High-content phosphogypsum pavement base material and preparation method thereof

Abstract

The application discloses a high-doped phosphogypsum pavement base material and a preparation method thereof, and belongs to the field of pavement base materials. The material comprises, by weight, 7-9 parts of a binding agent, 30-45 parts of phosphogypsum artificial fine aggregate, 45-60 parts of phosphogypsum artificial coarse aggregate and 0.05-0.1 parts of water glass; wherein the binding agent is formed by mixing 3.5-4.5 parts of phosphogypsum, 3-3.5 parts of slag powder, 0.3-0.7 parts of cement and 0.2-0.3 parts of phosphorus slag powder. The phosphogypsum artificial aggregate is prepared by mixing phosphogypsum, slag powder, cement, a performance regulator, water and a water reducing agent, and then pouring, curing, crushing, shaping and screening. The preparation method of the material comprises three steps of pretreating aggregate, mixing materials and shaping and curing. The application realizes high-doped utilization of phosphogypsum, solves the technical problems that the utilization rate of phosphogypsum and the road performance cannot be simultaneously considered and the construction convenience is poor in the current phosphogypsum pavement base material, and the obtained material has good road performance.

Description

Technical Field

[0001] This invention relates to the field of road base materials, specifically to a road base material with high phosphogypsum content and its preparation method. Background Technology

[0002] With the development of industrial production, the stockpiled amount of phosphogypsum, an industrial byproduct generated during the production of phosphate fertilizers, phosphoric acid, and their derivatives, is increasing year by year. This not only occupies a large amount of land resources but also may cause environmental pollution. Applying phosphogypsum to road base materials is one of the important ways to realize its resource utilization. Currently, there has been considerable research on the application of phosphogypsum in road base materials both domestically and internationally, and some progress has been made.

[0003] Phosphogypsum pavement base materials can be classified into three categories according to their raw material composition and material form: powder type, aggregate type, and fluid type. Powder type phosphogypsum pavement base materials are made by mixing phosphogypsum with cementitious materials, curing agents, and other auxiliary materials before being used as the pavement base. For example, patent CN114804773A proposes a composite solid waste pavement base binder, which is composed of pretreated alkaline phosphogypsum powder mixed with fly ash, slag powder, and cement. This binder can improve the strength of the pavement base, reduce shrinkage and cracking, and reduce cement usage, thus lowering costs. Patent CN119430836A discloses a phosphogypsum road base material comprising 850-900 parts phosphogypsum, 5-15 parts quicklime, 40-60 parts cement, 55-85 parts composite curing agent, and 8.5-13 parts curing activator. Through modification treatment of the phosphogypsum, the soluble phosphorus and soluble fluorine in the phosphogypsum are cured, improving the strength and stability of the base material.

[0004] Aggregate-based phosphogypsum pavement base material is prepared by mixing phosphogypsum, cementitious materials, curing agents, and auxiliary materials with aggregates. The aggregates are either natural aggregates or phosphogypsum aggregates prepared by centrifugal rolling, extrusion, or other methods, with phosphogypsum as the main raw material. For example, CN119638356A discloses a high-content phosphogypsum-cement stabilized crushed stone mixture, the raw materials of which, by weight, include 100-120 parts graded crushed stone, 60-80 parts phosphogypsum, 5-10 parts cement, 1-3 parts curing agent, and 5-15 parts water. By activating the undisturbed phosphogypsum with cement and curing agent, and stabilizing the crushed stone with water, the problem of poor engineering performance of phosphogypsum is solved. In their study, "Application Research of Modified Phosphogypsum Lightweight Aggregate in Subgrade Materials" (published in *Concrete & Cement Products*, 2022, No. 6, pp. 82-86), Lü Wei et al. proposed granulating phosphogypsum into pellets and sieving to obtain phosphogypsum lightweight aggregate, which could then partially replace crushed stone in the preparation of road stabilization layers. When the phosphogypsum content in the lightweight aggregate was 88%, the 7-day unconfined compressive strength of the stabilized layer was ≥3 MPa.

[0005] Flowable phosphogypsum road base material is made by mixing phosphogypsum, cementitious materials, aggregates, etc., then adding water and admixtures to form a base mixture with a certain degree of fluidity, which is then cast on-site. For example, CN119191800A proposes a self-compacting phosphogypsum road base material, whose components, by mass percentage, include 40-55% phosphogypsum, 4-13% cementitious materials, 35-50% aggregates, and 0.2-0.7% admixtures. This base material achieves an SF1 slump spread index (550-655mm) and a slump spread time T0. 500 Reaching VS1 level (≥2s), it has low cement consumption and high phosphogypsum utilization, which can effectively overcome or avoid the occurrence of early diseases in road base courses.

[0006] However, while the application of phosphogypsum in road base courses shows great promise, limitations in utilization methods make it difficult to achieve a balance between phosphogypsum utilization rate, road performance of base materials, ease of construction, and practicality. This restricts the large-scale application of phosphogypsum in road base courses. Specifically, the following problems exist:

[0007] First, in powdered phosphogypsum pavement base materials, phosphogypsum is not easy to mix evenly with the binder, requiring multiple rolling operations with various types of rollers, making construction complicated, and the compaction degree is difficult to meet the standard requirements, resulting in poor road performance and easy for pavement to suffer from defects after it is put into use.

[0008] Secondly, the addition of ordinary aggregates to aggregate-based phosphogypsum pavement base materials reduces the utilization rate of phosphogypsum. Furthermore, the low strength and predominantly rounded particle shape of the added phosphogypsum aggregates result in poor interlocking between aggregates, negatively impacting the performance of the base material.

[0009] Finally, the fluidized phosphogypsum pavement base material increases the construction process, requiring the installation of templates and the cutting and filling of joints, which makes it impractical and difficult to use on road sections with large longitudinal and transverse slopes.

[0010] Therefore, there is an urgent need to develop a high-content phosphogypsum pavement base material that can improve the utilization rate of phosphogypsum, ensure the road performance of the pavement base material, and have good construction convenience and practicality. Summary of the Invention

[0011] To address the problems existing in phosphogypsum pavement base materials regarding utilization rate, road performance, construction convenience, and practicality, this invention provides a high-dosage phosphogypsum pavement base material and its preparation method.

[0012] The technical solution adopted by this invention to solve its technical problem is as follows:

[0013] First, the present invention provides a high-content phosphogypsum pavement base material, which, by weight, comprises the following raw materials: 7-9 parts binder, 30-45 parts phosphogypsum artificial fine aggregate, 45-60 parts phosphogypsum artificial coarse aggregate, and 0.05-0.1 parts water glass.

[0014] Preferably, the binder is composed of the following components in parts by weight: 3.5 to 4.5 parts phosphogypsum, 3 to 3.5 parts slag powder, 0.3 to 0.7 parts cement, and 0.2 to 0.3 parts phosphogypsum powder.

[0015] Preferably, the phosphogypsum artificial fine aggregate and phosphogypsum artificial coarse aggregate are prepared by the following process: 45-55 parts of phosphogypsum, 25-37 parts of slag powder, 0-5 parts of cement, 5-8 parts of performance regulator, 0.23-0.24 times the total solid mass of water and 0.02-0.025 times the polycarboxylate superplasticizer are added, mixed and stirred, and then poured, cured, mechanically crushed, shaped and screened to form particles with gradation and particle shape that meet the requirements.

[0016] Preferably, the performance regulator is prepared by drying and mixing the following components in parts by weight: 2-3 parts fly ash, 1.5-2.5 parts metakaolin, 1-1.5 parts silica fume, and 0.5-1 parts steel slag powder.

[0017] The performance modifier can shorten the setting time of cast phosphogypsum artificial aggregate base material, accelerate strength growth, improve strength, and enhance its volume stability.

[0018] Preferably, the modulus of the water glass is 1.5 to 2.5. Low-modulus water glass has a higher content of free sodium oxide and stronger alkalinity, which can rapidly activate slag powder, accelerate hydration, and improve early strength. However, excessive alkalinity can lead to a loose structure of hydration products in the later stages, affecting later strength growth and the performance of the base material. High-modulus water glass, on the other hand, has a weaker early activation effect and slower strength development, but the hydration products have a denser structure, resulting in stable later strength development. Experimental verification of this invention confirms that water glass within this modulus range provides phosphogypsum pavement base material with good early strength and road performance.

[0019] Preferably, the phosphogypsum is undisturbed phosphogypsum with a particle size of less than 2.36 mm after being crushed; since undisturbed phosphogypsum is mostly in a water-containing state, crushing it through a 2.36 mm sieve is more practical and can ensure the quality of phosphogypsum aggregate and the performance of base material.

[0020] Preferably, the cement is P·O42.5 cement, the slag powder is S95 grade granulated blast furnace slag powder, and the polycarboxylate superplasticizer has a solid content of 8~12% and a water reduction rate of ≥25%.

[0021] Preferably, the phosphogypsum artificial coarse aggregate is a mixture of nominal particle sizes of 4.75-9.5 mm and 9.5-26.5 mm, in a ratio of 1:6-9, and meets the following specifications: for nominal particle sizes of 4.75-9.5 mm, the percentage of mass passing through a 13.2-mesh sieve is 100%, the percentage passing through a 9.5-mesh sieve is 90-100%, the percentage passing through a 4.75-mesh sieve is 0-10%, and the percentage passing through a 2.36-mesh sieve is 0-5%; for nominal particle sizes of 9.5-26.5 mm, the percentage of mass passing through a 31.5-mesh sieve is 100%, the percentage passing through a 26.5-mesh sieve is 90-100%, the percentage passing through a 9.5-mesh sieve is 0-10%, and the percentage passing through a 4.75-mesh sieve is 0-5%.

[0022] The phosphogypsum artificial fine aggregate meets the specification requirements of nominal particle size 0-4.75mm, with 100% of the mass passing through a 9.5mm sieve, 90-100% of the mass passing through a 4.75mm sieve, and 0-15% of the mass passing through a 0.075mm sieve.

[0023] This invention also provides a method for preparing the high-content phosphogypsum pavement base material, comprising the following steps:

[0024] (1) Pre-treatment of aggregates: Add water to the fine phosphogypsum artificial aggregate at a level 2-3% higher than its saturated surface dry water absorption rate, stir evenly, and let it sit for 24-48 hours; immerse the coarse phosphogypsum artificial aggregate in water for more than 24 hours, and drain until there is no water standing.

[0025] (2) Mixing materials: Mix the binder and pretreated phosphogypsum artificial coarse and fine aggregates evenly; dissolve water glass in water, add it to the mixture and mix evenly;

[0026] (3) Molding and curing: The mixture is molded and cured to obtain the base material.

[0027] The "saturated water + drained water" pretreatment process in this preparation method can solve the problem of the high water absorption rate of phosphogypsum aggregate affecting the construction state of the base material and ensure the construction performance of the base material.

[0028] Preferably, the simmering material in step (1) is sealed; in step (3), the water glass must be completely dissolved in water before the mixture is added.

[0029] Preferably, the amount of pretreated coarse and fine aggregates in step (2) is calculated based on the actual moisture content. Actual aggregate usage = dry mass of aggregate × (1 + moisture content after saturation).

[0030] Preferably, in step (2), the amount of water used = total water consumption - dry mass of aggregate × (moisture content after saturation - saturated surface dry water absorption rate), and the total water consumption is determined according to the compaction test.

[0031] The beneficial effects of this invention are as follows:

[0032] 1. Compared with powdered phosphogypsum pavement base materials, the base material of the present invention has good mixture uniformity, can be constructed with reference to traditional water-stabilized materials, and can achieve a compaction degree similar to that of traditional water-stabilized materials. The process is mature and the road performance is good.

[0033] 2. Compared with aggregate-type phosphogypsum pavement base materials, the base material of this invention, phosphogypsum artificial aggregate, has high strength, can completely replace ordinary aggregate, has tight interlocking between particles, high utilization rate of phosphogypsum, and good road performance.

[0034] 3. Compared with fluidized phosphogypsum pavement base materials, the base material of the present invention has strong versatility, is applicable to construction of the entire road section, and has a mature and simple construction process.

[0035] 4. This invention reduces the use of cement and ordinary aggregates in highway base construction, with the vast majority of raw materials being solid waste, thus saving resources and energy while effectively alleviating ecological and environmental pressures.

[0036] 5. The high-content phosphogypsum pavement base material of this invention has an unconfined compressive strength of 5.6 MPa at 7 days and 7.2 MPa at 28 days, and is suitable for base and subbase layers of expressways and first-class highways. Detailed Implementation

[0037] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0038] The processes, conditions, reagents, and experimental methods used in implementing this invention, except as specifically mentioned below, are all common knowledge and general knowledge in the field, and this invention does not have any particular limitations. Experimental methods in the embodiments that do not specify specific conditions are generally performed under conventional conditions or according to the conditions specified in relevant standards and procedures.

[0039] Unless otherwise stated, all technical terms and scientific terms used in this specification have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. However, in the event of any conflict, the specification containing the definitions shall prevail.

[0040] Example 1

[0041] The high-content phosphogypsum pavement base material of the present invention comprises the following raw materials in parts by weight: 8 parts binder, 38 parts phosphogypsum artificial fine aggregate, 52 parts phosphogypsum artificial coarse aggregate, and 0.07 parts water glass.

[0042] The binder is composed of 4 parts by weight of phosphogypsum, 3.3 parts by weight of slag powder, 0.5 parts by weight of cement, and 0.2 parts by weight of phosphate slag powder.

[0043] The artificial coarse and fine aggregates made from 50 parts by weight of phosphogypsum, 31 parts by weight of slag powder, 2.5 parts by weight of cement, 6.5 parts by weight of performance modifier, 21.15 parts by weight of water and 2.25 parts by weight of polycarboxylate superplasticizer are mixed and stirred, cast into molds and cured for 7 days, and then mechanically crushed, shaped and screened.

[0044] The modulus of the water glass is 2.0.

[0045] The phosphogypsum has a particle size of less than 2.36 mm, the cement is P·042.5 cement, and the slag powder is S95 grade granulated blast furnace slag powder.

[0046] The performance regulator is composed of 2.5 parts by weight of fly ash, 2 parts by weight of metakaolin, 1.3 parts by weight of silica fume, and 0.7 parts by weight of steel slag powder, which are mixed after drying.

[0047] The polycarboxylate superplasticizer has a solid content of 10% and a water reduction rate of 27%.

[0048] The phosphogypsum-based coarse and fine aggregates have the following specifications:

[0049] Phosphogypsum-based artificial coarse aggregate: a mixture of nominal particle sizes of 4.75-9.5mm and 9.5-26.5mm, in a ratio of 1:7.5. Its specifications are shown in Table 1. Table 1: Specifications of phosphogypsum-based artificial coarse aggregate in this embodiment.

[0050]

[0051] b. Phosphogypsum artificial fine aggregate: nominal particle size is 0-4.75mm, and the specific specifications are shown in Table 2 below.

[0052] Table 2 Specifications of phosphogypsum-based artificial fine aggregates in this embodiment

[0053]

[0054] The preparation method of the phosphogypsum-based road base material specifically includes the following steps:

[0055] Step 1: The saturated surface-dry water absorption rate of the phosphogypsum coarse aggregate was determined to be 5.7%, and the initial moisture content of the phosphogypsum fine aggregate was 4.5%, with a saturated surface-dry water absorption rate of 12.5%. Add 10% of the phosphogypsum fine aggregate's own weight in water (the amount of water added exceeds the surface-dry water absorption rate by 2%), stir evenly, and seal for 24 hours. Place the phosphogypsum coarse aggregate in water to saturate and absorb water for 24 hours, then remove and drain until no more water flows out. Measure the moisture content of the phosphogypsum coarse and fine aggregates after saturation; the coarse aggregate was 6.1%, and the fine aggregate was 13.8%.

[0056] Step 2: Weigh each component material. The actual mass of coarse and fine phosphogypsum aggregate = dry mass of coarse and fine phosphogypsum aggregate × (1 + water content after saturation). The actual mass of water = total water consumption - dry mass of coarse and fine phosphogypsum aggregate × (water content after saturation - water absorption rate of saturated surface dry material). The total water consumption was determined to be 5.7 parts by compaction test. See Table 3 for specific dosage.

[0057] Table 3. Theoretical and actual proportions of each material used in the preparation of this embodiment.

[0058]

[0059] Step 3: Mix the weighed binder and phosphogypsum artificial coarse and fine aggregates evenly to obtain a mixture. Dissolve water glass in water, mix it thoroughly, and then pour it into the evenly mixed mixture to obtain a base material mixture.

[0060] Step 4: Pour the mixture into a mold, shape and cure it to obtain the high-content phosphogypsum pavement base material.

[0061] Example 2

[0062] The high-content phosphogypsum pavement base material of the present invention comprises the following raw materials in parts by weight: 7 parts binder, 30 parts phosphogypsum artificial fine aggregate, 45 parts phosphogypsum artificial coarse aggregate, and 0.05 parts water glass.

[0063] The binder is composed of 3.5 parts by weight of phosphogypsum, 3 parts by weight of slag powder, 0.3 parts by weight of cement, and 0.2 parts by weight of phosphogypsum powder. The phosphogypsum-based artificial coarse and fine aggregates are made by mixing 45 parts by weight of phosphogypsum, 25 parts by weight of slag powder, and 5 parts by weight of performance modifier, then adding 17.25 parts by weight of water and 1.5 parts by weight of polycarboxylate superplasticizer, mixing, casting, curing for 7 days, and then mechanically crushing, shaping, and screening.

[0064] The modulus of the water glass is 2.5.

[0065] The phosphogypsum has a particle size of less than 2.36 mm, the cement is P·042.5 cement, and the slag powder is S95 grade granulated blast furnace slag powder.

[0066] The performance regulator is composed of 2 parts by weight of fly ash, 1.5 parts by weight of metakaolin, 1 part by weight of silica fume, and 0.5 parts by weight of steel slag powder, which are mixed after drying.

[0067] The polycarboxylate superplasticizer has a solid content of 10% and a water reduction rate of 27%.

[0068] The phosphogypsum-based coarse and fine aggregates have the following specifications:

[0069] Phosphogypsum-based artificial coarse aggregate: a. A mixture of nominal particle sizes of 4.75-9.5mm and 9.5-26.5mm, in a ratio of 1:6, with specifications shown in Table 4. Table 4 Specifications of phosphogypsum-based artificial coarse aggregate in this embodiment.

[0070]

[0071] Phosphogypsum-based artificial fine aggregate: nominal particle size 0-4.75mm, specific specifications are shown in Table 5 below. Table 5 Specifications of phosphogypsum-based artificial fine aggregate in this embodiment

[0072]

[0073] This invention also provides a method for preparing a phosphogypsum-based road base material, specifically including the following steps:

[0074] Step 1: The saturated surface-dry water absorption rate of the phosphogypsum coarse aggregate was determined to be 6.1%, and the initial moisture content of the phosphogypsum fine aggregate was 3.4%, with a saturated surface-dry water absorption rate of 12.9%. Add 11.5% (by weight) of water (the amount of water added exceeds the surface-dry water absorption rate by 2%) to the phosphogypsum fine aggregate, stir thoroughly, and seal for 36 hours. Place the phosphogypsum coarse aggregate in water to saturate and absorb water for 24 hours, then remove and drain until no more water flows out. Measure the moisture content of the phosphogypsum coarse and fine aggregates after saturation; the coarse aggregate is 6.5%, and the fine aggregate is 14.3%.

[0075] Step 2: Weigh each component material. Actual mass of coarse and fine phosphogypsum aggregate = dry mass of coarse and fine phosphogypsum aggregate × (1 + water content after saturation). Actual mass of water = water consumption - dry mass of coarse and fine phosphogypsum aggregate × (water content after saturation - saturated surface dry water absorption rate). The water consumption was determined to be 5.7 parts by compaction test. See Table 6 for specific dosage.

[0076] Table 6 shows the theoretical and actual proportions of each material used in the preparation of this embodiment.

[0077]

[0078] Step 3: Mix the weighed binder and phosphogypsum artificial coarse and fine aggregates evenly to obtain a mixture. Dissolve water glass in water, mix it thoroughly, and then pour it into the evenly mixed mixture to obtain a base material mixture.

[0079] Step 4: Pour the mixture into a mold, shape and cure it to obtain the high-content phosphogypsum pavement base material.

[0080] Example 3

[0081] The high-content phosphogypsum pavement base material of the present invention comprises the following raw materials in parts by weight: 9 parts binder, 45 parts phosphogypsum artificial fine aggregate, 60 parts phosphogypsum artificial coarse aggregate, and 0.1 parts water glass.

[0082] The binder is composed of 4.5 parts by weight of phosphogypsum, 3.5 parts by weight of slag powder, 0.7 parts by weight of cement, and 0.3 parts by weight of phosphogypsum powder. The phosphogypsum-based artificial coarse and fine aggregates are made by mixing 55 parts by weight of phosphogypsum, 37 parts by weight of slag powder, 5 parts by weight of cement, and 8 parts by weight of performance modifier, then adding 25.2 parts by weight of water and 2.625 parts by weight of polycarboxylate superplasticizer, mixing, casting, curing for 7 days, and then mechanically crushing, shaping, and screening.

[0083] The modulus of the water glass is 1.5.

[0084] The phosphogypsum has a particle size of less than 2.36 mm, the cement is P·042.5 cement, and the slag powder is S95 grade granulated blast furnace slag powder.

[0085] The performance regulator is composed of 3 parts by weight of fly ash, 2.5 parts by weight of metakaolin, 1.5 parts by weight of silica fume, and 1 part by weight of steel slag powder, which are mixed after drying.

[0086] The polycarboxylate superplasticizer has a solid content of 10% and a water reduction rate of 27%.

[0087] The phosphogypsum-based coarse and fine aggregates have the following specifications:

[0088] Phosphogypsum-based artificial coarse aggregate: a. A mixture of nominal particle sizes of 4.75-9.5mm and 9.5-26.5mm, in a ratio of 1:9, with specifications shown in Table 7. Table 7 Specifications of phosphogypsum-based artificial coarse aggregate in this embodiment.

[0089]

[0090] Phosphogypsum artificial fine aggregate: nominal particle size is 0-4.75mm, and the specific specifications are shown in Table 8 below. Table 8 Specifications of phosphogypsum artificial fine aggregate in this embodiment

[0091]

[0092] This invention also provides a method for preparing a phosphogypsum-based road base material, specifically including the following steps:

[0093] Step 1: The saturated surface-dry water absorption rate of the phosphogypsum coarse aggregate was determined to be 5.5%, and the initial moisture content of the phosphogypsum fine aggregate was 4.0%, with a saturated surface-dry water absorption rate of 12.2%. Add 11.2% of the phosphogypsum fine aggregate's own weight in water (the amount of water added exceeds the surface-dry water absorption rate by 3%), stir evenly, and seal for 48 hours. Place the phosphogypsum coarse aggregate in water to saturate and absorb water for 24 hours, then remove and drain until no more water flows out. Measure the moisture content of the phosphogypsum coarse and fine aggregates after saturation; the coarse aggregate was 6.0%, and the fine aggregate was 13.1%.

[0094] Step 2: Weigh each component material. The actual mass of coarse and fine phosphogypsum aggregate = dry mass of coarse and fine phosphogypsum aggregate × (1 + water content after saturation). The actual mass of water = water consumption - dry mass of coarse and fine phosphogypsum aggregate × (water content after saturation - water absorption rate of saturated surface dry material). The water consumption was determined to be 5.7 parts by compaction test. See Table 9 for specific dosage.

[0095] Table 9. Theoretical and actual proportions of each material used in the preparation of this embodiment.

[0096]

[0097] Step 3: Mix the weighed binder and phosphogypsum artificial coarse and fine aggregates evenly to obtain a mixture. Dissolve water glass in water, mix it thoroughly, and then pour it into the evenly mixed mixture to obtain a base material mixture.

[0098] Step 4: Pour the mixture into a mold, shape and cure it to obtain the high-content phosphogypsum pavement base material.

[0099] Comparative Example 1 differs from Example 1 in that the raw materials for preparing phosphogypsum artificial aggregate do not contain performance modifiers; otherwise, they are the same as in Example 1.

[0100] Comparative Example 2 differs from Example 1 in that the water glass modulus is 3.0, while the rest is the same as Example 1.

[0101] Comparative Example 3 differs from Example 1 in that the water glass modulus is 1.0, while the rest is the same as Example 1.

[0102] Comparative Example 4 differs from Example 1 in that the phosphogypsum-based fine aggregate was not subjected to pre-treatment with saturated water, and the phosphogypsum-based coarse aggregate was not subjected to saturated water-draining treatment. After the base material was mixed, the dry density was determined by a compaction test, and specimens were molded at this dry density. Due to the water absorption of phosphogypsum, the actual water content of the base material was lower than the optimum water content, and the dry density was lower than the maximum dry density in Example 1. The rest was the same as in Example 1.

[0103] Comparative Example 5 differs from Example 1 in that the phosphogypsum-based fine aggregate was not subjected to pre-saturation water treatment, and the phosphogypsum-based coarse aggregate was not subjected to saturation water draining treatment. The water usage also differs; the water usage is calculated as: water usage in Example 1 + saturated surface-dry water absorption of the phosphogypsum aggregate in Example 1. After mixing the base material, the dry density was determined through a compaction test, and specimens were molded at this dry density. Due to the influence of the water absorption and absorption rate of the phosphogypsum aggregate, the actual water content of the base material was higher than the optimum water content, and this dry density was less than the maximum dry density in Example 1. The rest was the same as in Example 1.

[0104] The performance of the base course materials prepared in Examples 1-3 and Comparative Examples 1-5 was tested according to the "Test Procedure for Inorganic Binder Stabilized Materials in Highway Engineering". The results are shown in Table 10.

[0105] Table 10. Performance of base materials in the examples and comparative examples

[0106]

[0107] The results of Examples 1-3 demonstrate that the high-content phosphogypsum pavement base material of this invention can achieve an unconfined compressive strength of 5.1-5.6 MPa at 7 days and 6.5-7.2 MPa at 28 days, making it suitable for base and subbase courses of expressways and Class I highways. It can completely replace ordinary aggregates, exhibits tight interlocking of particles, high utilization rate of phosphogypsum, and good road performance.

[0108] Compared with Example 1, Comparative Example 1 shows that the performance modifier has a significant impact on the performance of the base material. The performance modifier can improve the strength of phosphogypsum aggregate, improve its volume stability, and indirectly enhance the performance of the base material.

[0109] Compared with Example 1, Comparative Examples 2-3 show that the modulus of water glass has a significant impact on strength. A modulus that is too high has a weak activating effect on mineral powder, which affects the strength growth of the base material. A modulus that is too low can effectively improve early strength, but it will lead to a loose structure of the hydration products of the base material in the later stage, which will affect the later strength growth and the performance of the base material.

[0110] Comparative Examples 4-5, compared to Example 1, demonstrate the crucial role of phosphogypsum aggregate pretreatment. The "saturated water + drained water" process effectively addresses the impact of high water absorption by phosphogypsum aggregate on the construction condition of the base material. When base material is prepared using unequal-hydrated phosphogypsum aggregate, it continuously absorbs water during and after mixing, making it impossible to determine whether the base material is at its optimal moisture content during molding. The actual moisture content often deviates significantly from the optimal moisture content, thus affecting the compaction degree and reducing the performance of the base material.

[0111] The applicant declares that the above description is only a few embodiments of this application and is not intended to limit this application in any way. Although this application discloses preferred embodiments as described above, it is not intended to limit this application. Any changes or modifications made by those skilled in the art without departing from the scope of the technical solution of this application using the disclosed technical content are equivalent to equivalent implementation cases and all fall within the scope of the technical solution.

Claims

1. A high-content phosphogypsum pavement base material, characterized in that, The product comprises, by weight, the following raw materials: 7-9 parts binder, 30-45 parts phosphogypsum-based fine aggregate, 45-60 parts phosphogypsum-based coarse aggregate, and 0.05-0.1 parts water glass; wherein the binder is composed of the following components in parts by weight: 3.5-4.5 parts phosphogypsum, 3-3.5 parts slag powder, 0.3-0.7 parts cement, and 0.2-0.3 parts phosphogypsum slag powder; The phosphogypsum artificial fine aggregate and phosphogypsum artificial coarse aggregate are prepared by the following process: 45-55 parts of phosphogypsum, 25-37 parts of slag powder, 0-5 parts of cement, 5-8 parts of performance regulator are added to 0.23-0.24 times the total solid mass of water and 0.02-0.025 times the polycarboxylate superplasticizer. After mixing and stirring, the mixture is poured, cured, mechanically crushed, shaped, and screened to form particles with the required gradation and particle shape. The performance regulator is composed of the following components in parts by weight, which are dried and mixed: 2-3 parts fly ash, 1.5-2.5 parts metakaolin, 1-1.5 parts silica fume, and 0.5-1 parts steel slag powder; The modulus of the water glass is 1.5 to 2.

5.

2. The high-content phosphogypsum pavement base material according to claim 1, characterized in that: The phosphogypsum coarse aggregate is a mixture of 4.75-9.5 mm and 9.5-26.5 mm nominal particle sizes, with a ratio of 1:6-9. The phosphogypsum fine aggregate has a nominal particle size of 0-4.75 mm.

3. The high-content phosphogypsum pavement base material according to claim 1, characterized in that: The polycarboxylate superplasticizer has a solid content of 8-12% and a water reduction rate of ≥25%.

4. The high-content phosphogypsum pavement base material according to claim 1, characterized in that... The phosphogypsum is undisturbed phosphogypsum with a particle size <2.36mm after being crushed; the cement is P·O42.5 cement, and the slag powder is S95 grade granulated blast furnace slag powder.

5. A method for preparing a high-content phosphogypsum pavement base material as described in any one of claims 1 to 4, characterized in that, Includes the following steps: (1) Pre-treatment of aggregates: Add water to fine aggregates at a level 2-3% higher than their saturated surface dry water absorption rate, stir evenly, and let the aggregates sit for 24-48 hours; immerse coarse aggregates in water for more than 24 hours, and drain until there is no standing water. (2) Mixed materials: Mix the binder, pretreated phosphogypsum fine aggregate and phosphogypsum coarse aggregate evenly; dissolve water glass in water, add it to the mixture and mix evenly; (3) Molding and curing: The mixture is molded and cured to obtain the base material.

6. The preparation method according to claim 5, characterized in that, The amount of pretreated phosphogypsum fine aggregate and phosphogypsum coarse aggregate in step (2) is calculated based on the actual moisture content. The amount of pretreated aggregate = dry mass of aggregate × (1 + moisture content after saturation).

7. The preparation method according to claim 5, characterized in that, In step (2), the amount of water used = total water consumption - dry mass of aggregate × (moisture content after saturation - saturated surface dry water absorption rate). The total water consumption is determined by the compaction test.

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