A method for 3D printing simulated lunar soil concrete and its preparation by incorporating basalt fibers.

Abstract

This invention belongs to the field of building materials technology, specifically relating to an alkali-activated cementitious material based on simulated lunar soil and a 3D printing method, belonging to the direction of architectural 3D printing and in-situ lunar resource utilization. The particle size distribution of the simulated lunar soil is: 0-75μm 43%, 75-150μm 40%, and 150-300μm 17%. The activator is prepared by dissolving sodium hydroxide and sodium silicate nonahydrate in water. The preparation method includes: selection and gradation of simulated lunar soil raw materials, rational preparation of alkali activator solution, and stepwise stirring process. By controlling the modulus, alkalinity, and particle size distribution of the activator and simulated lunar soil, this invention ensures excellent slurry fluidity and printability while also possessing rapid structure formation capability and constructability. The average compressive strength of the cast cubic specimens cured at 60℃ for 48 days and then at room temperature for 28 days reaches 27MPa. In addition, the addition of basalt fiber at a mass fraction of 0.25% and 0.5% compared to the simulated lunar soil material further enhances printability.

Description

Technical Field

[0001] This invention belongs to the field of mortar, specifically a method for preparing alkali-activated simulated lunar soil concrete suitable for 3D printing. Background Technology

[0002] Constructing a future lunar base using in-situ lunar resources is the first step in humanity's lunar exploration. The lunar surface environment is extreme, with extreme temperature differences between day and night, and the risk of exposure to various forms of radiation and high-energy particle attacks from outer space. Transporting building materials from Earth to the Moon is prohibitively expensive, and artificial extraterrestrial construction is impossible. However, 3D-printed concrete technology already has concrete engineering applications on Earth. Therefore, developing a method for automatically constructing a lunar base using in-situ lunar resources as the primary material, combined with 3D-printed concrete technology, is a feasible research direction. Since large-scale acquisition of real lunar soil is currently impossible with existing technology, we are conducting preliminary basic technological research by simulating lunar soil.

[0003] Simulated lunar regolith is a material that simulates the chemical composition, physical characteristics, mineral phase composition, and amorphous matter of in-situ lunar regolith. Studies have shown that the surface of real lunar regolith is rich in basalt and anorthosite. The rock debris on the surface of lunar regolith contains aluminosilicates, and the aluminosilicates in its amorphous matter are highly reactive, capable of dissolving, depolymerizing, and repolymerizing under alkaline conditions to generate geopolymers with cementing properties. Exploration results indicate that the amorphous matter content of lunar regolith on the lunar highlands can reach approximately 30%. Therefore, 3D printing alkaline-activated simulated lunar regolith technology can serve as an important reference technology for exploring mechanized production on the lunar base.

[0004] Currently, 3D printing of alkali-activated simulated lunar soil generally faces the challenge of balancing printability and mechanical properties. For example, to achieve printability, various admixtures (such as retarders, water-reducing agents, and thickeners) are often required for adjustment, increasing the cost of future Earth-Moon transportation. Regarding mechanical properties, if the alkali activation reaction is too slow, the early strength development of the slurry is insufficient to support the weight of the upper printed layer, limiting its constructability; if the reaction is too fast, the slurry easily solidifies rapidly, resulting in a short "printing window" or even clogging the printing equipment. Existing research indicates that the printability of 3D-printed simulated lunar soil concrete is influenced by multiple factors, including particle size distribution, type of activator, type of admixture, and printing equipment. Furthermore, the ratio of the alkali activator to the amorphous material content in the lunar soil primarily affects its mechanical properties.

[0005] Existing research indicates that combining 3D printing technology with alkali-activated simulated lunar soil concrete can ensure that the main building materials are sourced locally from the lunar surface, while simultaneously solving the construction challenges under the extreme lunar environment. Furthermore, the lunar surface contains abundant basalt, providing raw materials for basalt fibers. Therefore, under the premise of in-situ lunar sourcing, minimizing the cost of transporting building materials between Earth and the Moon is the primary objective of developing 3D-printed alkali-activated simulated lunar soil concrete. Thus, developing a 3D-printed lunar soil-based material that requires no complex additives and can autonomously balance printability and mechanical properties can provide a crucial technological foundation for future lunar base construction. Summary of the Invention

[0006] To address the problems of existing technologies that rely on multiple admixtures and struggle to balance printing window and early strength, this invention provides a method for preparing 3D-printed alkali-activated simulated lunar soil. The core of this invention lies in: rationally designing the particle size distribution of the simulated lunar soil and optimizing a composite alkali activator system with a specific modulus and alkalinity; and controlling the rheological properties and setting / hardening process of the slurry by adjusting the ratio of sodium hydroxide to sodium silicate nonahydrate, thereby achieving printability and construction performance. Furthermore, this invention adds basalt fibers at mass fractions of 0.25% and 0.50% to further study printability.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: A 3D-printed alkali-activated simulated lunar soil concrete is composed of simulated lunar soil raw materials, a composite alkali activator, and water. The particle size distribution of the simulated lunar soil raw materials has been optimized through experimental screening, limiting the maximum particle size to 300 μm. Specifically, the particle size distribution is as follows: 0-75 μm accounts for 43%, 75-150 μm accounts for 40%, and 150-300 μm accounts for 17%.

[0008] The composite alkaline activator consists of 96% pure sodium hydroxide and sodium silicate nonahydrate particles with a modulus of 1. Based on the mass of simulated lunar soil, the sodium hydroxide content is 7.2%, and the sodium silicate nonahydrate content is 14.4%. The water-cement ratio is controlled between 0.25 and 0.3. The total alkalinity of this activator system is 8.5%, and the modulus is 0.37.

[0009] The simulated lunar soil material is based on the chemical composition and physical properties of the Apollo 16 highland lunar soil and LHS-1 simulants, and mainly contains active components such as basalt powder, γ-alumina, high-calcium slag, high-purity silica fume and calcium hydroxide powder.

[0010] Another aspect of this disclosure is to provide a method for preparing 3D-printed simulated lunar soil concrete, comprising the following steps: S1. Raw material pretreatment and gradation: After drying each raw material according to the proportions described in the patent, they are mixed according to the specified particle size distribution.

[0011] S2. Preparation of alkaline activator solution: Divide the total water volume into two parts: 40% and 60%. First, dissolve sodium hydroxide in the 40% water and let it stand for 24 hours to cool. Then, dissolve sodium silicate nonahydrate in the remaining 60% water and let it stand to cool.

[0012] S3. Stepwise mixing: First, dry-mix the graded dry materials for 120 seconds. Then, slowly and evenly add sodium hydroxide solution while stirring for 45 seconds. Stop stirring and let stand for 30 seconds. Restart stirring, slowly and evenly adding sodium silicate solution while stirring for 45 seconds. Finally, stir rapidly for 60 seconds to obtain a homogeneous slurry.

[0013] The reaction mechanism of this invention is as follows: This invention employs a composite activator system of sodium hydroxide and sodium silicate nonahydrate. Preliminary experiments with different moduli of the composite activator were conducted to determine the optimal ratio of the two activators. Because the NaOH solution provides a high concentration of OH- ions, it is primarily responsible for rapidly disrupting the network structure of aluminosilicates and other ions in the simulated lunar soil, causing them to dissolve and polymerize to form a gel structure. If the ratio is too high, the dissolution reaction is violent, resulting in excessively fluid slurry. However, the lack of readily available dissolved silica from the sodium silicate nonahydrate solution in the early stages to form N(C)-ASH gel leads to insufficient early strength and poor constructability.

[0014] Sodium silicate nonahydrate solution directly provides active dissolved silicon and small molecule silicate polymers. If its proportion is too high, the silicate concentration in the solution is high, but the OH- concentration is relatively insufficient, resulting in slow dissolution of the raw materials. At the same time, the high concentration of silicate will rapidly undergo a condensation reaction, causing the slurry to lose its fluidity instantly, solidify rapidly, and lose the printing window.

[0015] The formulation used in this invention was obtained from prior modulus gradient and alkalinity gradient experiments. Under this modulus and alkalinity activator ratio, the sodium hydroxide solution first reacts with the soil to fully dissolve the active components. The subsequently added sodium silicate nonahydrate solution provides active dissolved silica that immediately combines with the dissolved aluminum, calcium, and sodium ions, rapidly forming an early gel structure and providing initial strength. Simultaneously, the appropriate silicate concentration in the solution prevents excessively rapid gelation. The use of sodium silicate nonahydrate particles as an activator, which contain bound water molecules, alleviates the problem of rapid solidification to some extent. Furthermore, adding a cooled NaOH solution first, allowing it to stand, and then adding the sodium silicate nonahydrate solution is a method to control the reaction process. This ensures the slurry has good printability during extrusion and can quickly build structural strength after extrusion, thus perfectly matching the time-varying performance requirements of materials in 3D printing processes.

[0016] The basalt fiber raw material used is made from basalt, which is abundant on the lunar surface and can provide raw materials for basalt fiber production. Guided by the principle of in-situ lunar fabrication, basalt fiber was added for further printability testing. Since the addition of basalt fiber affects its flowability to some extent, the water-cement ratio was appropriately adjusted to 0.25-0.3. Theoretically, basalt fiber can improve the flexural and bending resistance of printed components, thereby enhancing their mechanical properties.

[0017] Compared with existing technologies, the beneficial effects of this invention are: Highly targeted: It simulates lunar soil from high-altitude regions, fully utilizing its high content of amorphous materials. Balanced printing and construction performance: By controlling the modulus and alkalinity of the composite alkali activator and employing a step-by-step feeding process, it achieves good printability and rapid strength development of the slurry without relying on complex admixtures (water-reducing agents, accelerators, retarders, etc.). Suitable strength: The resulting alkali-activated geopolymer has a dense structure, and its average compressive strength reaches approximately 27 MPa after 28 days (48 hours of high-temperature curing followed by room-temperature curing), meeting the mechanical performance requirements of extraterrestrial building materials. Clear process and easy implementation: The raw materials and preparation process are relatively simple, making it suitable for automated, in-situ preparation and printing construction of future lunar bases. Attached Figure Description

[0018] Figure 1 , Figure 2 , Figure 3 The 3D-printed alkali-activated simulated lunar soil concrete component prepared in Example 1 of this invention is shown in the physical object and constructability test.

[0019] Figure 4 , Figure 5 , Figure 6 The 3D-printed alkali-activated simulated lunar soil concrete component prepared in Example 2 of this invention was tested for its constructability, with a basalt fiber mass fraction of 0.25%.

[0020] Figure 7 , Figure 8 , Figure 9 The 3D-printed alkali-activated simulated lunar soil concrete component prepared in Example 3 of this invention was tested for its constructability, with a basalt fiber mass fraction of 0.5%.

[0021] Figure 10 , Figure 11 The images show the physical prototype of the 3D-printed simulated lunar soil concrete slab component and the printed test image of the cube component prepared in Example 4 of this invention.

[0022] Figure 12 The results are for compressive strength tests of cast cubes under the same materials and operating procedures as in Example 1, with the alkali-activated simulated lunar soil mix ratio of the present invention, after curing at high temperature of 60°C for 48 hours and then at room temperature for a total of 7 days and 28 days. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and specific proportioned embodiments. The following embodiments are merely illustrative and are not intended to limit the scope of protection of this invention.

[0024] Example 1: This invention designs a material simulant and activator for the preparation of alkali-activated simulated lunar soil concrete for 3D printing. The simulated lunar soil raw materials are as follows: 0-75μm accounts for 43%, 75-150μm accounts for 40%, and 150-300μm accounts for 17%. The proportions of each component in the simulated lunar soil are: basalt powder 67%, slag 23%, γ-alumina 2%, calcium hydroxide 1.5%, and silica fume 6.5%.

[0025] The composite alkaline activator consists of sodium hydroxide with a purity of 96% and sodium silicate nonahydrate particles with a modulus of 1. Based on the mass of simulated lunar soil raw material, the sodium hydroxide content is 7.2%, and the sodium silicate nonahydrate content is 14.4%. The total alkalinity of this activator system is 8.5%, and the modulus is 0.37.

[0026] Example 2: This invention also designs a method for preparing 3D-printed simulated lunar soil alkali-activated concrete. The following are the operation steps. S1. The raw materials were dried at 60℃ for 24 hours, and then the particle size distribution was as follows: 0-75μm 43%, 75-150μm 40%, and 150-300μm 17%. The raw material ratio was: basalt powder 67%, slag 23%, γ-alumina 2%, calcium hydroxide 1.5%, and silica fume 6.5%. Specifically, the basalt powder composition was 0-75μm 10%, 75-150μm 40%, and 150-300μm 17%. This mixture yielded simulated lunar soil dry material. S2. Calculate the total water consumption based on the water-cement ratio and divide it into two parts: sodium hydroxide water consumption accounts for 40% of the total water consumption, and sodium silicate nonahydrate water consumption accounts for 60% of the total water consumption. S3. Prepare the solution and let it stand for 24 hours to cool to room temperature to obtain sodium hydroxide solution and sodium silicate nonahydrate solution. S4. Put the simulated lunar soil dry material obtained in S1 into a vertical mixer and dry mix for 120 seconds. S5. While stirring, slowly and evenly add the prepared sodium hydroxide solution to the dry material. This process takes about 45 seconds. S6. Stop stirring and let stand for 30 seconds; S7. Restart stirring and add the prepared sodium silicate solution while stirring. Add it dropwise at a uniform rate, which takes about 45 seconds. S8. Finally, stir rapidly for 60 seconds to obtain a uniform, printable alkali-activated simulated highland lunar soil slurry.

[0027] Experimental example: Sources of some raw materials are as follows The simulated lunar soil material used in this invention consists of basalt powder, silica fume, slag, γ-alumina, and calcium hydroxide powder. XRF and XRD analysis showed that its chemical composition and physical properties matched those of the Apollo 16 highland lunar soil and LHS-1 simulants. The activator was a composite activator composed of sodium hydroxide and sodium silicate nonahydrate.

[0028] The sodium hydroxide used in this invention was provided by Xilong Scientific: solid granules with a purity of 96%. The sodium silicate nonahydrate used in this invention was provided by Tianjin Huasheng Chemical Reagent Co., Ltd.: solid granules with a modulus of 1.0-1.06 and a Na₂O content of 28.6%-29.6%.

[0029] The silica fume used in this invention was provided by Henan Yixiang New Materials Co., Ltd.: High-activity 96 micro silica fume The slag used in this invention was provided by Gongyi Longze Water Purification Materials Co., Ltd.: S105 grade slag powder The γ-alumina used in this invention was provided by Yangzhou Zhongtianli New Material Co., Ltd.: active powder alumina powder The calcium hydroxide used in this invention was provided by Tianjin Huasheng Chemical Reagent Co., Ltd.: in powder form. The basalt used in this invention was provided by Chengdu Weitu Road New Materials Co., Ltd.: three particle sizes, 0-75μm, 75-150μm, and 150-300μm.

[0030] The basalt fiber used in this invention was provided by Haining Anjie Composite Materials Co., Ltd.: 6mm in length, tensile strength 3000-4800MPa, and elastic modulus 91-100Gpa.

[0031] Experimental Example 1 The 3D-printed alkali-activated simulated lunar soil concrete used in this experiment consisted of the following proportions: the particle size distribution was as described in Example 1; the alkali activator consisted of sodium hydroxide with a purity of 96% and sodium silicate nonahydrate particles with a modulus of 1. Based on the mass of the simulated lunar soil raw material, the sodium hydroxide content was 7.2%, and the sodium silicate nonahydrate content was 14.4%. The total alkalinity of the activator was 8.5%, and the modulus was 0.37.

[0032] The 3D-printed alkali-activated simulated lunar soil concrete in this experiment consists of the aforementioned simulated lunar soil and alkali activator, with a water-cement ratio of 0.25.

[0033] The operating steps of this experimental example are performed according to Example 2. The 3D printing parameters for this experiment are: extrusion speed 1.8, moving speed 5.0. Experimental Example 2 The 3D-printed alkali-activated simulated lunar soil concrete used in this experimental example consisted of the following proportions: particle size distribution as described in Example 1; the alkali activator comprised 96% pure sodium hydroxide and sodium silicate nonahydrate particles with a modulus of 1; based on the mass of the simulated lunar soil raw material, the sodium hydroxide content was 7.2%, and the sodium silicate nonahydrate content was 14.4%; the total alkalinity of the activator was 8.5%, and the modulus was 0.37; the mass fraction of basalt fiber was 0.25%. The 3D-printed alkali-activated simulated lunar soil concrete in this experiment consists of the aforementioned simulated lunar soil and alkali-activated basalt fiber agent, with a water-cement ratio of 0.30.

[0034] The experimental procedure for this example is as follows: S1. The raw materials are dried at 60℃ for 24 hours, and then the particle size distribution is as follows: 0-75μm accounts for 43%, 75-150μm accounts for 40%, and 150-300μm accounts for 17%. The raw material ratio is 67% basalt powder, 23% slag, 2% γ-alumina, 1.5% calcium hydroxide, and 6.5% silica fume. Specifically, the basalt powder is 0-75μm accounting for 10%, 75-150μm accounting for 40%, and 150-300μm accounting for 17%. The mixture is then mixed to obtain simulated lunar soil dry material. Basalt fiber with a mass fraction of 0.25% is added to the simulated lunar soil dry material.

[0035] The remaining operating steps shall be performed in accordance with Example 2. The 3D printing parameters for this experiment are: extrusion speed 1.8, moving speed 5.0. Experimental Example 3 The 3D-printed alkali-activated simulated lunar soil concrete used in this experiment consisted of the following proportions: particle size distribution as described in Example 1; the alkali activator comprised 96% pure sodium hydroxide and sodium silicate nonahydrate particles with a modulus of 1; based on the mass of the simulated lunar soil raw material, the sodium hydroxide content was 7.2%, and the sodium silicate nonahydrate content was 14.4%; the total alkalinity of the activator was 8.5%, and the modulus was 0.37; the mass fraction of basalt fiber was 0.5%. The 3D-printed alkali-activated simulated lunar soil concrete in this experiment consists of the aforementioned simulated lunar soil and alkali-activated basalt fiber agent, with a water-cement ratio of 0.30.

[0036] The experimental procedure for this example is as follows: S1. The raw materials are dried at 60℃ for 24 hours, and then the particle size distribution is as follows: 0-75μm accounts for 43%, 75-150μm accounts for 40%, and 150-300μm accounts for 17%. The raw material ratio is 67% basalt powder, 23% slag, 2% γ-alumina, 1.5% calcium hydroxide, and 6.5% silica fume. Specifically, the basalt powder is 0-75μm accounting for 10%, 75-150μm accounting for 40%, and 150-300μm accounting for 17%. The mixture is then mixed to obtain simulated lunar soil dry material. Basalt fiber with a mass fraction of 0.5% is added to the simulated lunar soil dry material.

[0037] The remaining operating steps shall be performed in accordance with Example 2. The 3D printing parameters for this experiment are: extrusion speed 1.8, moving speed 5.0. Experiment Example 4 The operation steps and parameters of this experiment are the same as those of Experiment 1. A 3D printed alkali-activated simulated lunar soil bending plate component with a length of 300mm, a width of 120mm, and a height of 50mm was designed.

[0038] The 3D printing parameters for this experiment are: extrusion speed 1.8, moving speed 5.0. As can be seen from the above experimental examples, the printability and constructability of 3D printed simulated lunar soil alkali-activated concrete have been experimentally verified through reasonable particle size distribution and alkali activator control. Figure 1 The printing test showed that the basalt fiber content was 0% and the printed lines were smooth with reasonable layer spacing, proving that it has reasonable printability. Figure 2 , Figure 3 Printability tests were conducted with basalt fiber mass fractions of 0.25% and 0.5%, respectively, demonstrating its printability. Figure 4 This study presents printing experiments on mechanical components of alkali-activated simulated lunar soil concrete using 3D printing. This corresponds to Example 4. Constructability requires that the extruded concrete maintain its shape stability without lateral formwork support and not collapse under the additional pressure of subsequent layers of concrete. Examples 1, 2, and 3 all used cylindrical models with a height and diameter of 80 mm for testing. After mixing, the slurry was poured into the mold in three batches. After molding, the mold was lifted and its height was measured to evaluate its constructability. The height retention rates were 95%, 95.9%, and 96.8%, respectively, indicating good constructability.

[0039] The above experimental examples demonstrate that the 3D-printed alkali-activated simulated lunar soil concrete of this invention, through preliminary optimization of the simulated lunar soil particle size distribution and adjustment of the ratio of sodium hydroxide and sodium silicate nonahydrate to control the alkalinity and modulus of the activator, utilizes the advantages of different alkali activators to achieve excellent printability and constructability. The addition of basalt fiber is expected to effectively improve the mechanical properties and durability of the printed components. This further illustrates that, under the condition of utilizing lunar in-situ resources, this invention provides an effective basic research method for the further development of the field of 3D-printed simulated lunar soil. However, due to limitations, this experiment was conducted under Earth's gravity and climate conditions; the constructability risks under low gravity conditions require further investigation.

[0040] Finally, it should be noted that the above embodiments are merely preferred embodiments of the present invention and are only used to explain the present invention, not to limit the present invention. Any changes, substitutions, modifications, etc., made by those skilled in the art without departing from the spirit and essence of the present invention should fall within the protection scope of the present invention.

Claims

1. A method for preparing alkali-activated simulated lunar soil concrete mortar for 3D printing, characterized in that: The simulated lunar soil composition was as follows: basalt powder 67%, slag 23%, γ-alumina 2%, calcium hydroxide 1.5%, and silica fume 6.5%. The basalt powder particle size distribution was: 0-75 μm 10%, 75-150 μm 40%, and 150-300 μm 17%. The overall particle size distribution was: 0-75 μm 43%, 75-150 μm 40%, and 150-300 μm 17%.

2. The alkali-activated simulated lunar soil mortar for 3D printing according to claim 1, characterized in that: The alkaline activator is composed of sodium hydroxide, sodium silicate nonahydrate, and water, with the sodium silicate nonahydrate having a modulus of 1. The mass ratios of sodium hydroxide and sodium silicate nonahydrate to the simulated lunar soil are 0.072 and 0.144, respectively, and the water-cement ratio is 0.25~0.

3.

3. An alkali-activated simulated lunar soil mortar for 3D printing according to claim 2, characterized in that: The steps for the stepwise stirring of the alkali activator are as follows: first, add the cooled sodium hydroxide solution, stir for a period of time, and then add the sodium silicate nonahydrate solution.

4. An alkali-activated simulated lunar soil mortar for 3D printing, characterized in that: The preparation process includes the following steps: S1. Raw material preparation: The raw materials of each component of the simulated lunar soil are dried at 60°C for 24 hours, and then mixed according to the particle size distribution described in claim 1 to obtain the simulated lunar soil dry material. S2. Calculate the total water consumption based on the water-cement ratio and divide it into two parts: sodium hydroxide water consumption accounts for 40% of the total water consumption, and sodium silicate nonahydrate water consumption accounts for 60% of the total water consumption. S3. Prepare the solution and let it stand for 24 hours to cool to room temperature to obtain sodium hydroxide solution and sodium silicate nonahydrate solution. S4. Put the simulated lunar soil dry material obtained in S1 into a vertical mixer and dry mix for 120 seconds. S5. While stirring, slowly and evenly add the prepared sodium hydroxide solution to the dry material, which takes about 45 seconds. S6. Stop stirring and let stand for 30 seconds; S7. Restart stirring and add the prepared sodium silicate solution while stirring. This process should be done by adding the solution dropwise at a uniform rate, which should take about 45 seconds. S8. Finally, stir rapidly for 60 seconds to obtain a uniform, printable alkali-activated simulated lunar soil slurry.

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