of cement is reduced without a negative impact on the rheotechnological characteristics of the mixture for 3D printing and on the physical and mechanical properties of concrete.

Sources used

1. Bazhenov Yu.M. Concrete technology: textbook. builds for university students. specialist. 2003. 501 p.

2. Utkelbaeva A.O. The influence of temperature and humidity factors on the structure formation of concrete // Science and Technology of Kazakhstan. 2015. No. 1-2. P. 117-124.

3. Rudenko N.N., Doronina V.O. Features of caring for road cement concrete during the summer construction period // Science and Progress of Transport Bulletin of the Dnepropetrovsk National University of Railway Transport. 2009. No. 27. P. 199-202.

4. Vorobyov A.A., Elfimov V.I. Improving the quality of concrete work in a dry, hot climate // Bulletin of the Russian Peoples' Friendship University Series Engineering Research. 2005. No. 1. P. 85-88.

5. Popov D.Yu., Lesovik V.S., Meshcherin V.S. The influence of superabsorbent polymers on plastic shrinkage of cement stone // Bulletin of the Belgorod State Technological University named after. V.G. Shukhova. 2016. No. 11. P. 6-12.

6. Inozemtsev A.S. et al. Using a superabsorbent polymer solution in cement compositions for 3D printing. Immanuel Kant Baltic Federal University, 2023. P. 19-29.

7. Resan S., Kamil S., Abed M. Developing self-curing cement sand mortar using sodium polyacrylate // J. Eng. Sustain. Dev. 2019. Vol. 23. P. 95-107.

8. Moayyad Al-Nasra. Concrete Made For Energy Conservation Mixed With Sodium Polyacrylates // Moayyad Al-Nasra Int J. Eng. Res. Appl. 2013. Vol. 3, No. Issue 5. P. pp.601-604.

9. Korolev E.V., Than K.Z., Inozemtsev A.S. Method for providing internal care for cement hydration in compositions for 3D printing // Bulletin of MGSU. 2020. Vol. 15, No. 6. P. 834-846.

10. Manzur T., Iffat S., Noor M.A. Efficiency of sodium polyacrylate to improve durability of concrete under adverse curing condition // Adv. Mater. Sci. Eng. Hindawi, 2015. Vol. 2015. P. e685785.

11. Vsevolodovich N.E. et al. Characteristics of the scum formed during local treatment of fiber-containing wastewater: 4 // Chemistry of Plant Raw Materials. Russia, Barnaul: Federal State Budgetary Educational Institution of Higher Education "Altai State University", 2014. No. 4. P. 279-286.

Claims (2)

Modified fine-grained concrete mixture for construction 3D printing, including Portland cement CEM I 42.5, metakaolin, quartz sand, microfiber, polycarboxylate-based hyperplasticizer and water, characterized in that it contains metakaolin VMK-45 with a pozzolanic activity of at least 1200 mg/ g, quartz sand with a fineness modulus of 1.8, cellulose microfiber with an average fiber length of 3.2 mm, an average diameter of 0.032 mm, obtained from recycled water waste from pulp and paper mills, and the mixture additionally contains microcalcite, as well as a superabsorbent polymer - sodium polyacrylate , with the following ratio of components, wt.%: Portland cement CEM I 42.5 26.1-26.9 metakaolin VMK-45 3.04-3.24 microcalcite 17.4-18.6 quartz sand 39.1-40.7 cellulose microfiber 0.18-0.20 superabsorbent polymer 0.039-0.041 hyperplasticizer 0.13-0.14 water 11.8-12.1