Environment-friendly roadbed filler with high-content ardealite cooperating with multiple solid wastes as well as preparation and application of environment-friendly roadbed filler

Abstract

The invention relates to an environment-friendly roadbed filler with high-content phosphogypsum cooperating with multiple solid wastes as well as preparation and application of the environment-friendly roadbed filler. The environment-friendly roadbed filler comprises the following raw material components in percentage by weight: 72-95% of phosphogypsum, 4-10% of an alkali-activated solid waste cementing material and the balance of clay. Compared with the prior art, through the synergistic effect of the ardealite, the alkali-activated solid waste cementing material and the clay, the mechanical property, the water stability, the environmental safety and the like of the ardealite-based filler are remarkably improved. The high-content ardealite and the multiple solid wastes are used as the roadbed filler, so that the requirements of roadbed engineering can be met, and the problem of large-scale resource utilization of the ardealite is solved.

Description

Technical Field

[0001] The present invention belongs to the technical fields of industrial solid waste resource utilization and road engineering materials, and relates to an environment-friendly subgrade filler with high phosphorus gypsum content synergistically combined with multiple solid wastes, and its preparation and application. Background Art

[0002] Phosphogypsum is a by-product generated during the production of phosphate fertilizer and phosphoric acid, and has a huge global stockpile. Up to now, the global stockpile of phosphogypsum has exceeded 6 billion tons, and its storage method is mostly open-air storage, which not only occupies a large amount of land, but also easily causes serious environmental problems such as water and soil pollution due to the presence of harmful substances such as soluble phosphorus, fluorine and heavy metals. In addition, the annual global output of phosphogypsum is about 200 million tons, but the recycling rate is only about 15%, and there is great potential for resource utilization.

[0003] Due to the large demand for filling in road construction, the resource utilization of phosphogypsum in road engineering has the characteristics of large consumption and high utilization rate, and is considered to be one of the most effective strategies for realizing large-scale resource utilization of phosphogypsum. However, the mechanical properties of phosphogypsum are insufficient (powder texture, low plasticity), water sensitivity is strong (swelling or cracking when encountering water, especially more significant at high phosphogypsum content), and the high environmental risk caused by leachable pollutants severely limit its direct application in road engineering. To address these problems, phosphogypsum is usually modified by blending with other materials, among which lime and fly ash are the most commonly used additives.

[0004] Although many schemes for resource utilization of phosphogypsum have been proposed in the prior art, the following problems still need to be urgently solved in practical applications: First, the application of phosphogypsum in road materials mainly focuses on doping as an auxiliary material, and it is rarely used as a main aggregate, which to a certain extent limits the efficiency of resource utilization of phosphogypsum in road engineering; Second, a few utilization schemes for high-phosphogypsum content mainly rely on traditional high-energy-consuming materials such as lime for stabilization treatment, lacking low-energy-consuming and sustainable additive modification schemes, and it is difficult to meet the requirements of sustainable development; Third, when traditional materials such as lime stabilize high-phosphogypsum content, insufficient consideration is given to the water stability and environmental safety performance of materials in a water-rich environment, resulting in limited applicability in complex environments.

[0005] As disclosed in CN202210539775.0, a phosphogypsum subgrade filler solidified by a silicoaluminate cementing material and its preparation method include the following ingredients: silicoaluminate cementing material, phosphogypsum and water. The components of the silicoaluminate cementing material include slag powder, fly ash and activator. The molar ratios of the components contained in the phosphogypsum subgrade filler are as follows: SO3:Al2O3 is 7.3 to 12.4; CaO:Al2O3 is 6.9 to 11.5; SiO2:Al2O3 is 5.0 to 6.9. However, upon analysis, since this patent uses a traditional chemical alkali activator of "sodium hydroxide and water glass", the residual sodium ions may pose a risk of soil salinization. At the same time, sodium hydroxide is a high-energy-consuming chemical product and does not meet the low-carbon goal. In addition, the obtained subgrade filler is prone to brittle failure, affecting long-term reliability. Summary of the Invention

[0006] The purpose of the present invention is to provide an environmentally friendly subgrade filler with high-dosage phosphogypsum synergistically combined with multiple solid wastes, and its preparation and application. Through effective solidification and stabilization treatment of high-dosage phosphogypsum by a specific all-solid-waste-based alkali-activated cementing material, the water stability and environmental safety of high-dosage phosphogypsum are significantly improved, and the problem of unqualified leaching performance is solved.

[0007] The purpose of the present invention can be achieved through the following technical solutions:

[0008] On the one hand, the present invention provides an environmentally friendly subgrade filler with high-dosage phosphogypsum synergistically combined with multiple solid wastes, which includes the following raw material components by weight percentage: 72-95% of phosphogypsum, 4%-10% of alkali-activated solid waste cementing material, and the rest is clay.

[0009] Further, the phosphogypsum is modified phosphogypsum pretreated by lime neutralization, dried at 40-55°C to a moisture content ≤2%, with a CaSO4·2H2O content ≥90% and a soluble impurity content ≤0.5%.

[0010] Further, the alkali-activated solid waste cementing material is composed of fly ash, slag powder and carbide slag in a compound manner.

[0011] Furthermore, the mass ratio of fly ash, slag powder and carbide slag is (1.5-2.5):(1.5-2.5):1, preferably 2:2:1.

[0012] Furthermore, the fly ash is a grayish-black powdery solid, and the mass ratio of particles with a particle size less than 0.075mm is 4.5%. The content of silicon oxide and aluminum oxide in the fly ash is greater than 80%.

[0013] Furthermore, the slag powder is S95 grade high-activity slag powder, with an off-white appearance, and the mass ratio of particles with a particle size less than 0.075mm accounts for 4%.

[0014] Furthermore, the carbide slag is high-calcium carbide slag, with a light gray appearance and a calcium hydroxide mass content higher than 80%.

[0015] Further, the clay is low liquid limit clay, with a liquid limit ≤ 50% and a plasticity index ≤ 30%.

[0016] In a second aspect, the present invention provides a method for preparing an environmentally friendly subgrade filler with high-amount phosphogypsum synergistically combined with multiple solid wastes. Mix the phosphogypsum, alkali-activated solid waste cementitious material and clay evenly, then add water for mixing (the optimal water content determined according to the compaction test), and compact (the compaction degree of the compaction process is determined by the maximum dry density obtained from the compaction test) to obtain the environmentally friendly subgrade filler.

[0017] In a third aspect, the present invention provides an application of an environmentally friendly subgrade filler with high-amount phosphogypsum synergistically combined with multiple solid wastes in the filling of road construction.

[0018] In the above solution, through the synergistic effect of three components, namely phosphogypsum, alkali-activated solid waste cementitious material and clay (attached Figure 1 ), the present invention conducts efficient solidification and stabilization treatment on high-amount phosphogypsum, which not only meets the requirements of physical and mechanical properties, road use performance indicators and environmental safety, but also significantly overcomes the problems of poor water stability and insufficient environmental safety of high-amount phosphogypsum. The specific principle is as follows:

[0019] The alkali-activated solid waste cementitious material in the present invention plays a role in the overall solidification and stabilization of the material. It solidifies high doses of PG to enhance its physical properties and stabilizes toxic substances to meet environmental compliance requirements.

[0020] In the present invention, the high-amount phosphogypsum, as the object to be solidified, can be largely consumed. At the same time, phosphogypsum can be used as a calcium source to provide abundant Ca 2+ and SO4 2- ions to promote the hydration reaction.

[0021] The clay in the present invention: (1) Improves toughness: The addition of clay soil increases the peak strain energy and reduces brittle failure. (2) Optimizes the pore structure: Forms a finer pore distribution mainly composed of micropores, improving water permeability resistance and long-term durability. (3) Forms C-A-S-H gel: The Al3+ derived from clay promotes the formation of C-A-S-H gel, and its long-term stability is better than that of C-S-H gel. Therefore, the clay component will significantly improve the long-term performance of the sample. The ternary synergistic relationship among phosphogypsum, alkali-activated solid waste cementitious material and clay in the present invention is as Figure 1 .

[0022] The alkali-activated solid waste cementitious material in the present invention is prepared by compounding fly ash, slag powder and carbide slag, and the selection of solid waste raw materials is based on their complementary characteristics. The slag powder mainly provides the development of early strength. Fly ash shows excellent long-term strength enhancement effect due to its low reactivity. While carbide slag is incorporated in a controlled proportion to adjust the pH value of the mixture. This alkali-activated system can effectively increase the alkalinity of the cementitious system, significantly promote the activation of fly ash and slag powder, and at the same time reduce the risk of alkali-aggregate reaction caused by excessive calcium hydroxide.

[0023] The comprehensive strength development mechanism in the present invention effectively improves the physical and mechanical properties and long-term stability of the environmentally friendly subgrade filler that synergistically utilizes high-volume phosphogypsum and various solid wastes. The main action mechanisms between the hydration products and the mechanical strength properties can be summarized as follows (attached Figure 2 ).

[0024] One of the strength development mechanisms of the subgrade filler of the present invention is the skeleton strengthening effect of ettringite crystals (AFt): Needle-like ettringite forms an interlaced network structure, tightly bonding phosphogypsum and soil particles together. This rigid skeleton significantly improves the bearing capacity by redistributing stress in the matrix, directly contributing to the higher unconfined compressive strength (UCS). The calcium sulfate provided by phosphogypsum reacts in an alkaline environment, promoting the formation of ettringite, thus providing sufficient early strength. The content of ettringite is closely related to the development of early strength.

[0025] Traditional alkaline activation materials such as sodium hydroxide and sodium silicate directly activate the activity of cementitious materials through strong alkalinity. While the present invention uses carbide slag (containing high Ca(OH)2) to synergistically adjust the pH value of the system through a slow-release alkaline environment, avoiding the risk of alkali-aggregate reaction caused by local over-alkalinity. At the same time, carbide slag is an industrial solid waste, which can achieve the coordinated disposal of multiple solid wastes without additional production, meeting the low-carbon goal.

[0026] Another strength development mechanism of the subgrade filler of the present invention is the bond strengthening effect of C-(A)-S-H gel: Amorphous C-(A)-S-H gel fills the micropores and mesopores, thus making the structure more dense. Bonding the loose particles together and reducing the stress concentration at the interface. The degree of polymerization of the gel determines the stability of the long-term strength. A higher gel content can significantly improve the unconfined compressive strength. The hydration products (including AFt, C-S-H and C-A-S-H) enhance the bonding between particles, thus significantly increasing the strength.

[0027] The third strength development mechanism of the subgrade filler of the present invention is the optimization of ion exchange and binding: The ion exchange between phosphogypsum, soil particles and the added alkali-activated solid waste cementitious material changes the bonding state and promotes the redistribution of mass, thus further increasing the strength. The Ca in phosphogypsum 2+ Exchanges with Al in soil and fly ash / slag 3+ and Si 4+ Occurs, enhancing the cohesion between particles and thus improving the overall strength.

[0028] The fourth strength development mechanism of the subgrade filler of the present invention is the carbonation reaction and pore filling effect: The carbonation reaction driven by CO2 in the atmosphere enhances the long-term stability of the material by precipitating CaCO3 in the pores. Phosphogypsum provides an abundant source of calcium ions, which react with carbon dioxide and water in the air under alkaline conditions to form CaCO3. Although CaCO3 is a precipitate rather than a crystal structure and cannot directly contribute to strength, it fills some of the voids in the structure, reduces the porosity, and thus improves the density and long-term strength of the material.

[0029] The present invention shows through toxicity leaching and radioactivity tests that the reaction system can effectively solidify the harmful components in phosphogypsum. The mechanism effectively fixes toxic elements in the material structure physically or chemically, minimizing their leaching risk and ensuring the environmental safety of the material. The improvement of its environmental safety is mainly attributed to the following mechanisms:

[0030] (1) Physical encapsulation: Dense C-(A)-S-H gel fixes heavy metals through physical adsorption and encapsulation, and the mutual filling and cementing effects between acicular calcium aluminofeldspar crystals and the gel further enhance the solidification effect.

[0031] (2) Chemical bonding: Toxic ions are chemically fixed by AFt crystals through ion exchange. For example, Cr 3 + can replace Ca in AFt 2+ and Al 3+ , while chromate (CrO4 2- ) and arsenate (AsO4 3- ) can replace sulfate (SO4 2- ), thus realizing the chemical solidification of harmful ions.

[0032] (3) Precipitation: F - reacts with Ca 2+ to form insoluble CaF2, and F - is mainly fixed in the material system in the form of CaF2, thus significantly reducing its leaching risk. Description of the Drawings

[0033] Figure 1 Diagram of the ternary synergistic relationship among phosphogypsum, alkali-activated solid waste cementitious material and clay;

[0034] Figure 2 Diagram of the strength growth mechanism of the environmentally friendly subgrade filler with high-dose phosphogypsum synergistic multi-solid waste

[0035] Figure 3 It is a flow chart for the preparation method and use of an environmentally friendly subgrade filler with high-dose phosphogypsum synergistically combined with multiple solid wastes.

[0036] Figure 4 This is a typical cross-sectional microscopic morphology picture of a scanning electron microscope image of the environmentally friendly subgrade filler with high-dose phosphogypsum synergistically combined with multiple solid wastes of the present invention, magnified 10,000 times. Detailed implementation manners

[0037] The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments. This embodiment is implemented on the premise of the technical solution of the present invention, and detailed implementation manners and specific operation processes are given. However, the protection scope of the present invention is not limited to the following embodiments.

[0038] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the technical field to which this application belongs. The terms used in the description of this application herein are only for the purpose of describing specific embodiments and are not intended to limit this application.

[0039] The selection range of the terms "and / or", "or / and", and "and / or" used herein includes any one of two or more related listed items, and also includes any and all combinations of the related listed items. The said any and all combinations include combinations of any two related listed items, any more related listed items, or all related listed items. It should be noted that when at least two conjunctions selected from "and / or", "or / and", and "and / or" are used to connect at least three items, it should be understood that in this application, this technical solution undoubtedly includes the technical solution connected by "logical AND", and also undoubtedly includes the technical solution connected by "logical OR".

[0040] In this application, among the technical features described in an open-ended manner, it includes a closed technical solution composed of the listed features, and also includes an open technical solution containing the listed features.

[0041] In this application, regarding numerical ranges, unless otherwise specified, the above numerical ranges are considered continuous and include the minimum and maximum values of the range, as well as each value between such minimum and maximum values. Further, when the range refers to an integer, it includes each integer between the minimum and maximum values of the range. In addition, when multiple ranges are provided to describe features or characteristics, these ranges can be combined. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all sub-ranges subsumed therein.

[0042] This document specifically discloses only some numerical ranges. However, any lower limit can be combined with any upper limit to form a range not explicitly recited; and any lower limit can be combined with other lower limits to form a range not explicitly recited, and similarly any upper limit can be combined with any other upper limit to form a range not explicitly recited. In addition, each individually disclosed point or single numerical value by itself can be used as a lower limit or upper limit and combined with any other point or single numerical value or combined with other lower limits or upper limits to form a range not explicitly recited.

[0043] In this application, the temperature parameter, unless otherwise specifically limited, allows both constant temperature treatment and treatment within a certain temperature range. The constant temperature treatment allows the temperature to fluctuate within the accuracy range controlled by the instrument. Fluctuations within ranges such as ±5°C, ±4°C, ±3°C, ±2°C, ±1°C are allowed.

[0044] In this document, the "suitable combination method", "suitable method", "any suitable method", etc., the "suitable" mentioned therein is subject to being able to implement the technical solution of this application, solve the technical problems of this application, and achieve the expected technical effects of this application.

[0045] In this application, "further", "even further", "especially", etc. are used for descriptive purposes and represent differences in content, but should not be construed as limiting the scope of protection of this application.

[0046] In this application, "optionally", "optional", "option", mean having or not having, that is, any one selected from the two alternative schemes of "having" or "not having". If "optional" appears multiple times in a technical solution, without special instructions and without contradictions or mutual restrictions, each "optional" is independent of each other.

[0047] In the description of the application, the meaning of "multiple" is at least two, such as two, three, etc., unless otherwise specifically and clearly defined.

[0048] Unless otherwise specified, all preparations and tests occur in an environment of 25°C in this document.

[0049] In this document, "comprises", "includes", "contains", "has", or other variants are intended to cover non-closed inclusion, and no distinction is made between these terms. The term "contains" means that other steps and components can be added without affecting the final result. The compositions and methods / processes of the present invention contain, consist of, and consist essentially of the essential elements and limitations described herein and any additional or optional components, ingredients, steps, or limitations described herein. In this document, no distinction is made between the terms "efficacy", "performance", "effect", and "function".

[0050] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined with each other to form new technical solutions. Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form new technical solutions.

[0051] Unless otherwise specified, all steps of this application can be carried out sequentially or randomly, and preferably sequentially.

[0052] In the following examples, the phosphogypsum used is the modified phosphogypsum that has been pre-treated by lime neutralization and stored in a certain phosphate ore plant in Guizhou. It is dried at 40 - 55 °C until the moisture content ≤ 2%, its CaSO4·2H2O content ≥ 90%, and the soluble impurity content ≤ 0.5%.

[0053] The fly ash used is sourced from Lingshou County, Hebei Province, China. It is a grayish-black powdery solid, and the proportion of particles with a particle size less than 0.075 mm is 4.5%. The content of silicon oxide and aluminum oxide in the fly ash is greater than 80%.

[0054] The mineral powder used is sourced from Zhengzhou, Henan, China. It is a high-activity S95-grade mineral powder, with an off-white appearance, and the proportion of particles with a particle size less than 0.075 mm is 4%.

[0055] The carbide slag used is from Dingyuan County, Chuzhou City, China. It is a high-calcium carbide slag, with a light gray appearance, and the calcium oxide content is higher than 80%.

[0056] The molar ratios of the chemical components of the above raw materials are as follows:

[0057] Table 1: Chemical composition of raw materials

[0058]

[0059] Note: LOI a Indicates the loss on ignition.

[0060] For the remaining raw materials or treatment technologies without special instructions, it means that they are all conventional commercially available raw materials or conventional treatment technologies in this field.

[0061] Example 1

[0062] This example provides an environmentally friendly subgrade filler with a high dosage of phosphogypsum synergistically combined with multiple solid wastes. This example uses three components: phosphogypsum, alkali-activated solid waste cementitious material, and clay, with the mass percentage ratio being: phosphogypsum 81%, alkali-activated solid waste cementitious material 9%, and clay 10%.

[0063] The alkali-activated solid waste cementitious material used is composed of fly ash, mineral powder, and carbide slag, and the three are compounded according to the mass ratio of 2:2:1.

[0064] The clay used in this embodiment is low liquid limit clay, and its physical property indexes are shown in Table 2.

[0065] Table 2 Basic Physical Indexes of the Clay Used in the Embodiment

[0066] <![CDATA[Maximum dry density (g / cm 3 )]]> Optimum moisture content (%) Liquid limit (%) Plastic limit (%) Plasticity index 1.95 12 45.1 18.2 26.9

[0067] For the preparation process of the subgrade filler in this embodiment, please refer to the appendix Figure 3 , and the specific preparation steps are as follows:

[0068] Step 1: Add the solid waste materials into the mixing equipment according to the mass ratio and conduct dry mixing evenly for 3 minutes to ensure the uniform distribution of each component, and obtain Mixture 1 (alkali-activated solid waste cementitious material).

[0069] Step 2: Fully stir the dried phosphogypsum and clay with Mixture 1 to obtain Mixture 2.

[0070] Step 3: Add the corresponding amount of water into Mixture 2 according to the optimum moisture content determined by the compaction test, and stir evenly to prepare Mixture 3 (high-content phosphogypsum subgrade filler).

[0071] The optimum moisture content obtained from the compaction test for the material mixing system in this embodiment is 16.06%, and the maximum dry density is 1.548 g / cm 3 . Prepare the moisture content and compaction specimen according to this data. Use the static pressing specimen method to make 3 cylindrical specimens with a diameter of Φ50×100 mm. After demolding, place them in a standard curing room with a humidity of 95% and a temperature of 20±2°C for curing; conduct the unconfined compressive strength test after curing for 7 days and 28 days to obtain the unconfined compressive strength of the specimen. At the same time, immerse them in water for 24 hours before conducting the unconfined compressive strength test to obtain the water stability coefficient. The test results are shown in Table 3. Calculate the peak strain energy of the material (Table 7) according to the stress-strain curve to characterize the energy absorption capacity and toughness of the material.

[0072] For the prepared high-content phosphogypsum subgrade filler in this embodiment, conduct the CBR and CBR expansion experiments in accordance with JTG 3430 - 2020, and the test results are shown in Table 4.

[0073] For the prepared high-content phosphogypsum subgrade filler in this embodiment, conduct the ICP-OES toxicity leaching test and radioactivity test on the samples cured for 28 days, and the test results are shown in Tables 5 and 6.

[0074] Example 2

[0075] This embodiment provides an environmentally friendly subgrade filler with high phosphorus gypsum content synergistically combined with multiple solid wastes. This embodiment uses three components: phosphorus gypsum, alkali-activated solid waste cementitious material, and clay, with the mass percentage ratio as follows: phosphorus gypsum 85.5%, alkali-activated solid waste cementitious material 4.5%, and clay 10%.

[0076] The used alkali-activated solid waste cementitious material is composed of fly ash, mineral powder, and carbide slag, which are compounded in a mass ratio of 2:2:1.

[0077] The clay used in this embodiment is low liquid limit clay, and its physical property indexes are shown in Table 1.

[0078] For the preparation process of the subgrade filler in this embodiment, please refer to the appendix Figure 3 , and the specific preparation steps are as follows:

[0079] Step 1: Add the solid waste materials into the mixing equipment according to the mass ratio and conduct dry mixing evenly for 3 minutes to ensure the uniform distribution of each component, obtaining Mixture 1 (alkali-activated solid waste cementitious material).

[0080] Step 2: Thoroughly mix the dried phosphorus gypsum and clay with Mixture 1 to obtain Mixture 2.

[0081] Step 3: According to the optimal moisture content determined by the compaction test, add the corresponding amount of water into Mixture 2 and stir evenly to prepare Mixture 3 (subgrade filler with high phosphorus gypsum content).

[0082] The optimal moisture content obtained from the compaction test for the material mixing system in this embodiment is 15.833%, and the maximum dry density is 1.538 g / cm 3 . According to this data, conduct moisture content preparation and compaction sample making. Use the static pressing sample making method to make 3 cylindrical specimens with a diameter of Φ50×100 mm. After demolding, place them in a standard curing room with a humidity of 95% and a temperature of 20±2°C for curing; conduct unconfined compressive strength tests after 7 days and 28 days of curing to obtain the unconfined compressive strength of the specimens. At the same time, immerse them in water for 24 hours before conducting the unconfined compressive strength test to obtain the water stability coefficient. The test results are shown in Table 3. According to the stress-strain curve, calculate the peak strain energy of the material (Table 7) to characterize the energy absorption capacity and toughness of the material.

[0083] For the prepared subgrade filler with high phosphorus gypsum content in this embodiment, conduct CBR and CBR expansion experiments in accordance with JTG 3430 - 2020, and the test results are shown in Table 4.

[0084] For the prepared subgrade filler with high phosphorus gypsum content in this embodiment, conduct ICP-OES toxicity leaching tests and radioactive tests on the samples cured for 28 days, and the test results are shown in Tables 5 and 6.

[0085] Table 3. Unconfined Compressive Strength and Water Stability Test Results of Examples

[0086]

[0087] Table 4. CBR and CBR Swelling Test Results of Examples

[0088] Number CBR value CBR expansion value Example 1 81.47％ 0.68％ Example 2 77.01％ 0.74％

[0089] Table 5. Radioactivity Test Results of Examples

[0090]

[0091] Table 6. Toxicity Leaching Test Results of Examples

[0092]

[0093]

[0094] Remark: a Not detected

[0095] Comparative Example 1:

[0096] This comparative example provides a subgrade filler with synergistic multi-solid waste of phosphogypsum. In this example, three components of phosphogypsum, alkali-activated solid waste cementitious material and clay are used, and the mass percentage ratio is: phosphogypsum 90%, alkali-activated solid waste cementitious material 10%, and clay 0%.

[0097] The used alkali-activated solid waste cementitious material is composed of fly ash, mineral powder and carbide slag, and the three are compounded according to the mass ratio of 2:2:1.

[0098] The clay used in this example is low liquid limit clay, and its physical property indexes are shown in Table 1.

[0099] For the preparation process of the subgrade filler in this example, please refer to the appendix Figure 3 , and the specific preparation steps are as follows:

[0100] Step 1: Add the solid waste materials into the mixing equipment according to the mass ratio and perform dry mixing evenly for 3 minutes to ensure the uniform distribution of each component, and obtain Mixture 1 (alkali-activated solid waste cementitious material).

[0101] Step 2: Fully stir the dried phosphogypsum with Mixture 1 to obtain Mixture 2.

[0102] Step 3: According to the optimum moisture content determined by the compaction test, add the corresponding amount of water into Mixture 2, stir evenly, and prepare to obtain Mixture 3 (high-ratio phosphogypsum subgrade filler).

[0103] The optimal moisture content of the material mixing system of this comparative example obtained by compaction test is 17.045%, and the maximum dry density is 1.607g / cm 3 , and the moisture content was prepared and compacted according to this data. Three cylindrical specimens of Φ50×100mm were made by static pressing. After demoulding, the two were placed in a standard curing room with a humidity of 95% and a temperature of 20±2℃ for curing; after curing for 7 days and 28 days, the unconfined compressive strength test was carried out to obtain the unconfined compressive strength of the specimens. According to the stress-strain curve, the peak strain energy of the material was calculated (Table 7) to characterize the energy absorption capacity and toughness of the material.

[0104] Comparative Example 2:

[0105] This comparative example provides a roadbed filler composed of phosphogypsum and multiple solid wastes. This embodiment adopts three components: phosphogypsum, alkali-activated solid waste cementitious material and clay. The proportions by mass percentage are: 45% phosphogypsum, 5% alkali-activated solid waste cementitious material and 50% clay.

[0106] The alkali-activated solid waste cementitious material used is composed of fly ash, mineral powder and carbide slag, which are compounded in a mass ratio of 2:2:1.

[0107] The clay used in this embodiment is low liquid limit clay, and its physical property indicators are shown in Table 1.

[0108] For the preparation process of the roadbed filler in this embodiment, please refer to the attached Figure 3 , the specific preparation steps are as follows:

[0109] Step 1: Add the solid waste materials into a stirring device according to the mass ratio and dry-mix them evenly for 3 minutes to ensure that the components are evenly distributed to obtain a mixture 1 (alkali-activated solid waste gelling material).

[0110] Step 2: Mix the dried phosphogypsum and clay with mixture 1 to obtain mixture 2.

[0111] Step 3: According to the optimum moisture content determined by the compaction test, a corresponding amount of water is added to the mixture 2, and the mixture is fully stirred to obtain the mixture 3 (high-dosage phosphogypsum roadbed filler).

[0112] The optimal moisture content of the material mixing system of this comparative example obtained by compaction test is 17.045%, and the maximum dry density is 1.607g / cm 3, the water content is formulated and the specimens are compacted according to this data. Three cylindrical specimens with a diameter of Φ50×100mm are made by the static compaction method. After demolding, both are placed in a standard curing room with a humidity of 95% and a temperature of 20±2°C for curing; the unconfined compressive strength test is carried out after 7 days and 28 days of curing to obtain the unconfined compressive strength of the specimens. According to the stress-strain curve, the peak strain energy of the material is calculated (Table 7), which characterizes the energy absorption capacity and toughness of the material.

[0113] Table 7. Calculation results of peak strain energy of the examples and comparative examples at 7d and 28d

[0114]

[0115]

[0116] Compared with Example 1, in Comparative Example 1, the ratio of phosphogypsum to alkali-activated solid waste cementitious material remains fixed. The difference lies in whether clay is introduced into the material system. By comparing the peak strain energy, the peak strain energy of Example 1 at 7d and 28d is significantly better than that of Comparative Example 1, reflecting the importance of introducing clay in the present invention. Compared with Example 1, in Comparative Example 2, the ratio of phosphogypsum to alkali-activated solid waste cementitious material remains fixed. The difference is that in Comparative Example 2, the introduction ratio of clay in the material system is increased to 50%. By comparing the peak strain energy, the peak strain energy of Example 1 at 7d and 28d is significantly better than that of Comparative Example 2, reflecting the importance that the introduction content of clay must be appropriate and cannot exceed the scope defined in this application.

[0117] According to the test results of the present invention, the environmentally friendly subgrade filler with high-ratio utilization of phosphogypsum and multiple solid wastes proposed by the present invention has material strength, bearing capacity requirements and environmental safety that can meet the actual application requirements. This material system realizes the large-scale utilization of high-ratio phosphogypsum and the collaborative disposal of other solid waste materials. The C-(A)-S-H gel, AFt needle-like crystals and gel network structure formed by the hydration of specific alkali-activated solid waste cementitious materials fill and bond the phosphogypsum matrix, significantly improving the microstructure and pore distribution of the material, thereby enhancing its mechanical properties and water stability. Such as Figure 4As shown by the SEM observation of the microscopic morphological features, the surface structure and particle morphology of the material can be intuitively analyzed. A large number of needle-like ettringite (AFt) gel-phase products are generated around the unreacted phosphogypsum particles, densifying the microstructure by filling the pore particles. At the same time, the needle-like crystals cement the particles to form an integral structure, and the hydration products aggregate to form a dense floc, forming a dense surface layer on the surface of the gypsum particles. At the same time, the needle-like AFt crystals are intertwined and connected with the gypsum and soil particles to form a stable reticular lattice structure. The ion exchange between phosphogypsum, soil particles, and alkali-activated solid waste cementitious materials also improves the bonding state of the materials, promotes mass redistribution, and enhances the overall mechanical properties. In addition, phosphogypsum provides an abundant calcium ion source, reacts with carbon dioxide and water in the air to form CaCO3, filling some voids in the overall structure and further enhancing the strength of the material. For the high-ratio phosphogypsum subgrade filler treated by solidification / stabilization, the leaching concentrations of heavy metal ions and radioactive substances are lower than the regulatory limits, confirming the environmental compliance of the material. This is mainly attributed to the physical encapsulation and chemical bonding of the hydrated cementitious products, as well as the mutual filling and cementing of the needle-like ettringite crystals and the gel, effectively fixing the harmful ions in the phosphogypsum. In addition, ion exchange in the toxic ions and crystals also plays an important role in the stabilization of heavy metal ions. The clay in the material system plays a role in enhancing the toughness of the material, avoiding the brittle failure problem of the material, and at the same time promoting the formation of C-A-S-H gel and optimizing the pore structure distribution, which is beneficial for improving the long-term service performance of the high-ratio phosphogypsum-based subgrade material in a water-rich environment.

[0118] The above description of the embodiments is provided to enable those of ordinary skill in the art to understand and use the invention. It is obvious that those skilled in the art can easily make various modifications to these embodiments and apply the general principles described herein to other embodiments without creative effort. Therefore, the present invention is not limited to the above embodiments, and the improvements and modifications made by those skilled in the art without departing from the scope of the present invention should be within the protection scope of the present invention.

Claims

1. An environment-friendly subgrade filler with high phosphorus gypsum content synergistically mixed with multiple solid wastes, characterized in that It comprises the following raw material components by weight percentage: 72-95% of phosphogypsum, 4%-10% of alkali-activated solid waste cementitious material, and the balance being clay.

2. The environmentally friendly subgrade filler with high-ratio phosphogypsum synergistically combined with multiple solid wastes according to claim 1, characterized in that, The phosphogypsum is modified phosphogypsum pretreated by lime neutralization, dried at 40-55°C to a moisture content of ≤2%, with a CaSO4·2H2O content of ≥90% and a soluble impurity content of ≤0.5%.

3. An environment-friendly subgrade filler with high phosphorus gypsum content and collaborative use of multiple solid wastes according to claim 1, characterized in that, The alkali-activated solid waste cementitious material is compounded from fly ash, slag powder and carbide slag.

4. An environment-friendly subgrade filler with high-content phosphogypsum synergistically co-treated with multiple solid wastes according to claim 3, characterized in that, The mass ratio of fly ash, slag powder and carbide slag is (1.5-2.5):(1.5-2.5):

1.

5. An environmentally friendly subgrade filler with high phosphorus gypsum content and multi-solid waste synergism according to claim 3, characterized in that The fly ash is a grayish-black powdery solid, and the mass ratio of particles with a size less than 0.075 mm is 4.5%. The content of silicon oxide and aluminum oxide in the fly ash is greater than 80%.

6. An environmentally friendly subgrade filler with high-content phosphogypsum synergistically combined with multiple solid wastes according to claim 3, characterized in that, The slag powder is S95 grade high-activity slag powder, with an off-white appearance, and the mass ratio of particles with a size less than 0.075 mm accounts for 4%.

7. An environmentally friendly subgrade filler with high-ratio phosphogypsum and multi-solid waste synergism according to claim 3, characterized in that, The carbide slag is high-calcium carbide slag, with a light gray appearance, and the mass content of calcium hydroxide is higher than 80%.

8. An environment-friendly subgrade filler with high phosphorus gypsum content synergistically combined with multiple solid wastes according to claim 1, characterized in that, The clay is low liquid limit clay, with a liquid limit of ≤50% and a plasticity index of ≤30%.

9. The preparation method of the environment-friendly roadbed filler with high phosphorus gypsum content synergistically treating multiple solid wastes according to any one of claims 1-8, characterized in that, The phosphogypsum, alkali-activated solid waste cementitious material and clay are stirred evenly, then mixed with water and compacted to obtain an environment-friendly roadbed filler.

10. Application of the environment-friendly roadbed filler with high-loading phosphogypsum synergistically combined with multiple solid wastes according to any one of claims 1-8 in road construction fill.

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