A pavement composite soil stabilizer, its preparation method and application

Abstract

The application provides a road surface composite soil stabilizer and a preparation method and application thereof. The road surface composite soil stabilizer is prepared from the following raw materials: alkali-resistant urease, silicon powder, polycarboxylate sodium dispersant, calcium chloride, urea and modified nano silicon dioxide. The preparation raw materials of the modified nano silicon dioxide include nano silicon dioxide, imidazole-4-carboxylic acid and amino silane coupling agent. The composite soil stabilizer provided by the application can reduce the cement consumption, improve the bearing capacity and wear resistance of the stabilized soil, and achieve the technical targets of high strength, wear resistance and high frost resistance of the stabilized soil.

Description

Technical Field

[0001] This invention relates to the field of road hardener technology, and in particular to a road surface composite soil hardener, its preparation method, and its application. Background Technology

[0002] Soil stabilization technology is a key method that improves the physical and mechanical properties (such as unconfined compressive strength, water stability, impermeability, and durability) of natural soil by incorporating stabilizing agents, thereby meeting the load-bearing requirements of roads, subgrades, and foundations. It has been widely applied in highways, railways, municipal works, and construction. In recent years, with the deepening of ecological construction concepts, rural roads, cultural tourism scenic areas, and other scenarios have created an urgent demand for high-performance materials that can be directly used to solidify on-site soil into road surface layers—materials that not only meet the strength and wear resistance under general traffic loads but also possess excellent freeze-thaw resistance, fatigue resistance, and long service life. However, current mainstream curing agents struggle to achieve the aforementioned comprehensive performance: Inorganic agents (such as cement and lime) offer rapid strength development and low cost, but cement content is typically as high as 12%–15% of the raw soil mass, resulting in high carbon emissions. Furthermore, the cured body exhibits a high tendency to shrink and crack, with a coarse pore structure, and strength loss generally exceeds 15% after 15 freeze-thaw cycles, limiting their application in cold regions. Organic agents (such as epoxy resin and polyurethane) are flexible and impermeable, but are expensive, complex to apply, and prone to volatile emissions that pollute the environment, hindering large-scale application. Bioenzymes (such as proteases and ureases) are environmentally friendly, but when used alone, their 28-day strength is often below 8 MPa, and they have poor water and freeze resistance, requiring compounding with other components. While the currently common "cement + urease" compounding scheme attempts to balance strength and environmental friendliness, it still suffers from fundamental flaws: On the one hand, the highly alkaline environment (pH>12.5) generated during cement hydration easily deactivates urease, weakening its catalytic efficiency and making it difficult to achieve an overall strength exceeding 10 MPa; on the other hand, urea hydrolysis produces CO2 / CO3². - The process of forming CSH gel through cement hydration is disconnected from the process itself, lacking spatiotemporal coordination. This results in random distribution of calcium carbonate mineralization, weak interfacial bonding, and high internal porosity. After 15 freeze-thaw cycles, the strength loss rate often exceeds 20%, and the wear resistance is insufficient, making it unsuitable for use as a road surface layer. Although nano-silica powder can fill pores and improve density through secondary hydration reactions, its high surface energy easily leads to agglomeration and uneven dispersion. Furthermore, it cannot actively regulate enzyme activity or guide the mineralization reaction to occur directionally at key interfaces. Summary of the Invention

[0003] The present invention aims to develop a composite soil stabilizer that provides basic strength to cement-stabilized soil while taking into account early strength and long-term durability. It reduces the amount of cement used while improving the bearing capacity and wear resistance of the stabilized soil, thus achieving the technical goal of high strength, wear resistance and high frost resistance of the stabilized soil.

[0004] To achieve the above objectives, the present invention provides a road surface composite soil stabilizer, the raw materials of which include: alkali-resistant urease, silica powder, sodium polycarboxylate dispersant, calcium chloride, urea, and modified nano-silica;

[0005] The raw materials for preparing the modified nano silica include: nano silica, imidazole-4-carboxylic acid, and aminosilane coupling agent.

[0006] According to the first aspect of the present invention, at least the following beneficial effects are achieved:

[0007] Road solidified soil needs to meet both early strength and long-term durability requirements, but there is usually a clear contradiction between the two: cement needs to be rapidly hydrated to form a strength skeleton, while biomineralization relies on urease to catalyze the slow hydrolysis of urea to generate calcium carbonate to fill micropores; if the mineralization reaction is too early, CO2 will escape in the form of bubbles, destroying the early structure; if it is too late, it cannot effectively fill the pores in the early stage of cementitious network formation, making it difficult to balance early strength and durability.

[0008] In this invention, the long-term performance improvement and stability of the solidified soil stem from the slow release of carbon dioxide and the continued carbonation reaction of free calcium oxide. In the solidification system, a slow-release CO2 source gradually releases gas, which reacts directionally with free calcium oxide (CaO) in the soil and solidifying agent, continuously generating calcium carbonate (CaCO3) crystals. Test results confirm that with increasing age (7→28→90 days in the study), calcium carbonate crystals continuously grow, aggregate, and densely fill soil pores. They also gradually form a further dense structure with calcium silicate formed by cement hydration, significantly reducing porosity and continuously increasing strength.

[0009] This invention introduces modified nano-silica. In the initial stage, its carboxylic acid groups adsorb and slowly release urea, inhibiting carbon dioxide bursts, while the imidazole ring protects urease to maintain high activity in a strongly alkaline environment, simultaneously chelating calcium ions to form a "calcium reservoir." In the middle stage, as the cement initially hardens, urea is released in a controlled manner. The carbonate ions generated by the efficient catalysis of urease and the pre-enriched calcium ions precipitate in situ on the surface of the nanoparticles to form dense calcium carbonate, precisely filling the micropores without generating bubbles. In addition, the nano-silica itself participates in hydration and enhances interfacial bonding, improving early strength. Thus, a synergistic mechanism of "rapid cement hardening to form a skeleton and slow mineralization to reinforce the structure" is achieved, satisfying the early strength requirement while significantly improving long-term durability.

[0010] Specifically:

[0011] ① In solidified soil, cement is the main cementing material that provides strength. Its hydration reaction produces calcium silicate hydrate (CSH gel) and calcium hydroxide (Ca(OH)2), which can effectively fill the pores between soil particles and cement loose soil particles, thus laying the initial strength foundation for solidified soil.

[0012] Introducing nano-silica (i.e., highly active nano-sized silica) can significantly optimize the microstructure and mechanical properties of the cementitious system. Specifically, the Ca(OH)2 generated in the early stage of cement hydration undergoes a secondary hydration reaction with the nano-silica, which not only consumes the Ca(OH)2 with low strength contribution but also generates CSH gel with high strength properties, further enhancing the overall bonding ability of the solidified soil.

[0013] Furthermore, nano-silica fume, with its extremely high specific surface area and nanoscale particle size, can effectively fill the micropores between cement hydration products, significantly reducing the total porosity of the solidified soil and greatly refining the pore size distribution. The densification of the pore structure not only improves the compressive strength of the solidified soil but also significantly enhances its freeze-thaw resistance and durability, enabling it to maintain good engineering applicability under harsh environmental conditions.

[0014] ② Using alkali-resistant urease can catalyze the hydrolysis of urea to produce ammonia and carbon dioxide. The generated CO2 can react with calcium hydroxide released during cement hydration to form bicarbonate ions, and finally be converted into carbonate ions in an alkaline environment. Subsequently, the calcium chloride added provides Ca... 2+ With CO3 2- The reaction combines to form a stable calcium carbonate (CaCO3) precipitate. This reaction continues in an alkaline environment, and the resulting calcium carbonate crystals fill the pores of the solidified soil, significantly improving density and compressive strength, while also enhancing durability. The calcium carbonate precipitate can further fill the micropores not covered by the cement-silica fume system, strengthening the bonding force between particles. This is a composite reinforcement method of "cementing solidification + biomineralization," which can greatly improve the strength of the solidified soil and complement the core cementing system. It should be noted that ordinary urease biological reagents have low activity in highly alkaline environments and their reaction with urea is generally ineffective. Therefore, this invention uses a highly alkaline urease product that can be used normally in an environment with a pH of 12-13.

[0015] The specific reaction formula is shown below:

[0016] CO(NH2)2+ H2O → 2NH3+CO2 (I);

[0017] CO2 + 2NH3 → NH4 + +NH2COO - (IIa);

[0018] NH2COO - + H2O → NH4 + + HCO3 - (IIb);

[0019] HCO3- + OH - → CO3 2- + H2O (III);

[0020] Ca 2+ +CO3 2- →CaCO3↓ (IV);

[0021] Ca(OH)2+ CO2→ CaCO3↓ + H2O (V).

[0022] ③ Calcium chloride, on the one hand, produces Ca upon dissociation. 2+ It can combine with carbonate ions generated during biomineralization to form a dense calcium carbonate precipitate, effectively filling micropores and strengthening soil structure; on the other hand, its Cl content... - It has a significant setting-promoting effect, which can accelerate the early hydration process of cement, shorten the initial and final setting time, and optimize the spatial distribution of hydration products (such as CSH gel and calcium hydroxide), thereby promoting the rapid establishment of early strength of solidified soil, significantly improving the mechanical properties in the early stage of construction, and achieving synergistic optimization of early strength and long-term stability.

[0023] ④ In the early stages (the cement-dominant hydration stage), the carboxylic acid groups on the surface of the bifunctional "carboxylic acid-imidazole" modified nano-silica effectively adsorb and "lock" urea molecules through strong hydrogen bonding, significantly inhibiting their premature release—thus avoiding the explosive generation of CO2 and its disturbance to the slurry structure. Simultaneously, the imidazole rings, through π-π stacking and hydrogen bonding, construct a local microenvironment around the nanoparticles, effectively shielding the structure of alkali-resistant urease from the extremely high alkalinity during the early stages of cement hydration. Furthermore, the carboxylic acid groups can also efficiently chelate Ca released from calcium chloride. 2+ A "calcium ion pool" is formed on the surface of the nanoparticles, pre-enriching the raw materials for subsequent biomineralization reactions. Entering the mid-stage (the synergistic hydration-mineralization window), as cement hydration progresses, the local pH of the slurry slightly decreases and urea begins to be released in a controlled, slow manner. At this point, highly active urease efficiently catalyzes the hydrolysis of urea, and the generated carbonate ions then react in situ with the pre-enriched calcium ions on the nanoparticle surface, directionally inducing the formation of calcium carbonate on the nano-silica surface. This mineralization process occurs in the nanopores and particle interface region of the CSH gel.

[0024] According to an embodiment of the present invention, the aminosilane coupling agent comprises 3-aminopropyltriethoxysilane.

[0025] The present invention also provides a method for preparing a road surface composite soil stabilizer, comprising the following steps: dispersing the silica powder and then mixing it with the modified nano silica, the calcium chloride, and the alkali-resistant urease to obtain a stabilizer powder.

[0026] Pre-dispersion of silica powder avoids agglomeration and ensures that its pozzolanic activity is fully utilized. Modified nano-silica, as the core regulatory carrier, is pre-distributed with calcium chloride and urease in powder form, so that when it is mixed into the soil, it can simultaneously play multiple roles of "urea slow release, enzyme activity protection, calcium ion enrichment, directional mineralization, and interface enhancement".

[0027] According to an embodiment of the present invention, the raw materials for preparing the curing agent include: 0.8-1 parts of the alkali-resistant urease, 60-65 parts of the silica powder, 1-2 parts of the sodium polycarboxylate dispersant, 2-3 parts of the calcium chloride, 27-30 parts of the urea, and 2-3 parts of the modified nano-silica.

[0028] According to an embodiment of the present invention, the alkali-resistant urease includes industrial-grade highly alkali-resistant urease with an enzyme activity of 1000~1500 U / g and a total enzyme activity of not less than 50,000 units. After being mixed with soil and cement for 10 hours under pH 12.5 and 25℃ conditions, the enzyme activity residue rate is not less than 50%. Preferably, it is Soil-set® urease produced by Novozymes AG, Denmark.

[0029] According to an embodiment of the present invention, the calcium chloride is calcium chloride dihydrate powder with a CaCl2·2H2O content ≥75% and a particle size of not less than 300 mesh; preferably, it is calcium chloride dihydrate powder produced by Qinghai Salt Lake Industry Co., Ltd.

[0030] According to an embodiment of the present invention, the urea is of industrial superior grade, with a nitrogen content ≥46%, a biuret content ≤0.9%, a moisture content ≤0.3%, and is free of lumps; preferably, it is "Lutianhua" brand industrial grade urea produced by Lutianhua Co., Ltd.

[0031] According to an embodiment of the present invention, the silicon powder comprises ultrafine industrial-grade fumed silica, with a SiO2 content ≥80%, an average particle size of 0.1~0.3μm, and a specific surface area ≥100 m². 2 / g; preferably high-purity fumed silica produced by Zhejiang Xin'an Chemical Group Co., Ltd.

[0032] According to an embodiment of the present invention, the method for preparing the modified nano silica includes: refluxing the nano silica and the aminosilane coupling agent at 75-80°C for 6-8 hours, and then reacting them with the imidazole-4-carboxylic acid to obtain the modified nano silica.

[0033] According to an embodiment of the present invention, the nano-silica, the aminosilane coupling agent, and the imidazole-4-carboxylic acid are in a ratio of 100:5~20:3~15.

[0034] This formulation ensures that carboxylic acid groups and imidazole functional groups are fully grafted onto the surface of nano-silica, achieving effective adsorption of urea and stable protection of urease, while avoiding agglomeration or increased costs caused by excessive modifier.

[0035] According to an embodiment of the present invention, the raw materials for preparing the modified nano silica further include: 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride and 1 g N-hydroxysuccinimide.

[0036] According to an embodiment of the present invention, the step of dispersing silicon powder includes: mixing and dispersing the silicon powder and the sodium polycarboxylate dispersant.

[0037] According to an embodiment of the present invention, the silicon powder is pretreated with a polycarboxylate dispersant, wherein the dispersant has a solid content ≥40%, a pH of 7-8, is suitable for a highly alkaline environment, and the fluidity of the silicon powder slurry after dispersion is ≥250 mm; the amount of the dispersant is 2%-3% of the silicon powder mass, preferably PCA-1 type polycarboxylate dispersant produced by Jiangsu Subote New Material Co., Ltd.

[0038] This dispersion step, by mixing silicon powder with a polycarboxylate dispersant, effectively prevents the agglomeration of nano-silicon powder during preparation and storage, resulting in a more uniform distribution of it in the curing agent.

[0039] The present invention also provides the application of the pavement composite soil stabilizer prepared by the above preparation method in roads.

[0040] According to an embodiment of the present invention, the application includes the following steps:

[0041] S1. Remove impurities from the raw soil, crush it, and adjust the moisture content to 12%~18% to obtain pretreated raw soil;

[0042] S2. Mix the pretreated soil and the powder of the curing agent to obtain a mixture;

[0043] S3. The urea is dispersed and then mixed with the mixture to obtain the paving material;

[0044] S4. Spread the paving material in layers, compact it, and then keep it moist and cured.

[0045] The application method of this invention fully leverages the synergistic effect of each component by precisely controlling the mixing and reaction timing of raw materials in stages: In S1, the moisture content of the raw soil is controlled at 12%~18%, which satisfies the moisture required for subsequent hydration and mineralization reactions while avoiding excessive moisture that would affect the compaction effect; In S2, the pretreated raw soil is first dry-mixed with the curing agent powder (containing modified nano-silica, silica powder, calcium chloride, and alkali-resistant urease), so that the functional components are evenly dispersed in the soil, laying the foundation for subsequent reactions; In S3, urea is added separately and mixed, which effectively avoids premature hydrolysis of urea due to premature contact with urease, ensuring that CO2 is slowly released only after the initial hydration of cement, achieving a synergistic sequence of "first forming the skeleton, then filling the micropores"; In S4, layered paving and compaction combined with moisture retention and curing ensures early strength development and provides a stable environment for continuous biomineralization.

[0046] According to an embodiment of the present invention, the amount of curing agent added is 5% to 8% of the weight of the raw soil. When using it, it needs to be thoroughly mixed with cement and raw soil, and construction should be carried out within the range of the optimal moisture content of the raw soil ±2%.

[0047] According to an embodiment of the present invention, the cement includes P·O 42.5 grade ordinary Portland cement, with an admixture amount of 5% to 8% of the weight of the raw soil, and meets the following requirements: initial setting time ≥ 45 min, final setting time ≤ 600 min, 3-day compressive strength ≥ 17 MPa, and 28-day compressive strength ≥ 42.5 MPa.

[0048] According to an embodiment of the present invention, in step S2, the powder of the pretreated soil and the curing agent is in a weight ratio of 100:3.5~8.

[0049] According to an embodiment of the present invention, the subgrade soil includes at least one of silt, clay, silty sand and engineering waste soil.

[0050] According to an embodiment of the present invention, the soil has a particle size greater than 0.01 mm and less than 5 mm, a plasticity index of 10 to 50, and an organic matter content of ≤20%. Attached Figure Description

[0051] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0052] Figure 1 This is a schematic diagram of the 90-day cured soil of Embodiment 1 of the present invention.

[0053] Figure 2This is a schematic diagram of the 28-day cured soil of Embodiment 1 of the present invention.

[0054] Figure 3 This is a schematic diagram of the 7-day cured soil of Embodiment 1 of the present invention.

[0055] The realization of the objective, functional characteristics and advantages of the present invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0056] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0057] Furthermore, the technical solutions of the various embodiments of the present invention can be combined with each other, but only if they are based on the ability of those skilled in the art to implement them. When the combination of technical solutions is contradictory or cannot be implemented, it should be considered that such combination of technical solutions does not exist and is not within the scope of protection claimed by the present invention.

[0058] Components in the examples:

[0059] Alkali-resistant urease: Soil-set® urease manufactured by Novozymes;

[0060] Silica powder: High-purity fumed silica produced by Zhejiang Xin'an Chemical Group Co., Ltd., with SiO2 content ≥80%, average particle size 0.1-0.3 μm, and specific surface area ≥100 m². 2 / g;

[0061] Sodium polycarboxylate dispersant: HT-5040 from Nantong Hantai Chemical Co., Ltd. is a sodium polycarboxylate salt dispersant;

[0062] Nano-silica: Xi'an Bona Materials Technology Co., Ltd., 50-100nm nano-silica;

[0063] Aminosilane coupling agent: 3-aminopropyltriethoxysilane, Aladdin (commercial);

[0064] Imidazole-4-carboxylic acid: CAS: 1072-84-0.

[0065] Example 1

[0066] This embodiment provides a composite soil stabilizer and its preparation method, specifically:

[0067] The raw materials for preparing the composite soil stabilizer are: 0.8 parts of alkali-resistant urease, 65 parts of silica powder, 1.2 parts of sodium polycarboxylate dispersant, 3 parts of calcium chloride, 30 parts of urea, and 2 parts of carboxylic acid-imidazolium bifunctional modified nano-silica.

[0068] The preparation method of the composite soil stabilizer is as follows:

[0069] A1. Stir nano-silicon powder and sodium polycarboxylate dispersant at 1800 r / min for 12 min to obtain pre-dispersed silicon powder;

[0070] A2. The preparation method of carboxylic acid-imidazolium bifunctional modified nano-silica includes the following steps: First, 100g of nano-silica is dispersed in 500 mL of anhydrous ethanol, and 10g of 3-aminopropyltriethoxysilane is added. The mixture is refluxed at 78℃ for 6h. Then, the above-mentioned aminated nano-silica is dispersed in 300 mL of anhydrous ethanol, and 8g of imidazolium-4-carboxylic acid, 4g of 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride (EDC) and 1g of N-hydroxysuccinimide (NHS) are added. After activation at room temperature for 15min, the temperature is raised to 50℃ and the reaction is continued for 3h. After the reaction is completed, the mixture is centrifuged (8000r / min, 15min), washed three times with anhydrous ethanol, and vacuum dried to obtain modified nano-silica.

[0071] A3. The above-mentioned pre-dispersed silica powder, grafted modified nano silica, and calcium chloride are mixed and stirred at 600 r / min for 15 min. Then, urease powder is added and stirred at 600 r / min for 12 min. The mixture is then passed through an 80-mesh sieve to obtain curing agent powder, which is packaged and transported to the site.

[0072] A4. When using, dissolve the required amount of urea in water and then spray.

[0073] Example 2

[0074] This embodiment provides a composite soil stabilizer and its preparation method, specifically:

[0075] The difference between this embodiment and Embodiment 1 is that the ratio of the composite soil stabilizer is adjusted to 0.9 parts of alkali-resistant urease, 62 parts of silica powder, 1.5 parts of sodium polycarboxylate dispersant, 2.5 parts of calcium chloride, 28 parts of urea, and 2.5 parts of modified nano-silica. The remaining preparation and application steps are the same as in Embodiment 1.

[0076] Example 3

[0077] The difference between this embodiment and Embodiment 1 is that the amount of silicon powder used is 60 parts, the amount of urea used is 27 parts, the amount of modified nano-silica used is 3 parts, and the remaining components and application conditions are the same as in Embodiment 1.

[0078] Comparative Example 1

[0079] The difference between this comparative example and Example 1 is that no modified nano-silica was added; all other conditions are the same as in Example 1.

[0080] Comparative Example 2

[0081] This comparative example uses a mineral powder-based curing agent (10% of the weight of the raw soil), and the other conditions are the same as in Example 1.

[0082] Comparative Example 3

[0083] This comparative example uses a mineral powder-based curing agent (PO 42.5 cement, added at 8% of the raw soil mass + 0.03% polymer curing agent), and the other conditions are the same as in Example 1.

[0084] Comparative Example 4

[0085] This comparative example uses cement + nano-silica powder curing agent (8% PO 42.5 cement + 8% nano-silica powder, with other conditions the same as in Example 1).

[0086] Comparative Example 5

[0087] This comparative example uses a "cement + bio-enzyme" curing agent (8% PO 42.5 cement + 0.3% bio-enzyme added), and the other conditions are the same as in Example 1.

[0088] Test Example 1

[0089] S1. Remove impurities from the raw soil, crush it, and adjust the moisture content to 12% to obtain pretreated raw soil;

[0090] S2. The pretreated soil and the curing agent powder are mixed together, and a uniformly mixed material is obtained by plant mixing method;

[0091] S3. Dissolve urea (30% of the total mass of curing agent) in water and stir for 12 minutes to obtain a diluted urea solution. Then spray the mixture to obtain the paving material. For example, if the compacted weight of one cubic meter of plain soil is 2000 kg, 100 kg of curing agent should be added, including 70 kg of powder, 30 kg of urea, and 160 kg of cement.

[0092] S4. Spread the paving material in layers and compact each layer (thickness 18cm, compaction degree greater than 95%). After compaction, cover with plastic film for curing and then conduct performance tests. The results are shown in Table 1.

[0093] Performance test results (according to GB / T 50123-2019 Geotechnical Testing Standard, GB / T 50082-2009 Concrete Durability Standard, and T / CECS737-2020 Technical Specification for Application of Road Stabilized Soil):

[0094] Table 1. Performance Testing

[0095]

[0096] As can be seen from the performance test results in Table 1, the composite soil stabilized soil prepared in Example 1 of this invention has a compressive strength of 13.2 MPa at 7 days and a strength of 16.5 MPa at 28 days under low cement content conditions, which is significantly higher than that of the comparative examples, fully meeting the requirements of road surface layer for early bearing capacity. At the same time, its water absorption at 28 days is only 5.2%, and its strength loss rate after 15 freeze-thaw cycles is as low as 6.5%, which is far superior to traditional lime stabilized soil and existing compounding schemes, indicating that the material has excellent compactness and freeze-thaw durability.

[0097] Figure 1 , Figure 2 , Figure 3 The microstructure diagrams at different ages (7 days, 28 days, and 90 days) demonstrate the densification process of the co-evolution of CSH gel and calcium carbonate in the solidified soil of this invention, reflecting the effect of early rapid hardening and long-term continuous enhancement.

[0098] Test Example 2

[0099] This test case aims to evaluate the synergistic effect of grafted modified nano-silica on the early strength and long-term durability of solidified soil. A comparative test method was used, preparing samples under the same conditions for a formulation incorporating "carboxylic acid-imidazole" bifunctional grafted modified nano-silica and a basic formulation without this component. The mechanical properties, pore structure, freeze-thaw stability, and microstructure were systematically tested and analyzed according to relevant standards. The test results are shown in Table 2.

[0100] Table 2. Performance Testing

[0101]

[0102] As can be seen from the comparative test results in Table 2, Example 1 with modified nano-silica is significantly superior to the basic formulation of Comparative Example 1 without this component: the 7-day compressive strength increased from 8.18 MPa to 13.2 MPa, and the 28-day strength increased from 11.7 MPa to 16.5 MPa, fully meeting the requirements of road engineering for early-stage traffic strength (≥13 MPa). Simultaneously, its 28-day porosity decreased from 13.5% to 8.0%, and the strength loss rate after 15 freeze-thaw cycles decreased from 10.0% to ≤7.5%. The 28-day abrasion value also significantly improved, indicating a significant enhancement in material density and durability. The 90-day strength maintained a stable increase, demonstrating that long-term performance was not sacrificed for the pursuit of early strength. This proves that the present invention, through the introduction of grafted modified nano-silica, successfully achieved synergistic optimization of early high strength development and long-term high durability, effectively resolving the inherent contradiction in traditional solidified soil where "rapid hardening leads to looseness, and denseness leads to slow strength." The increased strength of the solidified soil at 7, 28, and 90 days is a result of the synergistic effect of hydrated calcium silicate (CSH) and calcium carbonate. At 7 days, CSH initially forms a short rod-shaped skeleton, with less calcium carbonate production, resulting in a loose structure and a compressive strength of 13.2 MPa. Within 28 days, CSH grows into fibers and interweaves into a network, while calcium carbonate continues to be produced and fuses, jointly filling the pores, reducing porosity, and significantly improving density, reaching a strength of 16.5 MPa. At 90 days, CSH forms a plate-like dense accumulation, further reducing porosity. The two together construct a three-dimensional dense structure, blocking seepage channels, and the final strength reaches 18.2 MPa.

[0103] The enzyme activity retention rate of the dry powder in the example was >85% after 6 months of storage, indicating that the "carboxylic acid-imidazole" bifunctional layer not only regulates the reaction, but also plays a physicochemical protective role against urease, ensuring functional stability during the construction period.

[0104] The above technical solutions of the present invention are merely preferred embodiments of the present invention and do not limit the patent scope of the present invention. All equivalent structural transformations made under the technical concept of the present invention using the contents of the present invention specification and drawings, or direct / indirect applications in other related technical fields, are included in the patent protection scope of the present invention.

Claims

1. A road surface composite soil stabilizer, characterized in that, The raw materials for preparation include: alkali-resistant urease, silica powder, sodium polycarboxylate dispersant, calcium chloride, urea, and modified nano-silica; The raw materials for preparing the modified nano silica include: nano silica, imidazole-4-carboxylic acid and aminosilane coupling agent; The aminosilane coupling agent includes 3-aminopropyltriethoxysilane; A method for preparing a composite soil stabilizer includes the following steps: dispersing the silica powder and then mixing it with the modified nano-silica, the calcium chloride, and the alkali-resistant urease to obtain a stabilizer powder; The urea is used as an independent component, and is mixed with the curing agent powder to obtain the road composite soil curing agent. The raw materials for preparing the curing agent, by weight, include: 0.8-1 parts of the alkali-resistant urease, 60-65 parts of the silica powder, 1-2 parts of the sodium polycarboxylate dispersant, 2-3 parts of the calcium chloride, 27-30 parts of the urea, and 2-3 parts of the modified nano silica. The method for preparing the modified nano silica includes: refluxing the nano silica and the aminosilane coupling agent at 75-80°C for 6-8 hours, and then reacting them with the imidazole-4-carboxylic acid to obtain the modified nano silica.

2. The road surface composite soil stabilizer according to claim 1, characterized in that, The nano-silica, the aminosilane coupling agent, and the imidazole-4-carboxylic acid are in a weight ratio of 100:5~20:3~15.

3. The road surface composite soil stabilizer according to claim 1, characterized in that, The step of dispersing the silicon powder includes: mixing and dispersing the silicon powder and the sodium polycarboxylate dispersant.

4. The application of a road surface composite soil stabilizer as described in any one of claims 1 to 3 in roads.

5. The application according to claim 4, characterized in that, The application includes the following steps: S1. Remove impurities from the raw soil, crush it, and adjust the moisture content to 12%~18% to obtain pretreated raw soil; S2. Mix the pretreated soil and the powder of the curing agent to obtain a mixture; S3. The urea is dispersed and then mixed with the mixture to obtain the paving material; S4. Spread the paving material in layers, compact it, and then keep it moist and cured.

6. The application according to claim 5, characterized in that, In step S2, the ratio of the pretreated soil to the powder of the curing agent is 100:3.5~8 by weight.

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