Polypropylene fiber reinforced lunar soil simulating geopolymer material and preparation method thereof

Abstract

The invention relates to the field of polypropylene fiber preparation, and particularly discloses a polypropylene fiber reinforced simulated lunar soil geopolymer material and a preparation method thereof, the polypropylene fiber reinforced simulated lunar soil geopolymer material comprises the following components by weight: TJ-1 simulated lunar soil; as a main raw material; the length of the polypropylene fiber is 3-9 mm, and the mixing amount of the polypropylene fiber is 0.1-0.6 wt% (based on the total weight of the TJ-1 simulated lunar soil); the composite alkali activator is composed of sodium hydroxide, calcium hydroxide and sodium silicate nonahydrate; by optimizing the length and the mixing amount of the polypropylene fiber (PPF), the compressive strength and the breaking strength of the simulated lunar soil geopolymer are remarkably improved, particularly when the length of the fiber is 6 mm and the mixing amount is 0.4%, the compressive strength and the breaking strength both reach the maximum value and are improved by 54.6% and 117.7% respectively compared with a reference group without the fiber, and the compressive strength and the breaking strength of the simulated lunar soil geopolymer are greatly improved. The improvement is crucial to the application of lunar building materials because it can enhance the structural stability and bearing capacity of lunar buildings.

Description

Technical Field

[0001] The present invention belongs to the field of polypropylene fiber preparation, and specifically relates to a polypropylene fiber reinforced simulated lunar soil geopolymer material and a preparation method thereof. Background Art

[0002] Deep space exploration activities, especially lunar exploration, have become a key area for human exploration of the universe and promotion of scientific and technological innovation. China's lunar exploration project has completed the mission objectives of the three stages of "orbiting, landing, and returning", and plans to further explore the lunar south pole and build a lunar research station. As the most widely distributed and largest in-situ resource on the moon, lunar soil has great application potential in the construction of lunar space stations and is expected to significantly reduce dependence on Earth resources.

[0003] The acquisition of real lunar soil provides valuable scientific basis for domestic and foreign scholars to prepare building materials using lunar soil. However, due to the limited reserves of real lunar soil, simulated lunar soil has become the main raw material for research. Existing studies show that the main material components of real lunar soil and simulated lunar soil are similar, mainly composed of elements such as SiO2 and Al2O3. Based on these components, researchers have tried to synthesize geopolymers using lunar soil as a new type of lunar building material. Geopolymers have better compressive strength and flexural strength than traditional cement, showing good application prospects.

[0004] However, the extreme conditions of the lunar surface environment, such as high and low temperatures, moonquakes, and meteorite impacts, pose more stringent requirements for building materials. Geopolymer materials have defects such as low tensile strength, easy cracking, and high brittleness, which limit their application in lunar construction. To improve the tensile and crack resistance of geopolymers, researchers have tried to use fibers as reinforcement materials to replace traditional steel bars. Studies have shown that the incorporation of fibers can significantly improve the mechanical properties and flexural toughness of geopolymers, but the length and dosage of fibers have a significant impact on the strengthening effect.

[0005] Currently, although there have been some studies on fiber-reinforced geopolymers, the strengthening effects of fibers vary for geopolymers with different matrices. Especially for simulated lunar soil geopolymers, the improvement of their mechanical properties and flexural toughness still needs to be verified. Therefore, based on the existing research results, this patent aims to use TJ-1 simulated lunar soil as the main raw material, and through compressive strength tests, flexural strength tests, and SEM scanning electron microscopy analysis, study the effects of the length and dosage of fibers (PPF) on the mechanical properties and flexural toughness of simulated lunar soil geopolymers, so as to achieve performance improvement under the optimal length and optimal dosage. This will provide technical reference and theoretical basis for subsequent impact resistance tests of simulated lunar soil geopolymers under extreme temperatures, and further promote the research and application of lunar building materials.

[0006] In particular, the existing lunar soil geopolymers have defects such as low tensile strength, easy cracking, and high brittleness, and the effects of the length and dosage of fiber-reinforced materials (PPF) on the mechanical properties and flexural toughness of simulated lunar soil geopolymers are not clear. Summary of the Invention

[0007] To solve the above technical problems, the present invention provides a polypropylene fiber-reinforced simulated lunar soil geopolymer material to solve the defects of the existing lunar soil geopolymer material such as low tensile strength, easy cracking, and high brittleness, and the unclear effects of the length and dosage of fiber-reinforced materials (PPF) on the mechanical properties and flexural toughness of simulated lunar soil geopolymers.

[0008] The polypropylene fiber-reinforced simulated lunar soil geopolymer material contains the following components by weight:

[0009] TJ-1 simulated lunar soil; as the main raw material;

[0010] Polypropylene fiber: with a length of 3-9 mm and a dosage of 0.1-0.6 wt% (calculated based on the total weight of TJ-1 simulated lunar soil);

[0011] Composite alkali activator: composed of sodium hydroxide, calcium hydroxide, and sodium silicate nonahydrate; among them, the dosage of sodium hydroxide is 6 wt%, the dosage of calcium hydroxide is 8 wt%, and the dosage of sodium silicate nonahydrate is 10 wt% (both calculated based on the total weight of TJ-1 simulated lunar soil);

[0012] Distilled water: used to mix with the composite alkali activator to form an alkali activator solution; the water-binder ratio (i.e., the ratio of distilled water to the total weight of TJ-1 simulated lunar soil and composite alkali activator) is 0.28;

[0013] Water reducer: with a dosage of 0.1 wt% (calculated based on the total weight of TJ-1 simulated lunar soil).

[0014] Preferably, the alkali activator is obtained by dissolving sodium hydroxide, calcium hydroxide, and sodium silicate nonahydrate in proportion and then stirring in distilled water.

[0015] A method for preparing the polypropylene fiber-reinforced simulated lunar soil geopolymer material as described above includes the following steps:

[0016] a. Weigh sodium hydroxide, calcium hydroxide, and sodium silicate nonahydrate in proportion and dissolve them in distilled water, and stir evenly to form an alkali activator solution;

[0017] b. Pour TJ-1 simulated lunar soil into a mixing pot, start the mixer, and at the same time add polypropylene fiber to the mixing pot in three batches and dry mix for 2 minutes;

[0018] c. Add the alkali activator solution prepared in step a to the stirring pot, stir at a low speed for 2 min first, and then stir at a high speed for 30 s to form a uniform mixture;

[0019] d. Pour the mixture into a mold, and carry out vibration, curing and sealing.

[0020] Preferably, the mold described in step d is a 40 mm×40 mm×160 mm cement mortar triple mold.

[0021] Preferably, the curing temperature is 100 °C.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] By optimizing the length and dosage of polypropylene fiber (PPF), the present invention significantly improves the compressive strength and flexural strength of the simulated lunar soil geopolymer. Especially when the fiber length is 6 mm and the dosage is 0.4%, the compressive strength and flexural strength both reach the maximum values, which are increased by 54.6% and 117.7% respectively compared with the reference group without fiber addition. This improvement is crucial for the application of lunar building materials because it can enhance the structural stability and bearing capacity of lunar buildings;

[0024] The present invention uses simulated lunar soil as the main raw material, and prepares high-performance lunar building materials by adding reinforcing materials such as PPF, which helps to reduce the dependence on Earth resources, promote the effective utilization and sustainable development of in-situ lunar resources. At the same time, the invention also provides a useful reference for resource utilization and environmental protection in future deep space exploration activities. Description of the Drawings

[0025] Figure 1 are the physical and mechanical properties of PPF;

[0026] Figure 2 is the mix proportion of PPF-reinforced simulated lunar soil geopolymer;

[0027] Figure 3 are the fluidities of three PPF lengths;

[0028] Figure 4 is the influence of PPF dosage on the compressive strength of simulated lunar soil geopolymer;

[0029] Figure 5 are the maximum compressive strengths of each length PPF test group;

[0030] Figure 6 is the influence law of PPF dosage on the flexural strength of simulated lunar soil geopolymer;

[0031] Figure 7is the maximum flexural strength of simulated lunar soil geopolymers reinforced with different lengths of PPF;

[0032] Figure 8 is the three-point bending load-deflection curve of simulated lunar soil geopolymers reinforced with different dosages of PPF

[0033] Figure 9 is the maximum mid-span deflection of simulated lunar soil geopolymers reinforced with different lengths of PPF;

[0034] Figure 10 is the relationship curve of PPF length, dosage and flexural toughness coefficient;

[0035] Figure 11 is the microstructure of PPF toughened simulated lunar soil geopolymers. Specific implementation manners

[0036] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0037] Embodiment 1:

[0038] 1 Test materials and methods

[0039] 1.1 Raw materials

[0040] The main raw material used in the present invention is TJ-1 simulated lunar soil, which has a high similarity with the lunar soil collected by Apollo 14 in terms of chemical composition, mineral composition and microscopic morphology. The alkali activator is prepared by mixing sodium hydroxide, calcium hydroxide, sodium silicate nonahydrate and distilled water in proportion. Among them, sodium hydroxide is flaky NaOH with a purity of 99% produced by Henan Jiuling Chemical Industry, calcium hydroxide is powdery calcium hydroxide produced by Tianjin Dengfeng Chemical Reagent Factory, and sodium silicate nonahydrate is granular water glass produced by Tianjin Dengfeng Chemical Reagent Factory with a modulus of 1.03. The polypropylene fiber is produced by Hebei Chuangsheng Building Materials and Chemical Industry. The specific physical and mechanical properties are shown in Figure 1 . The water reducer used is a polycarboxylic acid superplasticizer produced by Shanghai Chenqi Chemical Technology Co., Ltd., and the water reduction efficiency is 21%.

[0041] 1.2 Mix proportion design

[0042] To explore the effects of PPF length and dosage on the mechanical properties and flexural toughness of simulated lunar soil geopolymers, based on existing research results, the fixed variable method was used for mix design, that is, the water-binder ratio and the dosage of alkali activator were fixed, and the fiber length and mass fraction were changed. The water-binder ratio of the test was 0.28, and the dosages of sodium hydroxide, calcium hydroxide, and sodium silicate nonahydrate in the composite alkali activator were 6wt%, 8wt%, and 10wt% respectively. The dosage of water reducer was 0.1wt%. The fiber lengths were selected as 3mm, 6mm, and 9mm respectively, and the dosages were selected as 0.1wt%, 0.2wt%, 0.3wt%, 0.4wt%, 0.5wt%, and 0.6wt% by mass percentage. The test mix proportions are shown in Figure 2 .

[0043] 1.3 Specimen Preparation and Curing

[0044] First, weigh sodium hydroxide, calcium hydroxide, and sodium silicate nonahydrate according to the ratio and dissolve them in distilled water, and stir evenly; secondly, weigh the simulated lunar soil and pour it into the mixing pot, start the mixer, and add the PPF into the mixing pot in three batches, and dry mix with the simulated lunar soil for 2 min; add the previously mixed and prepared alkali activator, stir at low speed for 2 min, and then stir at high speed for 30 s; pour the mixed specimen into a 40mm×40mm×160mm cement mortar triple mold for vibration, curing, and sealing.

[0045] According to the research by Zhou S et al., the mechanical properties of simulated lunar soil geopolymers are greatly improved when cured at 100°C. At the same time, combined with the lunar surface temperature captured by the Diviner Lunar Radiometer Experiment on the Diviner Lunar Reconnaissance Orbiter (LRO), the temperature in the lunar equator and the 30° north latitude area where it is suitable to build a scientific research station can reach 100°C. Therefore, the curing temperature in this study was set at 100°C to explore the strengthening effect of PPF on the mechanical properties and flexural toughness of simulated lunar soil geopolymers.

[0046] 1.4 Test Methods

[0047] The workability of simulated lunar soil geopolymers was measured according to the "Determination Method for Fluidity of Cement Mortar" GB / T2419-2005. Using a JJ-5 type cement mortar mixer, pour the mixed specimen into a frustum cone mold with an upper diameter of 70mm, a lower diameter of 100mm, and a height of 60mm; after scraping and tamping, remove the mold; after 25 jumping table tests, measure the diffusion diameters in two mutually perpendicular directions and calculate the average value as the basis for the workability of the geopolymer.

[0048] According to the "Testing Methods for Strength of Cement Mortar (ISO Method)" GB / T 17671-2021, a WHY-300 type microcomputer-controlled compression testing machine was used to test the compressive strength and flexural strength. The loading rate for flexural strength was 50 N / s ± 10 N / s, and the loading rate for compressive strength was 2400 N / s ± 200 N / s. For each mix proportion, 3 parallel tests were carried out and the average value was taken as the final result. Formulas (1) and (2) were used to calculate the flexural strength R f and the compressive strength R c .

[0049]

[0050]

[0051] Where: F f is the load when the specimen breaks in the middle; L is the span between the support cylinders (100 mm); b is the side length of the specimen cross-section (40 mm); F c is the maximum load when the specimen fails; A is the compression area (40 mm);

[0052] During the flexural test, the mid-span deflection was measured using an electronic displacement gauge. Before the test, a special glass sheet was pasted in the center of one side of the specimen, and the displacement sensor was placed under the glass sheet. The sensor connector end was appropriately compressed and made to contact the glass sheet. The YBY-2001 strain test and analysis system was used to measure the mid-span deflection of the specimen, with a sampling frequency of 50 Hz. The compression testing machine was controlled by displacement, and the loading rate was 0.02 mm / min. The displacement sensor, compression testing machine, and acquisition system were connected, and the load and deflection values of the specimen could be synchronously collected at the computer end to obtain the load-mid-span deflection curve of the specimen. For the test, a Czech TESCAN MIRALMS type scanning electron microscope was used. Samples were taken at the fracture surface, and specimens with a length and width of 5 mm and a thickness of 2 mm were prepared. The surface was sputter-coated with gold, and an appropriate magnification was selected to observe the internal microtopography of the specimen.

[0053] Example 2:

[0054] 2 Test Results and Analysis

[0055] 2.1 Workability

[0056] Figure 3 shows the influence of the PPF length and dosage on the fluidity of simulated lunar soil geopolymers. From Figure 3It can be seen that with the increase of fiber content, the fluidity of geopolymers gradually decreases. When the fiber content increases to 0.6%, the fluidities of P3, P6, and P9 decrease by 23%, 25%, and 28% respectively, which is also consistent with the research results of Ferrara L et al. The reason for the decrease in the fluidity of geopolymers with higher fiber content is that the increase in fiber content in geopolymers forms a network structure that restricts the flow of geopolymers, and PPF has an adsorption effect on water, resulting in a decrease in the content of free water. Further analysis shows that when the fiber length increases at the same content, the fluidity of geopolymers shows a decreasing trend. For example, P9-0.6 is 10% and 7.5% lower than P3 and P6 respectively. The reason is that the increase in fiber length will enhance the bonding effect on geopolymers, and at the same time, the entanglement and aggregation of longer fibers will increase the flow resistance of geopolymers and reduce the fluidity.

[0057] 2.2 Analysis of the influence on compressive strength

[0058] Figure 4 shows the influence of PPF content on the compressive strength of simulated lunar soil geopolymers. From Figure 4 it can be obtained that after adding fibers, the compressive strengths of the P3, P6, and P9 test groups are all higher than those of the control group. For example, at a content of 0.1%, the compressive strengths of P3, P6, and P9 are 11.6 MPa, 12 MPa, and 12.8 MPa respectively; the increases compared with the reference group P0 are 17.2%, 21.2%, and 29.3% respectively. The compressive strength of long-fiber geopolymers increases rapidly at low contents. The reason is that at the same content, the number of long fibers decreases, and they will not cluster at low contents, which can effectively bond the matrix inside the specimen; although the number of short fibers is large, their lengths are short and they cannot provide enough tensile stress to limit the cracking of the matrix. With the increase of fiber content, this phenomenon gradually changes. Taking the P9 test group as an example, the increases of P9-0.1% - 0.6% compared with the reference group P0 are 29.3%, 34.3%, 40.4%, 33.3%, 29.3%, and 20.2% respectively. At higher contents, the compressive strength of long fibers decreases rapidly. The reason is that when the fiber content is high enough, it is difficult for long fibers to be evenly dispersed, resulting in stress concentration. Although the compressive strengths of the P3, P6, and P9 test groups decrease to varying degrees after a content of 0.3% and 0.4%, they are still higher than the reference group P0. The reasons are as follows: when the specimen is damaged under compression, there will be an interaction bite force between the fiber and the matrix, thus forming axial cracks parallel to the load direction. The bite force generated by the fiber offsets part of the transverse tensile stress between these cracks. At the same time, the random distribution of the fiber inhibits the expansion of cracks in the direction of the compressive load and reduces the stress concentration effect at the crack tip, which can effectively improve the compressive strength of the specimen.

[0059] Figure 5 shows the maximum compressive strength of simulated lunar soil geopolymers strengthened by different lengths of PPF. From Figure 5It can be seen that P3 - 0.3% is 12.8 MPa, P6 - 0.4% is 15.3 MPa, and P9 - 0.3% is 13.9 MPa. At this time, the P3, P6, and P9 test groups reach the maximum values, and the increases compared with the reference group P0 are 29.3%, 54.6%, and 40.4% respectively. The compressive strength of P6 - 0.4% increases by 10.1% and 19.5% compared with P9 - 0.3% and P3 - 0.3% respectively, indicating that the compressive effect of P6 - 0.4% geopolymers is the best under the same mix ratio.

[0060] 2.3 Analysis of Flexural Strength Influence

[0061] Figure 6 shows the influence law of PPF content on the flexural strength of simulated lunar soil geopolymers. From Figure 6 it can be obtained that with the increase of fiber content, the flexural strength of simulated lunar soil geopolymers shows a trend of first increasing and then decreasing. For example, the P6 test group is increased by 64.7%, 82.4%, 94.1%, 117.7%, 94.1%, and 88.2% respectively compared with the reference group P0. The reason for the increase in flexural strength after fiber incorporation is that PPF restricts the longitudinal expansion and cracking of geopolymers, enhancing the flexural and tensile capacity. Similar to the influence on compressive strength, the reason for the decrease in flexural strength when the fiber content continues to increase after reaching the optimal value may be that a large amount of fiber content affects the uniformity of geopolymers. The aggregation of fibers reduces the bonding area with the matrix, and a large number of voids are formed between multiple fibers. The fibers themselves do not connect the matrix and cannot bear the tensile stress, thus reducing the bearing capacity of geopolymers. Whether the fibers are too long or too short will also have a certain impact on the flexural strength of geopolymers. For example, P3 - 0.6%, P6 - 0.6%, and P9 - 0.6% are increased by 41.2%, 88.2%, and 58.8% respectively compared with the reference group P0. The author analyzes that when the fiber length is short, the length embedded in the matrix is short, the stress area at the internal crack bridging is reduced, and insufficient bonding force cannot be provided to connect the matrix at both ends of the crack; when the fiber length is long, the number of fibers will decrease, increasing the difficulty of dispersion, and the long fibers are prone to clustering, resulting in a reduction in the bonding area with the matrix cross-section and a decrease in the bridging effect.

[0062] Figure 7 shows the maximum flexural strength of simulated lunar soil geopolymers enhanced by different lengths of PPF. From Figure 7 it can be seen that P3 - 0.3% is 2.9 MPa, P6 - 0.4% is 3.7 MPa, and P9 - 0.3% is 3.5 MPa. At this time, the flexural strengths of P3, P6, and P9 reach the peak values, and the increases compared with the reference group P0 are 70.6%, 117.7%, and 105.9% respectively; consistent with the compressive strength results, P6 - 0.4% has the most obvious improvement in the flexural strength of geopolymers.

[0063] 2.4 Analysis of Bending Load Toughness

[0064] Figure 8 The three-point bending load-deflection curves of geopolymer reinforced with different dosages of PPF in simulated lunar soil are shown as follows. It can be seen from Figure 8 that after the fiber dosage reaches the optimal value, the mid-span deflection of the P9 test group decreases rapidly. The increases compared with the reference group P0 are 10%, 30%, 55%, 45%, 10%, and 1% respectively. There is no obvious difference between P9-0.6% and P0. The reason is that the entanglement in the matrix intensifies due to the large fiber dosage. The load borne by the specimen is transferred to the fibers that have aggregated into clusters. At the initial stage of loading, the fibers do not break or only a few break. As the displacement distance increases, the fibers are stretched and suddenly break after reaching the critical value. Due to the large fiber dosage, a clear cracking sound is emitted when the specimen fails. At this time, the failure mode of the specimen is brittle failure. When the fiber content is less than 0.3%, the mid-span deflection of the P3 and P9 test groups increases slightly with the increase of the fiber dosage. For example, the increases of P3-0.1% and P9-0.1% compared with the reference group P0 are 5% and 10% respectively. However, the mid-span deflection of the P6 test group increases significantly with the increase of the fiber dosage. For example, P6-0.1% has an increase of 20% compared with P0. When the fiber dosage exceeds 0.4%, the mid-span deflection decreases. Different from this, the inflection points of the P3 and P9 test groups appear at 0.3%, which is consistent with the mechanical property results.

[0065] Figure 9 The maximum mid-span deflection of geopolymer reinforced with different lengths of PPF in simulated lunar soil is shown as follows. The trend is the same as that of the flexural strength test results. The mid-span deflections of the P3, P6, and P9 test groups reach their peaks at 0.3%, 0.4%, and 0.3% respectively, with increases of 50%, 90%, and 55% compared with the reference group P0. When the fiber reaches the optimal dosage, the toughness of the geopolymer is greatly improved. No clear cracking sound appears when the specimen fails. Although the failure mode is still brittle failure at this time, the ductility is greatly improved.

[0066] At present, there are few research results on the prediction model of the toughness of fiber-reinforced geopolymer. In this paper, the JCI flexural toughness coefficient method is adopted and combined with the mid-span deflection of PPF-reinforced simulated lunar soil geopolymer, aiming to construct the relationship curve between the mid-span deflection and the flexural toughness coefficient under different lengths and dosages of PPF. This method stipulates that when the deflection of the specimen deforms to 1 / 150 times of the span, the flexural toughness coefficient is obtained from the area under the load-deflection curve and parameters such as the specimen size to measure the flexural toughness of the material. The flexural toughness coefficient of the specimen is obtained by Equation (3).

[0067]

[0068] In the formula, σ b is the flexural toughness coefficient (N / mm); T b is the envelope area of the load-deflection curve; σ tbis the span / 150 (mm); L is the span (mm); b is the cross-sectional width (mm); h is the cross-sectional height (mm);

[0069] Figure 10 is the relationship curve of PPF length, dosage and flexural toughness coefficient. From Figure 10 it can be seen that the toughness of the geopolymer is greatly improved with the incorporation of fibers, showing a trend of first increasing and then decreasing as a whole. This indicates that the toughness of the geopolymer decreases after the fiber dosage reaches the optimal value. Comparing the flexural toughness coefficients of the geopolymer toughened by three fiber lengths, the fitting degree of the P6 test group is the best, which shows that the length of PPF is an important parameter to improve the flexural toughness of the geopolymer, and the energy of the load on the geopolymer can be effectively absorbed and transferred when the fiber length is 6 mm.

[0070] The enhancement effect of PPF on the flexural toughness of simulated lunar soil geopolymer is mainly reflected in two aspects: on the one hand, after the fibers are incorporated, the original stress distribution inside the geopolymer is disrupted, preventing crack propagation and matrix cracking, so that more energy needs to be consumed during the tensile process, improving the toughness of the material; on the other hand, in addition to the chemical properties and physical properties of the fibers themselves, the overall effect of the entire fiber network, fiber length, content, and whether they are evenly distributed in the matrix are also important factors controlling the overall performance of the composite material. There is an optimal fiber content in the fiber-reinforced composite material to obtain the highest mechanical strength.

[0071] 2.5 Microscopic pore structure and mechanism analysis

[0072] Figure 11 is the microstructure of PPF toughened simulated lunar soil geopolymer. From Figure 11 (a) and (b), it can be observed that the crack distribution on the fracture surface of the reference group P0 is intricate and the crack width is large. After the fibers are incorporated, the cracks on the fracture surface become significantly narrower. The reason is that when the geopolymer is stressed, relative displacement occurs between the fibers and the geopolymer, and frictional resistance will be generated between the two to hinder crack propagation, thus playing a strengthening role. Further comparative analysis Figure 11 (a) and (c) shows that PPF is embedded at both ends of the crack and hinders its deformation under the action of tensile stress, enhancing the matrix bonding degree, indicating that PPF can effectively inhibit the crack propagation and matrix cracking of the geopolymer through frictional resistance and embedding effects, which also coincides with the research conclusions of Guo et al.

[0073] Observation Figure 11 (d) shows that PPF is closely bonded to the matrix, and some hydration products adhere to the fiber surface, generating cohesive action between the two, indicating that PPF has good compatibility with the cementitious material, which is also the main reason for the decrease in the fluidity of the geopolymer. From Figure 11(e) Traces of PPF pull-out failure can be observed. Most of the fibers are intact as a whole, without necking at the ends. It is mainly pulled out and damaged. When the specimen is stressed and fractured, the PPF bridging both ends of the matrix at the fracture surface breaks free from the bonding force during crack propagation and undergoes pull-out failure. However, the residual fibers will prevent the crack from possibly continuing to develop in any direction. The stress is transmitted to the matrix surface through the fibers, enabling the matrix around the fibers to continue to bear the stress, resulting in the specimen having residual strength and slowing down the fracture speed, and the toughness of the specimen also increases accordingly. From Figure 11 (f), it can be seen that when the fiber content is relatively large, some PPF in the matrix aggregates into clusters, which will reduce the bonding area between the fibers and the matrix, leading to stress concentration during the stress process of the specimen and causing a decrease in strength. This is the reason for the reduction in the strength of long fibers.

[0074] 3 Conclusions

[0075] This paper studied the enhancement effects of PPF length and content on the workability, compressive strength, flexural strength, and mid-span deflection of simulated lunar soil geopolymers, and constructed a prediction model for the flexural toughness of PPF on simulated lunar soil geopolymers. The main conclusions are as follows:

[0076] (1) The fluidity of PPF-reinforced simulated lunar soil geopolymers decreases with the increase in fiber content and length. When the fiber content increases to 0.6%, the fluidity of P3, P6, and P9 decreases by 23%, 25%, and 28% respectively. The P9 test group has the greatest impact on fluidity.

[0077] (2) PPF can effectively improve the mechanical strength of geopolymers. With the increase in fiber content, the compressive strength of each fiber length test group first increases and then decreases, reaching the maximum values at P3-0.3%, P6-0.4%, and P9-0.3% respectively, with increases of 29.3%, 54.6%, and 40.4% compared with P0; the flexural strength has the same change trend as the compressive strength, and the maximum increase compared with P0 is 70.6%, 117.7%, and 105.9%. The P6-0.4% has the best strengthening effect.

[0078] (3) The change law of the flexural toughness of fiber-reinforced simulated lunar soil geopolymers is consistent with that of the flexural strength. The flexural toughness of the P3-0.3%, P6-0.4%, and P9-0.3% test groups increases by 50%, 90%, and 55% respectively compared with the reference group P0; a prediction model for the relationship between the mid-span deflection and the flexural toughness coefficient under fiber length and content is constructed. Analyzing the relationship curve shows that the P6 test group has the best fitting degree, and P6-0.4% has the greatest improvement in the flexural toughness of geopolymers, which provides a scientific basis for subsequent impact resistance tests under extreme temperature environments.

[0079] All the standard parts used in the present invention can be purchased from the market. The special-shaped parts can be customized according to the description in the specification and the attached drawings. The specific connection methods of each part all adopt conventional means such as bolts, rivets, welding, etc. that are mature in the prior art. The machines, parts and equipment all adopt conventional models in the prior art. In addition, the circuit connection adopts the conventional connection method in the prior art, which will not be elaborated here. The content not described in detail in this specification belongs to the prior art well-known to those skilled in the art.

[0080] In the description of the present invention, the terms "first" and "second" are only used for descriptive purposes and cannot be construed as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, the features defined with "first" and "second" may explicitly or implicitly include one or more of such features. The meaning of "a plurality" is two or more unless otherwise specifically defined.

[0081] In the present invention, unless otherwise clearly specified and defined, the terms such as "mounted", "connected", "connected to", "fixed" and the like should be understood in a broad sense. For example, it may be a fixed connection, a detachable connection, or integrated; it may be a mechanical connection or an electrical connection; it may be directly connected or indirectly connected through an intermediate medium, and it may be the internal connection of two components or the interaction relationship between two components. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0082] In the present invention, unless otherwise clearly specified and defined, the first feature being "on" or "under" the second feature may be that the first and second features are in direct contact, or the first and second features are indirectly in contact through an intermediate medium. Moreover, the first feature being "above", "over" and "on top of" the second feature may be that the first feature is directly above or obliquely above the second feature, or merely indicates that the first feature is at a higher level than the second feature in terms of horizontal height. The first feature being "under", "below" and "beneath" the second feature may be that the first feature is directly below or obliquely below the second feature, or merely indicates that the first feature is at a lower level than the second feature in terms of horizontal height.

[0083] In the description of this specification, the description referring to terms such as "one embodiment", "some embodiments", "examples", "specific examples", or "some examples" means that the specific features, structures, materials, or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic expressions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described can be combined in a suitable manner in any one or more embodiments or examples. In addition, without contradiction, those skilled in the art can combine and combine the different embodiments or examples described in this specification and the features of different embodiments or examples.

[0084] In the accompanying drawings of the disclosed embodiments of the present invention, only the structures related to the disclosed embodiments are involved. For other structures, reference can be made to the general design. Without conflict, the same embodiment and different embodiments of the present invention can be combined with each other.

[0085] Although the present invention has been described in detail with reference to the foregoing embodiments, for those skilled in the art, they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements for some of the technical features. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. Polypropylene fiber reinforced simulated lunar soil geopolymer material, characterized in that: By weight, it contains the following components: TJ-1 simulated lunar soil; as the main raw material; Polypropylene fiber: 3-9 mm in length, 0.1-0.6 wt% (based on the total weight of TJ-1 simulated lunar soil); Composite alkaline activator: composed of sodium hydroxide, calcium hydroxide and sodium silicate nonahydrate; wherein the dosage of sodium hydroxide is 6wt%, the dosage of calcium hydroxide is 8wt%, and the dosage of sodium silicate nonahydrate is 10wt% (all calculated based on the total weight of TJ-1 simulated lunar soil); Distilled water: used to mix with the composite alkali activator to form an alkali activator solution; the water-to-binder ratio (i.e., the ratio of distilled water to the total weight of TJ-1 simulated lunar soil and composite alkali activator) is 0.28; Water reducing agent: The dosage is 0.1wt% (calculated based on the total weight of TJ-1 simulated lunar soil).

2. The polypropylene fiber reinforced simulated lunar soil geopolymer material according to claim 1, characterized in that: The alkaline activator is prepared by mixing sodium hydroxide, calcium hydroxide and sodium silicate nonahydrate in proportion, dissolving the mixture in distilled water and stirring.

3. The method for preparing the polypropylene fiber reinforced simulated lunar soil geopolymer material according to claim 1 or 2, characterized in that: The following steps are involved: a. Dissolve sodium hydroxide, calcium hydroxide and sodium silicate nonahydrate in distilled water according to the weighed proportions and stir evenly to form an alkaline activator solution; b. Pour TJ-1 simulated lunar soil into a mixing pot, start the mixer, and add polypropylene fibers into the mixing pot in three batches, and dry mix for 2 minutes; c. Add the base activator solution prepared in step a to the stirring pot, stir at low speed for 2 min, then stir rapidly for 30 s to form a uniform mixture; d. Pour the mixture into a mold, vibrate, cure and seal.

4. The preparation method according to claim 3, characterized in that: The mold described in step d is a 40mm×40mm×160mm cement mortar triple test mold.

5. The polypropylene fiber reinforced simulated lunar soil geopolymer material according to claim 3, characterized in that: The curing temperature is 100°C.

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