A method for preparing a 3D printing concrete incorporating plant fibers

Abstract

The present application relates to the technical field of 3D printing concrete, and discloses a preparation method of 3D printing concrete mixed with plant fibers, which comprises the following steps: step 1, soaking and drying the plant fibers treated with water glass in saturated limewater; step 2, blending the plant fibers with sulphoaluminate cement; step 3, preparing alkali-activated 3D printing concrete and pumping it by taking 30-50 parts of water glass, 20-40 parts of sodium hydroxide, 100-200 parts of limestone powder, 1000-1200 parts of sand, 100-200 parts of extra-fine sand, 400-500 parts of mineral powder, 50-150 parts of rice husk ash, 20-40 parts of hydroxypropyl methyl cellulose, 220-300 parts of water and 5-10 parts of water reducing agent according to mass fraction; step 4, forcibly stirring the concrete and adding the product obtained in step 2; and step 5, printing the concrete and spraying a setting agent between the concrete layers. The present application helps to improve the constructability of 3D printing concrete and reduce its shrinkage.

Description

Technical Field

[0001] This invention relates to the field of 3D printed concrete technology, and in particular to a method for preparing 3D printed concrete incorporating plant fibers. Background Technology

[0002] 3D printed concrete (3DCP) is a digital construction technology based on additive manufacturing principles. It involves using CNC extrusion equipment to stack layers of customized concrete slurry according to a three-dimensional model, directly forming buildings or components. Compared to traditional concrete construction processes, 3D printed concrete has unique advantages: First, formwork-free construction significantly reduces construction costs; second, it can print complex shapes with high precision while maximizing material savings; and third, because 3D printing is an automated process, it saves manpower and shortens construction time.

[0003] While 3D printing technology offers numerous advantages, its development in the construction field still faces many limitations. The success of 3D-printed concrete hinges on the material meeting a set of mutually constraining "golden triangle" properties in its freshly mixed state: pumpability, extrudability, and constructability. However, pumpability and constructability present a significant contradiction: pumpability requires high fluidity in the concrete, while constructability demands that the concrete maintain its shape under its own weight and the pressure of subsequent layers, without collapsing or significantly deforming.

[0004] To simultaneously satisfy the pumpability and constructability of 3D printed concrete, it often uses a lot of materials with high water absorption (such as attapulgite soil, clay, recycled aggregate, recycled cementitious materials, etc.). At the same time, to satisfy extrudability, 3D printed concrete does not use coarse aggregate and uses a lot of cement. This will undoubtedly bring greater shrinkage deformation to the concrete, making 3D printed concrete more prone to cracking.

[0005] Adding plant fibers is an effective way to reduce shrinkage in 3D-printed concrete and improve concrete cracking.

[0006] Patent 201711409838.6 discloses a type of concrete for 3D printing and its preparation method, comprising the following raw materials in parts by weight: sewage sludge, wood ash, silicate cement, sulfoaluminate cement, plant fiber, polyethylene elastomer, titanium fiber, potassium sulfate, polycarboxylate superplasticizer, basalt, silica sol, tourmaline powder, calcium sulfate whiskers, oxalic acid, and lychee shell. The printed product sets quickly without delamination, and has good compressive and flexural strength, meeting people's usage needs.

[0007] Patent 201811632896.X discloses a plant fiber-reinforced geopolymer for 3D printing the Zhaozhou Bridge and its preparation method. The geopolymer consists of: fly ash, calcium hydroxide powder, plant fiber, slag, silica fume, clay, quartz sand, composite alkali activator, sodium bentonite, viscosity modifier, polyvinyl alcohol treatment solution, coupling agent, and water. This geopolymer utilizes plant fiber as a toughening material and has the advantages of low cost, low density, renewability, and environmental friendliness, which is conducive to promoting the practical engineering application of 3D printed geopolymer materials.

[0008] Patent 201911422938.1 discloses a composite material for 3D printing of construction waste soil, its preparation method and application. The material includes construction waste soil, curing agent, recycled sand powder, plant fiber and water. Compared with the prior art, the present invention uses construction waste soil as the base material, controls the soil properties by compounding the curing material, improves the toughness of the soil material by using plant fiber, and combines the homogeneity and plasticity of the soil to make the composite soil a new material for 3D printing of buildings, providing a new idea for the disposal of construction waste soil.

[0009] Patent 202010745022.6 discloses a method for preparing 3D printing ink from waste 3D printing concrete, comprising the following components: cement; recycled 3D printing concrete mixture; plant fiber; metakaolin; silica fume; water glass; water-reducing agent; cellulose; and water. By fully utilizing waste 3D printing concrete to prepare a recycled mixture, and then using it to prepare 3D printing ink, the recycling and reuse of 3D printing concrete can be achieved.

[0010] Patent 202311345792.1 discloses a 3D-printed refractory geopolymer concrete material and its preparation method. The concrete material, by mass parts, includes cementitious materials, coarse aggregates, fine aggregates, soil, ceramic powder, alkaline activator, plant fibers, lignin, and water. The resulting geopolymer concrete material meets the requirements of 3D printing construction while also possessing excellent mechanical and fire-resistant properties.

[0011] This invention provides a method for preparing 3D printed concrete with plant fiber admixture, aiming to resolve the contradiction between the pumpability and constructability of 3D printed concrete and reduce cracking of 3D printed concrete. Summary of the Invention

[0012] Purpose of the invention: To address the problems existing in the prior art, this invention provides a method for preparing 3D printed concrete with plant fiber admixture, which solves the problems of incompatibility between pumpability and constructability of traditional 3D printed concrete and the easy cracking of 3D printed concrete.

[0013] Technical solution: This invention provides a method for preparing 3D printed concrete mixed with plant fibers, characterized by the following steps: Step 1: Completely immerse 10-20mm of plant fiber treated with water glass in a saturated lime water solution for a period of time, then dry it; Step 2: Blend the plant fibers treated in Step 1 with sulfoaluminate cement; Step 3: Prepare alkali-activated 3D printing concrete, and transport and pump it; by weight, the alkali-activated 3D printing concrete includes 30-50 parts water glass, 20-40 parts sodium hydroxide, 100-200 parts limestone powder, 1000-1200 parts sand, 100-200 parts ultrafine sand, 400-500 parts mineral powder, 50-150 parts rice husk ash, 20-40 parts hydroxypropyl methylcellulose, 220-300 parts water, and 5-10 parts water-reducing agent; Step 4: Force mix the alkali-activated 3D printing concrete obtained in Step 3 and add the plant fiber and sulfoaluminate cement blend obtained in Step 2; the amount of plant fiber used per cubic meter of alkali-activated 3D printing concrete is 2kg~4kg. Step 5: Print the concrete layer by layer and spray a setting agent between the concrete layers.

[0014] Further, in step 3, the preparation method of the shaping agent is as follows: 50-70% lithium slag, 20-30% steel slag and 10-20% calcium hydroxide are mixed by mass percentage, and steam-cured for 3-5 hours under a water-cement ratio of 0.3-0.4 and a pressure of 0.8-1.0 MPa. Then, the mixture is crushed, 5-8% gypsum is added externally and it is ground to a specific surface area greater than 350 m2 / kg.

[0015] Further, in step 1, the water glass treatment specifically involves: diluting the water glass solution by 8 to 10 times, and then completely immersing the plant fiber in the solution for 12 to 24 hours, followed by drying; wherein the volume ratio of the plant fiber to the diluted water glass solution is 1 to 5:10.

[0016] Furthermore, in step 1, the volume ratio of the plant fiber to the saturated lime water solution is 1~5:10, and the plant fiber is completely submerged in the solution during the soaking process.

[0017] Furthermore, in steps 1 and 3, the modulus of the water glass is 2.4 to 3.3.

[0018] Furthermore, in step 2, the mass ratio of the plant fiber to the sulfoaluminate cement is 1:1 to 2:3.

[0019] Furthermore, in step 3, during the preparation of the alkali-activated 3D printed concrete, water glass and sodium hydroxide need to be dissolved in water and allowed to stand at room temperature before being stirred and mixed with other materials.

[0020] Furthermore, in step 3, the fineness modulus of the ultrafine sand is less than 1.0.

[0021] Further, in step 3, the rice husk ash is wet-milled in a 0.5-2.0% sodium hydroxide or potassium hydroxide solution until the specific surface area is greater than 350 m². 2 / kg.

[0022] Furthermore, in step 5, the amount of the setting agent sprayed between concrete layers is: 100~300g of setting agent per square meter of concrete, calculated based on the area between concrete layers.

[0023] Beneficial effects: Compared with the prior art, the specific beneficial effects of this invention are as follows: 1. Unlike ordinary alkali treatment of plant fibers, this invention uses water glass to treat plant fibers: on the one hand, water glass can remove the wax on the surface of plant fibers, making the fiber surface rougher and reducing the water absorption rate of the fibers; on the other hand, water glass can also react with the subsequent saturated calcium hydroxide solution to form hydration products such as hydrated calcium silicate and calcium carbonate on the surface of plant fibers, further increasing the roughness of plant fibers and accelerating the reaction of hydration products on the surface of plant fibers.

[0024] 2. By blending plant fibers with sulfoaluminate cement and incorporating them into alkali-activated cementitious materials, water can be rapidly absorbed and reacted. This reduces free water in the slurry while accelerating hydration, allowing the slurry to quickly transition from a highly fluid state to a buildable state. During the later stages of hydration, when the hardened slurry is dehydrated, the plant fibers release water. Simultaneously, the blending of sulfoaluminate on the surface of the plant fibers forms a large amount of ettringite, reducing shrinkage.

[0025] 3. Traditional 3D concrete, to achieve extrudability, does not use coarse aggregate, but only cement and fine aggregate. This undoubtedly increases the amount of cement per cubic meter of concrete and greatly increases concrete shrinkage, leading to cracking. Therefore, this invention uses alkali-activated cementitious materials instead of traditional cement. Compared to traditional cement, alkali-activated cementitious materials have higher fluidity, shorter setting time, and higher strength. Furthermore, to achieve strength similar to traditional cement, this invention reduces the amount of cementitious materials used, increases the amount of sand, and uses limestone powder and ultrafine sand as fillers, replacing precursors such as mineral powder while ensuring extrudability, thus reducing costs and shrinkage.

[0026] 4. A sizing agent is prepared by autoclaving lithium slag, steel slag, and calcium hydroxide, which produces a large amount of CSH, topsoil mullite, and calcium carbonate nanocrystals. On the one hand, these nanocrystals have small particle sizes and can adsorb excess water between layers; on the other hand, these nanocrystals act as nuclei to accelerate the hydration of cementitious materials, increasing the density of the interface. Simultaneously, the added gypsum reacts with the large amount of AFm formed by the autoclaving of lithium slag, steel slag, and calcium hydroxide, rapidly growing into calcareous vanadate, which intercalates between layers, thereby improving interlayer adhesion. Detailed Implementation

[0027] The present invention will now be described in detail with reference to the embodiments. Example

[0028] This embodiment provides a method for preparing 3D printed concrete incorporating plant fibers, specifically including the following steps: Step 1: Dilute a water glass solution with a modulus of 3.3 by 10 times, then immerse 20mm long sisal fibers in the solution for 12 hours, ensuring the plant fibers remain submerged in the solution throughout. Remove and dry. The volume ratio of plant fibers to diluted water glass solution is 1:10. Immerse the water glass-treated plant fibers in a saturated lime solution for 24 hours and dry. The volume ratio of water glass-treated plant fibers to saturated lime solution is 1:10, ensuring the plant fibers are completely submerged during immersion. Step 2: Blend the plant fibers treated in Step 1 with sulfoaluminate cement at a mass ratio of 1:1; Step 3: Dissolve water glass and sodium hydroxide (modulus 3.3) in water and let stand to room temperature before mixing with other materials to prepare alkali-activated 3D printing concrete, which is then transported and pumped. By weight, the alkali-activated 3D printing concrete comprises 50 parts water glass, 20 parts sodium hydroxide, 200 parts limestone powder, 1000 parts sand, 200 parts ultrafine sand, 500 parts mineral powder, 100 parts rice husk ash, 40 parts hydroxypropyl methylcellulose, 300 parts water, and 5 parts water-reducing agent. The ultrafine sand has a fineness modulus of 0.7. The rice husk ash needs to be wet-milled in a 0.5% potassium hydroxide solution to a specific surface area of ​​400 m². 2 / kg; Step 4: Force mix the alkali-activated 3D printing concrete obtained in Step 3 and add the plant fiber and sulfoaluminate cement blend obtained in Step 2; wherein, the amount of plant fiber used per cubic meter of alkali-activated 3D printing concrete is 4 kg. Step 5: Stack the concrete obtained in Step 4 layer by layer for printing, and spray a setting agent between the concrete layers; the setting agent is prepared by mixing 70% lithium slag, 20% steel slag and 10% calcium hydroxide by mass percentage, autoclaving at a water-cement ratio of 0.4 and a pressure of 0.8 MPa for 5 hours, then crushing, adding 5% gypsum, and grinding to a specific surface area greater than 400 m². 2 / kg; The amount of setting agent is calculated based on the interlayer area of ​​concrete, with 100g of setting agent sprayed per square meter of concrete.

[0029] Example 2 This embodiment provides a method for preparing 3D printed concrete incorporating plant fibers, specifically including the following steps: Step 1: Dilute a water glass solution with a modulus of 2.4 by 8 times, then immerse 10mm long sisal fibers in the solution for 24 hours, ensuring the plant fibers remain submerged in the solution throughout. Remove and dry. The volume ratio of plant fibers to diluted water glass solution is 5:10. Immerse the water glass-treated plant fibers in a saturated lime solution for 24 hours and dry. The volume ratio of water glass-treated plant fibers to saturated lime solution is 5:10, ensuring the plant fibers are completely submerged during immersion. Step 2: Blend the plant fibers treated in Step 1 with sulfoaluminate cement at a mass ratio of 2:3; Step 3: Dissolve water glass and sodium hydroxide (modulus 2.4) in water and let stand to room temperature before mixing with other materials to prepare alkali-activated 3D printing concrete, which is then transported and pumped. By weight, the alkali-activated 3D printing concrete comprises 30 parts water glass, 40 parts sodium hydroxide, 100 parts limestone powder, 1200 parts sand, 100 parts ultrafine sand, 400 parts mineral powder, 150 parts rice husk ash, 20 parts hydroxypropyl methylcellulose, 220 parts water, and 8 parts water-reducing agent. The ultrafine sand has a fineness modulus of 0.5. The rice husk ash needs to be wet-milled in a 2.0% potassium hydroxide solution to a specific surface area of ​​400 m². 2 / kg; Step 4: Force mix the alkali-activated 3D printing concrete obtained in Step 3 and add the plant fiber and sulfoaluminate cement blend obtained in Step 2; wherein, the amount of plant fiber used per cubic meter of alkali-activated 3D printing concrete is 2 kg. Step 5: Stack the concrete obtained in Step 4 layer by layer for printing, and spray a setting agent between the concrete layers; the setting agent is prepared by mixing 50% lithium slag, 30% steel slag and 20% calcium hydroxide by mass percentage, autoclaving at a water-cement ratio of 0.3 and a pressure of 1.0 MPa for 3 hours, then crushing, adding 8% gypsum, and grinding to a specific surface area of ​​400 m². 2 / kg; The amount of setting agent is calculated based on the interlayer area of ​​concrete, with 300g of setting agent sprayed per square meter of concrete.

[0030] Example 3 This embodiment provides a method for preparing 3D printed concrete incorporating plant fibers, specifically including the following steps: Step 1: Dilute a water glass solution with a modulus of 2.8 by 9 times, then immerse 15mm long sisal fibers in the solution for 18 hours, ensuring the plant fibers remain submerged in the solution throughout. Remove and dry. The volume ratio of plant fibers to diluted water glass solution is 4:10. Immerse the water glass-treated plant fibers in a saturated lime solution for 24 hours and dry. The volume ratio of water glass-treated plant fibers to saturated lime solution is 4:10, ensuring the plant fibers are completely submerged during immersion. Step 2: Blend the plant fibers treated in Step 1 with sulfoaluminate cement at a mass ratio of 1:1; Step 3: Dissolve water glass and sodium hydroxide (modulus 2.8) in water and let stand to room temperature before mixing with other materials to prepare alkali-activated 3D printing concrete, which is then transported and pumped. By weight, the alkali-activated 3D printing concrete comprises 40 parts water glass, 30 parts sodium hydroxide, 150 parts limestone powder, 1100 parts sand, 150 parts ultrafine sand, 500 parts mineral powder, 50 parts rice husk ash, 30 parts hydroxypropyl methylcellulose, 230 parts water, and 7 parts water-reducing agent. The ultrafine sand has a fineness modulus of 0.5. The rice husk ash needs to be wet-milled in a 1.0% potassium hydroxide solution to a specific surface area of ​​400 m² / g. 2 / kg; Step 4: Force mix the alkali-activated 3D printing concrete obtained in Step 3 and add the plant fiber and sulfoaluminate cement blend obtained in Step 2; wherein, the amount of plant fiber used per cubic meter of alkali-activated 3D printing concrete is 3 kg. Step 5: Stack the concrete obtained in Step 4 layer by layer for printing, and spray a setting agent between the concrete layers; the setting agent is prepared by mixing 60% lithium slag, 20% steel slag and 20% calcium hydroxide by mass percentage, autoclaving at a water-cement ratio of 0.35 and a pressure of 0.85 MPa for 4 hours, then crushing, adding 6% gypsum, and grinding to a specific surface area greater than 400 m². 2 / kg; The amount of setting agent is calculated based on the interlayer area of ​​concrete, with 200g of setting agent sprayed per square meter of concrete.

[0031] Example 4 This embodiment provides a method for preparing 3D printed concrete incorporating plant fibers, specifically including the following steps: Step 1: Dilute a water glass solution with a modulus of 2.8 by 10 times, then immerse 20mm long sisal fibers in the solution for 24 hours, ensuring the plant fibers remain submerged in the solution throughout. Remove and dry. The volume ratio of plant fibers to diluted water glass solution is 3:10. Immerse the water glass-treated plant fibers in a saturated lime solution for 24 hours and dry. The volume ratio of water glass-treated plant fibers to saturated lime solution is 3:10, ensuring the plant fibers are completely submerged in the solution during immersion.

[0032] Step 2: Blend the plant fibers treated in Step 1 with sulfoaluminate cement at a mass ratio of 2:3; Step 3: Dissolve water glass and sodium hydroxide (modulus 2.8) in water and let stand to room temperature before mixing with other materials to prepare alkali-activated 3D printing concrete, which is then transported and pumped. By weight, the alkali-activated 3D printing concrete comprises 40 parts water glass, 40 parts sodium hydroxide, 200 parts limestone powder, 1100 parts sand, 200 parts ultrafine sand, 450 parts mineral powder, 100 parts rice husk ash, 20 parts hydroxypropyl methylcellulose, 250 parts water, and 10 parts water-reducing agent. The ultrafine sand has a fineness modulus of 0.4. The rice husk ash needs to be wet-milled in a 0.6% potassium hydroxide solution to a specific surface area of ​​400 m². 2 / kg; Step 4: Force mix the alkali-activated 3D printing concrete obtained in Step 3 and add the plant fiber and sulfoaluminate cement blend obtained in Step 2; wherein, the amount of plant fiber used per cubic meter of alkali-activated 3D printing concrete is 3 kg. Step 5: Stack the concrete obtained in Step 4 layer by layer for printing, and spray a setting agent between the concrete layers; the setting agent is prepared by mixing 60% lithium slag, 30% steel slag and 10% calcium hydroxide by mass percentage, autoclaving at a water-cement ratio of 0.35 and a pressure of 0.9 MPa for 4 hours, then crushing, adding 7% gypsum, and grinding to a specific surface area greater than 400 m². 2 / kg; of which, the amount of setting agent is calculated based on the interlayer area of ​​concrete, 300g of setting agent is sprayed per square meter of concrete.

[0033] Performance testing Table 1 lists the performance evaluation indicators for this invention. The concrete compressive and flexural strength tests are performed according to the following standards: GB / T 17671-2021 "Test Method for Strength of Cement Mortar (ISO Method)"; the interlayer splitting tensile strength test is performed according to the following standards: GB / T 50081-2019 "Standard for Test Methods of Mechanical Properties of Ordinary Concrete"; and the concrete shrinkage performance test is performed according to the following standards: GB / T 50082-2024 "Standard for Test Methods of Long-Term Performance and Durability of Concrete". For the compressive and flexural strength tests, the 3D-printed concrete is poured into a 40mm×40mm×160mm mold, cured for 24 hours according to standard, and then tested at 3d and 28d. The interlayer splitting tensile strength test is performed by cutting the 3D-printed concrete into 150mm cube specimens. The concrete drying shrinkage test is performed by pouring the concrete into a 100mm×100mm×515mm mold. Constructability is determined by visually observing whether the concrete is prone to collapse.

[0034] In the comparative example, the mix proportion of the 3D printed concrete is as follows: by mass, it includes 1200 parts of sand, 600 parts of ordinary silicate cement, 200 parts of sulfoaluminate cement, 320 parts of water, 50 parts of hydroxypropyl methylcellulose, 50 parts of redispersible latex powder, and 30 parts of water-reducing agent.

[0035]

[0036] As shown in Table 1, under the condition that the compressive strength of the present invention is similar to that of the comparative example under the condition of 28-day test, the present invention has higher early 3-day strength (including flexural strength and compressive strength), while the present invention has higher interlayer splitting tensile strength and lower shrinkage, and no collapse occurred during the layer-by-layer 3D printing process.

[0037] The above embodiments are only for illustrating the technical concept and features of the present invention, and are intended to enable those skilled in the art to understand the content of the present invention and implement it accordingly. They should not be construed as limiting the scope of protection of the present invention. All equivalent transformations or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing 3D-printed concrete incorporating plant fibers, characterized in that, Specifically, the following steps are included: Step 1: Completely immerse 10-20mm of plant fiber treated with water glass in a saturated lime water solution for a period of time, then dry it; Step 2: Blend the plant fibers treated in Step 1 with sulfoaluminate cement; Step 3: Prepare alkali-activated 3D printing concrete, and transport and pump it; by weight, the alkali-activated 3D printing concrete includes 30-50 parts water glass, 20-40 parts sodium hydroxide, 100-200 parts limestone powder, 1000-1200 parts sand, 100-200 parts ultrafine sand, 400-500 parts mineral powder, 50-150 parts rice husk ash, 20-40 parts hydroxypropyl methylcellulose, 220-300 parts water, and 5-10 parts water-reducing agent; Step 4: Force mix the alkali-activated 3D printing concrete obtained in Step 3 and add the plant fiber and sulfoaluminate cement blend obtained in Step 2; the amount of plant fiber used per cubic meter of alkali-activated 3D printing concrete is 2kg~4kg. Step 5: Print the concrete layer by layer and spray a setting agent between the concrete layers.

2. The method for preparing 3D printed concrete with plant fiber as described in claim 1, characterized in that: In step 5, the preparation method of the sizing agent is as follows: 50-70% lithium slag, 20-30% steel slag, and 10-20% calcium hydroxide are mixed by mass percentage, and autoclaved for 3-5 hours under a water-cement ratio of 0.3-0.4 and a pressure of 0.8-1.0 MPa. Then, the mixture is crushed, 5-8% gypsum is added, and it is ground to a specific surface area greater than 350 m². 2 / kg.

3. The method for preparing 3D printed concrete with plant fiber as described in claim 1, characterized in that: In step 1, the water glass treatment specifically involves: diluting the water glass solution by 8 to 10 times, and then completely immersing the plant fiber in the solution for 12 to 24 hours, followed by drying; wherein the volume ratio of the plant fiber to the diluted water glass solution is 1 to 5:

10.

4. The method for preparing 3D printed concrete with plant fiber as described in claim 1, characterized in that: In step 1, the volume ratio of the plant fiber to the saturated lime water solution is 1~5:

10.

5. The method for preparing 3D printed concrete with plant fiber as described in claim 1, characterized in that: In step 1, the modulus of the water glass is 2.4 to 3.3; In step 3, the modulus of the water glass is 2.4 to 3.

3.

6. The method for preparing 3D printed concrete according to claim 1, characterized in that: In step 2, the mass ratio of plant fiber to sulfoaluminate cement is 1:1 to 2:

3.

7. The method for preparing 3D printed concrete according to claim 1, characterized in that: In step 3, during the preparation of alkali-activated 3D printed concrete, water glass and sodium hydroxide need to be dissolved in water and allowed to stand at room temperature before being stirred and mixed with other materials.

8. The method for preparing 3D printed concrete according to claim 1, characterized in that: In step 3, the fineness modulus of the ultrafine sand is less than 1.

0.

9. The method for preparing 3D printed concrete according to claim 1, characterized in that: In step 3, the rice husk ash is wet-milled in a 0.5-2.0% sodium hydroxide or potassium hydroxide solution until the specific surface area is greater than 350 m². 2 / kg.

10. The method for preparing 3D printed concrete according to claim 1, characterized in that: In step 5, the amount of the setting agent sprayed between concrete layers is 100-300g per square meter of concrete, calculated based on the area between the concrete layers.

Images