A phosphogypsum-based, highly absorbent, volume-stabilized roadbed filler, its preparation method, and its application.

Abstract

This invention belongs to the technical field of road engineering materials, and discloses a phosphogypsum-based high water absorption volume-stabilized roadbed filler, its preparation method, and its application. The phosphogypsum-based high water absorption volume-stabilized roadbed filler of this invention comprises the following raw materials in parts by weight: 70-90 parts phosphogypsum, 5-15 parts high water absorption volume-stabilized modifier, 3-9 parts curing agent, and 1-6 parts activation agent; wherein, the high water absorption volume-stabilized modifier uses anhydrous calcium sulfate and calcium aluminate as active components, which are obtained by surface modification with nano-silica and citric acid, followed by heating activation, and then coating with polydopamine. This invention, by introducing a high water absorption volume-stabilized modifier, solves the problem of easy softening and volume expansion of existing phosphogypsum roadbed fillers after water absorption, achieving stable utilization of phosphogypsum under high dosage conditions. The phosphogypsum-based high water absorption volume-stabilized roadbed filler of this invention is suitable for highway and railway subgrade filling, especially suitable for areas with high rainfall and high groundwater levels.

Description

Technical Field

[0001] This invention belongs to the field of road engineering materials technology, specifically relating to a phosphogypsum-based high water absorption volume-stabilized roadbed filler, its preparation method, and its application. Background Technology

[0002] Phosphogypsum is an industrial solid waste generated during the wet-process phosphoric acid production process, producing approximately 4-5 tons of phosphogypsum for every ton of phosphoric acid produced. While the annual production of phosphogypsum is enormous, its comprehensive utilization rate is low, and large-scale stockpiling not only occupies land resources but also causes serious environmental pollution. Using phosphogypsum as a filler in roadbeds for highways and railways is an effective way to achieve its large-scale resource utilization.

[0003] However, using phosphogypsum as a roadbed filler presents significant technical challenges. Firstly, phosphogypsum contains soluble phosphorus and fluorine impurities, which are easily dissolved in water, leading to a decrease in strength. Secondly, phosphogypsum softens and expands after absorbing water, causing uneven deformation and cracking of the roadbed. These problems are particularly pronounced in rainy areas or regions with high groundwater levels.

[0004] Existing technologies have attempted to improve water absorption capacity by introducing materials such as superabsorbent polymers (SAP) in an attempt to solve the aforementioned problems caused by phosphogypsum's water absorption. However, traditional absorbent materials exhibit significant volume expansion after absorbing water, introducing new problems and exacerbating the risk of roadbed deformation. Therefore, developing a phosphogypsum-based roadbed filler that combines high water absorption capacity with volume stability has significant engineering application value. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to address the shortcomings of the existing technology by providing a phosphogypsum-based high water absorption and volume-stable roadbed filler, its preparation method and application. By introducing a high water absorption and volume-stable modified material, the problem of easy softening and volume expansion of existing phosphogypsum roadbed fillers after water absorption is solved, and the stable utilization of phosphogypsum under high dosage conditions is realized.

[0006] To solve the technical problem proposed in this invention, this invention provides a phosphogypsum-based high water absorption and volume-stabilized roadbed filler, comprising the following raw materials in parts by weight: 70-90 parts of phosphogypsum, 5-15 parts of high water absorption and volume-stabilized modified material, 3-9 parts of curing agent, and 1-6 parts of active activator.

[0007] In the above scheme, the phosphogypsum has a calcium sulfate dihydrate content of ≥85%, a moisture content of ≤15%, a soluble phosphorus content (calculated as P2O5) of ≤0.3%, a fluoride content of ≤0.1%, and a pH of 6.5~8.0.

[0008] In the above scheme, the particle size of the phosphogypsum is <1.18mm.

[0009] In the above scheme, the highly absorbent volume-stable modified material uses anhydrous calcium sulfate and calcium aluminate as active components, which are modified with nano-silica and citric acid and then activated by heating before being coated with polydopamine. The specific preparation method is as follows: 1) Anhydrous calcium sulfate and calcium aluminate are mixed and then pulverized to obtain the active component; 2) Add nano-silica and citric acid to the active components, mix evenly, and then heat to activate to obtain the active substrate; 3) Dissolve dopamine hydrochloride in Tris-HCl buffer to obtain a dopamine monomer solution; 4) Add the active substrate to the dopamine monomer solution and stir to react, thereby obtaining a highly water-absorbing, volume-stable modified material.

[0010] Furthermore, the mass ratio of anhydrous calcium sulfate to calcium aluminate is 3:1 to 5:1.

[0011] Furthermore, the anhydrous calcium sulfate has a calcium sulfate content of ≥95% and a free water content of ≤0.5%.

[0012] Furthermore, the calcium aluminate has an aluminum oxide content of ≥50% and a calcium oxide content of ≤35%.

[0013] Furthermore, the particle size of the active component is 100-150 mesh.

[0014] Furthermore, the nano-silica is hydrophilic fumed nano-silica with a purity ≥99.5%, a particle size of 20~50nm, and a specific surface area of ​​150~250m². 2 / g.

[0015] Furthermore, the amount of nano-silica added is 1% to 3% of the mass of the active component.

[0016] Furthermore, the purity of the citric acid is ≥99%.

[0017] Furthermore, the amount of citric acid added is 0.1% to 0.5% of the mass of the active ingredient.

[0018] Furthermore, in step 2), high-speed mixing is used, with a mixing speed of 300~400 r / min and a mixing time of 10~20 min.

[0019] Furthermore, the heating activation temperature is 150~250℃, and the time is 1~2h.

[0020] Furthermore, the purity of the dopamine hydrochloride is ≥98%.

[0021] Furthermore, the pH of the Tris-HCl buffer solution is 7.0 to 9.0.

[0022] Furthermore, the concentration of dopamine in the dopamine monomer solution is 2-5 mg / mL.

[0023] Furthermore, the solid-liquid ratio of the active substrate and the dopamine monomer solution is 1:8 to 1:15 (g / mL).

[0024] Furthermore, the stirring reaction is carried out at room temperature for 12-24 hours, allowing polydopamine to self-polymerize and deposit on the surface of the active substrate particles.

[0025] Furthermore, the highly absorbent volume-stable modified material is filtered from the solution, washed sequentially with water and anhydrous ethanol, and then dried at 35~60℃.

[0026] In the above scheme, the curing agent is a mixture of steel slag powder, blast furnace slag powder and cement.

[0027] Furthermore, the mass ratio of the steel slag powder, blast furnace slag powder and cement is 1:(1.5~2.5):(2.0~4.0).

[0028] Furthermore, the cement is ordinary Portland cement with a strength grade ≥42.5, an initial setting time ≥45min, and a final setting time ≤600min.

[0029] Furthermore, the specific surface area of ​​the slag powder is ≥400m². 2 / kg, 28-day activity index ≥95%.

[0030] Furthermore, the specific surface area of ​​the steel slag powder is ≥450 m². 2 / kg, free calcium oxide content ≤3%, metallic iron content ≤1%.

[0031] In the above scheme, the active activator is a mixture of water-soluble aluminum salt and sodium silicate.

[0032] Furthermore, the mass ratio of water-soluble aluminum salt to sodium silicate is 1:2 to 1:4.

[0033] Furthermore, the water-soluble aluminum salt is aluminum sulfate, with an aluminum oxide content ≥15.5% and a pH value ≥2.5 for a 1% aqueous solution.

[0034] Furthermore, the sodium silicate has a modulus of 2 to 3 and a solid content of ≥40%.

[0035] In the above scheme, the roadbed filler material needs to be mixed with water to make the moisture content of the roadbed filler material 14%~16%.

[0036] Furthermore, the pH of the mixing water is 7-8.

[0037] In the above scheme, the saturated water absorption rate of the roadbed filler is 80 to 150 times its own mass, the volume expansion rate after water absorption is ≤1.5%, the time required to reach the saturated water absorption rate is ≤30 minutes, the CBR value is >8%, and the 7-day unconfined compressive strength is ≥0.7MPa, which meets the technical requirements of highway roadbed filler.

[0038] The present invention also provides a method for preparing the above-mentioned phosphogypsum-based high water absorption volume-stabilized roadbed filler, comprising the following steps: 1) After mixing the phosphogypsum with the curing agent and the activator evenly, add a portion of the mixing water and stir evenly; 2) Continue to add the high water absorption volume-stabilized modified material and the remaining mixing water, stir evenly, and obtain the roadbed filler.

[0039] In the above scheme, step 1) adds 70%~80% of the mixing water, and step 2) adds 20%~30% of the mixing water.

[0040] In the above scheme, the stirring rate after adding mixing water in step 1) is 150~250 r / min, and the stirring time is 1~2 min.

[0041] In the above scheme, the stirring rate after adding mixing water in step 2) is 450~600 r / min, and the stirring time is ≤30s.

[0042] The present invention also provides the application of the above-mentioned phosphogypsum-based high water absorption volume-stabilized roadbed filler in road subgrade. It is suitable for highway and railway subgrade filling, especially suitable for rainy areas with high groundwater levels. The application method is as follows: spread the mixed roadbed filler on the road, and then put it into use after rolling and curing.

[0043] In the above scheme, the mixed roadbed fill material is paved and compacted within 20 minutes.

[0044] In the above scheme, the maintenance is moisturizing maintenance, maintaining a moisture content of 14%~16% during the maintenance period, and putting it into use after 28 days of maintenance.

[0045] The main technical concept of this invention is as follows: This invention uses phosphogypsum as the main component of roadbed filler, which is the core carrier for the resource utilization of industrial solid waste in the entire system. Impurities such as phosphoric acid and fluorides in phosphogypsum can inhibit subsequent solidification reactions; therefore, this invention controls the impurity content of phosphogypsum. Even so, in its unmodified state, phosphogypsum still suffers from softening upon contact with water, volume expansion, and strength reduction. To address this, this invention introduces a highly absorbent and volume-stable modified material. This material is a crystallization-conversion type preferential water-absorbing material, made with anhydrous calcium sulfate and calcium aluminate as active components, modified with nano-silica and citric acid, and activated at low temperature. Its surface is coated with a polydopamine film. This material has the characteristics of preferentially capturing free water and maintaining volume stability after water absorption. When water enters the filler system, this material, with its active components, preferentially binds to free water before phosphogypsum, and converts free water into crystal water through a chemical hydration reaction. This quickly intercepts and blocks the channels for water migration to phosphogypsum, fundamentally preventing expansion and damage, maintaining volume stability, and improving the water stability and structural integrity of the filler. In the highly absorbent, volume-stable modified material of this invention, each raw material performs a different function, specifically including: The active components, composed of anhydrous calcium sulfate and calcium aluminate, react with water to form calcium sulfate dihydrate and ettringite-like hydration products, converting free water into water of crystallization and thus achieving rapid fixation of free water. This hydration reaction is accompanied only by slight expansion, fundamentally different from the water-absorbing swelling characteristic of traditional water-absorbing materials. In the presence of water, calcium aluminate reacts synergistically with anhydrous calcium sulfate and aluminum sulfate in the active activator to generate ettringite (AFt) and hydration products with a high water of crystallization content. Each mole of ettringite can bind 32 moles of water of crystallization, significantly enhancing the material's water absorption capacity. Furthermore, the introduction of calcium aluminate not only improves the water absorption rate but also enhances the compactness of the filler structure by forming needle-like ettringite crystals that fill the pores, thereby improving the material's strength. Nano-silica and citric acid are used as modifying components. Nano-silica, with its extremely high surface activity, is uniformly dispersed on the surface of anhydrous calcium sulfate and calcium aluminate particles during dry mixing. Firstly, it improves particle size distribution through physical filling. Furthermore, during low-temperature activation, it undergoes surface activation with calcium and aluminum ions, enhancing the reactivity of the active components and enabling them to bind free water more quickly and fully in subsequent hydration reactions. Simultaneously, the addition of nano-silica reacts with calcium hydroxide in the anhydrous calcium sulfate system to form hydrated calcium silicate (CSH) gel. This reaction itself produces chemical shrinkage, offsetting the micro-expansion caused by the hydration of anhydrous calcium sulfate. Citric acid, acting as a crystal growth regulator, adsorbs onto the surface of anhydrous calcium sulfate and calcium aluminate particles during dry mixing, inhibiting excessive sintering and crystal coarsening during low-temperature activation. This maintains the active components' high specific surface area and reactivity, ensuring rapid response to moisture intrusion in roadbed fillers. Polydopamine, as a coating component, undergoes a self-polymerization reaction of dopamine hydrochloride in Tris-HCl buffer, depositing a polydopamine film on the surface of active substrate particles. This film remains dense and stable under acidic to neutral conditions, effectively isolating the active component from external moisture and preventing premature hydration during storage, transportation, and initial mixing. When an alkaline environment (pH≥9) is created by the activator, the phenolic hydroxyl groups in the polydopamine film undergo deprotonation, the film structure gradually relaxes, and the active component is released slowly, thus achieving precise timing matching with the compaction and curing process of the roadbed filler. This slow-release mechanism ensures both the operability of the construction window and the continued water absorption and conversion function of the active component after the roadbed is formed.

[0046] This invention also utilizes a curing agent composed of cement, slag powder, and steel slag powder to jointly construct the main strength and long-term water stability of the filler. Cement provides an early alkaline environment, hydrating to generate calcium hydroxide and hydrated calcium silicate gel. This gel serves two purposes: firstly, it binds phosphogypsum particles and modified high-absorbency, non-expanding material particles; secondly, it provides alkaline activation conditions for the pozzolanic reaction of slag powder and steel slag powder. The main chemical components of slag powder are calcium silicate and calcium aluminosilicate glass. Under the combined action of calcium hydroxide generated from cement hydration and the active activator, a pozzolanic reaction occurs, generating secondary hydrated calcium silicate and ettringite, further densifying the filler structure and improving later-stage strength and impermeability. Steel slag powder contains active minerals such as dicalcium silicate and tricalcium silicate, exhibiting certain self-cementing properties. Simultaneously, its iron and magnesium phases promote the diverse development of hydration products. The introduction of slag powder and steel slag powder not only enhances the cementing ability of the curing system but also achieves the synergistic utilization of various industrial solid wastes, reducing material costs.

[0047] This invention also uses an active activator composed of water-soluble aluminum sulfate and sodium silicate. Aluminum sulfate, when dissolved in water, hydrolyzes to become acidic. However, when mixed with phosphogypsum and a curing agent, the system becomes alkaline due to the formation of calcium hydroxide from cement hydration. The aluminum ions in the aluminum sulfate rapidly transform into aluminum hydroxide colloid, which further reacts with silicate and sulfate ions to form hydrated aluminates and ettringite, promoting early strength development of the filler. Sodium silicate hydrolyzes to generate silicate ions and sodium hydroxide, significantly increasing the pH of the system and providing the necessary alkaline conditions (pH≥9) for the structural relaxation of the polydopamine membrane, thus activating the slow-release water absorption function of the modified superabsorbent and non-swelling material. Furthermore, silicate ions react with calcium ions to form hydrated calcium silicate gel, which synergistically binds with the hydration products of the curing agent, further enhancing the integrity and water stability of the filler.

[0048] In terms of preparation process, the present invention adopts a step-by-step water addition process. 70% to 80% of the water volume is added first to fully hydrate the curing agent and form a preliminary mixed system. The remaining 20% ​​to 30% of the water is quickly mixed when the high water absorption volume-stable modifier is added. Taking advantage of its preferential water absorption characteristics, the active components begin the hydration reaction before rolling, quickly fix the free water, and prevent water from migrating to the phosphogypsum matrix.

[0049] Compared with the prior art, the beneficial effects of the present invention are as follows: 1) This invention introduces a highly absorbent, volume-stable modified material. The chemical hydration reaction of its active components converts free water into crystal water, resulting in slight volume shrinkage after water absorption. This avoids the expansion and damage problems of traditional absorbent materials. At the same time, by rapidly intercepting free water, it blocks the path of water migration to the phosphogypsum matrix. Its polydopamine film layer relaxes under alkaline activation conditions, allowing the active components to be released slowly. This matches the alkaline environment of the curing agent in the roadbed filler, achieving a synergistic effect of water absorption and curing. This improves the long-term water stability of the filler, thus solving the technical problems of easy softening and volume expansion of existing phosphogypsum roadbed fillers after water absorption. It also enables the stable utilization of phosphogypsum under high dosage conditions.

[0050] 2) This invention uses a curing agent composed of cement, slag powder and steel slag powder to jointly build the main strength and long-term water stability of the filler. The introduction of slag powder and steel slag powder not only enhances the bonding ability of the curing system, but also realizes the synergistic utilization of various industrial solid wastes, reduces material costs, and has significant environmental benefits.

[0051] 3) The roadbed filler of this invention has good adaptability to construction process. By adding water in stages and mixing rapidly, the dispersion and activation timing of the modified high water absorption and non-expansion material are controlled, ensuring that it can play a priority water absorption function before the roadbed is compacted. The construction window period is reasonable and it is convenient for on-site operation. Attached Figure Description

[0052] Figure 1 This is a photograph of the roadbed filler prepared in Example 1 of the present invention after 7 days of curing. Detailed Implementation

[0053] To better understand the present invention, the following embodiments further illustrate the content of the present invention, but the content of the present invention is not limited to the following embodiments.

[0054] The phosphogypsum used in the following examples is dihydrate phosphogypsum, a byproduct of the wet-process phosphoric acid production. Its main chemical component is calcium sulfate dihydrate, with a content of ≥85%. Since impurities such as phosphoric acid and fluoride remaining in the wet-process phosphoric acid production process can inhibit the subsequent curing reaction, pretreatment steps such as washing, neutralization, and drying are used to ensure that the phosphogypsum has a moisture content of ≤15%, a soluble phosphorus content (calculated as P2O5) of ≤0.3%, a fluoride content of ≤0.1%, a pH of 6.5~8.0, and a particle size of <1.18mm.

[0055] The anhydrous calcium sulfate used in the following examples is industrial grade, with a calcium sulfate content ≥95% and a free water content ≤0.5%; the calcium aluminate is industrial grade, with an alumina content ≥50% and a calcium oxide content ≤35%; the nano-silica is hydrophilic fumed silica, with a purity ≥99.5%, a particle size of 20~50nm, and a specific surface area of ​​150~250m². 2 / g; Citric acid is industrial grade citric acid monohydrate, purity ≥99%; Dopamine hydrochloride is industrial grade, purity ≥98%; Cement is P·O 42.5 ordinary Portland cement, initial setting time ≥45min, final setting time ≤600min; Slag powder is granulated blast furnace slag, specific surface area ≥400m² 2 / kg, 28-day activity index ≥95%; steel slag powder is converter steel slag, specific surface area ≥450m² 2 / kg, free calcium oxide content ≤3%, metallic iron content ≤1%; water-soluble aluminum salt is industrial grade aluminum sulfate octadechydrate, alumina content ≥15.5%, 1% aqueous solution pH value ≥2.5; sodium silicate modulus is 2~3, solid content ≥40%; mixing water meets the requirements of JGJ 63 "Standard for Water Used in Concrete", pH value is 7~8, and it does not contain harmful impurities such as oil, acid, alkali, and organic matter.

[0056] Example 1 A phosphogypsum-based, highly absorbent, volume-stabilized roadbed filler comprises the following raw materials in parts by weight: 80 parts phosphogypsum, 10 parts highly absorbent, volume-stabilized modified material, 6 parts curing agent, and 3 parts activation agent. After removing the moisture from the phosphogypsum, 7 parts of water are added to bring the moisture content to 15%. The curing agent is a mixture of steel slag powder, blast furnace slag powder, and cement in a mass ratio of 1:2:3. The activation agent is a mixture of water-soluble aluminum salt and sodium silicate in a mass ratio of 1:3. The preparation method of the highly absorbent, volume-stabilized modified material is as follows: 1) Anhydrous calcium sulfate and calcium aluminate were mixed at a mass ratio of 4:1 and then pulverized to obtain an active component with a particle size of 120 mesh; 2) Add 2% by weight of nano-silica (30nm particle size) and 0.3% by weight of citric acid to the active component. Mix at high speed of 400r / min for 15min, then heat to 200℃ for 1.5h to activate and obtain the active substrate. 3) Dissolve dopamine hydrochloride in Tris-HCl buffer at pH 8.5 to obtain a dopamine monomer solution with a dopamine concentration of 3 mg / mL; 4) Add the active substrate to the dopamine monomer solution, with a solid-liquid ratio of 1:10. Stir and react for 18 hours. Filter out the solids, wash them with deionized water and anhydrous ethanol in sequence, and dry them at 40°C to obtain a highly water-absorbing, volume-stable modified material.

[0057] The preparation and construction of the phosphogypsum-based high water absorption volume-stabilized roadbed filler in this embodiment includes the following steps: 1) After mixing the phosphogypsum with the curing agent and the activator evenly, add 80% of the mixing water and stir at 150 r / min for 1.5 min; 2) Continue to add the high water absorption volume-stabilized modified material and the remaining 20% ​​of the mixing water, stir at 450 r / min for 25 s to obtain the mixed roadbed filler; 3) Spread and compact the mixed subgrade fill within 18 minutes, then keep it moist and maintain the moisture content at 14%~16% during the curing period. It can be put into use after 28 days of curing.

[0058] Example 2 A phosphogypsum-based, highly absorbent, volume-stabilized roadbed filler comprises the following raw materials in parts by weight: 70 parts phosphogypsum, 15 parts highly absorbent, volume-stabilized modified material, 9 parts curing agent, and 6 parts activation agent. After removing the moisture from the phosphogypsum, 8.5 parts of water are added to bring the moisture content to 15.5%. The curing agent is a mixture of steel slag powder, blast furnace slag powder, and cement in a mass ratio of 1:1.5:2.5. The activation agent is a mixture of water-soluble aluminum salt and sodium silicate in a mass ratio of 1:2.5. The preparation method of the highly absorbent, volume-stabilized modified material is as follows: 1) Anhydrous calcium sulfate and calcium aluminate were mixed at a mass ratio of 3:1 and then pulverized to obtain an active component with a particle size of 100 mesh; 2) Add 1% by weight of nano-silica (particle size 20nm) and 0.1% by weight of citric acid to the active component. Mix at high speed of 350r / min for 20min, then heat to 150℃ for 2h to activate and obtain the active substrate. 3) Dissolve dopamine hydrochloride in Tris-HCl buffer at pH 8 to obtain a dopamine monomer solution with a dopamine concentration of 2 mg / mL; 4) Add the active substrate to the dopamine monomer solution with a solid-liquid ratio of 1:12. Stir and react for 24 hours. Filter the solid and wash it with deionized water and anhydrous ethanol in sequence. Dry at 40°C to obtain a highly water-absorbing and volume-stable modified material.

[0059] The preparation and construction of the phosphogypsum-based high water absorption volume-stabilized roadbed filler in this embodiment includes the following steps: 1) After mixing the phosphogypsum with the curing agent and the activator evenly, add 75% of the mixing water and stir at 200 r / min for 2 min; 2) Continue to add the high water absorption volume-stabilized modified material and the remaining 25% of the mixing water, stir at 500 r / min for 30 s to obtain the mixed roadbed filler; 3) Spread and compact the mixed roadbed fill within 20 minutes, then keep it moist and maintain the moisture content at 14%~16% during the curing period. It can be put into use after 28 days of curing.

[0060] Example 3 A phosphogypsum-based, highly absorbent, volume-stabilized roadbed filler comprises the following raw materials in parts by weight: 90 parts phosphogypsum, 5 parts highly absorbent, volume-stabilized modified material, 3 parts curing agent, and 1 part activation agent. After removing the moisture from the phosphogypsum, 5.36 parts of water are added to bring the moisture content to 14.5%. The curing agent is a mixture of steel slag powder, blast furnace slag powder, and cement in a mass ratio of 1:1.5:3. The activation agent is a mixture of water-soluble aluminum salt and sodium silicate in a mass ratio of 1:2. The preparation method of the highly absorbent, volume-stabilized modified material is as follows: 1) Anhydrous calcium sulfate and calcium aluminate were mixed at a mass ratio of 5:1 and then pulverized to obtain an active component with a particle size of 150 mesh; 2) Add 3% by weight of nano-silica (50nm particle size) and 0.5% by weight of citric acid to the active component. Mix at 400r / min for 10min and then heat to 250℃ for 1h to activate and obtain the active substrate. 3) Dissolve dopamine hydrochloride in Tris-HCl buffer at pH 9 to obtain a dopamine monomer solution with a dopamine concentration of 5 mg / mL; 4) Add the active substrate to the dopamine monomer solution with a solid-liquid ratio of 1:8. Stir and react for 12 hours. Filter the solid and wash it with deionized water and anhydrous ethanol in sequence. Dry at 40°C to obtain a highly water-absorbing, volume-stable modified material.

[0061] The preparation and construction of the phosphogypsum-based high water absorption volume-stabilized roadbed filler in this embodiment includes the following steps: 1) After mixing the phosphogypsum with the curing agent and the activator evenly, add 70% of the mixing water and stir at 250 r / min for 1 min; 2) Continue to add the high water absorption volume-stabilized modified material and the remaining 30% of the mixing water, stir at 600 r / min for 20 s to obtain the mixed roadbed filler; 3) Spread and compact the mixed roadbed fill within 15 minutes, then keep it moist and maintain the moisture content at 14%~16% during the curing period. It can be put into use after 28 days of curing.

[0062] Example 4 A phosphogypsum-based, highly absorbent, volume-stabilized roadbed filler comprises the following raw materials in parts by weight: 75 parts phosphogypsum, 12 parts highly absorbent, volume-stabilized modified material, 7 parts curing agent, and 4 parts activation agent. After removing the moisture from the phosphogypsum, 7.2 parts of water are added to bring the moisture content to 15%. The curing agent is a mixture of steel slag powder, blast furnace slag powder, and cement in a mass ratio of 1:2:3. The activation agent is a mixture of water-soluble aluminum salt and sodium silicate in a mass ratio of 1:3. The preparation method of the highly absorbent, volume-stabilized modified material is as follows: 1) Anhydrous calcium sulfate and calcium aluminate were mixed at a mass ratio of 4.5:1 and then pulverized to obtain an active component with a particle size of 120 mesh; 2) Add 2.5% by mass of nano-silica (40nm particle size) and 0.4% by mass of citric acid to the active component. Mix at high speed of 350r / min for 12min, then heat to 220℃ for 1.2h to activate and obtain the active substrate. 3) Dissolve dopamine hydrochloride in Tris-HCl buffer at pH 9 to obtain a dopamine monomer solution with a dopamine concentration of 4 mg / mL; 4) Add the active substrate to the dopamine monomer solution, with a solid-liquid ratio of 1:15. Stir and react for 20 hours. Filter the solids and wash them with deionized water and anhydrous ethanol in sequence. Dry at 40°C to obtain a highly water-absorbing, volume-stable modified material.

[0063] The preparation and construction of the phosphogypsum-based high water absorption volume-stabilized roadbed filler in this embodiment includes the following steps: 1) After mixing the phosphogypsum with the curing agent and the activator evenly, add 80% of the mixing water and stir at 200 r / min for 1.8 min; 2) Continue to add the high water absorption volume-stabilized modified material and the remaining 20% ​​of the mixing water, stir at 500 r / min for 22 s to obtain the mixed roadbed filler; 3) Spread and compact the mixed subgrade fill within 16 minutes, then keep it moist and maintain the moisture content at 14%~16% during the curing period. It can be put into use after 28 days of curing.

[0064] Example 5 A phosphogypsum-based, highly absorbent, volume-stabilized roadbed filler comprises the following raw materials in parts by weight: 85 parts phosphogypsum, 8 parts highly absorbent, volume-stabilized modified material, 5 parts curing agent, and 2 parts activation agent. After removing the moisture from the phosphogypsum, 6 parts of water are added to bring the moisture content to 14.5%. The curing agent is a mixture of steel slag powder, blast furnace slag powder, and cement in a mass ratio of 1:2.5:4. The activation agent is a mixture of water-soluble aluminum salt and sodium silicate in a mass ratio of 1:3. The preparation method of the highly absorbent, volume-stabilized modified material is as follows: 1) Anhydrous calcium sulfate and calcium aluminate were mixed at a mass ratio of 3.5:1 and then pulverized to obtain an active component with a particle size of 140 mesh; 2) Add 1.5% by mass of nano-silica (particle size 25nm) and 0.2% by mass of citric acid to the active component, mix at high speed of 400r / min for 18min, and then heat to 180℃ for 1.8h to obtain the active substrate; 3) Dissolve dopamine hydrochloride in Tris-HCl buffer at pH 8.5 to obtain a dopamine monomer solution with a dopamine concentration of 2.5 mg / mL; 4) Add the active substrate to the dopamine monomer solution, with a solid-liquid ratio of 1:10. Stir and react for 22 hours. Filter the solids and wash them with deionized water and anhydrous ethanol in sequence. Dry at 40°C to obtain a highly water-absorbing, volume-stable modified material.

[0065] The preparation and construction of the phosphogypsum-based high water absorption volume-stabilized roadbed filler in this embodiment includes the following steps: 1) After mixing the phosphogypsum with the curing agent and the activator evenly, add 70% of the mixing water and stir at 250 r / min for 1.2 min; 2) Continue to add the high water absorption volume-stabilized modified material and the remaining 30% of the mixing water, stir at 600 r / min for 28 s to obtain the mixed roadbed filler; 3) Spread and compact the mixed subgrade fill within 17 minutes, then keep it moist and maintain the moisture content at 14%~16% during the curing period. It can be put into use after 28 days of curing.

[0066] Comparative Example 1 The only difference between Comparative Example 1 and Example 1 is that no highly absorbent volume-stabilized modifier is added.

[0067] Comparative Example 2 The only difference between Comparative Example 2 and Example 1 is that the superabsorbent volume-stabilized modified material was replaced with commercially available sodium polyacrylate superabsorbent polymer (SAP).

[0068] Comparative Example 3 The only difference between Comparative Example 3 and Example 1 is that steps 3) and 4) are omitted when preparing the highly absorbent volume-stable modified material, and the active substrate without polydopamine coating is used directly as the highly absorbent volume-stable modified material.

[0069] The performance of the subgrade fillers obtained in each embodiment and comparative example was tested. The test methods were as follows: the CBR (California Bearing Ratio) value was determined according to T / CECS 1757-2024 "Standard Test Methods for Stabilized Soil in Road Engineering"; the unconfined compressive strength was determined according to the provisions of JTG 3441-2024 "Test Procedures for Inorganic Binder Stabilized Materials in Highway Engineering" (T0805), with the specimen size being a cylinder with a diameter of 150 mm and a height of 150 mm; the saturated water absorption rate test was conducted according to the weighing method framework for moisture content test in GB / T 50123-2019 "Standard Geotechnical Test Methods"; the volume expansion rate after water absorption was measured according to the measurement framework of expansion rate test in Chapter 25 of GB / T 50123-2019 "Standard Geotechnical Test Methods", and the volume expansion rate after reaching saturated water absorption rate was tested; the water absorption rate was determined according to ASTM C1585-20 "Standard Test Method for Measurement of Rate of Absorption of Water". The water absorption kinetics of Hydraulic Cement Concrete are demonstrated by the time required to reach saturation water absorption. All tests were conducted using samples cured for 7 days, and the results are shown in Table 1.

[0070] Table 1

[0071] As shown in Table 1, the roadbed filler of the present invention can achieve the synergistic effects of high water absorption (saturated water absorption rate is 80 to 150 times its own mass), stable volume (volume expansion rate after water absorption is ≤1.5%), and fast water absorption rate (time required to reach saturated water absorption rate is ≤30 min). Moreover, the CBR value is >8% and the 7-day unconfined compressive strength is ≥0.7MPa, which meets the technical requirements of highway roadbed filler.

[0072] Comparative Example 1, without the addition of a highly absorbent and volume-stabilized modifier, exhibited poor water absorption capacity, significant volume expansion, and insufficient mechanical properties, failing to meet the requirements for roadbed filler. Comparative Example 2 used commercially available sodium polyacrylate superabsorbent resin, which, while possessing a high and rapid water absorption rate, caused rapid volume expansion after water absorption, easily leading to uneven deformation of the roadbed and offering limited strength improvement. Comparative Example 3 directly used an uncoated active substrate. Due to the lack of a slow-release regulation mechanism, the active components prematurely contacted and reacted with moisture during preparation, resulting in poor water absorption, volume expansion, and a decreased strength improvement effect.

[0073] The above embodiments are merely examples for clear illustration and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations, and any obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A phosphogypsum-based, highly absorbent, volume-stabilized roadbed filler, characterized in that, The raw materials include the following parts by weight: 70-90 parts of phosphogypsum, 5-15 parts of high water absorption volume-stabilized modifier, 3-9 parts of curing agent, and 1-6 parts of activator; the high water absorption volume-stabilized modifier is prepared by coating polydopamine with anhydrous calcium sulfate and calcium aluminate as active components after surface modification with nano silica and citric acid and heating activation.

2. The phosphogypsum-based high-water-absorption, volume-stabilized roadbed filler according to claim 1, characterized in that, The preparation method of the highly water-absorbing, volume-stable modified material is as follows: 1) Anhydrous calcium sulfate and calcium aluminate are mixed and then pulverized to obtain the active component; 2) Add nano-silica and citric acid to the active components, mix evenly, and then heat to activate to obtain the active substrate; 3) Dissolve dopamine hydrochloride in Tris-HCl buffer to obtain a dopamine monomer solution; 4) Add the active substrate to the dopamine monomer solution and stir to react, thereby obtaining a highly water-absorbing, volume-stable modified material.

3. The phosphogypsum-based high water absorption volume-stabilized roadbed filler according to claim 2, characterized in that, The mass ratio of anhydrous calcium sulfate to calcium aluminate is 3:1 to 5:1; the particle size of the active component is 100 to 150 mesh; the amount of nano silica added is 1% to 3% of the mass of the active component; the amount of citric acid added is 0.1% to 0.5% of the mass of the active component; the temperature for heating activation is 150 to 250°C, and the time is 1 to 2 hours.

4. The phosphogypsum-based high water absorption volume-stabilized roadbed filler according to claim 2, characterized in that, The pH of the Tris-HCl buffer solution is 7.0~9.0; the concentration of dopamine in the dopamine monomer solution is 2~5 mg / mL; the solid-liquid ratio of the active substrate and the dopamine monomer solution is 1:8~1:15, and the reaction time is 12~24h; the highly absorbent volume-stable modified material is washed sequentially with water and anhydrous ethanol, and then dried at 35~60℃.

5. The phosphogypsum-based high water absorption volume-stabilized roadbed filler according to claim 1, characterized in that, The phosphogypsum has a particle size <1.18mm, a calcium sulfate dihydrate content ≥85%, a moisture content ≤15%, a soluble phosphorus content (calculated as P2O5) ≤0.3%, a fluoride content ≤0.1%, and a pH of 6.5~8.0; the curing agent is a mixture of steel slag powder, blast furnace slag powder, and cement; the activation agent is a mixture of water-soluble aluminum salt and sodium silicate; the roadbed filler requires the addition of mixing water during use to ensure that the moisture content of the roadbed filler is 14%~16%.

6. The phosphogypsum-based high-water-absorption, volume-stabilized roadbed filler according to claim 1, characterized in that, The curing agent is a mixture of steel slag powder, blast furnace slag powder, and cement in a mass ratio of 1:(1.5~2.5):(2.0~4.0); the cement is ordinary Portland cement with a strength grade ≥42.5, initial setting time ≥45min, and final setting time ≤600min; the blast furnace slag powder has a specific surface area ≥400m². 2 / kg, 28-day activity index ≥95%; specific surface area of ​​the steel slag powder ≥450m² 2 / kg, free calcium oxide content ≤3%, metallic iron content ≤1%.

7. The phosphogypsum-based high water absorption volume-stabilized roadbed filler according to claim 1, characterized in that, The active activator is a mixture of water-soluble aluminum salt and sodium silicate in a mass ratio of 1:2 to 1:4; the water-soluble aluminum salt is aluminum sulfate with an alumina content ≥15.5% and a pH value ≥2.5 for a 1% aqueous solution; the sodium silicate has a modulus of 2 to 3 and a solid content ≥40%; the nano-silica is hydrophilic fumed silica with a particle size of 20 to 50 nm and a specific surface area of ​​150 to 250 m². 2 / g.

8. A method for preparing a phosphogypsum-based, highly absorbent, volume-stabilized roadbed filler as described in any one of claims 1 to 7, characterized in that, Includes the following steps: 1) After mixing the phosphogypsum with the curing agent and the activator evenly, add a portion of the mixing water and stir evenly; 2) Continue to add the high water absorption volume-stabilized modified material and the remaining mixing water, stir evenly, and obtain the roadbed filler.

9. The preparation method of the phosphogypsum-based high water absorption volume-stabilized roadbed filler according to claim 8, characterized in that, Step 1) Add 70%~80% of the mixing water, mix at a rate of 150~250 r / min, and mix for 1~2 min; Step 2) Add 20%~30% of the mixing water, mix at a rate of 450~600 r / min, and mix for ≤30 s; The mixed subgrade fill should be laid and compacted within 20 min, and put into use after 28 days of moisture curing.

10. The application of a phosphogypsum-based high water absorption volume-stabilized subgrade filler as described in any one of claims 1 to 7 in road subgrades.

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