Sand-fixing coarse particle, preparation method thereof and combined sand-fixing method

Abstract

This application relates to the field of desertification control technology, and discloses a coarse sand-fixing particle, its preparation method, and a combined sand-fixing method. The coarse sand-fixing particle comprises the following components by weight: 60-90 parts of in-situ desert sand, 0.5-5 parts of plant fiber, and 5-30 parts of a solidification activation reaction component, which is either an alkali-activated solidification component or a biomineralization reaction component. When using an alkali-activated solidification component, the coarse sand-fixing particle also includes 5-40 parts of an active material, selected from at least one of fly ash, granulated blast furnace slag, metakaolin, volcanic ash, or tailings powder, with a total SiO2 and Al2O3 content of not less than 30 wt%. The particle size range of the coarse sand-fixing particle is 5-200 mm. The technical solution provided by this application can achieve the goal of sand fixation control with low external source dependence, scalable construction, and long-term wind erosion resistance.

Description

Technical Field

[0001] This application relates to the field of desertification control technology, and in particular to a sand-fixing coarse particle, its preparation method, and a combined sand-fixing method. Background Technology

[0002] Desertification and wind erosion are global ecological and environmental problems, caused by drought and wind erosion, leading to land degradation and ecosystem decline. Existing windbreak and sand-fixing technologies include straw checkerboard barriers, crushed stone compaction, chemical solidification, and biological sand fixation, each with its limitations. For example, straw checkerboard barriers are limited by climatic conditions, crushed stone compaction relies on exogenous materials and is costly, chemical solidification may cause soil pollution and has poor durability, while biological mineralization sand fixation lacks strength and has low construction efficiency in windy and sandy environments.

[0003] Therefore, how to replace exogenous crushed stone with coarse-grained sand-fixing particles with a coarse-grained skeleton and cemented phase to achieve the goal of sand fixation with low external dependence, large-scale construction and long-term wind erosion resistance is a technical problem that urgently needs to be solved. Summary of the Invention

[0004] This application provides a coarse sand-fixing particle, its preparation method, and a combined sand-fixing method, which achieves the technical effect of sand-fixing treatment with low external source dependence, large-scale construction capability, and long-term wind erosion resistance.

[0005] To achieve the above objectives, the main technical solutions adopted in this application include:

[0006] In a first aspect, embodiments of this application provide coarse sand-fixing particles, which comprise the following components in parts by weight:

[0007] The mixture consists of 60-90 parts desert in-situ sand, 0.5-5 parts plant fiber, and 5-30 parts a solidification and activation reaction component, wherein the solidification and activation reaction component is an alkali-activated solidification component or a biomineralization reaction component; wherein...

[0008] When using the alkali-activated solidification component, the coarse sand-fixing particles further include 5-40 parts of active material. The active material is selected from at least one of fly ash, granulated blast furnace slag, metakaolin, volcanic ash, or tailings powder, and the total content of SiO2 and Al2O3 in the active material is not less than 30 wt%.

[0009] The particle size range of the coarse sand-fixing particles is 5–200 mm.

[0010] In one embodiment, when the alkali-activated curing component is used, the active material undergoes a dissolution-condensation reaction to generate a NASH gel phase and / or a C-(A)-SH gel phase, so that the compressive strength of the sand-fixing coarse particles reaches 0.5 to 10 MPa.

[0011] In one embodiment, when the alkali-activated curing component is used, the mass ratio of the desert in-situ sand to the active material is 70:30 to 85:15.

[0012] In one embodiment, the plant fiber is selected from at least one of straw fiber, wheat straw fiber, rice straw fiber, reed fiber, bulrush fiber, coconut shell fiber, coconut fiber, jute fiber, flax fiber, sisal fiber, bast fiber, bamboo fiber, and wood fiber.

[0013] The plant fibers have a length of 2–30 mm, a diameter of 10–500 μm, and an aspect ratio of 10–150.

[0014] In one embodiment, the alkali-activated curing component is an alkali activator solution, wherein the proportions of each component in the alkali activator solution, calculated by alkali equivalent, are: sodium hydroxide 30-70%, sodium silicate 20-60%, and sodium carbonate 0-30%; the total alkali concentration of the alkali activator solution is 2-10 mol / L, and the total alkali concentration is the sum of the amounts of each alkaline component converted to hydroxide or carbonate equivalents;

[0015] The mass ratio of sodium hydroxide to sodium silicate in the alkaline activator solution is 1:0.5 to 1:2;

[0016] When the alkaline activator solution contains sodium carbonate, the sodium carbonate accounts for 5-30% of the total alkaline equivalent of the alkaline activator solution.

[0017] In one embodiment, the biomineralization reaction component includes an EICP reaction component or a MICP reaction component; wherein...

[0018] The EICP reaction components include urea at a concentration of 0.5–3 mol / L, calcium salt at a concentration of 0.5–3 mol / L, and urease with an activity of 5–30 mmol / (L•min). The molar ratio of urea to calcium salt in the EICP reaction components is 1:1 to 1.5:1.

[0019] The MICP reaction component includes a urease-producing microbial culture with a urease activity of 5–30 mmol / (L•min), urea with a concentration of 0.5–3 mol / L, and calcium salt with a concentration of 0.5–3 mol / L. The molar ratio of urea to calcium salt in the MICP reaction component is 1:1 to 1.5:1.

[0020] In one embodiment, the biomineralization reaction component further includes a colloidal material, which is sodium alginate, xanthan gum, or chitosan, and the mass fraction of the colloidal material is 0.1 to 1.0 wt%.

[0021] Secondly, embodiments of this application provide a method for preparing the aforementioned coarse sand-fixing particles.

[0022] When using the alkali-activated curing component, the preparation method includes:

[0023] The desert in-situ sand is used as aggregate and mixed with the active material, the alkali-activated solidification component, and the plant fiber. The mixture is then left to cure at 20–40°C for 3–14 days. The resulting solidified body is then crushed and sieved to obtain solidified coarse particles; or

[0024] When using the aforementioned biomineralization reaction component, the preparation method includes:

[0025] The desert in-situ sand is used as aggregate and mixed with the biomineralization reaction components and the plant fiber. The mixture is then left to stand and cure at 15-40°C for 2-5 days to form a solidified whole. The solidified coarse particles are obtained by crushing and screening.

[0026] In one embodiment, the preparation method further includes:

[0027] EICP solution and / or MICP solution are sprayed uniformly 1 to 5 times on the outer surface of the integral solidified body. The EICP solution and / or the MICP solution penetrate into the integral solidified body so that the generated calcium carbonate is deposited on the surface of the integral solidified body and in the internal micropores of the integral solidified body.

[0028] For the integral solidified body after uniformly spraying the EICP solution and / or the MICP solution, after being left to stand and cure in a natural environment for 1 to 3 days, the resulting composite solidified body is crushed and screened to obtain solidified coarse particles for sealing and reinforcing.

[0029] The EICP solution contains urea at a concentration of 0.05–1.0 mol / L, calcium salt at a concentration of 0.05–1 mol / L, and urease activity at a concentration of 5–15 mmol / (L•min); the MICP solution contains urea at a concentration of 0.1–1.0 mol / L, calcium salt at a concentration of 0.05–0.5 mol / L, and urease activity of the urease-producing microbial culture at a concentration of 5–30 mmol / (L•min).

[0030] Thirdly, embodiments of this application provide a combined sand fixation method, the combined sand fixation method comprising:

[0031] The sand-fixing coarse particles described above or prepared by the above preparation method are evenly spread on the surface of the desert area to be treated, with a thickness of 1 to 30 cm, to form a solidified coarse particle skeleton layer.

[0032] EICP solution and / or MICP solution are uniformly sprayed onto the surface of the solidified coarse particle skeleton layer to form a calcium carbonate cementing layer, thereby achieving combined sand fixation.

[0033] The technical solutions provided in this application, using one or more real-time methods, offer a robust skeletal structure with in-situ desert sand as the main component. The sand particles range in size from 5-200 mm, ensuring good packing properties and stability. Furthermore, added solidification-activating reaction components, such as alkali-activated solidification components or biomineralization reaction components, can form a strong cementing phase between sand particles. Especially when using alkali-activated solidification components, the addition of active materials further enhances the cementing strength, thereby improving the durability of the solidified body. This design not only improves wind erosion resistance and forms an effective protective barrier, but also reduces reliance on exogenous crushed stone by using locally sourced materials, simplifying the construction process, reducing costs, and achieving an eco-friendly construction method, providing an effective solution for desertification control and ecological restoration. Attached Figure Description

[0034] The accompanying drawings, which are included to provide a further understanding of this application and form part of this application, illustrate exemplary embodiments and are used to explain this application, but do not constitute an undue limitation of this application. In the drawings:

[0035] Figure 1 The diagram illustrates a specific application of the embodiments described in this application. Detailed Implementation

[0036] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0037] Desertification and wind erosion are prominent global ecological and environmental problems, caused by wind erosion in arid, semi-arid, and desert regions. Wind erosion drives the movement, migration, and redeposition of surface sand particles, leading to the expansion of mobile dunes, decreased soil fertility, and loss of surface stability. Ultimately, this results in land degradation and ecosystem decline, directly threatening ecological security, infrastructure stability, and the sustainable economic and social development of the region. Against this backdrop, constructing a sand-fixing technology system that combines engineering stability, environmental friendliness, and sustainability has become a core need that urgently requires addressing.

[0038] Existing windbreak and sand-fixing measures can be divided into five categories: straw checkerboard sand fixation, crushed stone sand compaction, chemical solidification, biological sand fixation, and combined technologies. Each type of technology has significant limitations, as detailed below:

[0039] While grass checkerboard planting and sand fixation have ecological benefits, they are significantly constrained by rainfall, temperature, soil moisture, and the vegetation establishment cycle, and have weak early resistance to wind erosion. In areas with extreme drought or frequent strong winds, the survival and maintenance costs of vegetation are high, making it difficult to promote on a large scale.

[0040] Crushed stone compaction increases surface roughness, reduces near-ground wind speed, and weakens the conditions for sand particle initiation by laying a layer of crushed stone or gravel. The engineering effects are direct and the application is mature. However, this technology is highly dependent on external aggregate materials. In the heart of deserts and areas with inconvenient transportation, aggregates need to be transported over long distances, resulting in high material and transportation costs, high construction intensity, and long cycle. At the same time, external material sourcing will cause resource consumption and secondary ecological disturbance, which limits its application in large-scale governance projects.

[0041] Chemical solidification for sand fixation uses materials such as cement, resin, polymers, or salts to form a cementing layer on the ground surface, resulting in significant short-term consolidation effects. However, some materials are prone to causing soil salinization, alkalization, or organic pollution. Under the long-term effects of strong ultraviolet radiation, thermal cycling, and wind erosion, the cementing layer is prone to brittleness and pulverization, leading to a significant decrease in durability. Furthermore, traditional cement-based materials suffer from high energy consumption and large carbon emissions, which does not align with the development direction of low-carbon and eco-friendly desertification control projects.

[0042] Alkali-activated sand fixation materials can utilize industrial solid wastes such as fly ash, slag, and metakaolin, or natural minerals as cementing phase sources. They have advantages such as adjustable cementing properties, strong environmental adaptability, and reduced use of traditional cementing materials, making them highly popular in the field of geotechnical engineering. However, the content of active Si and Al components in in-situ aeolian sand in deserts is insufficient, making it difficult to form a continuous and stable cementing structure by alkali activation of in-situ sand alone. If alkali-activated slurry is directly applied to large-area surface sand fixation, it will also face problems such as difficulty in controlling the construction moisture content, easy cracking of the solidified body in the early stage, and insufficient surface wind erosion resistance.

[0043] Biomineralization sand fixation technologies, represented by microbial-induced calcium carbonate precipitation (MICP) and enzyme-induced calcium carbonate precipitation (EICP), have received widespread attention in recent years due to their eco-friendly nature. MICP utilizes urease-producing microorganisms to hydrolyze urea, generating carbonate ions which then react with calcium ions to precipitate calcium carbonate, thus cementing sand particles. EICP, on the other hand, uses externally added urease to catalyze the hydrolysis of urea, offering advantages such as controllable system, no introduction of live microorganisms, and low biosafety risks. However, these technologies have significant drawbacks when applied alone: ​​the cemented layer formed in aeolian environments has limited thickness and is susceptible to wind erosion, wet-dry cycles, and salt migration, leading to strength degradation. Furthermore, issues such as poor penetration and deposition uniformity of the reaction solution, weak early-stage erosion and crack resistance of the solidified body, and high material consumption and low efficiency in large-scale on-site construction all require further optimization.

[0044] In summary, how to replace exogenous crushed stone with coarse-grained sand-fixing particles with a coarse-grained skeleton and cemented phase to achieve the goal of sand fixation with low external dependence, scalable construction and long-term wind erosion resistance is a technical problem that urgently needs to be solved.

[0045] To address the aforementioned technical problems, according to an embodiment of this application, a coarse sand-fixing particle embodiment is provided. The coarse sand-fixing particle comprises the following components in parts by weight: 60-90 parts of in-situ desert sand, 0.5-5 parts of plant fiber, and 5-30 parts of a solidification activation reaction component, which is either an alkali-activated solidification component or a biomineralization reaction component. Wherein, when using an alkali-activated solidification component, the coarse sand-fixing particle further comprises 5-40 parts of an active material, selected from at least one of fly ash, granulated blast furnace slag, metakaolin, volcanic ash, or tailings powder, and the total content of SiO2 and Al2O3 in the active material is not less than 30 wt%. The particle size range of the coarse sand-fixing particle is 5-200 mm.

[0046] Specifically, in-situ desert sand is used as the main raw material, with a particle size controlled between 0.075 and 1 mm (after pretreatment and sieving), forming the physical skeleton of coarse particles. Sand particles within this size range have good packing characteristics, providing sufficient attachment sites for the cementing phase while reducing the strength deficiency caused by excessively large internal pores in the skeleton. The core design principle of high admixture (60-90 parts) is to maximize the use of local resources, avoid long-distance transportation of external aggregates, conform to the engineering logic of "using local materials," and ensure the stability and structural integrity of the coarse particle skeleton.

[0047] The plant fiber is selected from at least one of the following: straw fiber, wheat straw fiber, rice straw fiber, reed fiber, bulrush fiber, coconut shell fiber, coconut fiber, jute fiber, flax fiber, sisal fiber, hemp fiber, bamboo fiber, and wood fiber. It is a natural and biodegradable material. The parameters of its length (2–30 mm), diameter (10–500 μm), and aspect ratio (10–150) are designed to allow it to form a three-dimensional fiber network within the sand grain skeleton. Preferably, the plant fiber has a length of 5–20 mm, a diameter of 20–200 μm, and an aspect ratio of 20–100; more preferably, the plant fiber has a length of 5–15 mm and a diameter of 30–150 μm. On the one hand, the three-dimensional fiber network can inhibit shrinkage cracking during the curing process through "bridging effect", improve the toughness and erosion resistance of the cured body, and avoid brittle fracture and detachment caused by wind erosion and thermal cycling. On the other hand, the microstructure of the surface of the three-dimensional fiber network provides deposition and attachment sites for calcium carbonate (EICP / MICP reaction product), promotes the bridging effect of the cement phase, strengthens the interfacial bonding force between sand particles and cement phase, and further improves the overall stability of coarse particles.

[0048] The solidification activation reaction components include alkali-activated solidification components or biomineralization reaction components. The alkali-activated solidification component is an alkali activator solution that, under a strongly alkaline environment, undergoes a dissolution-condensation reaction with the active material to generate a NASH gel phase and / or a C-(A)-SH gel phase. These gel phases fill the pores of the coarse-grained physical framework, consolidating the dispersed desert sand into a unified whole through interfacial bonding, forming a solidified body with a certain strength. The concentration (2–10 mol / L) and ratio design of the alkali activator (the ratio of each component in the alkali activator solution, based on alkali equivalent, is: sodium hydroxide 30–70%, sodium silicate 20–60%, sodium carbonate 0–30%; the mass ratio of sodium hydroxide to sodium silicate in the alkali activator solution is 1:0.5–1:2; when the alkali activator solution contains sodium carbonate, sodium carbonate accounts for 5–30% of the total alkali equivalent of the alkali activator solution) aims to control the reaction rate and the amount of gel phase generated, avoiding internal stress concentration due to excessively rapid reaction or affecting engineering efficiency due to excessively slow reaction.

[0049] Biomineralization reaction components include EICP or MICP reaction components, which achieve cementation and solidification through enzymatic catalysis or microbial metabolism. In the EICP reaction component system, urease catalyzes the hydrolysis of urea to produce carbonate ions, which react with calcium ions to form calcium carbonate precipitate. In the MICP reaction component system, urease-producing microorganisms hydrolyze urea to produce carbonate ions, which also combine with calcium ions to form calcium carbonate. Calcium carbonate, as a natural cementing agent, fills the gaps between sand particles in situ in the desert and coats the surface of the sand, forming a stable cemented structure. The EICP reaction components in the reaction system include urea at a concentration of 0.5–3 mol / L, calcium salt at a concentration of 0.5–3 mol / L, and urease with an activity of 5–30 mmol / (L•min). The molar ratio of urea to calcium salt in the EICP reaction components is 1:1–1.5:1. The MICP reaction components include urease-producing microbial culture with an activity of 5–30 mmol / (L•min), urea at a concentration of 0.5–3 mol / L, and calcium salt at a concentration of 0.5–3 mol / L. The molar ratio of urea to calcium salt in the MICP reaction components is 1:1–1.5:1, which ensures the full formation and uniform deposition of calcium carbonate.

[0050] The active material is selected from at least one of fly ash, granulated blast furnace slag, metakaolin, volcanic ash, or tailings powder, with a core requirement that the total content of SiO2 and Al2O3 is not less than 30 wt% (preferably not less than 60 wt%). Under the action of the alkali-activated curing components, the active Si and Al groups of these materials are activated, participating in the formation and reconstruction of the gel phase, thus improving the density and strength of the cemented phase. Since the active Si and Al components in desert in-situ sand are insufficient, the addition of the active material precisely compensates for this deficiency, enabling the alkali-activated reaction to form a continuous and stable cemented structure, avoiding problems such as insufficient strength and poor durability of the solidified body caused by using in-situ sand alone for alkali activation. Simultaneously, the mass ratio of the active material to the desert in-situ sand is controlled at 70:30–85:15 to balance the dual requirements of skeletal support and cementation enhancement.

[0051] The final coarse sand-fixing particles, ranging in size from 5 to 200 mm, significantly improve surface roughness, effectively reduce near-ground wind speed, and inhibit sand particle initiation and migration. Their wind erosion prevention effect is comparable to that of traditional crushed stone sand compaction, and they avoid secondary ecological disturbance caused by external crushed stone material extraction.

[0052] This embodiment provides a coarse-grained sand-fixing material that uses in-situ desert sand as the main component, providing a robust skeletal structure. Its particle size ranges from 5-200 mm, ensuring good packing properties and stability. Furthermore, added solidification activation reaction components, such as alkali-activated solidification components or biomineralization reaction components, can form a strong cementing phase between sand particles. Especially when using alkali-activated solidification components, the addition of active materials further enhances the cementing strength, thereby improving the durability of the solidified body. This design not only improves wind erosion resistance and forms an effective protective barrier, but also reduces reliance on exogenous crushed stone by using locally sourced materials, simplifying the construction process, reducing costs, and achieving an eco-friendly construction method, providing an effective solution for desertification control and ecological restoration.

[0053] In one embodiment, the biomineralization reaction component further includes a colloidal material, which is sodium alginate, xanthan gum, or chitosan, and the mass fraction of the colloidal material is 0.1 to 1.0 wt%.

[0054] Specifically, sodium alginate, xanthan gum, and chitosan are all natural polymeric colloids that can form a viscous colloidal system in aqueous solution through molecular chain entanglement and hydrogen bonding, significantly increasing the viscosity and yield stress of the EICP or MICP reaction components. This optimization of rheological properties can effectively reduce the rapid infiltration and loss of reaction components in the interparticle gaps of desert sand, avoiding uneven distribution of urea and calcium salt concentrations caused by excessively rapid evaporation or infiltration of water, and providing a stable physical environment for the calcium carbonate precipitation reaction.

[0055] Colloidal materials and plant fibers form a dual-reinforcing network within the coarse sand-fixing particles: plant fibers act as a macroscopic toughening skeleton, suppressing macroscopic cracking of the particles through a three-dimensional interwoven structure; colloidal materials, as a microscopic cementing network, fill the tiny gaps between plant fibers and in-situ desert sand and calcium carbonate, strengthening the synergistic effect between the components and further enhancing the toughness, crack resistance, and erosion resistance of the coarse sand-fixing particles. This synergistic effect makes the coarse sand-fixing particles less prone to breakage under wind erosion and impact, significantly improving their structural stability.

[0056] Furthermore, the amount of colloidal material added is only 0.1–1.0 wt%, which is low in quantity and cost, and does not significantly increase the difficulty of preparation or the construction load. Its good compatibility allows it to be seamlessly adapted to existing EICP / MICP construction processes (such as spraying and impregnation), without the need for major modifications to construction equipment, facilitating large-scale application in large-scale sand fixation projects.

[0057] In this embodiment, the addition of colloidal materials (such as sodium alginate, xanthan gum, or chitosan) to the biomineralization reaction components significantly enhances the viscosity and yield stress of the material, thereby forming a stable cemented network. This optimized rheological property effectively reduces the rapid infiltration and loss of reaction components within the intergranular spaces of desert sand particles, ensuring the effectiveness of the cementing material and thus replacing exogenous gravel, reducing dependence on external resources. Furthermore, through the synergistic effect of the colloidal materials and plant fibers, the coarse sand-fixing particles form a doubly reinforced network structure, improving toughness, crack resistance, and wind erosion resistance, ensuring the long-term stability of the sand-fixing effect. The natural properties and appropriate mass fraction of the colloidal materials make the preparation process of the sand-fixing material simple and easy, conforming to the concept of eco-friendly construction. It not only supports the goal of low external dependence but also achieves the ideal effects of scalable construction and long-term wind erosion resistance.

[0058] This application also provides a method for preparing coarse sand-fixing particles.

[0059] When using alkali-activated curing components, the preparation method includes:

[0060] Desert sand in situ is used as aggregate and mixed with active materials, alkali-activated solidification components and plant fibers. The mixture is then left to stand and cure for 3 to 14 days in an environment of 20 to 40°C. The resulting solidified body is then crushed and screened to obtain solidified coarse particles.

[0061] Specifically, in-situ desert sand serves as the core aggregate, providing the physical framework of the substrate material. Its high-volume design ensures both the porosity of the framework and maximizes the utilization of low-cost raw materials. Under the strong alkaline environment of the alkali-activated curing components, the active material undergoes a dissolution-condensation reaction, generating a NASH / C-(A)-SH composite gel phase. This phase fills the gaps in the in-situ desert sand and bonds it together, forming a continuous and stable monolithic solidified body. Plant fibers form a three-dimensional interwoven network within the monolithic solidified body. On the one hand, this network inhibits cracking caused by water evaporation and gel phase shrinkage during alkali-activated curing; on the other hand, it enhances the toughness and impact resistance of the solidified body through a bridging effect, preventing the solidified coarse particles from breaking and peeling off under the scouring of wind, waves, and water flow. Static curing at 20–40℃ is crucial for the full formation and structural stability of the gel phase. This temperature range accelerates the alkali-activated reaction rate, promotes the cross-linking and densification of the gel phase, and avoids internal stress concentration caused by rapid water evaporation at high temperatures. A curing cycle of 3–14 days ensures that the gel phase completely encapsulates the in-situ desert sand and plant fibers, enabling the compressive strength of the solidified coarse particles to reach 0.5–10 MPa.

[0062] The solidified body is mechanically crushed (jaw crusher + roller shaping, etc.) and screened to obtain solidified coarse particles of 5-200mm (preferably 10-30mm). This particle size range ensures both air permeability and water permeability of the paving, and forms a stable stacking structure through the interlocking action between particles to resist water flow impact and wind and wave erosion.

[0063] Alternatively, when using biomineralization reaction components, the preparation method includes:

[0064] Desert sand in situ is used as aggregate and mixed with biomineralization reaction components and plant fibers. The mixture is then left to stand and cure for 2 to 5 days at 15 to 40°C. The resulting solidified body is then crushed and screened to obtain solidified coarse particles.

[0065] Specifically, the biomineralization reaction components generate a calcium carbonate cementing phase through enzymatic catalysis / microbial metabolism—in EICP, urease catalyzes the hydrolysis of urea to produce carbonate ions, which react with calcium salts to form calcium carbonate; in MICP, urease-producing microorganisms (non-pathogenic strains) metabolize urea to produce carbonate ions, which also combine with calcium ions to form calcium carbonate. Calcium carbonate, as a natural inorganic cementing agent, is uniformly deposited on the surface and interstices of sand particles in situ in the desert, forming a "sand-calcium carbonate" composite structure that combines cementing strength and ecological compatibility. Plant fibers (macroscopic toughening framework) and colloidal materials (such as sodium alginate, 0.1–1.0 wt%, microporous cementing network) work synergistically—fibers inhibit the cracking of solidified coarse particles, while colloids regulate the deposition morphology of calcium carbonate (generating fine and dense precipitates), while simultaneously improving the water retention of solidified coarse particles, preventing the biomineralization reaction from being interrupted due to insufficient moisture; both together improve the erosion resistance and structural integrity of the solidified body. The static curing temperature of 15–40℃ is in line with the characteristics of biomineralization reaction. This temperature range can ensure urease activity or microbial metabolic efficiency without the need for artificial temperature control. The curing cycle of 2–5 days matches the rate of biomineralization reaction, allowing calcium carbonate to be deposited quickly and form a stable cement, avoiding over- or under-reaction.

[0066] The solidified body is mechanically crushed (jaw crusher + roller shaping, etc.) and screened to obtain solidified coarse particles of 5-200mm (preferably 10-30mm). This particle size range ensures both air permeability and water permeability of the paving, and forms a stable stacking structure through the interlocking action between particles to resist water flow impact and wind and wave erosion.

[0067] It should be noted that mechanical crushing adopts a single-stage or multi-stage crushing process. The single-stage crushing can be selected from one of the following: jaw crusher, hammer crusher, impact crusher, roller crusher, or cone crusher. The multi-stage crushing is preferably a combination of "jaw crusher + roller crusher / impact crusher + closed-loop screening" to control the particle size distribution of the finished product and reduce over-crushing.

[0068] Furthermore, the crushing equipment is preferably a jaw crusher, hammer crusher, impact crusher, roller crusher, or a combination thereof. Among them, the jaw crusher is used for coarse crushing, suitable for crushing monolithic solids to 10-100mm; the roller crusher is used for shaping and particle control, suitable for obtaining a particle size of 5-50mm and reducing fine powder; the impact crusher or hammer crusher is used for secondary crushing, suitable for increasing the yield of 10-30mm particle size.

[0069] In specific crushing methods, the moving jaw speed of a jaw crusher should be 150–400 r / min, preferably 200–350 r / min; the discharge opening size of the jaw plate should be 10–80 mm, preferably 20–60 mm. The roller speed of a roll crusher should be 50–300 r / min, preferably 80–200 r / min, with a roller gap of 5–50 mm, preferably 10–30 mm. The rotor speed range of an impact crusher is 500–1800 r / min, preferably 800–1500 r / min; while the main shaft / rotor speed of a hammer crusher is 800–2500 r / min, preferably 1000–2000 r / min.

[0070] In addition, screening control is adopted during the crushing process, with screen aperture ranging from 5 to 200 mm; preferably, two-stage screening is used: the upper screen aperture is set to 30 to 50 mm (for re-crushing of recycled material), and the lower screen aperture is set to 5 to 10 mm (for removing fine material), so that the finished particle size is preferably concentrated in the range of 10 to 30 mm. The feed particle size is not greater than 300 mm, preferably not greater than 150 mm; when the overall solidified body size is large, it is preferable to first use a hydraulic breaker or jaw crusher for pre-crushing, and then perform secondary crushing and screening.

[0071] To avoid over-crushing and reduce the content of fine particles <5mm, a closed-loop circulation method can be adopted in the crushing process: the material oversizes is returned to the crusher for further crushing, while the material undersizes is used as finished product or sorted into bins according to particle size. The crushing time or number of crushing cycles can be controlled to 1 to 5 times, preferably 1 to 3 times. Finally, the crushing components of the crusher are preferably made of wear-resistant alloy steel or high-manganese steel; when the overall solidified body has high strength or a large sand content, wear-resistant liners and replaceable hammer / tooth plate structures are preferred to improve equipment durability and ensure stable particle shape.

[0072] This embodiment provides a method for preparing coarse sand-fixing particles. By mixing in-situ desert sand with active materials, alkali-activated solidification components, and plant fibers, the resulting monolithic solidified body effectively constructs a composite structure of a coarse-particle skeleton and a cementing phase. This design not only enhances the mechanical strength of the monolithic solidified body but also achieves low external dependence, as the use of local sand avoids the need for external gravel, thereby reducing material costs and carbon emissions from transportation. Furthermore, after 3–14 days of static curing, the resulting cementing phase improves the stability of the monolithic solidified body, making it more resistant to wind erosion under natural conditions such as wind and water flow, ensuring the long-term effectiveness of sand fixation. Similarly, the use of natural calcium carbonate generated through biomineralization as a cementing material also achieves the advantages of ecological compatibility and rapid formation of a stable structure, meeting the needs of large-scale construction.

[0073] In one embodiment, the preparation method further includes:

[0074] The EICP solution and / or MICP solution are evenly sprayed 1 to 5 times on the outer surface of the solidified body. The EICP solution and / or MICP solution penetrate into the solidified body so that the generated calcium carbonate is deposited on the surface of the solidified body and in the micropores inside the solidified body.

[0075] For the overall solidified body after uniform spraying of EICP solution and / or MICP solution, after being left to cure in a natural environment for 1 to 3 days, the resulting composite solidified body is crushed and screened to obtain solidified coarse particles for sealing and reinforcement.

[0076] The EICP solution contained urea at a concentration of 0.05–2.0 mol / L, calcium salt at a concentration of 0.05–2.0 mol / L, and urease activity at a concentration of 5–15 mmol / (L•min); the MICP solution contained urea at a concentration of 0.05–1.0 mol / L, calcium salt at a concentration of 0.05–2.0 mol / L, and urease activity of the urease-producing microbial culture at a concentration of 5–30 mmol / (L•min).

[0077] Specifically, the sprayed EICP and / or MICP solutions, through gravity penetration, can both cover the overall surface of the solidified body and penetrate into the internal micropores (including the gaps between the cementitious phases in alkali-activated solidified bodies and the calcium carbonate deposition voids in biomineralized solidified bodies). Under the catalysis of urease (EICP) or the action of microbial metabolism (MICP), urea in the solution hydrolyzes to produce carbonate ions, which react with calcium ions to form calcium carbonate precipitate. The surface deposits to form a dense protective shell, while the internal pores are deposited to form a filling cementitious phase, achieving dual reinforcement of external sealing and internal filling.

[0078] The newly formed calcium carbonate precipitate forms chemical bonds and physical bonds with the original cementing phase of the solidified body (alkali-activated NASH / C-(A)-SH gel and biomineralized initial calcium carbonate), eliminating microcracks and internal pore defects on the surface of the original solidified body and improving the overall density of the solidified body. At the same time, the calcium carbonate precipitate can bind to the active sites on the surface of plant fibers, further strengthening the interfacial adhesion between the fibers and the cementing phase, and consolidating the effect of the three-dimensional fiber toughening network.

[0079] A 1-3 day natural curing period provides ample time for calcium carbonate deposition, ensuring sufficient reaction time (avoiding insufficient deposition due to inadequate curing) while preventing excessive moisture evaporation and subsequent shrinkage cracking due to an excessively long curing period. Natural curing requires no additional temperature or humidity control equipment, making it suitable for on-site construction conditions.

[0080] In this embodiment, EICP solution and / or MICP solution are uniformly sprayed onto the outer surface of the solidified body. The resulting calcium carbonate not only forms a dense protective layer on the surface of the solidified body but also penetrates and deposits in the internal micropores, thereby significantly improving the density and wind erosion resistance of the solidified body and reducing material loss. After 1 to 3 days of natural curing, the resulting composite solidified body, after crushing and screening, yields solidified coarse particles that seal and reinforce the pores. These particles, by constructing a composite structure of coarse particle skeleton and cementing phase, further enhance the mechanical strength and stability of the solidified body. This method achieves low external dependence while reducing the demand for traditional building materials, has good adaptability to large-scale construction, and can effectively meet the needs of large-scale sand fixation management.

[0081] This application also provides a combined sand fixation method, which includes:

[0082] The coarse sand-fixing particles described above or prepared by the above method are evenly spread on the surface of the desert area to be treated, with a thickness of 1 to 30 cm, to form a solidified coarse particle skeleton layer; EICP solution and / or MICP solution are evenly sprayed on the surface of the solidified coarse particle skeleton layer to form a calcium carbonate cementing layer, so as to achieve combined sand fixation.

[0083] Specifically, coarse sand-fixing particles with a diameter of 5–200 mm (preferably 10–30 mm) are evenly laid (3–30 cm thick) to form a skeleton structure similar to traditional crushed stone sand compaction. The interlocking and accumulation of the coarse sand-fixing particles significantly increases surface roughness, reduces near-surface wind speed, weakens the dynamic conditions for sand particle initiation, and inhibits sand migration and wind erosion from the source. The coarse sand-fixing particles themselves possess a compressive strength of 0.5–10 MPa (alkali-activated system) or equivalent structural stability (biomineralization system). After being laid, they form a continuous support layer that can resist strong wind impact and water erosion, preventing the surface cementing layer from failing due to lack of support. At the same time, the porous structure of the skeleton layer (formed by the accumulation of coarse sand-fixing particles) provides space for subsequent surface solution infiltration and calcium carbonate deposition, achieving a tight bond between the skeleton and the cementing layer.

[0084] This embodiment provides a combined sand-fixing method. By uniformly spreading coarse sand-fixing particles on the surface of the desert area to be treated, a solidified coarse-particle skeleton layer with a thickness of 1-30 cm is formed. This method effectively constructs a stable physical structure. This skeleton layer not only provides support but also significantly increases the surface roughness through the interlocking and accumulation of particles, reducing near-ground wind speed and thus inhibiting sand migration and wind erosion. Furthermore, by uniformly spraying EICP solution and / or MICP solution onto the surface of the skeleton layer, a calcium carbonate cementing layer is formed, achieving a tight bond between the skeleton and the cementing phase. This further enhances the overall structural stability, improves wind erosion resistance, and ensures long-term effective sand-fixing. Therefore, this combined sand-fixing method not only achieves low external dependence, reducing the need for traditional external crushed stone, but also has good adaptability to large-scale construction, enabling efficient implementation under different engineering site conditions. This effectively addresses desertification problems and achieves the goal of long-term, wind-erosion-resistant, and stable sand-fixing treatment.

[0085] The following is combined Figure 1 The specific applications of the present invention will be described.

[0086] Step 1: In-situ sand solidification to produce coarse particles

[0087] In-situ desert sand, plant fibers, active materials (such as fly ash) are mixed with an activating liquid (alkali-activated solidification components or biomineralization reaction components), and after solidification reaction, the mixture is crushed and screened to obtain coarse sand-fixing particles of 5-200 mm, thus achieving sand particle consolidation using locally sourced materials.

[0088] Step 2: Seed sowing and laying of coarse sand-fixing particles

[0089] First, plant seeds are sown on the surface of the desert area to be treated. Then, the prepared sand-fixing coarse particles are evenly spread on the surface, with the thickness controlled between 1 and 30 cm, forming a basic skeleton layer of "seeds + coarse particles", which not only inhibits sand flow but also provides protection for the seeds.

[0090] Step 3: EICP solution spray curing

[0091] EICP solution (containing urea, calcium salt, and urease) is evenly sprayed onto the surface of the coarse particle skeleton layer. The solution penetrates into the gaps and surface of the coarse particles, and calcium carbonate is generated through an enzyme-catalyzed reaction. This forms a cementing layer between the coarse particles, "bridging" the discrete coarse particles into a whole and enhancing the wind erosion resistance.

[0092] Step 4: Plant maintenance and solidification monitoring

[0093] Regular maintenance (watering, pest control, etc.) is carried out on the plants in the paving area, while monitoring the solidification status of the coarse particles (such as the cementing effect of calcium carbonate and structural stability). In the end, a composite sand-fixing system of "coarse particle skeleton + calcium carbonate cementation + vegetation cover" is formed to achieve synergy between sand fixation and ecological restoration.

[0094] To better explain and facilitate understanding of this application, a detailed description of its specific embodiments is provided below. Unless otherwise specified, all quantities in the embodiments refer to parts by weight, and all raw materials used in the embodiments of this application were purchased commercially.

[0095] Example 1: A combined sand fixation method

[0096] Step S1: Preparation of coarse sand-fixing particles

[0097] The composition of the alkali activator solution consists of 60 parts of in-situ desert sand with a particle size of 0.075 mm, 0.5 parts of wheat straw fiber (2–30 mm in length, 10–500 μm in diameter, and an aspect ratio of 10–150), 5 parts of alkali activator solution, and 5 parts of fly ash as active material, with the total SiO2 and Al2O3 content in the fly ash not less than 60 wt%. The alkali activator solution is formulated with the following proportions based on alkali equivalent: sodium hydroxide 30% and sodium silicate 20%. The total alkali concentration of the activator solution is 2 mol / L. The mass ratio of sodium hydroxide to sodium silicate in the alkali activator solution is 1:0.5. The mass ratio of in-situ desert sand to fly ash as active material is 70:30. After mixing the above materials, the mixture was left to stand and cure at 20°C for 14 days. EICP solution was sprayed evenly three times on the outer surface of the resulting solidified body. The EICP solution contained urea at a concentration of 0.05 mol / L, calcium salt at a concentration of 0.05 mol / L, and urease activity at 5 mmol / (L•min). The mixture was then left to stand and cure in a natural environment for 3 days. The resulting composite solidified body was then crushed and sieved to obtain solidified coarse particles with a particle size range of 5–200 mm for sealing and reinforcement.

[0098] Step S2, Combined Sand Fixation

[0099] The solidified coarse particles prepared in step S1 are evenly spread on the surface of the desert area to be treated, with a thickness of 2 cm, to form a solidified coarse particle skeleton layer; EICP solution is then evenly sprayed on the surface of the solidified coarse particle skeleton layer to form a calcium carbonate cementing layer, so as to achieve combined sand fixation.

[0100] Example 2: A combined sand fixation method

[0101] Step S1: Preparation of coarse sand-fixing particles

[0102] The composition of the alkali activator solution consists of 70 parts of in-situ desert sand with a particle size of 0.5 mm, 2 parts of coconut shell fiber (coconut shell fiber length 5–20 mm, diameter 20–200 μm, aspect ratio 20–100), 20 parts of alkali activator solution, and 25 parts of granulated blast furnace slag as active material, with a total SiO2 and Al2O3 content of not less than 30 wt%. The alkali activator solution is composed of the following components in alkali equivalent: sodium hydroxide 50%, sodium silicate 45%, and sodium carbonate 15%. The total alkali concentration of the alkali activator solution is 6 mol / L, and sodium carbonate accounts for 5% of the total alkali equivalent. The mass ratio of sodium hydroxide to sodium silicate in the alkali activator solution is 1:1. The mass ratio of in-situ desert sand to fly ash as active material is 85:10. After mixing the above materials, the mixture is left to stand and cure at 30°C for 10 days. The resulting solidified body is then crushed and sieved to obtain solidified coarse particles with a particle size range of 5–200 mm.

[0103] Step S2, Combined Sand Fixation

[0104] The solidified coarse particles prepared in step S1 are evenly spread on the surface of the desert area to be treated, with a thickness of 15 cm, to form a solidified coarse particle skeleton layer; EICP solution is then evenly sprayed on the surface of the solidified coarse particle skeleton layer to form a calcium carbonate cementing layer, so as to achieve combined sand fixation.

[0105] Example 3: A combined sand fixation method

[0106] Step S1: Preparation of coarse sand-fixing particles

[0107] The composition of the alkali activator solution consists of 90 parts of in-situ desert sand with a particle size of 1 mm, 5 parts of flax fiber (flax fiber length 5–15 mm, diameter 30–150 μm, aspect ratio 20–100), 30 parts of alkali activator solution, and 40 parts of volcanic ash as the active material, with the total SiO2 and Al2O3 content in the volcanic ash not less than 50 wt%. The alkali activator solution is composed of the following components in alkali equivalent: sodium hydroxide 70%, sodium silicate 60%, and sodium carbonate 30%. The total alkali concentration of the alkali activator solution is 10 mol / L. The mass ratio of sodium hydroxide to sodium silicate in the alkali activator solution is 1:2. The mass ratio of in-situ desert sand to fly ash as the active material is 85:15. After mixing the above materials, the mixture was left to stand and cure at 40°C for 3 days. The outer surface of the resulting solidified body was then sprayed with MICP solution 5 times. The urea concentration in the MICP solution was 1.0 mol / L, the calcium salt concentration was 0.5 mol / L, and the urease activity of the urease-producing microbial solution was 30 mmol / (L•min). The mixture was then left to stand and cure in a natural environment for 2 days. The resulting composite solidified body was then crushed and sieved to obtain solidified coarse particles with a particle size range of 5–200 mm for sealing and reinforcement.

[0108] Step S2, Combined Sand Fixation

[0109] The solidified coarse particles prepared in step S1 are evenly spread on the surface of the desert area to be treated, with a thickness of 2 cm, to form a solidified coarse particle skeleton layer; MIP solution is then evenly sprayed on the surface of the solidified coarse particle skeleton layer to form a calcium carbonate cementing layer, so as to achieve combined sand fixation.

[0110] Example 4: A combined sand fixation method

[0111] Step S1: Preparation of coarse sand-fixing particles

[0112] The experiment consisted of 60 parts of in-situ desert sand with a particle size of 0.075 mm, 0.5 parts of bamboo fiber (the length of bamboo fiber was 5–15 mm, the diameter was 30–150 μm, and the aspect ratio was 20–100), and 5 parts of EICP reaction components. The EICP reaction components included urea at a concentration of 0.5 mol / L, calcium salt at a concentration of 0.5 mol / L, and urease with an activity of 5 mmol / (L•min). The molar ratio of urea to calcium salt in the EICP reaction components was 1:1. Sodium alginate, a colloidal material, was also included at a mass fraction of 0.1 wt%. After mixing the above materials, the mixture was left to stand and cure at 15°C for 5 days. EICP solution was sprayed evenly three times on the outer surface of the resulting solidified body. The EICP solution contained urea at a concentration of 0.05 mol / L, calcium salt at a concentration of 0.05 mol / L, and urease activity at 5 mmol / (L•min). The mixture was then left to stand and cure in a natural environment for 3 days. The resulting composite solidified body was then crushed and sieved to obtain solidified coarse particles with a particle size range of 5–200 mm for sealing and reinforcement.

[0113] Step S2, Combined Sand Fixation

[0114] The solidified coarse particles prepared in step S1 are evenly spread on the surface of the desert area to be treated, with a thickness of 2 cm, to form a solidified coarse particle skeleton layer; EICP solution is then evenly sprayed on the surface of the solidified coarse particle skeleton layer to form a calcium carbonate cementing layer, so as to achieve combined sand fixation.

[0115] Example 5: A combined sand fixation method

[0116] Step S1: Preparation of coarse sand-fixing particles

[0117] The experiment consisted of 80 parts of in-situ desert sand with a particle size of 0.5 mm, 2 parts of rice straw fiber (the length of the rice straw fiber was 5–15 mm, the diameter was 30–150 μm, and the aspect ratio was 20–100), and 18 parts of MICP reaction components. The MICP reaction components included a urease-producing microbial culture with a urease activity of 20 mmol / (L•min), urea at a concentration of 1.5 mol / L, and calcium salt at a concentration of 2 mol / L, with a molar ratio of urea to calcium salt of 1.5:1; and 1.0 wt% of the colloidal material chitosan. After mixing the above materials, the mixture was left to stand and cure at 40°C for 2 days. The outer surface of the resulting solidified body was then sprayed twice with a MICP solution. The MICP solution contained 1.0 mol / L urea, 0.5 mol / L calcium salt, and 30 mmol / (L•min) urease activity of the urease-producing microbial culture. After standing and curing in a natural environment for 2 days, the resulting composite solidified body was crushed and sieved to obtain solidified coarse particles with a particle size range of 5–200 mm for sealing and reinforcement.

[0118] Step S2, Combined Sand Fixation

[0119] The solidified coarse particles prepared in step S1 are evenly spread on the surface of the desert area to be treated, with a thickness of 2 cm, to form a solidified coarse particle skeleton layer; MIP solution is then evenly sprayed on the surface of the solidified coarse particle skeleton layer to form a calcium carbonate cementing layer, so as to achieve combined sand fixation.

[0120] Example 6: A combined sand fixation method

[0121] Step S1: Preparation of coarse sand-fixing particles

[0122] The mixture consisted of 90 parts of in-situ desert sand with a particle size of 1 mm, 4 parts of reed fiber (reed fiber length 5–15 mm, diameter 30–150 μm, aspect ratio 20–100), and 28 parts of MICP reaction component. The MICP reaction component included a urease-producing microbial culture with a urease activity of 30 mmol / (L•min), urea at a concentration of 3 mol / L, and calcium salt at a concentration of 3 mol / L, with a molar ratio of urea to calcium salt of 1.2:1; and 0.8 wt% xanthan gum as a colloidal material. After mixing the above materials, the mixture was allowed to cure at 30°C for 5 days. The resulting solidified body was then crushed and sieved to obtain solidified coarse particles with a particle size range of 5–200 mm for sealing and reinforcement.

[0123] Step S2, Combined Sand Fixation

[0124] The solidified coarse particles prepared in step S1 are evenly spread on the surface of the desert area to be treated, with a thickness of 2 cm, to form a solidified coarse particle skeleton layer; MIP solution is then evenly sprayed on the surface of the solidified coarse particle skeleton layer to form a calcium carbonate cementing layer, so as to achieve combined sand fixation.

[0125] Comparative Example 1 is the same as Example 1, except that no plant fiber is added.

[0126] Comparative Example 2 is the same as Example 2, except that no alkaline activator solution is added.

[0127] Comparative Example 3 was the same as Example 3, except that 150 parts of alkaline activator solution were added.

[0128] Comparative Example 4 is the same as Example 4, except that no EICP reaction component is added.

[0129] The coarse sand-fixing particles prepared in Examples 1-6 and Comparative Examples 1-4 were evaluated. To ensure comparability between groups, a particle size of 10-30 mm was uniformly selected as the test particle size, and the quartering method was used to reduce the particle size to obtain representative particle samples.

[0130] In addition, 500mm×500mm×150mm trays were used to prepare combined sand-fixing samples. A permeable isolation layer was laid at the bottom of the tray to prevent the loss of fine sand. In-situ sand was filled and lightly compacted until the surface was flat. Coarse sand particles were evenly laid on top to form a skeleton layer with a uniform thickness of 2cm and a coverage of 70%. EICP solution and / or MICP solution were evenly sprayed once on the surface of the skeleton layer according to the group. The spraying control standards were as follows: the urea concentration in the EICP solution was 0.05mol / L, the calcium salt concentration was 0.05mol / L, and the urease activity was 7mmol / (L•min); the urea concentration in the MICP solution was 0.05mol / L, the calcium salt concentration was 0.05mol / L, and the urease activity of the urease-producing microbial solution was 5mmol / (L•min). The spraying volume of EICP solution or MICP solution was 4L / m³. 2 After spraying, the samples were left to stand naturally for 48 hours to obtain samples for combined sand fixation.

[0131] The testing standards are explained as follows:

[0132] 1. Compressive strength σ of a single particle sample p test

[0133] Using an electronic universal testing machine, 20 representative particle samples were randomly selected, and the three dimensions a, b, and c (mm) of each particle were measured. The results were then calculated according to formula d. e =(abc) 1 / 3 Calculate the equivalent diameter d eThe particle was placed in the center of the upper and lower pressure plates and loaded at a displacement rate of 1 mm / min until it showed obvious signs of breakage. The peak load P was recorded. max (N). The compressive strength of a single particle is calculated using the formula σ. p =P max / A e Calculate, where, This represents the equivalent stress area. Results for each group are expressed as mean ± standard deviation.

[0134] 2. Water absorption rate W a test

[0135] Five representative particulate samples (approximately 200g each) were taken from each group. The samples were first dried at 40–60℃ to constant weight (the difference between two consecutive weighings ≤ 0.1%), and the dry weight m was recorded. d After soaking in water for 24 hours, remove the product and quickly wipe off the surface free water with absorbent paper. Immediately weigh the wet mass m. w Water absorption rate is calculated using the formula W. a =(m w -m d ) / m d Calculated at ×100%, each result is expressed as mean ± standard deviation.

[0136] 3. Wind erosion weight loss W w test

[0137] The combined sand-fixation specimens were tested in a wind erosion chamber or a small wind tunnel. The specimens were placed in the center of the test section, with an incoming wind speed of 18 m / s, and continuous blowing for 10 minutes. The wind speed was checked at the windward side of the specimens. Before the test, the total mass M0 of the tray + specimens was weighed; after the test, the external deposits were removed and the total mass M1 was weighed. The wind erosion weight loss per unit area was calculated using the formula W. w =Calculated as (M0-M1) / A, where A is the wind-receiving area of ​​the tray (m²). Each group of joint sand-fixing samples was tested 3 times, and the results are expressed as mean ± standard deviation.

[0138] 4. Resistance to erosion and weight loss W r test

[0139] The combined sand-fixation samples were tested using a rainfall simulation method. The samples were placed under a rainfall device with a rainfall intensity of 80 mm / h, and the rainfall lasted for 10 minutes. The tray slope was uniformly set to 20° (a fixed slope of 10°–30° or an enhanced slope of 45° could also be used, but this should be consistent across groups). Runoff sediment was collected during the experiment, dried to constant weight afterward, and the sediment mass (m) was measured. s The weight loss per unit area due to scouring is calculated using the formula W. r =ms / A, where A is the rain-receiving area of ​​the tray (m²). 2 Each group of samples was tested three times, and the results are expressed as mean ± standard deviation.

[0140] 5. Durability evaluation (wet-dry cycles and freeze-thaw cycles)

[0141] Representative particle samples were evaluated using two methods: wet-dry cycling and freeze-thaw cycling, with 6 cycles in each method.

[0142] 5.1 Dry and wet cycle

[0143] Single cycle: sample soaked in water for 12 hours → dried at 40℃ for 12 hours, completing 6 cycles.

[0144] 5.2 Freeze-thaw cycle

[0145] Single cycle: After immersing the sample in water for 4 hours to saturate it, wrap it with plastic wrap to prevent moisture loss, freeze it at -20℃ for 12 hours, then thaw it at 20℃ for 12 hours, completing 6 cycles.

[0146] 5.3 Calculation of Strength Retention Rate

[0147] The average single-particle compressive strength σ of the representative particle sample before cycling p0 After cycling, the dry and wet cycle strength σ was tested respectively. pDW6 Freeze-thaw cycle strength σ pFT6（ The test method is the same as that for the compressive strength σ of representative particle samples. p Test (particle count n=20). Strength retention rate is calculated using the formula:

[0148] Dry and wet cycle strength retention rate R DW =σ pDW6 / σ p0 ×100%

[0149] Freeze-thaw cycle strength retention rate R FT =σ pFT6 / σ p0 ×100%

[0150] Results are expressed as mean ± standard deviation.

[0151] 6. Plant growth tests (germination rate and soil pH)

[0152] For the combined sand-fixing sample, before laying the coarse-particle sand-fixing skeleton layer, desert plant seeds were evenly sown and buried 1-2 cm below the sand in situ, with a sowing rate of 50-100 seeds per tray (or the area was calculated according to the recommended sowing rate); the thickness of the laying layer was uniformly 3 cm, with a coverage rate of 70%. After laying the skeleton layer, EICP solution and / or MICP solution were evenly sprayed on the surface of the skeleton layer once and cured for 48 hours. Then, watering and curing began: deionized water / low saline solution (3 L / m²·time) was sprayed every 3 days for 14 consecutive days.

[0153] On the 14th day of maintenance, the germination rate G is calculated according to the formula (number of germinated seeds / total number of seeds sown × 100%).

[0154] 24 hours after the first water replenishment, in-situ sand samples were taken from 0 to 2 cm below the skeleton layer. The water-to-soil ratio 1:5 extraction method was used: 10 g of air-dried soil sample was added to 50 mL of deionized water, shaken for 30 min, and the pH of the supernatant was measured after standing.

[0155] Each group of samples was tested three times, and the results are expressed as mean ± standard deviation.

[0156] The test results are shown in Table 1:

[0157]

[0158] As shown in Table 1, the embodiments of this application generally exhibit excellent sand-fixing and stabilization effects. Among them, the combined technical solution of using alkali-activated solidification to construct a coarse-particle framework, along with biomineralization spraying, demonstrates significant advantages in wind erosion resistance, scour resistance, and durability. Furthermore, within a reasonable range of activation solution dosage, it can also ensure plant growth friendliness. Specific analysis is as follows:

[0159] Comparing Example 1 (alkali activation + sealing reinforcement + surface spraying) with Example 2 (alkali activation + surface spraying, no sealing reinforcement), it can be seen that the single-particle compressive strength of Example 1 increased from 5.2±0.6MPa to 6.3±0.6MPa, the water absorption rate decreased from 9.5±1.0% to 7.8±0.8%, and the wind erosion weight loss decreased from 32±4.9g / (m³) 2 The concentration of 18.5 g / (m·min) decreased to 18±1.7 g / (m·min) 2 The scouring weight loss was 43±2.9 g / (m³). 2 The concentration of 1,000 mg / (min) decreased to 34 ± 2.7 g / (m 2 •min), wet and dry cycle strength retention rate (R DW ) and freeze-thaw cycle strength retention rate (R FT The percentages of 4% and 5% increased from 77±6% / 64±6% to 85±5% / 73±5%, respectively. These results indicate that introducing EICP / MICP sealing and reinforcement technology during the overall solidification process can effectively reduce particle pore connectivity and water absorption, achieving densification of the micropores on the particle surface and inside. This significantly improves the material's resistance to wind erosion and abrasion, as well as its strength stability under wet-dry and freeze-thaw cycles.

[0160] Comparative Example 1, a control sample with plant fibers removed, maintained a single-particle compressive strength of 5.9 ± 0.7 MPa, but its erosion weight loss significantly increased to 51 ± 3.6 g / (m²). 2 ·min), R DW With R FTThe values ​​decreased to 61±8% and 49±8%, respectively. This result indicates that plant fibers can inhibit the propagation of microcracks through bridging and toughening, significantly improving the material's resistance to spalling and breakage under water erosion and cyclic loading. Without plant fibers, the material is prone to brittle fracture and particle detachment, leading to a significant deterioration in erosion resistance and durability.

[0161] Comparative Example 2, without the addition of an alkaline activator solution, had a single-particle compressive strength of only 0.6 ± 0.1 MPa, a water absorption rate of 16.0 ± 1.7%, and wind erosion and scour losses of 155 ± 3.4 g / (m³). 2 ·min) and 193±5.4g / (m 2 ·min), R DW With R FT The percentages were only 50±9% and 37±10%. This result confirms that the cementitious phase generated by the alkali-activated reaction is the core of constructing a continuous and stable cemented structure inside the particles. Without this cementitious phase, the skeleton layer cannot form an effective consolidation and will quickly break down and fail under the action of strong winds and runoff.

[0162] Comparative Example 3, using an excessive amount of activating solution, achieved a single-particle compressive strength of 6.7±0.7 MPa. Its wind erosion weight loss, scour weight loss, and durability retention rates were all at high levels, indicating that the skeletal particles could form a strong cemented structure. However, the pH of the underlying in-situ sand, extracted at a 1:5 ratio, increased to 9.7±0.3, and the plant germination rate on day 14 was only 56±6%, significantly lower than Example 1 (pH 8.4±0.2, germination rate 72±6%). These results demonstrate that excessive activating solution can lead to residual alkali increasing soil alkalinity after leaching by water replenishment or rainfall, resulting in salt-alkali stress that inhibits plant seed germination. Therefore, the amount of activating solution used must be controlled within a reasonable range to achieve a synergistic effect between sand fixation strength and ecological restoration.

[0163] Comparative Example 4, without the addition of EICP reaction components, had a single-particle compressive strength of only 0.8 ± 0.1 MPa, a water absorption rate of 16.8 ± 1.8%, and wind erosion and scour weight losses of 128 ± 2.5 g / (m³). 2 ·min) and 178±2.5g / (m 2 ·min), R DW With R FT The concentrations decreased to 48±10% and 35±10%, respectively. These results indicate that the calcium carbonate cement structure generated by the biomineralization reaction is crucial for forming a stable cement network and surface consolidation. Without this component, the system cannot achieve effective consolidation, and the combined sand-fixing effect is significantly reduced.

[0164] In summary, the test results verify the combined sand fixation mechanism of this application, which consists of an in-situ solidified coarse-grained skeleton layer, (optional) pore sealing reinforcement, and a single spraying of EICP / MICP after laying to form a surface cementation layer. This mechanism can significantly reduce material loss caused by wind erosion and scouring, and maintain high strength stability under wet-dry and freeze-thaw cycles. At the same time, by controlling the appropriate dosage of the activating liquid, the appropriate pH of the soil can be maintained and a high plant germination rate can be ensured, thus achieving synergistic effects of sand fixation and ecological restoration.

[0165] It should also be noted that the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0166] The above description is merely an embodiment of this application and is not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principle of this application should be included within the scope of the claims of this application.

[0167] Although embodiments of this application have been described in conjunction with the accompanying drawings, those skilled in the art can make various modifications and variations without departing from the spirit and scope of this application, and such modifications and variations all fall within the scope defined by the appended claims.

Claims

1. A method of sand stabilization in combination, characterized in that, The combined sand fixation method includes: The coarse sand-fixing particles are evenly spread on the surface of the desert area to be treated, with a thickness of 1 to 30 cm, to form a solidified coarse particle skeleton layer. EICP solution and / or MICP solution are uniformly sprayed onto the surface of the solidified coarse particle skeleton layer to form a calcium carbonate cementing layer, thereby achieving combined sand fixation. The coarse sand-fixing particles comprise the following components in parts by weight: 60-90 parts of in-situ desert sand, 0.5-5 parts of plant fiber, and 5-30 parts of a solidification activation reaction component, wherein the solidification activation reaction component is an alkali-activated solidification component or a biomineralization reaction component; the biomineralization reaction component includes an EICP reaction component or a MICP reaction component. When using the alkali-activated solidification component, the coarse sand-fixing particles further include 5-40 parts of active material. The active material is selected from at least one of fly ash, granulated blast furnace slag, metakaolin, volcanic ash, or tailings powder, and the total content of SiO2 and Al2O3 in the active material is not less than 30 wt%. The particle size range of the coarse sand-fixing particles is 5–200 mm; The method for preparing the coarse sand-fixing particles includes: When using an alkali-activated curing component, the preparation method includes: Desert in-situ sand is mixed with active materials, the aforementioned alkali-activated curing components, and plant fibers, and then cured statically at 20–40°C for 3–14 days to form a solidified whole; or When using biomineralization reaction components, the preparation method includes: The desert in-situ sand is used as aggregate and mixed with the biomineralization reaction components and the plant fiber. The mixture is then left to stand and cure at 15-40°C for 2-5 days to form a solidified whole. EICP solution and / or MICP solution are sprayed uniformly 1 to 5 times on the outer surface of the integral solidified body. The EICP solution and / or the MICP solution penetrate into the integral solidified body so that the generated calcium carbonate is deposited on the surface of the integral solidified body and in the internal micropores of the integral solidified body. For the integral solidified body that has been uniformly sprayed with the EICP solution and / or the MICP solution, after being left to stand in the natural environment for 1 to 3 days, the resulting composite solidified body is crushed and screened to obtain solidified coarse particles for sealing and reinforcement.

2. The method of claim 1, wherein, When the alkali-activated curing component is used, the active material undergoes a dissolution-condensation reaction to generate a NASH gel phase and / or a C-(A)-SH gel phase, so that the compressive strength of the coarse sand particles reaches 0.5 to 10 MPa.

3. The method of claim 1, wherein, When using the alkali-activated curing component, the mass ratio of the desert in-situ sand to the active material is 70:30 to 85:

15.

4. The method of claim 1, wherein, The plant fiber is selected from at least one of the following: straw fiber, wheat straw fiber, rice straw fiber, reed fiber, bulrush fiber, coconut shell fiber, coconut fiber, jute fiber, flax fiber, sisal fiber, bast fiber, bamboo fiber, and wood fiber. The plant fibers have a length of 2–30 mm, a diameter of 10–500 μm, and an aspect ratio of 10–150.

5. The method of claim 1, wherein, The alkaline-activated curing component is an alkaline activator solution. The proportions of each component in the alkaline activator solution, calculated by alkaline equivalent, are: sodium hydroxide 30-70%, sodium silicate 20-60%, and sodium carbonate 0-30%. The total alkaline concentration of the alkaline activator solution is 2-10 mol / L, and the total alkaline concentration is the sum of the equivalent amounts of each alkaline component converted to hydroxide or carbonate ions. The mass ratio of sodium hydroxide to sodium silicate in the alkaline activator solution is 1:0.5 to 1:2; When the alkaline activator solution contains sodium carbonate, the sodium carbonate accounts for 5-30% of the total alkaline equivalent of the alkaline activator solution.

6. The combined sand fixation method according to claim 1, characterized in that, The EICP reaction components include urea at a concentration of 0.5–3 mol / L, calcium salt at a concentration of 0.5–3 mol / L, and urease with an activity of 5–30 mmol / (L·min). The molar ratio of urea to calcium salt in the EICP reaction components is 1:1 to 1.5:

1. The MICP reaction component includes a urease-producing microbial culture with a urease activity of 5–30 mmol / (L·min), urea with a concentration of 0.5–3 mol / L, and calcium salt with a concentration of 0.5–3 mol / L. The molar ratio of urea to calcium salt in the MICP reaction component is 1:1 to 1.5:

1.

7. The method of claim 6, wherein, The biomineralization reaction components also include colloidal materials, which are sodium alginate, xanthan gum, or chitosan, and the mass fraction of the colloidal materials is 0.1 to 1.0 wt%.

8. The method of claim 1, wherein, The EICP solution sprayed on the outer surface of the monolithic solidified body contained urea at a concentration of 0.05–2.0 mol / L, calcium salt at a concentration of 0.05–2.0 mol / L, and urease activity of 5–15 mmol / (L·min); the MICP solution sprayed on the outer surface of the monolithic solidified body contained urea at a concentration of 0.1–1.0 mol / L, calcium salt at a concentration of 0.05–2.0 mol / L, and urease activity of the urease-producing microbial culture at a concentration of 5–30 mmol / (L·min).

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